17. Basics of Nutrition

This part examines the basics of nutrition, starting with warning about the abundance of bad advice and “experts” with no knowledge and understanding of nutrition.
It will contain the following sections:

You are what you eat- Ralph Emerson

If you wish to go directly to one of the topics above, click on the blue underlined title

Nutrition is essential for health and the prevention of disease. Much is known about it, but there is a vast amount of untrue and potentially dangerous information being peddled by people with no knowledge of the subject. This chapter aims to give evidence-based advice as well as advice on how to spot a charlatan or just bad advice. This is a field in which much good research is advancing knowledge and there is a great deal of basic science which is beyond reasonable doubt. It is also a field in which there are considerable advances being made and hence changes to expert advice. When evidence changes, expert advice changes too.

There is much good science in the field of nutrition, but there is also a vast amount of advice based on pseudoscience, junk science and self-appointed gurus in this field. The intention for this chapter is to give a grounding on the basic facts on nutrition, to help to identify fact from fiction and to weed out the fantastic and fraudulent claims.

Amazon has more 60,000 titles on diets in its collection, advocating more than 25,000 diets. A great many are diets for weight loss. Some are supposed to be for a healthy life or to aid physical training. The vast number of titles shows that most are useless or there would be no need for new ones. For weight loss, there is no quick fix. Often the diets are endorsed by celebrities, which for some reason, many people seem to think gives them credibility. Many are “guaranteed” ways to lose weight or to eat yourself fit. You get fit through exercise, not eating, but diet can help.

During the Second World War, the Ministry of Food analysed many foods and with this information and an assessment of the needs of the population, they did an excellent job of maintaining adequate nutrition in the country during very difficult times.

The cartoon image of Popeye with his spinach

The cartoon of Popeye the Sailor Man dates back to 1929. In 1870, a German chemist called Erich von Wolf was researching the amount of iron in spinach and other green vegetables. He made a mistake in his notebook when he wrote that 100 grams of spinach contains 35 milligrams of iron, when the true figure is 3.5 milligrams. This is the origin of Popeye getting his superhuman strength from spinach. The iron content of spinach is not very different from other green vegetables. This was a single slip and a genuine error. My concern is with misrepresentation and totally unsubstantiated claims.

False Prophets

Beware of false teachers with no knowledge of the subject

There are a great many people who lay claim to expertise in nutrition when they have none. They may claim to be at the cutting edge of research, but they do not have a single paper published in a reputable, peer reviewed scientific journal and often no meaningful qualification in the field either. In his book “Bad Science”1(Bad Science by Ben Goldacre) Ben Goldacre points out that some titles are protected. Claims to be a dietician, physiotherapist or nurse require appropriate qualifications. Terms such as nutritionist, nutritional therapist and nutritional consultant can be used by anyone. Titles such as doctor or professor can apparently also be claimed with impunity. Be careful about people who call themselves nutritionists. There are many good and scientifically qualified nutritionists but also many who are not. Titles such as nutritional therapist and nutritional consultant should immediately raise suspicion. Again, they might be genuine, but such titles always make me wary.

Qualifications are not always what are claimed

In “Bad Science” Ben Goldacre devotes an entire chapter to someone who styles herself as Dr Gillian McKeith PhD. She is not a medical doctor but has a PhD from Clayton College of Natural Health in Birmingham, Alabama. Normally a PhD is a higher degree that requires a thesis based on at least three years of personal research, but from this school the only qualification that was required was a valid credit card. The school closed in 2010, largely in the face of lawsuits from former students who were accusing it of fraud. The school was taking their money and awarding qualifications that no one accepted. Look out for her on television and remember who she is. Uncritical media people who do not understand science are still happy to welcome her.

Ben Goldacre also devotes a whole chapter to Professor Patrick Holford. He was awarded a lower second-class degree in Psychology by the University of York after which he worked as a salesman of supplement pills. A year later, with just his BSc in psychology, he started to treat patients. He started an MPhil degree in nutrition at the University of Surrey, but he never finished it. In 1995 he was awarded a diploma by the Institute of Optimal Nutrition. This is a body which he set up in 1984 and he was director until 1998. I looked for research in his name by searching for “Holford P” in an author search of PubMed. This returned 12 papers with Holford P as one of the authors. None appeared to be him, and no paper was about nutrition. Despite his lack of qualifications or publications in respected scientific journals he was appointed visiting professor at Teesside University, almost certainly because they thought that he could bring money to the department. He resigned soon after, in 2008, amidst a great outcry about his appointment.

Mr Holford still assumes the title of professor. Although I believe that professor is not a protected title, it should really be used only by an active professor or one who is retired and has been given the award of professor emeritus. This accolade was certainly not bestowed. He accuses anyone who challenges him of being in the pay of big pharmaceutical firms, but he is the one who has made a great deal of money from selling vitamin pills and it is the big pharmaceutical firms which produce these pills. Remember that it is a basic feature of fake news to accuse your detractors of having your own vices. He has also published many books which make such claims as vitamin C is more effective than antiretroviral therapy in the treatment of AIDS. I found six of his books in my local library. It has quite an extensive section on medical and health matters but about three quarters of these books should really be classified as science fiction or fantasy.

He’s not the Messiah!
He’s a very naughty boy!

Quacks and charlatans are often invited to expound their views on television by totally uncritical presenters and they may come over as plausible. The presenters usually have a degree in the humanities and no understanding of science. Websites such as Sense About Science and the American Quackwatch are worth a visit.

There are people who try to bring the public the truth, but they are fighting a losing battle in the face of widespread public ignorance. As a nation we spend millions of pounds each year on so called complementary and alternative medicine that is of no value and millions more on vitamin pills and supplements. People will believe what they want to believe. They seem quite determined to be taken in. They want a quick fix.

Beware of food bloggers

Some good advice from the European Conference on obesity, held in Glasgow in 2019, was 2Avoid Food Bloggers When Looking for Nutritional Advice. Christina Sabbagh, of the University of Glasgow said that nine leading UK weight management blogs were assessed using 12 credibility indicators and given a score. In addition, the 10 most recent recipes posted by the social media influencers were compared against official calorie and nutritional content criteria. She found that just one of the nine blogs passed their credibility test for being transparent, trustworthy, and unbiased. That was the only one run by an accredited nutritionist. One blog, run by a medical doctor, did not pass their test. Only three blogs assessed recipes that met the nutritional criteria, with more than half exceeding recommended Calorie limits.

At a press conference after, she said that her findings show that weight management blogs from social media influencers cannot be recommended as credible resources for weight management. She said: “We cannot ignore the online environment and social media influencers. They exist and they have a huge influence, and this influence can cause misinformation to spread, which could be harmful.” I think that a successful blogger is one who gives the followers what they want, rather than what they should have. To be successful, be confident, be dogmatic, pretend to be scientific but do not worry about accuracy.

Calories and Body Measurement

The three main sources of energy in the diet are carbohydrate, protein and fat. Scientists measure energy in joules or kilojoules (kJ) which are 1,000 joules. However, in nutrition it is common to use the calorie which is the amount of heat required to raise one gram of water from 14.5 ºC to 15.5ºC. There are 4.18 joules in a calorie. These are rather small units and for diet and exercise it is more usual to use kilojoules and kilocalories (kcal). Kilocalories are often called Calories (Cal) with a capital C for simplicity and this is what I shall do here.

As a rough guide, 100 grams of protein gives 410 Calories as does 100 grams of carbohydrate while 100 grams of fat gives more than twice as much at 930 Calories. Alcohol provides 700 Calories per 100 grams, so it is also a potent source of calories.

Height and weight are important but not everything

Before we examine obesity and weight loss diets in the next chapter, it is worth discussing body mass index or BMI. BMI is defined as weight in kilograms divided by height in metres squared. Thus, a person who is 175cms tall and weighs 73kg has a BMI of 73/1.752 = 23.8. An acceptable BMI is said to be 20 to 25. Below 20 is underweight. Overweight is 25 to 30 and over 30 is obese. A BMI above 40 is called morbidly obese as it is an imminent threat to health and life. It means that the person weighs literally twice as much as he or she should.

Important exceptions are:

  • A very strong person may have a great mass of muscles and bone to support the muscles to give a high BMI without surplus fat. Many elite athletes in rugby, football and other sports have a BMI in excess of 25.
  • BMI alone is inappropriate to assess children. BMI must be moderated by use of the UK90 charts3Growth reference charts for use in the United Kingdom or the like.
  • BMI is inappropriate in pregnancy where weight gain is expected without increase in height and so BMI before conception or at booking may be the best index.
  • It is also inappropriate in disease with fluid retention as with chronic heart failure or ascites (fluid in the abdomen).
  • In the elderly, the lowest morbidity is in the group with a BMI of 25 to 30 rather than 20 to 25. There may be an innocent explanation for this and a healthy older person with a BMI below 25 should not try to gain weight.
A muscular person can have a high BMI without being fat

Some people suggest that a normal BMI is 18 or 19 to 25. I think that for adults, especially men, a BMI below 20 is too low. The range of “normal” BMI does not distinguish between men and women and yet if a man and a woman are the same height and both are lean, we would expect the man to be heavier because of heavier muscles and bones to go with this.

An alternative parameter is the waist-to-hip ratio (WHR). It indicates abdominal fat and more accurately predicts cardiovascular risk than BMI in different ethnic populations as well as being more valuable in those over 75 years old.4Weight, shape, and mortality risk in older persons The upper limit for acceptable is 0.90 in men and 0.85 in women, although some give the normal ratio for men as up to 1.0. Even in young people, waist circumference has an impact on blood cholesterol and blood pressure.5Waist measures in and the lipid and blood pressure assessment of adolescents

Nowadays the waist circumference alone seems to have taken over from waist-hip ratio (WHR). Waist circumference indicates abdominal fat which is very important for coronary risk. The NHS suggests an upper waist circumference of 94cm (37 inches) for men and 80cm (31.5 inches) for women, even if BMI is normal. It regards 102cm (40 inches) for men and 88cm (34 inches) for women as high risk. 6Why is my waist size important? Here I have included inches as clothes sizes in the UK are usually given in inches.

A classic J-curve of mortality rate with BMI from 1979

Body fat measurement scales are available. However, I am uncertain about their accuracy and they do not consider the important factor of fat distribution. This is where waist circumference is so valuable.

BMI in children should not be used without modification. The UK90 charts have been amalgamated with WHO data. Many charts, covering many different aspects of childhood are available from the Royal College of Paediatrics and Child Health.7RCPCH Growth Charts


Protein is required to replace tissues and enzymes as a normal part of life. It is essential for building muscle and for growth in children. Men aged 19 to 50 need about 55 grams of protein a day whilst women of that age need around 45 grams.8NHS Choices. Bodybuilding and sports supplements: the facts. The average daily intake in this country is 88 grams a day for men and 64 grams a day for women which suggests that very few of us eat a diet that is deficient in protein. However, there may be times when more protein is needed as in vigorous training or when trying to build muscle. Hence there are protein supplements for sale in gyms, pharmacies, sports goods shops and health food stores. They are usually whey protein which is the residue after making cheese. They are very expensive, especially considering that it is basically a waste product from cheese manufacture.

Protein supplements are extremely expensive despite being a waste product of cheese making

I have seen whey protein sold in 2kg tubs for £44 which is £22 a kilo. The gym where I go sells 30g scoops for £1. That works out at £33 a kilo. Some good meat, fish, eggs or diary produce would be cheaper and nicer. Furthermore, they are totally unnecessary as the body’s requirements for protein can be met through a normal varied diet. A person who is in training will burn more calories and hence will eat more. This should include more protein. One of the NHS Choices websites about protein supplements was called “Getting ripped or getting ripped off?” Unfortunately, it is no longer available.

When people who are not protein deficient are given protein supplements, urine tests show that over the next 24 hours the nitrogen from that protein is excreted. The protein is not retained in the body but it is simply burned for energy or laid down as fat. These protein supplements give 410 Calories per 100 grams. They do not accelerate muscle building unless protein deficiency is the limiting factor which is very unlikely and they may well contain heavy metals such as arsenic, cadmium, lead and mercury.9Consumer Reports magazine NHS Choices warns that taking too much protein can have side effects, including diarrhoea.

An analysis of just over 68,000 people, between about 60 and 65 years old and roughly equal numbers of men and women was derived from the UK Biobank data.10Associations Between Diet and Handgrip Strength: A Cross-Sectional Study From UK Biobank. They used handgrip strength to indicate muscle health and strength and compared the results with nutritional data.

  • Increased intake of carbohydrate was associated with lower grip strength.
  • A higher intake of oily fish, retinol and magnesium intake was associated with increased grip strength.
  • In women only, red meat, fruit and vegetables, vitamin E, iron, vitamin B12, folate and vitamin C increased hand grip strength.
  • In men only, high consumption of bread and processed meat was associated with lower grip strength.
Most of us eat far more protein each day than our basic needs

In people with a poor intake of protein, an increase will be beneficial for osteoporosis but for those on a very high protein diet it may aggravate it.11Dietary protein and bone health Osteoporosis is bone thinning which increases the risk of fracture. The instructions on packages should be clear about maximum daily amounts because of potential risks of harm. The Department of Health advises adults not to consume more than twice the recommended daily intake of protein.

I often see people training in the gym with what I am sure is a protein supplement in their water bottles. Others like to drink a protein supplement when they have finished training. They are deluded and wasting their money as well as taking in extra calories. Just eat proper food.


Fat is a very concentrated form of calories. This is one reason for trying to restrict it in the diet. Excess fat is often laid down in the abdomen, especially in men and this increases the risk of coronary heart disease. Fat is also important in the metabolism of the sex hormones and so an excess or a deficit can cause hormone imbalance. An excess may cause hairiness in women due to excess androgens. This occurs in polycystic ovary syndrome, which usually occurs with obesity. In men it may cause “man boobs” due to excess oestrogens. In anorexia nervosa, hormone levels are low, menstruation stops and there is risk of osteoporosis.

Unsaturated fatty acids have double bonds between carbon atoms and 2 fewer hydrogen atoms at that bond

The biochemistry of fat can be quite complex, especially if phospholipids and the synthesis of cholesterol are included. The ordinary fats, called triglycerides, have three carbon chains in their structure so that each carbon atom is attached to the next carbon as well as to hydrogen atoms. Sometimes there are double rather than single bonds between the carbon atoms and this means that it is possible to insert two more hydrogen atoms and to convert the double bond to a single one. Fats with double bonds are called unsaturated fats as they can take more hydrogen atoms. Those without double bonds are called saturated fats as they will take no more. Fats with more than one double bond are called polyunsaturated fats. By and large, saturated fats such as animal fats are solid at room temperature whilst unsaturated fats such as fish oils and vegetable oils are liquid.

The NHS Choices website gives evidence-based advice about fats.12Fats- the facts. NHS Choices It suggests that in this country we probably eat about 20% more fat than we should. Men should limit consumption of saturated fat to about 30 grams a day with 20 grams a day for women.

Usually, skimmed milk has a red top, semi skimmed is green and unskimmed is blue

We need a certain amount of fat in our diets to provide the fat-soluble vitamins as well as some of the substances used in making cells, especially the cell walls. Children younger than five should not have skimmed milk as they need some of the fats for development of the brain.13Milk and dairy foods. NHS Choices. These types of fat are much more abundant in human breast milk than in cows’ milk.

High levels of saturated fats in the diet are associated with increased blood levels of cholesterol. This is a risk factor for coronary heart disease and, to a lesser extent stroke. This can be improved by replacing some saturated fats with unsaturated fats such as fish oils and vegetable oils. Saturated fats are usually solid at room temperature and unsaturated fats are liquid and so are called oils.

Coconut milk is high in saturated fat

An exception to the rule is coconut milk. This contains 24 grams of fat per 100 grams of which 21 grams are saturated. That does not stop some websites from promoting coconut milk as a “healthy alternative”. There have been a number of papers that have lauded the properties of coconut oil but the best that can be said for it is that it might not be quite as bad as I would have expected. A systematic review and meta-analysis showed that it does increase LDL or “bad” cholesterol”.14The Effect of Coconut Oil Consumption on Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Clinical Trials An American review in 2016 found that 73% of people saw coconut milk as a healthy food. This is a triumph of marketing over evidence.

An article on the BBC food website was called 15How to eat fat and stay healthy It said that no more than 35% of daily calories should come from fat. This is around 70 grams for women and 90 grams for men. Remember that fat contains more than twice as many calories per 100 grams than protein or carbohydrate. Not many people exceed this, but commonly people eat too much of the wrong type of fat and not enough of the good type. A maximum of 10% of daily calories should come from saturated fat. This is 20 grams for women or 30 grams for men, but many exceed this. Saturated fats are found in cakes, biscuits, cheese, butter, cream, coconut oil and fatty cuts of meat. It says that the popularity of coconut products has soared in recent years, but these “superfoods” are misleading. Coconut oil is 86% saturated fat, which higher than butter at 52% and olive oil at 14.3%.

I have also seen coconut milk recommended for rehydration. As it contains water, it will rehydrate but as it contains a significant amount of fat, it will slow emptying of the stomach and so it will be expected to rehydrate rather slowly. However, a study of different drinks to correct dehydration showed that although it was no worse than other fluids in the study, it was no better either.16Postexercise rehydration: potassium-rich drinks versus water and a sports drink

Hydrogenated or trans fats are often found in cakes

Sometimes unsaturated fats are made to accept extra hydrogen atoms to make them saturated and more solid at room temperature and these are called hydrogenated fats. This is an artificial process. They may be found in cakes and biscuits. Hydrogenated fats, also known as trans fats, should be avoided. They tend to represent a very small amount of our diet in the UK and many food manufacturers have stopped using them. An NHS website says that a ban on trans fats would save thousands of lives.17UK ban on trans fats ‘would save thousands of lives’ This was based on an article in the BMJ in 2015.18Potential of trans fats policies to reduce socioeconomic inequalities in mortality from coronary heart disease in England

There are different types of cholesterol

Cholesterol is not the same as fat. High levels of saturated fat in our diet increase cholesterol levels. Only about half the cholesterol in the body is eaten as such and the rest is synthesised by the body.19Balancing cholesterol synthesis and absorption in the gastrointestinal tract. Cholesterol is discussed on several NHS websites. 20What is High Cholesterol? is a good example. There are two types of cholesterol called high- and low-density cholesterol. Basically, low-density cholesterol is bad, and high-density cholesterol is good. The latter seems to offer a protective effect against heart disease. Therefore, rather than measuring total cholesterol, it is better to measure both. The figure for total cholesterol is usually divided by high-density cholesterol (TC/HDC) to give a meaningful figure in terms of risk.21Cholesterol. Patient UK

Factors that affect this level and risk include genetics, obesity and excessive alcohol consumption. Stopping smoking appears to increase HDL (good) cholesterol.22The effect of quitting smoking on HDL-cholesterol Exercise also gives a small benefit to HDL cholesterol.23Exercise-mediated changes in high-density lipoprotein Another NHS website called 24Lower your cholesterol advises, “Eating a healthy diet and doing regular exercise can help lower the level of cholesterol in your blood.” By and large, the dictum tends to be “saturated fat bad, unsaturated fat good” but keep down the total level of fat. Use olive oil or other vegetable oils rather than lard.

The level of blood cholesterol in the general population follows a Gaussian distribution and so it is possible to find a “normal” range which is within two standard deviations of the mean. The coronary risk is raised for high levels and it falls as cholesterol levels fall. However there seems to be no plateau where there is no further benefit from further reduction. The lower the better is also true for blood pressure provided that the person does not faint on standing up. There is a limit to how much reduction in cholesterol may be achieved by any one method and so it is best to look at several approaches, especially if risk is high. Advice may include:

  • Avoid obesity
  • Eat less saturated fat and more unsaturated fat but less total fat
  • Avoid trans or hydrogenated fats as they raise the bad low-density cholesterol and lower the good high-density cholesterol.
  • Do not smoke
  • Take regular exercise
  • Drugs such as the statins can reduce cholesterol synthesis in the body and some of the newer ones are very potent
  • Substances called stanols and sterols that are added to certain proprietary preparations such as Flora pro-active™ and Benicol™ can reduce absorption of cholesterol25Cholesterol-lowering Sterols and Stanols
  • Avoid excessive alcohol consumption
The right side is the omega end. The double bond is 3 carbon atoms in. This is an Ω 3 fatty acid

Accepted wisdom is that saturated fats are bad whilst unsaturated fats are good and may alleviate some of the problem but the total amount of fat in the diet should be kept in moderation. Cholesterol-rich LDL is a major cause of atherosclerosis because it delivers its cholesterol load to the arterial wall and causes obstruction and inflammation. The precise relationship between saturated and unsaturated fats, omega (Ω) fatty acids, long and short chain fatty acids and risk of coronary heart disease and stroke is quite complicated and not yet fully elucidated. There is still a great deal of uncertainty and debate among proper scientists. The results seem to suggest a beneficial effect.26Controlled Trials and Cohort Studies of Omega-3 Fatty Acids and Coronary Heart Disease Risk. An NHS website says that they give minimal benefit for heart disease.27Minimal evidence to show omega-3 prevents heart disease. NHS This was based on a Cochrane review.28Omega-3 intake for cardiovascular disease. Cochrane has also reviewed Ω-3 fatty acids in many other conditions. Some of the same authors were involved in a systematic review and meta-analysis called 29Polyunsaturated fat for prevention and treatment of type 2 diabetes which found that increasing Ω-3, Ω-6, or total polyunsaturated fatty acids has little or no effect on prevention and treatment of type 2 diabetes. It is too soon to return to complete acceptance of saturated fats but hydrogenated fats are definitely bad and butter is not as demonised as it was.

Another Cochrane review called 30Polyunsaturated fatty acids for the prevention of cardiovascular disease concluded “This is the most extensive systematic review of RCTs conducted to date to assess effects of increasing polyunsaturated fatty acids on cardiovascular disease, mortality, lipids or adiposity. Increasing polyunsaturated fatty acids intake probably slightly reduces risk of coronary heart disease and cardiovascular disease events, may slightly reduce risk of coronary heart disease mortality and stroke (though not ruling out harms), but has little or no effect on all-cause or cardiovascular disease mortality. The mechanism may be via lipid reduction but increasing polyunsaturated fatty acids probably slightly increases weight.” This is a great disappointment considering how we have been told over the years to reduce saturated fatty acids and to increase polyunsaturated fatty acids. However, science changes when the evidence changes.

This is quite complex, and the science is often difficult to understand. Hence, what was advised in the past may be different from now and different again in the future. However, it is all based on the best available evidence. This is more than can be said for any celebrity endorsed or fad diet.

The role of Ω-3 fatty acids in malignancy seems contradictory. A trial found that high levels were associated with increased malignancy in prostate cancer.31Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial. Other have found that these Ω-3 fatty acids are protective.32Omega-3 Fatty Acids Survey in Men under Active Surveillance for Prostate Cancer I find this very confusing and I struggle with the biochemistry in these papers. I think that we need to watch and wait for clarity about these substances and cancer.

Features of hypertriglyceridemia include fatty deposits called xanthalasma around the eyes

Less common than high cholesterol is the problem of high triglycerides. They are also a risk factor for heart disease. Vitamin D, as found in oily fish, may be helpful but there have not been many good, large trials.33Update on the Vitamin D and OmegA-3 trial

In January 2020, the NHS in England announced that they were to fast-track approval of a novel new drug that silences genes as a strategy for lowering cholesterol. 34 NHS to Fast Track as Yet Unapproved Cholesterol Drug The drug, called Inclisiran will be studied in a large NHS trial. It is predicted to save around 30,000 lives in the next 10 years. The drug is injected twice a year which could improve adherence to treatment. It prevents production of the PCSK9 molecule to lower LDL blood cholesterol and is said to have few side effects. 35 Silencing Novel Target Genes: A New Strategy for Lipid Lowering I am always a little wary about fast-tracking on the grounds of “approve in haste and repent at leisure”.


A single glucose molecule

These are the third major group of foods that contribute Calories. They consist of carbon, hydrogen and oxygen, the hydrogen and oxygen being in a ratio of 2:1 as in water. The simplest carbohydrates are sugars. Those with a single carbon ring are called monosaccharides such as glucose. They usually have six carbon atoms and a formula of C6H12O6 but the structure of the molecule can be different. Three different sugars with the same basic formula are glucose, fructose and galactose. Although they have the same basic formula, the 3-D structure is slightly different and they are called isomers.

Two rings may form disaccharides. Two glucose rings make maltose. Glucose and fructose make sucrose or table sugar. Glucose and galactose make lactose which is the sugar in milk. Much longer glucose chains produce starch and very long, complex chains include cellulose which the body is unable to break down. However, bacteria in the gut can do so and they release gases. Hence, high fibre foods have a reputation for causing flatulence. Baked beans and Brussels sprouts are examples. In animals, glucose is stored in muscles and the liver in chains of glucose called glycogen rather than starch.

The three main types of disaccharide sugars with two carbon rings

Complex carbohydrates such as starch are broken down to shorter chains by enzymes and then to disaccharides which are split in the gut wall and monosaccharides are absorbed. Disaccharides have two carbon rings and monosaccharides have one. This starts with the enzyme amylase in saliva with more in the secretions from the pancreas. Sugars are rapidly broken down and absorbed and the blood glucose level shoots up. Starch is broken down more slowly and so it gives a slower rise in blood sugar. Smaller starch molecules are broken down and absorbed as glucose faster than larger molecules. The glycaemic index (GI) of a food indicates how fast it will raise blood glucose levels.

A rising level of blood glucose stimulates the pancreas to produce insulin and this facilitates the active absorption of glucose into the muscles and liver where it is stored as glycogen to be used for energy or it may be laid down as fat. The blood glucose level must not fall too far as the brain needs glucose as it is unable to use any other food source of energy. It does not actively absorb glucose but it enters by diffusion and so a certain blood level is required if the brain is not to be starved of glucose. That is not to suggest that high levels make the brain work any better. The pancreas produces the hormones insulin which lowers blood glucose and glucagon which raises it.

Sometimes people talk of white, beige and green carbohydrates. The white are the fast releasing ones including sugars and short-chain starch. The beige carbohydrates take longer to release the glucose. The green ones are like cellulose and are not digested but add to roughage. Not everyone accepts the concept of white versus beige starch.

Glucose chains make part of a starch molecule

Animal, including humans, do not store carbohydrates as starch but as glycogen, which is also a long chain, complex carbohydrate or polysaccharide. It is stored in muscles and in the liver and when required, it is broken down to glucose. Insulin pushes glucose into muscles or liver where it may be stored as glycogen or fat. Glucagon, also produced by the pancreas, stimulated the breakdown of glycogen to glucose, especially in the liver.

Diabetes is a condition in which there is a relative shortage of insulin. In type 1 diabetes, there is damage to the pancreas, and it is unable to make enough insulin. This commonly starts in children or adolescents. In type 2 diabetes, levels of insulin may be high but there is resistance to its actions. This usually occurs later in life and often in people who are overweight or obese. Smoking and lack of exercise are also risk factors. Body fat increases insulin resistance. A variant called MODY which stands for maturity onset diabetes in the young can occur in obese teenagers and even children.

Slow release glucose from a low GI index is best

Foods that give a rush of sugar are regarded as bad and may well be a greater contributor than fat to the current epidemic of obesity. It is generally accepted that the British diet has too much sugar in it. However, there seems to be some confusion about fast sugars being bad and the need to avoid all carbohydrates, including those with a low glycaemic index (GI). The glycaemic index is a measure of how fast glucose is released into the blood. Calories must be eaten in some form, and a diet that is low in carbohydrate is high in protein and fat. As we have seen, high levels of protein can be bad and even lean meat contains a significant amount of fat. On the other hand, food rich in starch often contains plenty of fibre which has benefits as well as reducing constipation and fibre does not give Calories. A systematic review and meta-analysis concluded that high protein diets, either with high or low-fat levels, had no effect on obesity, coronary artery risk of control of diabetes.36Long-term effects of low-fat diets either low or high in protein on cardiovascular and metabolic risk factors It could not recommend high protein diets for the management of overweight or obesity.

The American fast food and soda culture contributes to much obesity in the UK too

A paper from 2013 found that American adults consume on average about 15% of their calories from sugars added to foods during processing.37Added sugar intake and cardiovascular diseases mortality among US adults Of the added sugar, 37% is consumed in sugar-sweetened drinks. The authors project that regularly drinking as little as one 12-ounce sugary soda a day (about 320ml) may increase the risk of cardiovascular disease by about 30%. This is independent of total calories, obesity, or other risk factors. An accompanying commentary adds that the risk rises exponentially as sugar intake increases and it is safest to consume less than 15% of daily calories as added sugar.38New unsweetened truths about sugar

There is evidence that fast sugars, as found in fast foods, may lead to a state of dependence rather like addiction.39The obesity epidemic and food addiction: clinical similarities to drug dependence Drinks containing sugar and caffeine are often consumed with such food and they may substantially aggravate the problem.

“Energy drinks” cause obesity and tooth decay

There is a general agreement that foods and drinks that give a rapid release of sugar are bad although the will to tackle the problem is meagre. A major factor may be the considerable lobbying power of the food industry, especially in the United States. Young people walk the streets carrying bottles of drinks that contain sugar and caffeine believing that it gives them energy. It is addictive, rots their teeth and makes them fat. An excessive intake of caffeine may also contribute to poor sleep and with it, increased appetite. This will be discussed later. The belief that they need to drink frequently to avoid dehydration is a myth that will be addressed in a later chapter.

Sugary drinks are a major problem. A prospective study from France found that consumption of sugary drinks, including fruit juice, was associated with an increased overall risk of cancer, especially breast cancer.40Sugary drink consumption and risk of cancer The study involved data from just over 100,000 healthy French adults of whom 21% were men, 79% were women and the average age was 42 years. From these results, the team calculated that an increase of 100ml a day in the consumption of sugary drinks was associated with an 18% increased overall risk for cancer. No risk was identified with artificial sweeteners. This does not mean that we should give up fruit. It contains sugar, which is not a problem if kept in moderation. The trouble is that too often, fruit juices have further sugar added to them by manufacturers. They also tend to take out the pith which provides fibre and slow the absorption of sugars.

It is an enormous and profitable market

As expected, demands for a “sugar tax” have been met by opposition from the soft drinks industry. Nevertheless, we tax tobacco and alcohol with a view to improving habits and the same may be done for sugary drinks. The United Kingdom Soft Drinks Industry Levy (SDIL) was implemented in April 2018 and charges manufacturers and importers at 24p per litre for drinks with more than 8 grams of sugar per 100 ml, 18p per litre for drinks with 5 to 8 grams of sugar per 100 ml, and no charge for drinks with less than 5 grams of sugar per 100 ml. Fruit juices and milk-based drinks are exempt.

A survey measured the impact of the SDIL on price, product size, number of soft drinks on the marketplace, and the proportion of drinks over the lower levy threshold of 5 grams of sugar per 100 ml. This survey, published in 2020, found that many manufacturers reduced the amount of sugar in soft drinks. It concluded that “These changes could reduce population exposure to liquid sugars and associated health risks.” 41 Impact of the announcement and implementation of the UK Soft Drinks Industry Levy on sugar content, price, product size and number of available soft drinks in the UK It seems that the sugar tax has been beneficial.

Artificial sweeteners are not the answer

So, should we turn to artificial sweeteners instead? Researchers love to give their trials clever names. The European Prospective Investigation into Cancer and Nutrition is called the EPIC trial. It has been the source of several studies. This one involved 451,743 participants from Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden, and the United Kingdom, so it was epic. The conclusion was that consumption of total soft drinks, sugar-sweetened drinks, and artificially sweetened soft drinks was associated with an increase in all-cause mortality.42Soft Drink Consumption and Mortality in 10 European Countries The results support public health campaigns aimed at limiting the consumption of soft drinks.

Are artificial sweeteners as bad a sugar? It is quite possible that many of the study participants could have recently changed to diet drinks after a lifetime of poor diet and high sugar intake.43How bad for your health are diet soft drinks? A paper looking at 44Intake of non-sugar sweeteners and health outcomes noted that the trials that showed poor outcomes related to non-sugar sweeteners, tended to be the smaller studies of poorer methodology. Overall, they did not find bad outcomes related to these sweeteners. Perhaps the problem is those who say, “I’ll have a super-size burger with cheese, a large fries and a diet Coke.”

Diet drinks are not all you may hope

A very large American prospective cohort study of nearly 200,000 nurses and other health professionals, giving 2,783,210 person-years of follow-up, found 11,906 new cases of type 2 diabetes. After adjustment for BMI and changes in diet and lifestyle, they found that increased consumption of drinks with sugar in them, whether sugar-sweetened drinks or pure fruit juice, increased the risk of diabetes by 16%. For those who used artificially sweetened drinks, there was an 18% increase in the risk of diabetes. This might suggest that artificial sweeteners give a higher risk of diabetes than sugar, but the difference was not statistically significant with considerable overlap of confidence intervals. Instead, the inference must be that artificial sweeteners do not give protection from diabetes compared with sugar. On the other hand, replacing one daily sweet drink with coffee, tea or water, gave a 2 to 10% lower incidence of diabetes.45Changes in Consumption of Sugary Beverages and Artificially Sweetened Beverages and Subsequent Risk of Type 2 Diabetes

Hence, it appears that artificial sweeteners may be a useful intermediary when trying to give up excessive intake of sugar. However, if the “sweet tooth” can be discarded in favour of a more refined palate, that would be preferable. They do not seem to be a completely safe alternative to sugar.

At rest, about 20% of the body’s metabolic needs are accounted for by the brain and this can only use glucose. It is possible to get some glucose from some amino acids from proteins, but a slow release form of glucose is desirable. The Dietary Guidelines for Americans46Dietary Guidelines for Americans recommends that carbohydrates make up 45% to 65% of total daily calories. Do not confuse carbohydrates and sugars.


Fibre does not contribute to calories or nutrients such as minerals and vitamins, but it is very important for health. Fibre is composed of very long chains of glucose and the human digestive system is unable to break it down. Hence it passes through the gut. Some may be digested by bacteria and the importance of bacteria in the gut is discussed below. It provides roughage or bulk to the diet, enabling the contents of the bowel to be moved along relatively easily.

Fibre is very important in the diet

Lack of roughage causes constipation and the muscle in the bowel wall has to produce higher pressures to force it along. This causes pain from spasm and it may lead to little sacs or pouches blowing our from the gut wall. This occurs in the weakest spots which is where the arteries come in. They are called diverticula. They can easily get infected and inflammation in them causes diverticulitis. A low roughage diet is also associated with an increased risk of bowel cancer.

A high fibre diet may also slow the absorption of food from the gut, giving a lower glycaemic index and it may even reduce the total number of calories that are absorbed. The bulk gives a greater feeling of satiety than a low fibre diet which may give less inclination to feel satisfied and stop eating. Processed foods tend to be low in fibre as we as high in salt and sugar.


Having examined protein, fat and carbohydrates, a brief mention of alcohol is on order. It is very high in energy, at 700 Calories per 100 grams, and if taken to excess there is no doubt about its adverse effects: physically, mentally and socially. These are too many and too well known to enumerate here. However, alcohol is also claimed to have beneficial properties. An article in The Times was called 47Red wine is healthy for gut and figure. An accompanying editorial said that Rufus of Ephesus, a Greek physician of the first century, wrote a treatise on the effects of alcohol consumption: “Wine is more praiseworthy for health than any other thing; however, anyone who drinks it must be wise, if he does not wish to suffer some irreparable ill…”

A little of what you like

There are plenty of “good news stories” about alcohol, especially wine, but only if taken in moderation. What is moderation? Moderation is what I do. Anything more is to excess. When I was a student, a standing joke was that the definition of an alcoholic is a person who drinks more than his doctor. This digs at both the traditional high consumption of alcohol in the profession, although I have reason to believe that it is lower these days. It also shows that this is a value judgement.

Red wine is claimed to have health giving properties, especially for the heart.48Wine and Cardiovascular Health This is often attributed to a substance called resveratrol.49Resveratrol and Cardiovascular Diseases Resveratrol levels in wine are very variable. It is also found in peanuts and chocolate. It is said to have antioxidant effects, but antioxidants will be discussed later. The French are said to have what should be, in theory, an unhealthy diet, but their life expectancy does not reflect this. This is called “the French paradox” and much is attributed to drinking wine, especially red wine.50The French paradox: lessons for other countries

Perhaps the major difference is the amount of processed food and fast sugars

Many have argued that it is not just wine or red wine that is beneficial in moderation. All alcohol, including beer may promote health if kept in moderation.51Effects of moderate beer consumption on health and disease

Life expectancy graph with alcohol intake at age 62. From the Pearl Life Assurance Company 1926

A graph of mortality rates and alcohol consumption gives a J-shape. This means that a low consumption is better than abstention but as levels of consumption rise, mortality rises swiftly. We are taught to be very wary of J-shaped graphs. They can be misleading and there is often an innocent reason for the apparently worse outcome at low or zero levels compared with moderate levels.

Alcohol in moderation can enhance the quality of life but some people have problems with it and if they cannot control their intake, they should abstain completely. It is difficult to distinguish between the benefits of a relaxed lifestyle and the risk of anyone who does anything to excess. If you enjoy a drink with moderate consumption of alcohol, keep it up but association and causation are not the same, so do not tell yourself that you drink because it is good for you. We have noted before that people often think that if a little of something is good, then a lot must be even better. High levels of alcohol consumption raise blood pressure and increase the risk of a fatty liver. It has an adverse effects on blood lipids which is a risk factor for heart disease. This is before moving on to cirrhosis and the many other bad effects of excessive alcohol consumption. Enjoy alcohol but keep it in moderation.


Another “naughty but nice” for which health benefits are claimed is chocolate, or at least dark chocolate. It contains many substances, some of which are beneficial to health whilst others, such as sugar and fat are certainly not. The best-known beneficial substances are called flavonoids. They are much more marked in dark chocolate than in milk chocolate. The biochemistry is rather complicated, but it seems that dark chocolate has, on balance, a good effect on the heart and circulation.52The cardiovascular benefits of dark chocolate

However, I was rather shocked to find that chocolate is usually more than 50% sugar. Cadburys have made strides with a chocolate bar which contains 30% less sugar than the usual Cadburys Dairy Milk. The figures are from the Cadburys website. They all refer to content per 100 grams of the chocolate. Except for energy, all figures are grams per 100 grams bar.

Cadburys Chocolate 100 grams bar Dairy Milk traditional Dairy Milk low sugar Bournville dark chocolate
Energy in Kcal 534 503 524
Carbohydrates 57 42 60
Sugar 56 37 58
Total Fat 30 31 28
Unsaturated Fat 18 18 17
Protein 7.3 5.8 4.1
Fibre 2.1 18.0 6.0

The low sugar version has been achieved by replacing sugar with fibre, but it is disappointing that the number of calories in a bar is not lower. I had been expecting it to result in more fat, but they have avoided that. I was also disappointed that the classic Bournville dark chocolate was not lower in sugar and fat but at least it can be expected to be high in flavonoids. Cadburys are to be congratulated on addressing the issue of sugar in chocolate.

We do not have to give up chocolate but keep it in proportion.

The Importance of Bacteria in the Gut

The large intestine contains about 2kg of contents of which about half is roughage and water and the other kilogram is bacteria. The number of bacterial cells markedly outnumbers the number of human cells in the body. It is only in recent years that their enormous importance for health is being understood. The bacteria and other organisms in the gut are often called the gut biome.

The contents of our bowels are affected by what we eat. This is the substrate in which the flora feed. A wide variety of bacteria is good. Certain species are known to be beneficial. As well as a poor diet, antibiotics may affect the flora, especially in people who need frequent or prolonged courses, and this has a bad effect.

The detrimental effects of processed food result may come from their elevated sugar, fat, and sodium content, whilst they are low in protein and fibre and too easy to digest. A small randomised controlled trial by the US National Institutes of Health showed that people eating a diet of ultra-processed food, consumed more calories and gained more weight than those on a minimally-processed diet, despite meals being matched.53Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain In the trial, 20 inpatients received ultra-processed and unprocessed diets for 14 days each. They were 10 men and 10 women, average age 31 and average BMI was 27 and stable. The diets were matched for the number of calories presented, sugar, fat, fibre, and macronutrients. There was an ad libertum (free) intake whilst on the diets. Those on the processed foods took in roughly 500 Calories a day more than those on the unprocessed diet. Participants gained nearly 0.9kg during the ultra-processed diet and lost a similar amount of weight while on the unprocessed diet. Because processed food is so easy to digest, it may be easier to extract more Calories from it, aggravating weight.

The number and diversity of bacteria in the gut is enormously important in many ways

A study of more than 100,000 French people found that a 10% increase in the proportion of ultra-processed foods in the diet was associated with a significant increase of greater than 10% in risks of all cancers, especially breast cancer.54Consumption of ultra-processed foods and cancer risk

A study from the Royal Marsden Hospital in London, a world-renowned cancer treatment centre, found that patients with poor diversity of their gut biome were more susceptible to side effects of radiation.55Microbiota- and Radiotherapy-Induced Gastrointestinal Side-Effects Radiotherapy is aimed at the tumour but, inevitably, surrounding structures will be irradiated and that may include the gut. One of the authors said, “Radiotherapy to the prostate and pelvic lymph nodes is an important way to manage cancer but it can result in damage to the gut and unpleasant side effects for the patient, which can often be long-lasting and quite severe.” They were looking even at the prospects of faecal transplant, but if a person has a good diet, with plenty of fibre, there should be good microbial diversity and he should be at lower risk of side effects from radiation.

Researchers who tracked 165 Norwegian children found that the range of organisms known as microbiota in their digestive system at the age of two accurately foretold those who would have a body mass index (BMI) that qualified them as overweight or obese at the age of 12.56Gut Microbiota in the First 2 Years of Life and Body Mass Index at Age 12 The 33 children who became overweight did not have a higher BMI than their peers at the age of two.

In obesity there is less diversity of bacteria in the gut. However, according to a review from 2009, it is unclear if this is the cause or the consequence of obesity.57Changes in intestinal microflora in obesity: cause or consequence? A study from 2007, led by the same author, concluded that the bacteria in the gut can influence both weight loss and weight gain.58Mechanisms underlying the resistance to diet-induced obesity in germ-free mice He regards the gut bacteria from an early age as important in programming the person’s metabolism.59Programming of host metabolism by the gut microbiota

Someone who has had a major impact on our understanding of the importance of the gut flora is Professor Tim Spector. He is professor of genetics at Kings College London with clinical appointments at Guy’s and St Thomas’ Hospitals. Whether we gain or lose weight is based largely on the balance of Calories in and Calories out. I would not dispute the first law of thermodynamics, that energy can neither be created nor destroyed but the gut biome has a very important role in terms of weight control. His book 60(The Diet Myth by Tim Spector) is an interesting read. He has followed many identical twins over many years. We think of identical twins as being identical, as they usually are and they have identical DNA, but sometimes they are rather different. Often this can be traced to a course of antibiotics that upset the gut flora or perhaps one has a much healthier diet with plenty of roughage while the other likes processed food and the latter has much less bacterial diversity in the gut. His book 61(Identically Different by Tim Spector) is also very interesting. Sometimes they have rather different diets and the fat one is the one who eats junk food. Again, it is the gut biome.

Identical twins are not always so identical

A study of identical twins examined levels of the hormone ghrelin which is known to be important in appetite control. They examined 43 pairs of twins who were both lean, and 46 pairs who were both obese as well as 23 pairs of whom just one was obese.62Fasting plasma total ghrelin concentrations in monozygotic twins discordant for obesity They concluded that plasma total ghrelin levels are affected by acquired obesity independent of genetic background. In other words, fat people reset their appetite control for the worse. It seems likely that the gut biome is at least in part responsible for this change in appetite control.63Obesity: An overview of possible role(s) of gut hormones, lipid sensing and gut microbiota

In a previous chapter, I have mentioned epigenetics. Our DNA may be fixed but which parts of it are expressed is highly variable and this is the basis of epigenetics. Several factors can change this including the gut biome, some chemicals and exercise.

Still on genetics, a reduced telomere length is thought to be a marker of aging. Both smoking and obesity accelerate this, at least in women.64Obesity, cigarette smoking, and telomere length in women This study investigated 1,122 white women aged 18 to 76 years, but no men. I do not know why they investigated only women. The conclusion is that both smoking and obesity accelerate the aging process.

Probiotics vary greatly in type and effect

Probiotics will not be discussed here as they are addressed in their section of the chapter Other Natural Products in the part about complementary and alternative medicine. There are a great variety of probiotics which have a wide variety of effects. It is not “one size fits all” as different organisms do different jobs. It is not always easy to see what organisms are in the advertised pot or where to get what you want. Some may not be available in food in this country.

Further Resources


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Site Index

This website is now completed, although I shall continue to do updates. The following list shows the sections or chapters. Just click on the topic in blue to go to that part of the site.

1 Introduction
2 A Very Brief History of Science And Medicine
  Fundamentals of Medical Science
3 Finding Good Medical Advice and Evidence Based Medicine
4 Randomised Controlled Trials
5 Cohort or Longitudinal and Epidemiological Studies
6 Qualitative Research
7 Basic Maths in Medical Research and Decision Making
8 How Good is the Evidence?
9 Ethics in Practice and Research
  Public Health Issues
10 Screening Programmes
11 Fake News and Vaccine Scares
12 Electronic Cigarettes (E-Cigarettes)
13 Motor Vehicle Emissions, Air Pollution and Health
14 COVID-19. What You Need to Know
15 Who is at Risk from COVID-19
16 What we Must Learn from the COVID-19 Pandemic
17 Basics of Nutrition
18 Exercise, Obesity and Diets for Weight Loss
19 Diets and Nutrition for Health and Fitness
20 Supplements
  Complementary and Alternative Medicine
21 Introduction to Alternative Healthcare
22 Homeopathy
23 Acupuncture
24 Manipulation of the Spine
25 Reflexology
26 Herbal Remedies
27 Other Natural Products
28 Chelation Therapy
29 Hypnosis
30 Other Modalities of Complementary and Alternative Medicine
  Some Controversial Diseases
31 Fibromyalgia
32 Chronic Fatigue Syndrome (CFS) or Myalgic Encephalitis (ME)
33 Systemic Candidiasis and Leaky Gut Syndrome
34 Mobile Phones, Masts, Wi-Fi and Electro-sensitivity
  The Environment
35 Global Warming and Climate Change
36 Alternative Energy
  Some Final Thoughts
37 Still Searching for the Age of Reason