The Diet Myth: The Real Science Behind What We Eat

by Tim Spector

Cubans, despite eating on average twice the total amount of sugar as Americans, are poorer but far healthier.

At the start of this experiment the average weight of these twelve highly selected female twins was 86 kg (13½ stone) and their average BMI was 34. Now, you might have predicted that the twin who had the willpower to diet regularly would have something to show for her years of sacrifice. Instead, I found absolutely no difference in weight between the twin who had dieted regularly for the past twenty years and her identical twin who had never been on a serious diet. Similar results were found in younger twins who started off at the same weight at the age of sixteen. The twin who had dieted was on average 1.5 kilos heavier when the two were compared at the age of twenty-five.2

I want to demolish the myth that obesity is simply a matter of counting calories in and out or about eating less and exercising more or cutting out one food type.

No other field of science or medicine sees such professional infighting, lack of consensus and lack of rigorous studies to back up the health claims of the myriad dietary recommendations. Moreover, no other field of science feels to me so much like a mass of competing religions – all with their high priests, zealots, believers and infidels. And as with religion most people, even at the risk of death, are unwilling to change their faith.

The missing piece of the jigsaw There is an enormous piece of the nutrition puzzle missing. Why can one person eat a certain meal regularly and gain weight while another ingests exactly the same food and yet loses pounds? Lean people (by which we now mean those of healthy weight and a BMI less than 25) are now the minority group in most populations. What makes them so different from ‘normal’ overweight people? Perhaps we should be studying them as the ‘abnormal’ ones? Some of these differences are clearly down to our genes, which influence both our appetites and our eventual weight. My studies of twins in the UK (the TwinsUK study) and others from around the world have shown that identical twins are much more similar to each other in body weight and fat than fraternal twins. Since they are effectively genetic clones and share the same DNA, this shows the importance of genetic factors, which explain around 60–70 per cent of the differences between people.

On average, identical adult twins are less than 1 kilo different in weight. These

However, just because a trait is 60 or 70 per cent ‘genetic’ doesn’t mean it is predestined.

In the UK in 1980 only 7 per cent of men and women were obese – now it is 24 per cent. Genes, made up of variations in DNA, cannot change that fast and traditionally need a minimum of around one hundred generations to adapt by natural selection.

Imagine how many grains of sand there are on earth – or, if you prefer, how many stars there are in the universe. Someone has actually counted the stars – well, made a very good estimate – and came up with a figure of 1024 (which is 1 + 24 zeros – an awful lot). If you multiply the estimate for all possible stars a million-fold you get a vast figure which, at 1030 (also called a ‘nonillion’), is the estimated number of bacteria on earth. If you are a gardener and by accident swallow a tiny fleck of earth it contains billions of bacterial cells, and a handful of earth contains more microbes than stars in the universe. You are no ‘safer’ swimming in the water, where a million bacterial cells are found in every millilitre of fresh or sea water. These microbes are the true and permanent inhabitants on earth; we humans are just passing through.

The diets were designed to keep weight constant, but the trans-fat group gained weight and scored three times the harmful visceral (belly) fat and much worse insulin profiles (meaning that glucose in the blood is not disposed of quickly) compared to the other group.1 This suggests that all calories are not the same. Two thousand fast-food calories will have very different energy consequences from 2,000 calories made up of whole grains, fruits and vegetables. For too long we have taken the accuracy of our food labels for granted, but the formulas behind them are over a hundred years old. They depend on burning the foods and applying calculations to account for different rates of digestion and absorption. The formulas disregard the effects of how old food is and also the different effects of cooking, which can dictate how much is absorbed as well as the speed glucose can rise in the blood. Also, people with longer large intestines can extract more calories from food than those with short ones, and some studies have shown differences of up to

counting calories to lose weight is often misleading and that trying to lose weight by exercise alone is futile. However, until we come up with a better system, calories are here to stay, and they give us at least a rough guide to the overall energy content of foods. The rest of the details on food labels show us the other macronutrient components of food that the industry and the government have agreed we can see. They were introduced so we could judge for ourselves which products are healthy and which we should be wary of. But

veins in cheeses such as Roquefort and Stilton. The US FDA (Food and Drug Administration) in their wisdom have also decided that having bacteria in cheese is a bit risky (unlike firearms), and have banned a number of other artisanal cheeses made from raw unpasteurised milk such as Comté, Reblochon and Beaufort.

Far from being a risk for heart disease, full-fat cheese (but not butter), despite the saturated-fat content, now shows not only no harmful effects but a consistent protective effect on heart disease and mortality.

Other products like milk and fermented products containing microbes may also offer some advantages,

We looked recently at rare twin pairs containing one depressed twin and one happy one. In the affected twin’s blood we found altered levels of the key brain chemical serotonin. This chemical comes from our food except when we are fasting, when our gut microbes manufacture it for us. So changes in our microbes will alter this key brain chemical and, potentially, our mood. This could explain the odd sensations of a euphoric high reported by some people after fasting.

The overall conclusion here is that for most of us saturated fat is not the villain to be avoided at all costs. The saturated fat many people eat in products like cheese and yoghurt is not, as we have so often been told, unhealthy, but likely to be beneficial. This is provided the food is ‘real’ and contains living microbes, and is not over-processed or full of other unwanted chemicals and sweeteners.

the massive global experiment of replacing the total fat component of our diet with extra (mainly highly refined) carbs in recent decades has turned out to be a total health disaster.4 5

People that really enjoy their food may actually, via their brains, be able to both make themselves feel happier and stimulate their microbes.

As noted in an earlier chapter, cultures like those of the French and the Mediterranean countries love their food and food traditions, and they still spend far more time eating and talking about food than the Anglo-Saxons. And their strong food culture tells them that whatever their grandmothers ate is generally good for them, and they continue learning to cook and prepare the same meals.

US on the evils of high-fat dairy foods emerged in the 1970s and 80s. These countries simply went on eating their healthy yoghurt and high-fat cheeses and meats. They are probably better off as a result, as they didn’t replace the fat with refined carbohydrates. This contrasts sharply with most Americans and Brits, who with little or no common food culture reacted to the next wave of erroneous advice in a state of considerable stress. So not only do they make bad choices about the best diets for them and their families, by swapping real foods like meat and fresh cheese for margarine and processed-cheese pizza, but the associated stress and guilt may have adversely affected their microbes and their health.

The main characteristics of this diet are a high consumption of whole grains, legumes, other vegetables, nuts and fruits; a relatively high fat consumption (up to 40 per cent of total energy intake), mostly from mono-unsaturated fatty acids (MUFA, providing up to 20 per cent of energy) mainly from olive oil; moderate to high fish consumption; poultry and dairy products (usually as yoghurt or cheese) consumed in

moderate amounts; low consumption of red meats, processed meats and other meat products; and moderate alcohol intake, usually in the form of red wine with meals.

Each species of microbe has a preference for certain food sources, which allows them to feed and reproduce. They therefore have their own evolutionary drive to maintain their ecological niche and will do anything to ensure their survival. This includes sending signals to the hosting human that they want more of the same junk food that they thrive on.

This idea is now more than just a wild theory. It has actually been shown in mice that have been bred to artificially lack an immune receptor (TLR5). This disrupts normal gut–immune-system communications and leads to

a change in gut microbes that tri...

The notion that microbes could affect our food behaviour by providing us with brain-chemical rewards triggering us to eat more burgers is not so crazy – indeed, for our highly evolved and specialised bacteria it should be a piece of cake.37

Several studies have shown that strong religious belief confers health benefits regardless of diet.

Our twins studies have shown belief in God has a partially genetic basis, as does a tendency to follow strict dietary patterns like veganism. Vegetarianism in many parts of the world started as part of religious movements, such as Hinduism, often as a way to distinguish them from other religious groups.

indulging in an occasional steak may not be harmful. But should we be worried about L-carnitine rather than meat itself?

Even when all these other factors were accounted for, diet and nutrition remained the dominant factor in determining the microbiome and its relation to health in the elderly. The residents with the least diverse gut microbiomes were far more likely to be frail and suffer from illnesses – and whatever the cause, were more likely to die within a year.

When Claire Steves in my lab looked at 400 of our older UK twins living independently who were generally frail, she found that they had a less diverse microbiome than average and lower numbers of microbes associated with suppressing inflammation and gut leakiness, such as F. prausnitzii. They also had fewer beneficial lactobacilli.

Superfoods may seem a fun concept, but they are also a marketing con, as virtually every fresh fruit and vegetable is a superfood.

They are all packed with hundreds of different chemical compounds that people can dream up long lists of attributes about. Some consider yoghurt, quinoa, eggs and most nuts to be superfoods, and from the earlier chapters of this book we could add traditional cheeses, olive oil and garlic – the potential list is endless.

This indicates that some people eating exactly the same bowl of potatoes or pasta will have a greater amount deposited as fat because of the effect of their genes on their microbes. So a potato is not a potato to everyone – to some people that potato, energy-wise, is like a double portion.

Finding more of these gene copies could help us in the future to divide people into different groups of food eaters. People like Linda who find themselves in a high-grain-eating environment but lack the right genes may be better off reducing the high-carb starches and eating fats instead, which their bodies and microbes may be better designed for.

Most doctor-prescribed medicine is flushed down the toilet; less than 50 per cent is taken, even for serious conditions; and I see many patients who refuse all medications. But if you call the medicine ‘a vitamin’, some seem very eager to take them, even if they are proved not to work. This is what I call vitamin loyalty. There is no proven benefit to the non-diseased person; in fact, the evidence so far suggests taking vitamin supplements regularly, especially in large amounts, has risks.

It seems to me that the bottom line is this: unless you have a proven deficiency disease or are on a bizarre diet, vitamins don’t help, and may cause harm to you and your microbes. Empty the bathroom cabinet of the whole family supply, and start afresh. We