William Banting was a highly successful west London undertaker whose famous family firm organised royal funerals. His health was good but he had always been on the heavy side. This had become an increasing problem in his thirties, and his waist had expanded way beyond all his peers’. Friends and dietitians had recommended different diets, and his doctor said he wasn’t exercising enough. He was determined to lose weight. For the next three decades he tried different restrictive dietary regimes and many forms of exercise. For several years he tried rowing for one or two hours a day, but this just made him very hungry, so he turned to hours of swimming which didn’t help either. He tried power walks, and steam-bath treatments in spas. But nothing worked and his weight remained the same.
Finally he consulted a private consultant, one Dr Harvey, an ENT surgeon in London who also dabbled in diet advice. He recommended a meat and fruit only diet, and after so many failures William was amazed by the results. He lost 29 kg in the next year and kept the weight off until he died, at eighty-one. His booklet Letter on corpulence, Addressed to the public was a controversial bestseller in 1864 Britain – a century before Atkins.
Most of the protein in our diets comes from just a few sources. These include meat like beef and chicken, which are over 30 per cent protein, fish like salmon and tuna at over 20 per cent, beans and nuts such as peanuts (24 per cent) and soybeans (12 per cent). Other artificially higher amounts come from soybean extracts and whey protein (from milk). Vegetarians and vegans can achieve a normal protein intake too, but they have to eat a greater volume of food. In a world where we raise and eat over 50 billion chickens a year, one of the big ongoing debates of our time is whether meat eating is good or bad for you.
Some social historians have called our switch from happy hunter-gathering to oppressed agrarian cultures ‘mankind’s greatest mistake’.1 Eating like our ancestors used to before farming started ten thousand years ago seems on the face of it logical. The Palaeolithic (paleo) diet, a variant of the amazingly successful Atkins high-protein diet, is hugely popular in the US, and there are thousands of paleo cookbooks available to prove it, as well as increasing numbers of trendy paleo restaurants (they make an exception for wine). Paleo meals contain plenty of animal protein and are low in carbs, without grains, cereals and most sugars. I met a woman from LA who said that she was ashamed to be the only member of her gym class not on a paleo diet (she couldn’t bear giving up bread).
The proponents of high-protein/low-carb diets say you lose weight faster this way than by any other method, and keep it off. It supposedly also stops or reverses diabetes, reduces cholesterol and heart disease, and can cure allergies and auto-immune disease. Although rates of meat eating have declined in most Western countries, we are still highly dependent on animals for our calories, culture and family feasts. In the UK we eat an average of 84 kg per year, similar to our European neighbours but less than burger- and steak-loving Americans, who consume 127 kg annually. With meat plentiful and relatively cheap, should we all be embracing this ‘back to our meat roots’ organic philosophy?
The Atkins religion
Dickie looked into the bedroom mirror and didn’t like what he saw. His rugby and squash playing days were over. He had to admit it: he was definitely podgy, he had a beer belly. His wife had been nagging him to do something for a while and she was right. His best days were behind him: a fifty-five-year-old surgeon, he was no longer in prime shape. He was always tired. He found being on his feet operating all day exhausting. Even playing golf was hard work, and his knee ached. He wanted to do something. He liked meat and liked the sound of the Atkins Diet. His brother had tried it and was still doing well after six months, having lost over 20 lb.
The first few days were easy; bacon and eggs to start the day, a couple of boiled eggs or a cheese omelette for lunch, and fish or steak plus salad for dinner. Once or twice he found himself, without thinking, going to grab a biscuit, a piece of bread or some grapes. After two weeks he felt good and noticed the difference in his waistline; he was already shedding several pounds. Strangely, he didn’t feel as hungry as he thought he would have.
He continued for another month and managed to lose a stone. He was proud of his willpower and his family were supportive. However, he started to notice a few annoying side effects: constipation was becoming a problem, he was waking up with bad breath, and his initial burst of energy was waning. At the hospital he got a colleague to test his blood.
His blood lipid tests showed that his total cholesterol had increased about 5 per cent, which is within the error of the measurement, so wasn’t very helpful. His unhealthy lipoprotein (LDL) had increased slightly, but reassuringly his levels of healthy HDL more than balanced it. More worryingly, his liver test results were slightly worse, as were his uric acid levels, a risk factor for gout. He phoned his brother to ask his advice, but he had not experienced any similar issues and was now slimmer and stable on a nearly zero-carb diet. Discouraged, Dickie began to ruminate on the idea of a nice piece of bread with his cheese and fruit. He soon relapsed and gradually slipped back into his old habits and, unfortunately, into his old trousers.
The Atkins Diet revolution started life in the 1970s as an alternative to the many low-fat or low-GI diets of the time. Dr Atkins, although a hundred years after Banting, was going against the flow, and it took a while for his diet to become mainstream. But like a successful religion it would spread to millions of devoted followers.2 When I suggested in my last book that Atkins himself was ‘allegedly’ overweight and had ‘allegedly’ had heart problems, I got more letters correcting me than on any other topic.
His idea, successful as it was, differed from most other diets of the era. It was simple and alluring, with no limits on quantity. This appealed to dieters who had been confused by complex regimes of mixing or alternating food types, by eating times and having to count calories and portion sizes. Just avoid carbs and have as much protein as you liked was the simple and effective message. Most people lost weight on the plan within a couple of weeks, and many sustained this for a few months.
The weight loss on an Atkins-style diet was often reported to be more rapid and noticeable than on low-fat regimes. Studies confirmed this was true for the first six months, though the evidence was less clear when the two diets were compared beyond a year. Trials also showed some benefits such as an increase in healthy HDL levels.3 The combination of the high-protein and very low carb diet is also called a ketogenic diet, because the body deprived of glucose produces ketone bodies as fuel, made from groups of fatty acids in the liver stuck together. This is a less efficient fuel source, but a vital method of keeping our brains and other vital organs supplied with energy.4
The large metabolic changes in people on ketogenic diets cause side effects that can have strange advantages in treating some medical conditions, such as preventing seizures in children with epilepsy. High-protein diets may produce more weight loss short term than low-fat ones, as converting the essential energy from protein and fat is much less efficient than doing it from carbs: the body has to use more calories to do the same job. Another reason is that fat and protein provide a greater feeling of fullness (satiety) than most carbs, owing to the release of gut hormones that signal the brain. The high-protein and high-fat intakes may slightly reduce the laying down of fat, although this is controversial. And of course, the reduction in available food choices, as with many diets, may also reduce the total intake of calories.
For many people like Dickie, dieting for more than a few months is difficult. In fact fewer than one in six dieters said they have ever managed to maintain a 10 per cent weight loss for more than twelve months, and that is probably a big over-estimate.5 This is due to boredom and lack of variety, and the other major explanation is metabolic.
Carefully controlled studies have shown that after a period of around six weeks of intensive dieting on any regime that has achieved a weight loss of over 10 per cent, energy expenditures and metabolism diminish so as to compensate as the body tries to regain its previous fat stores. This metabolic slow-down can be effectively as much as 10 per cent of daily calories. In trials, low-fat diets generally seem to provoke the greatest effect on this resetting mechanism, and high-protein/low-carb Atkins-style diets the least.6
But even high-protein diets can’t fool the body for long. After a while, cortisol levels rise and thyroid levels fall, because both have the effect of increasing fat retention and reducing energy levels.7 So although the mechanisms vary depending on the diet, the body always has a trick up its sleeve to ensure the replenishment of its fat stores. We all know people who have done well on some diets and not on others, and some who fail on most. This may not just be a case of willpower. Well-intentioned people may possess some factor that makes it more difficult for their bodies to respond to dieting. Most diets work for people in the first week or two, but much of the early weight loss is water. As the body reacts to lower calories longer term, major differences appear in how easily we burn off fat and how our metabolisms slow down to compensate. These mechanisms are complex, and regardless of whether they are due to gut or brain chemicals or psychological factors (as we learned in the introductory story of twins on diets) they are strongly influenced by genes as well as by microbes.
It is hard to distinguish in high-protein diets between how much the benefits and side effects can be put down to the lack of carbs and how much to the extra protein. During the recent evolution of the Atkins Diet the high priests of the billion-dollar corporation behind it have increasingly stressed the importance of low rather than zero carbs and reduced the emphasis on heavy meat eating. They have also tried to encourage the inclusion of more plant fibre in the diet. But despite more liberal regimes some people still have side effects like gout, constipation and bad breath. Strangely, mice have done badly too when put on Atkins-style diets for twenty-two weeks, which equates to several years for humans. They develop abnormal cholesterol and lipids, a pro-inflammatory state, increased liver fat, glucose intolerance and a shrinking of the pancreas, without even the merest weight loss to show for their trouble.8
Microbes predict your weight loss
The particular metabolic state of your body may influence your variable response to particular diets. My colleague Dusko Ehrlich was in charge of a large €20 million EU-funded microbiome project called Meta-Hit that answered some of the main questions. The researchers were able to look at gut microbes by sequencing the DNA of not just one gene (as with standard methods) but of every gene in every single microbe, and then putting them back together like a giant jigsaw puzzle. This is called shotgun meta-genomics because of the size of the data generated and the enormous scale of the computing problem in putting the pieces back together; and it costs several thousand euros per person.
They tested the microbe responses to diets. Forty-nine volunteers lost weight after six weeks on a special low-calorie (1,200) diet comprising 44 per cent healthy high-fibre carbs and high protein (35 per cent). They were then given another 20 per cent more calories for a further six weeks. They lost weight as expected in the first six weeks and then stabilised; some individuals then rapidly put on weight again. The prediction of who would lose the most was not based on their willpower or on their starting weight, but related to their gut contents.9
Although everyone benefited to some extent from this six-week low-calorie and high-protein diet, those subjects with the least rich and diverse community of microbes did the worst. They didn’t manage to reduce the levels of inflammation in the blood and experienced the fastest rebound to their pre-diet weights. This low-diversity group made up 40 per cent of the French volunteers, and 23 per cent in a larger study of 292 Danish patients. The low-diversity group were on average more obese and had higher insulin and visceral-fat levels plus abnormal lipids, giving them an increased risk of diabetes and heart disease.10
The investigators found there were certain keystone species that were always present in the healthy subjects with rich and diverse microbe communities and usually sparse or absent in the unhealthy group. These included many of our friendly bacteria already discussed, like the bifidobacteria F. prausnitzii, lactobacillus, and the ancient methane-gas-producing bug (Methanobrevibacter). An analogy here is with keystone species in biodiverse habitats such as the case of the loss and subsequent reintroduction of wolves to the Yellowstone National Park. Without our keystone species the natural balance of the ecosystem falls apart.
The team found less inflammation and more of the beneficial fatty acid butyrate in the diverse group. They proposed that testing our guts for diversity (or richness) could be a new and better way to determine health as well as the future risk of many diseases like diabetes, and they are developing a clinical test.11
For the unhealthy subjects short of diverse microbes, the low-calorie/high-protein diet wasn’t a total failure. After six weeks they did lose weight and managed to improve their microbiome diversity significantly. The problem was the rebound afterwards. The duration and intensity of the trial may not have been enough of a shake-up to permanently alter the microbe community. It wasn’t clear from this study if it was the calorie restriction, the lack of carbs or the increased protein that had the major effects on the microbes.
Several studies have shown that the fewer fruits and vegetables and fibre you consume, the less diverse your microbiome, but the reverse is also likely to be true. Although I haven’t tested it, one possible way to improve the outcome of an intensive low-carb/high-protein diet would be to start beforehand with a six-week fruit and vegetable feast to prime your microbes.
Reductionarians could save the planet
If weight loss is not your primary goal, what about the health effects of regularly eating meat? Vegetarians argue that meat is unnecessary for humans, causes animal suffering and adds to global warming. Studies have estimated that, because of the energy inefficiency of raising cattle with modern industrial methods, meat and dairy farming could contribute up to a fifth of greenhouse gasses globally, thereby contributing to climate change. This has led to calls for people to reduce consumption regardless of health or animal concerns and to become ‘reductionarians’ so as to save the planet. Although definitions are often movable, nearly 10 per cent of people in the UK now claim to be vegetarian or non-meat-eating, and the trend is increasing in many Western countries.
We surveyed 3,600 pairs of our British-born twins with a mean age of fifty-six in order to explore the causes of not eating meat. There were 104 pairs (9 per cent) of identical twins that were both vegetarian compared to only 55 (7 per cent) of non-identical pairs. This meant that although there was a small genetic component, it was outweighed by environmental and life-experience effects. These might include factors such as who they married, peer groups and where they lived. Vegetarians often like to quote studies of groups of vegans who avoid eggs, dairy and meat and live long and happy lives – but is this true?
Many Seventh Day Adventists (the protestant sect living in the US), who embrace healthy living, are vegans. When 34,000 of them were studied, researchers found that males, as well as being thinner, live on average seven years longer (females, four years) than average meat-eating Americans.12 When the studies were extended to a further 70,000 Adventists across America they were able to compare, within the same group, the roughly equal proportions of meat-eating and non-meat-eating Adventists.
The vegetarian Adventists showed around 15 per cent reduced mortality (mainly from heart disease and cancer), but this more rigorous study translated into only about a two-year increase in longevity. This demonstrated the importance of controlling for other factors such as being Californian, being sporty, not drinking and being very religious.13 These subjects believed that God wanted them to have the healthiest lifestyle possible, so they may also have been helped by divine forces? Several studies have shown that strong religious belief confers health benefits regardless of diet. Intriguingly, psychological studies of Dutch twins also show a connection between holding strong religious views and being unreliable responders to questionnaires. It wasn’t that they deliberately lied, but rather that they had a tendency to tell people what they wanted to hear, which distorted their answers.14
The UK has over twice the proportion of vegetarians as the US, and the gap is increasing each year. This is in complete contrast to the numbers practising religion, where the steady threefold greater numbers in the US are outstripping the diminishing UK numbers. This may not be just coincidence. 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.
The health benefits of their dietary regime to over 30,000 British vegetarians and pescatarians (fish eaters) have been shown to be less clear cut than in Adventists, and it has been difficult to distinguish the effects of the lack of meat from those of a greater health consciousness. Although most studies show a reduction in cancers (up to 40 per cent in the latest fifteen-year follow-up) and 20 per cent in heart disease, this is balanced by increases in other diseases like strokes and little or no reductions in total mortality.15 16 There is also a suggestion that British vegetarians are somehow less healthy than vegetarian Americans, which may be due to differences in culture, lifestyle, lack of religious beliefs, or to other not so healthy components of the British vegetarian diet such as baked beans, crisps or extra sugar.
Identical-twin studies are a great way to adjust for cultural and genetic factors and explore meat eating without many of the biases of observational studies. We looked closely in our TwinsUK study at our 122 British identical twin pairs who differed in their meat-eating habits, one being vegetarian or vegan and the other a meat eater. Remarkably, there was only a small difference in obesity within the twins as measured by BMI. The vegetarian was slightly slimmer by an average of just 1.3 kg (although the range went up to a 40-kg difference in one pair). This compares with much larger differences of about 4–5 kg in the Adventist studies, showing the significant effects of genes and culture which are hard to account for in non-twin studies.
Intriguingly, in our study we found that even if you were a regular meat eater, having a sister who was vegetarian made you healthier than the average UK twin, in that you’d be slimmer and less likely to smoke. Although we haven’t accounted for the amount of meat eaten in the discordant twins, what is clear is that the differences in weight due purely to avoiding meat are exaggerated when you don’t account for genes and upbringing.
Meat eaters and paleo-diet converts point to the facts of our evolutionary past as a solid basis for a dietary theory. There is no doubt we are omnivores, with bodies and digestive systems built to eat a variety of foods, both vegetables and meat. Our jawbones and teeth are made for chewing tough foods, and although the process is helped by cooking, we are different from fruit-eating primates in this respect. We also have an armoury of hormones and enzymes to break down proteins – not forgetting our ever-helpful microbes.
One big argument against totally excluding meat from our diets would be the lack of other easily available nutrients. Many vegans and some vegetarians run into nutritional problems as meat contains many essential nutrients like vitamin B12, zinc and iron that are very hard to find in vegetables. Vitamin B12 deficiency is very common in non-meat eaters and it is possible that this offsets some of the advantages of the vegetarian diet.
The British are still known by their stereotype as big strong meat eaters – les rosbifs as the French ironically call us (and we sometimes choose to call them ‘Frogs’). One theory why British cuisine is traditionally so bland is to do with the alleged high quality of our meats over the last centuries, due to our fertile soil and wet grass. This is contrasted to the scrawny animals in France and Italy that have needed inventive and flavoursome sauces to mask their bad taste and texture. Yet in 2015 there are four to five times more vegetarians in the UK than in France, although the French might argue that our overcooking of dull meat could account for this.
Vegan vitamins
I mentioned earlier that I had a brief moment of veganism. This trial only lasted about six weeks, as I found life too tough without cheese and my fine dining was hampered when I was travelling abroad. But giving up meat was not a problem as long as I could eat fish. I happily did this for a year until I went for a medical check-up and noticed my blood levels of vitamin B12 and folate were low and my homocysteine level – a marker of heart disease risk – was high. I was ingesting plenty of folate from my vegetables, but the key vitamin B12 from meat was lacking and this lack was blocking my absorption of folate too.
This was annoying, as I had lost a few kilos and was feeling good; but my blood pressure was slightly raised and the low B12 was possibly making things worse. I started taking increasingly large amounts of B12 supplements each morning, but they had little effect on my blood levels. I tried eating a few eggs a week as they have some B12, but that didn’t work either. Finally in desperation I tried B12 injections in my bottom. They worked, and my B12 and then my homocysteine level too finally returned towards normal. A few months later, as I was about to get myself (via instructions to my wife) another shot in the bottom, a thought came to me. This is daft. I am trying to be fit and healthy, yet having injections every month feels neither healthy nor particularly natural.
I decided I should eat just one steak a month and see what happened. So that’s what I did – either a rare steak or a raw French-style steak tartare, once or twice a month, did the trick, and gave me the vitamins I needed without any artificial supplements. And the little experiment brought home to me not only that my body wasn’t adapted to change so rapidly to a meat-free diet but that even my microbes couldn’t manufacture all the necessary nutrients.
So if a little meat was good for me, was this a quirk or down to evolution?
The world according to paleo
The full paleo-diet doctrine prohibits grains, legumes (which includes peanuts), milk, cheese, refined carbs, sugars, alcohol and coffee. It also bans tomatoes, potatoes, and aubergines as they are all nightshade plants and thought to cause auto-immune disease via leaky guts. The diet encourages organic grass-fed meats and poultry, fish, coconut and olive oil and other vegetables and a small amount of fruits, though some adherents eat only berries. Like most religions paleo belief comes in different degrees of orthodoxy and strictness. The diet is broadly based on what we think was consumed for a million years or so before our very recent history, items for which we are perfectly adapted.17 The main theory, the rationale (which is common to other diets such as those that avoid grains), is that our bodies haven’t had time to evolve or adapt. But it has major flaws.
In my view the theory’s chief shortcoming is that it doesn’t account for the latest genetic or evolutionary studies and treats humans as rigid unchanging automatons. It also forgets about the trillions of microbes we carry around with us that have also been adapting and evolving. And can we, anyway, be certain what our ancestors actually ate? Was it the lean steaks and rocket salad that gym fanatics in LA imagine? As our ancestors didn’t leave us any recipe books or DVDs, the situation calls for a good deal of speculation, relying on the observation of a few remaining hunter-gatherer tribes and archaeological remains, including bones, and the examination of prehistoric human dung.
Early hominids like Australopithecus who lived between two and five million years ago were half our size and had much bigger molars than we have. These humans probably didn’t eat much meat apart from insects or reptiles, as they were not fast, agile or bright enough to catch much unless it was already dead. A couple of million years ago during the ice age Africa cooled down and fruit became scarcer. Our Homo erectus ancestors, in order to survive, now had to find better hunting and gathering techniques. Studies of chimps show they can take up to eleven hours to chew raw meat properly, so humans wanting better things to do with their time had to work around this. They initially developed stone tools to cut up the tubers, roots and raw meat into smaller pieces.
Then another even more crucial breakthrough occurred about a million years ago: using fire to cook food in a controlled way (our information comes from ash found in a cave in South Africa). This opened up many more possibilities, as cooked food reduced toxins and the incidence of food poisoning, and allowed much more energy to be extracted from food in a short time. Importantly, it freed up the valuable time we had previously spent collecting, then eating and digesting the tough roots we’d gathered and the occasional bit of raw meat.
Now that we were eating cooked food, we needed less of the digestive juices and enzymes as well as less fermentation time, so the lower part of our guts shrank accordingly. With the intestines using less energy and receiving more calories from the cooked vegetables and meat, our brains rapidly grew bigger and we became vastly more proficient at hunting meat, a great source of calories.
The few remaining hunter-gather tribes in existence allow us to explore their diets and their microbes as a possible window on the past and on our ancestors. Although the risk is that, once studied, they are no longer totally isolated. One such group are the Hadza tribe living at the site of early man’s origins around the Rift Valley in Tanzania. They live in flexible and mobile groups of thirty to fifty and divide food duties by gender: the males hunt in small groups for game and occasionally honey, and the women gather plants and berries and dig for tubers. The hunting produce varies by season: it is very low in the wet season and increases in the dry periods when animals go to seek water. The tribe has little or no access to modern processed foods, medicines or antibiotics.
An eccentric colleague of mine, Jeff Leach, co-founder of the American Gut Project, lived with them for a good six months, following their diet and lifestyle to see how he and, importantly, his microbes got on with their diet. His only contact with the outside world was the satellite internet on his laptop that he used to write his weekly blogs.
He reported that while he at first maintained his Western diet his microbes had changed just slightly in the African environment. He then spent another few months eating exactly like the locals. This included zebra meat, kudu, dik dik, honey and many different roots and berries. He swabbed himself and everything else in sight, but was disappointed to discover that his microbes, although they had a better profile, were still ‘Western’ and not yet real Hadza.
Another group who closely resemble Stone Age hunter-gatherers are the Yanomami living in one of the remotest parts of the Amazon on the Brazilian–Venezuelan border. They still live essentially similar lifestyles to their ancestors’ and are split into about two hundred villages of groups of around a hundred people, and some move camp every few years. They have no domesticated animals but live off a wide variety of crops comprising staples of cooked bananas and manioc (cassava), vegetables, fruit and insects, and episodically kill monkeys, peccaries, birds, frogs, caterpillars, grubs and fish. When sampled, they showed one of the lowest blood-lipid levels of any population and no signs of obesity.18 Two independent teams managed to acquire the right contacts, permits and insect repellent and after parlaying with the chiefs of some of the remotest villages obtained stools from these rare populations. The results were both fascinating and worrying.19 20
The most striking result was that each tribesman and woman carried a vastly increased diversity of microbial species compared to Europeans. Each tribe also had its own extra 20 per cent of microbes that are totally unknown to us. Exploring just one bug in detail, E. coli (the most comprehensively studied bacteria), produced over fifty-six novel strains never seen before. Several common European microbes were completely absent in the tribes. For example, our friendly bifidobacteria that we get from yoghurt and that all Westerners have, was totally absent in all the Hadza and most of the Yanomami.
Both groups had an excess of Prevotella, which other populations whose diet is grain-based also have, plus many bacteria useful for breaking down plants. Oddly, in the West these same ‘healthy’ microbes have been associated with auto-immune diseases like arthritis. A microbial difference was noticed between men and women, which probably reflects their different roles in food collecting and eating. Men are in charge of the hunting and eat more meat at irregular intervals, and women can spend considerable time preparing the main staple food, manioc. These differences are not seen in Western populations, where women have the same access to supermarkets as men.
These two studies demonstrate that a group of microbes that may be unhealthy in one population can have the opposite influence in another very different environment. They also tell us that the microbial community as a whole is more important than one or two species. Moreover, they give us an idea of how many of our gut microbes may have become extinct since the introduction or farming, pesticides and antibiotics.
The sad fact is that we have a very depleted microbiome compared to our ancestors.
Meat, hearts and microbes
From the observational studies of meat eating so far performed in Western countries, there is no clear evidence that eating non-processed poultry meat is harmful, but eating red meat has been consistently associated with an increased risk of heart disease and cancer and an overall increase in the risk of dying. No proper randomised trials have been done – it’s hard to force these diets on people over years – but reasonably good data now emerges from combining large observational studies.
Two large US cohorts of 84,000 nurses and 38,000 male health professionals were followed for a cumulative total of three million person years. They showed that eating just one extra red-meat serving per day increased globally the risk of death by 13 per cent for red meat and 20 per cent for processed meats, with slightly greater effects for heart disease and a 16 per cent increased risk of cancer.21
Shortly after, data from the European EPIC study engaged in following 450,000 people from ten countries indicated a modest 10 per cent increased risk of mortality with red meat. An even stronger risk of up to 40 per cent was seen for processed meats like sausages, ham and salami, or those unclassifiable meats in prepared meals.22 Using this data, the Harvard group estimated that reducing everyone’s meat consumption to half a serving or less per day (45g) could prevent 8 per cent of US deaths. In the UK, to produce similar benefits in men, this would mean halving their current meat intake.
Eating a bacon sandwich or a hot dog daily will reduce your life expectancy by two years or, more strikingly, by one hour per sandwich. The equivalent for a packet of cigarettes would be five hours. The caveat is that these results so far only hold for Europeans; a study of 300,000 Asians found that although red meat intakes are lower, they are increasing in parallel with increases in heart disease. But unlike the Western studies there was no obvious direct meat–heart-disease correlation.23 Clearly, not all people suffer the same side effects of eating red meats, and there are other factors involved too.
With the collapse of the theory claiming that it was the fat in meat that caused the increased mortality, we need to look more closely now at other possible causes and at what our ancestors ate. We talked earlier of the work of the wandering dentist Weston Price who found that isolated tribes, and presumably our ancestors, often preferred the fattiest cuts of meat, which contain most of the nutrients and vitamins.
As we noted earlier, why some people in the West can eat large quantities of meat without problems and others develop heart disease and cancer has remained largely unexplained. One theory was that we all have different heart-disease-predisposing genes that interact with the meat in some way, but this has not been proven. In 2013 a series of experiments exploring our gut microbes totally changed our views on our relationship with meat.
Cardiologists have long suspected that a build-up of a harmless-looking but stinky substance called trimethylamine (TMA) – a porridge-like plaque in the arteries leading to heart failure, high blood pressure and heart attacks – is a major trigger of atherosclerosis. In fact, the harmful effects occur only when TMA is converted by the addition of an oxide molecule into its nasty sister compound TMAO. This TMAO is solid and odourless and sharks and some other fish have a lot of it. When fish goes off, the whiff is partly due to the solid TMAO changing back to TMA, which is smelly and liquid.
A US team from Cleveland confirmed this suspicion by measuring TMAO levels in the blood of several thousand patients. They found that those with higher than average levels had a nearly threefold risk of major heart problems.24 The team went on to feed rats a dietary source of TMAO derived from two components of red meat, choline and L-carnitine. They found that microbes in the rat guts were needed to convert the TMA into its dangerous form TMAO, which led to the atherosclerosis.
This was confirmed in humans when they fed omnivore volunteers an 8-ounce steak. The gut microbes greedily used the L-carnitine for energy, and in the process converted the TMA in L-carnitine to TMAO as a waste product a few hours later. What was fascinating was that when they repeated the experiment after giving a broad-spectrum antibiotic (which wipes out most types of bacteria in the guts), no toxic TMAO was produced. This showed definitively that specific gut microbes were feeding off the L-carnitine to produce the nasty amine. Potentially, this demonstrated that heart disease could be prevented by manipulating our gut microbes.
The effect of the antibiotic was temporary and a couple of weeks later, after continued meat eating, the TMAO was being produced again. Between individuals there was a big difference in how much TMAO, which can be measured in blood, was being produced. When the researchers looked at a group of vegans and vegetarians whose microbes rarely encounter L-carnitine or meat and fed them (apparently without duress) steak, very little happened and TMAO levels hardly changed.
This clearly shows once again why we don’t all react in the same way to food. Vegetarians, as well as having different microbial profiles from meat eaters, also have some inherent genetic differences. The researchers found that people tend to have microbes that cluster into three or four communities, known as enterotypes, which can be thought of a bit like blood groups. Some of these increased risk and others were protective against the side effects of meat eating. The protective profiles included low levels of Prevotella and high levels of Bacteroidetes, although these are probably over-simplistic and still need to be confirmed in larger populations.
Vegetarians are therefore protected, but if they were to change to a regular meat or L-carnitine diet for several weeks beforehand their rare meat-loving microbes would wake up, start reproducing and make TMAO in larger amounts.25 These studies were done in vegetarian mice, but the principle is the same: eating or abstaining from regular meat can change your microbes for the better or for the worse. It should be possible, however, to improve the microbiome of a regular meat eater by having a meat/carnitine holiday. In other words, indulging in an occasional steak may not be harmful. But should we be worried about L-carnitine rather than meat itself?
Fishy tales and bigorexics
Concern is one thing, outright banning another. One problem is that there is also L-carnitine in fish. Cod, sea bass, sardines, tiger prawns and squid, for example, have 5 to 6 mg of L-carnitine per 100 grams, though this is only a tenth of the amount in beef which has 95 mg. Fish eat plankton and they also feed off L-carnitine and produce TMAO. Everyone thinks that fish is good for you, and provides good vitamins like D and E. Most people know that the longest-lived people on the planet, the Japanese living in Okinawa, exist exclusively on a fish and carbohydrate diet.
So is fish necessary for a long life?
Parents get annoyed when their children reject it. My son only ever ate fish disguised in breadcrumbs, and we lovingly called it ‘underwater chicken’ until he learned that chickens are poor swimmers. Strangely, fish aversion is common in kids, who are at their fussiest between three and five years old, and as it has a genetic basis it can continue into adulthood, although it’s hard to think of an evolutionary advantage as lobster allergy, for instance, is rare.
The main way fish gets into the health news is via stories of contamination by deadly pollutants like mercury, dioxin or polychlorinated biphenyls (BCP), which can affect babies or lead to brain damage or (in theory) cancer. Contamination generally affects longer-lived species like shark or swordfish and is not yet a major problem in smaller fish. I mentioned earlier how many lab studies find fish oils to have protective effects on the heart due to their major polyunsaturated omega-3 fats, and fish eating is widely promoted because of this. Nonetheless, the hard scientific data to back up the claim that fish is the perfect health food is, surprisingly, not that convincing.
There are no good trials of actual fish eating, only of supplements. Recent meta-analysis of all the trials of fish oils concluded that the benefits of fish-oil supplements are hard to detect and have been previously overestimated.26 Meta-analyses of observational studies of fish eaters have shown a 17 per cent reduction in their mortality and a 36 per cent reduction in heart deaths, but these may well be biased by a general healthy-lifestyle effect.27
Other large prospective US studies have looked at people taking up fish eating in middle age and found a very modest 9 per cent reduction in heart deaths in women, but no benefit whatsoever to men.28 This could be due to the crude observational nature of the studies or we may have overestimated the health advantages. In this case, the mild beneficial effects of the fish oils are perhaps being balanced by the bad effects of the L-carnitine and the microbes that feed off them.
So fish, while not being harmful and containing many good nutrients, may not be the secret of eternal life for everyone. You don’t have to live in Okinawa to live for ever. Other exceptional long-lived groups around the world often eat little or no fish, such as the many Sardinian mountain villagers or the Californian Seventh Day Adventists.
The L-carnitine we ingest in fish and meat, as well as in milk and many other foods that can cause heart disease, is an unusual nutrient. It is produced inside most animals by a mix of two amino-acids, but can only be broken down and metabolised by microbes. It is widely promoted as a supplement on nutrition websites with the claim that it helps glucose metabolism in the body’s energy cells, the mitochondria, to burn fat. Surprisingly, in short and unconvincing studies it has been tried in diabetics and (brave) heart-disease patients, with some reported success. It has even recently been marketed in the UK as a weight-loss drink to take before meals. The company that makes the product Full and Slim claims it acts like a gastric band.29
Carnitine is also much loved by fitness fanatics and bodybuilders, who some doctors refer to as ‘bigorexics’, meaning sufferers from a new form of eating and behavioural obsessive disorder. Users are encouraged to take 2–4 grams of carnitine a day as a fat-burning and muscle-building potion. In fact, this could be contributing to the increasing heart problems seen in this group, many of whom also abuse anabolic steroids. In a recent survey of gyms, 61 per cent of bodybuilders took L-carnitine supplements at very high doses.30 To get 4 grams of carnitine per day naturally you’d have to eat a lot of steaks – over twenty, by my calculations. The average meat eater consumes around 120 mg of the substance a day, and yet vegans exist on only 10 mg a day and show no obvious deficiencies. Certainly, carnitine supplements seem both unnecessary and an extremely bad idea as far as your heart is concerned – and another example of how we take one isolated chemical nutrient out of context and promote it as super-healthy, while the opposite is true.
Going walkabout
If the paleo diet lacks much biological or evolutionary logic, that doesn’t mean it is necessarily bad in the short term, particularly if eating more fruit and vegetables is encouraged at the expense of refined carbs. A real-life experiment in the 1980s took a group of humans back to Palaeolithic times and saw how they fared.31 Australian Aborigines have suffered most from the loss of their hunter-gatherer lifestyle and have high rates of disease. Even today half of Aboriginal men in Australia will die by the age of forty-five, and there are no clear signs of improvement.
An intrepid Australian researcher, Kerin O’Dea, found ten overweight and diabetic middle-aged Aborigine volunteers living in a modern settlement and suffering a host of Western ailments. She persuaded them to return to the bush for seven weeks with her, to live off the land like their ancestors had done.
They went to a remote unpopulated area of Australia that had been their original tribal lands, near a place called Derby in northern West Australia. There they existed on a high-protein (65 per cent), low-fat (13 per cent) and low-carb (22 per cent) diet, living off three principal sources of food: kangaroos (which have little fat), freshwater fish, and yams for carbs. Other occasional treats came from turtles, birds, rodents, insects, other vegetables and honey. Despite the impressive grocery list, the unfit and out-of-practice hunter-gatherers only managed to take in around 1,200 calories a day. At the end of the ordeal they had lost an average of 8 kg in weight. Their blood sugars had normalised and their unhealthy lipids and triglycerides had dropped dramatically.
O’Dea admitted that the reasons for the (paleo) diet’s success were hard to fathom, as it simultaneously reduced calories, increased protein, reduced carbs and increased exercise. This study was a one-off, but is mentioned on paleo websites as proof that the diet can cure obesity and diabetes. It is certainly impressive, but other strict calorie-restriction diets have produced similar results, albeit short term. Several years later, the fate of the Aborigines was unclear.
There are plenty of anecdotes about tough-minded individuals who have normalised their diabetes and reduced heart disease risk through severe calorie restriction and exercise, and sometimes by totally cutting out carbs.32 However, although change is possible in some highly motivated individuals, in the long term the practical reality in most patients is very different. In one study, the very expensive nine years of monitoring and constant nutritional support of 5,000 US diabetics ended in dismal failure. The intensive-weight-loss group lost only 3 per cent more weight and failed to prevent any diabetes-related complications.33
The only clear success story comes from a massive social experiment in Cuba, where the population had to suffer a five-year economic crisis in the mid-1990s. Motorised transport ground to a halt and free bicycles were issued, food was limited and people ate local produce. As a consequence they exercised more and ate less but more healthily, and the average weight of the population dropped by 5.5 kg. This was followed by a major drop in the incidence of diabetes and a reduction of 53 per cent in heart disease.34 Sadly, when the economic crisis was over they returned to their old ways and the health problems resumed.
The Aborigines exemplify the kind of population who, we believe, had been very healthy on their omnivorous diet and became very unwell when they changed to a Western diet. This suggests that eating protein was not the main problem. The other odd example is the Masai of East Africa who consume large amounts of meat and milk but few vegetables. A survey of four hundred tribesmen in the 1960s found little evidence of heart disease and they had low cholesterol levels similar to rural Chinese.35 They must have had interesting microbes.
Groups of humans that have over centuries evolved to eat large amounts of animal protein and fat seem to experience few health problems, and this could be because their gut microbes have adapted with them. It is only when diets change dramatically in a short time and our core microbes haven’t had time to evolve that problems develop.
I have learnt that for me an occasional piece of meat is probably good for my health, but I believe eating red meat every day or as part of a long-term restrictive high-protein diet is too much. As for white meat, if you disregard the fast or processed kind, no one has found anything particularly bad, at least healthwise, about the 50 billion chickens the world kills and eats annually. The chickens might disagree – they do of course suffer from regular salmonella and campylobacter infections due to their poor housing conditions and defective immune systems. Studying meat reinforced my decision to avoid processed foods that often contain meat of dubious quality or of uncertain origin. Having fish once or twice a week is probably healthy, and observational studies show pescatarians enjoy similar health benefits to non-meat eaters, so for the moment I’ll carry on eating my seafood.
As the definitions of vegetarianism become vaguer and ‘flexitarianism’ is a bit too woolly a term too, all of us should now consider becoming reductionarians – if not for the sake of our health, then to reduce global warming. If everyone cut out meat just one day a week, we would all reap the benefits. Although we lack hard data to support this, switching to organically raised meat may also be a slightly healthier option, as you’d hope it would be hormone- and antibiotic-free and so the animals would have had healthier microbes as well as healthier lives. Importantly, although more expensive, organic meat is also potentially more carbon-neutral. But maybe, rather than frequenting gyms and eating steak, we should all have a go at being part-time hunter-gatherers. Our ancestors, having no year-round supply of meat, had to regularly rely on other sources of protein.