Diet Books

You’re a professor of genetic epidemiology and an expert on diet, having written two bestselling books on the subject. Firstly, would you tell us how diet ties into your work as an epidemiologist? I had understood epidemiology as the study of the spread of disease.

Well, ‘epidemiology’ used to mean ‘the study of epidemics’. Then, as we thought we’d got rid of them, it changed to the study of the causes of disease in large populations. So, in a way, looking at diet is a bit like looking at smoking and cancer; it’s one of the risk factors for disease that hasn’t had that much attention paid to it, other than knowing that it was quite important, but also difficult to measure properly.

The study of epidemiology and diet has in the past generally relied upon quite dodgy questionnaires; maybe 100,000 people would fill in a questionnaire about their eating habits in the past year, with the results then compared to how many people later then die of cancer or heart disease. That’s been a very crude tool and has misled us a bit, although it’s getting better. There are lots of different ways of studying this. At the moment I’m interested in personalised medicine and diet.

In your book Spoon-Fed, you suggest that a great deal of what we think we know about nutrition and diet is “dangerously inaccurate” or, at the very least, misleading. Can you tell me a bit more about what prompted you to write the book?

Well, it followed from my previous book, The Diet Myth, where I introduced the gut microbiome as one of the things we’ve overlooked or gotten wrong; we’ve been oversimplifying diet. It was a logical move from there to say, okay, well, how have other myths gotten embedded in our culture? You know, like: why do we have these rules about all calories being equal? Why is everyone obsessed with the labels on foods, while we are losing track of the quality of food.

It really started as my wanting to tell people about the influence of the food industry, our lack of food culture, and the very weak scientific basis of nutrition that allowed this to happen. Food companies are dictating—usually indirectly, usually quite subtly—our ideas about food: what’s good, what’s not good. In the UK, we became the ultra-processed food capital of Europe, and we’ve just sleepwalked into it.

“All diet books are fatally flawed because they suggest there’s only one way to do things”

At the same time, I have an increasing interest in personalised nutrition, and the fact that our studies have shown that everyone is unique in their response to food. That is contrary to all our previous beliefs, for example, that 2,000 calories as intake works for the majority of women, and that’s all you need to know, or that you can spend an hour in the gym and burn off exactly 400. When you start thinking about why these myths are so widely embedded, there’s almost always someone who benefits, and it’s generally not us, the public.

What you have to say about the influence of the food industry on our behaviour reminded me a little of what Seth Godin, the marketing guru, told us; that many aspects of culture—happy hour, bumming a cigarette, even the concept of halitosis—were actually invented by marketers.

I have an enquiring mind, and I like to be surprised by things. So when I started researching my salt chapter, for example, five years ago, I didn’t have any doubt that it was bad for you and best avoided. But now the latest research is really questioning all that. I love that kind of stuff.

When we do change our minds in nutrition, for some reason, there’s just a block about people saying, ‘we’ve got it wrong’, unlike every other branch of science I’ve worked in. Whether that’s clinical medicine, and we do a test wrong, or genetics, chemistry, physics… people are always making mistakes. You say, ‘okay, we got this wrong, and we’re going to change it.’ But that never happens in nutrition.

I hope this book will open these debates, once we realise how much we don’t know.

Absolutely. I wonder if it’s because healthy diet guidance depends so much on the buy-in by the general public. People want clear rules, and they want to trust who they’re coming from if they’re going to change their habits of their own accord. So admitting that advice has been wrong risks losing their faith. But do you have any hesitation about ‘diet books’ as a general concept?

Well, depending on how you define diet, all diet books are fatally flawed because they suggest there’s only one way to do things. In general, the genre is outdated. And it preys on human weakness: peddling that there’s a quick fix for everything. You know, ‘you might have failed after the last 50 diet books you read, but this new one is going to get you motivated to start again.’

They’re still selling. There are something like 30,000 diet books on Amazon. It’s quite frightening that it doesn’t seem to matter that they don’t work.

Well, maybe that brings us to your first book choice: Banting’s Letter on Corpulence, written in 1863. It begins: “Of all the parasites that affect humanity, I do not know, nor can I imagine, any more distressing than that of Obesity.” His suggested dietary plan clearly didn’t cure us of corpulence. Why is the Banting letter still interesting to look at now?

I think it’s the first fad diet, that we know of in detail. In the 19th century, this really quite powerful personality, the undertaker to the royal family, was suddenly getting fat. He sought advice, tried all kinds of diets, was rowing up and down the Thames for two hours a day, all the time he just kept getting fatter. Then he decided to go on this diet, which he called after himself—basically a modern day Atkins diet of meat and fruit. And he lost 30 kilograms. As well as writing a book, he also gave out these free pamphlets, which at the time was very important because books were so expensive. He became a real celebrity and lived to the age of 81, which was quite unusual at the time.

What it illustrates to me is that he went against the advice of the time, which was that exercise could cure you of anything. Every time he exercised, his muscles would get bigger, but he would get hungrier and his metabolism would slow down. So he was one of the first to disprove the easy solution that you just need to run a bit more to get the weight off. The more you run—or row, in his case—the slower your metabolism, and the more your body tries to fight it. Hormones send signals to say, ‘you should eat more!’

“The more you run, the slower your metabolism”

I like the idea, and also just the fact that over 110 years before the Atkins diet it had all already been done. There are also some great quotes in there, and plenty of social history. Because in his day, seeing someone obese was really quite unusual. Kids would point at him in the street, and laugh at the fat man going down the road, which you wouldn’t really get now.

Yes. And there’s a very recognisable sense of desperation in the way he writes about being out of control of his weight. He writes about all the other things he tries—bathing in the sea, taking “gallons of physic and liquid potassæ”, drinking sulphurous water… You really get a sense of the depths people are willing to plumb in the pursuit of losing weight.

Yes. It’s not a new phenomenon, except in those days it was just a very small percentage of the population that suffered from obesity. But he’s a great example of self-experimentation which I’m a big fan of; clearly his metabolism suited a high fit, low carb diet, at a time when his physicians were telling him that calories were the crucial thing.

Well, continuing on this these, the next diet book you want to recommend is John Yudkin’s Pure, White and Deadly. It zeroes in specifically onto the dangers of sugar, which is an argument that we hear quite often now—although it was, I think, highly controversial when it was published in the 1970s.

This is an interesting story, a battle between two academics: one in the UK and one in the US. John Yudkin was British academic who made up his mind that the reason people were getting fatter in the 1960s and 1970s was due to our increased use of sugar in foods, and the increased processing of foods. He thought that sugary beverages were the reason that people were getting heart disease—at the time there were various theories about heart disease including ‘executive stress’ and all these other weird ideas we’ve given up on now.

Yudkin makes a pretty good case for cutting back on sugar, if you read the book, but no one really heard him because he lost the battle with a guy called Ancel Keys, an American who was famous for creating K rations.

These were ration packs for US soldiers during the Second World War.

He also did studies across the world which correlated heart disease and obesity and diabetes with rates of fat intake. He argued it was nothing to do with sugar, and all to do with fat. Keys won the argument and persuaded the US government to back this and got the food companies on board, who were happy to reformulate their foods because they they could moving away from dairy and other things that were hard to transport, towards margarine, these grey margarines, dyed yellow, that they could say had less saturated fat in them.

That battle led us to 20 years of artificial low fat diets, and led to trans fats coming in.

I’ve heard of trans fats. They’re bad for you, right?

They’re nasty, chemically-produced hydrogenated fats that you can’t digest properly, and hang around in your blood and cause heart disease. They came from the food industry and probably led to an extra half-million deaths in the US alone. We still have some trans fats in our food today.

So Ancel Keys won the argument, in as much as fat in general was accepted to be bad, and saturated fat in particular. People prefer to blame just one thing, rather than accepting that, well, both sugar and fat are important.  So that was a pivotal moment. If Yudkin had won the global argument, we’d be eating different food today. He was ahead of his time. Ancel Keys is the reason we’ve still got low-fat stickers on everything in our supermarkets; it’s very hard still to buy full-fat milk or yoghurt.

You outline some other instances in your book of how the food industry’s marketing has defined how we eat, and what we think of as ‘healthy’. I’m thinking in particular of the breakfast cereal companies’ role in convincing us that breakfast is ‘the most important meal of the day’. Is it possible, do you think, to keep a level head with a bit of healthy scepticism? Or is it getting harder and harder to know what’s true when it comes to eating a healthy diet?

It’s hard to know what’s real because companies will quote real research papers, which sound genuine. But that paper may be 30 years old and based on a trial of eight people, which wouldn’t stand up today. More worrying, food companies are now using vanity journals. They’ll print anything you want: simply pay the fee and see your paper published in a journal with a nice title. Or they might get researchers to write new articles that sow confusion.

A good example of that is that there is increasing evidence that artificial sweeteners aren’t good for you. They’ve been linked to a lot of problems in the gut microbiome. So a company might pay for an ‘independent’ research group that does commercial work to write a literature review that says ‘it’s all very confused, we don’t really understand what’s going on, it’s hard to draw conclusions, there’s no firm evidence that artificial sweeteners are bad.’ That comes from an independent group, they pay for publication in a crummy journal that doesn’t really peer review. Then the company can say, we’re not quite sure what’s going on.

It’s exactly the same tactic that the cigarette companies used, and that the oil industry is using for global warming. It’s a tried and tested technique. One reason I’ve been able to do the research that I do is that I don’t work in a nutrition department that’s funded by the food industry.

Coming back to John Yudkin’s book, am I right in thinking that his warnings about sugar have come back into favour?

That’s right. The idea has come back. Like Banting’s diet came back as Atkins, some of Yudkin’s ideas have stood the test or time, or with new science have started to make more sense. That’s another point: we shouldn’t abandon old theories; we always need to keep updating our information based on the latest science rather than, as so often happens in this field, sticking rigidly to dogma. That’s what I’m absolutely against.

Next on our list of landmark diet books is The F-Plan Diet by Audrey Eyton. This was published in 1982. I believe she invented the high fibre diet?

Well, she put it into the popular consciousness. I vaguely remember this: people would joke about how it would make you fart. Reading the book now, it is dated, and some of the recipes are dreadful, most of them involving All-Bran breakfast cereal or baked beans. They’re also still very low in fat, using skimmed milk. But the reason I’ve included it is that fibre has been making a comeback.

“Some people are much better off skipping breakfast. Others are better off eating it. We shouldn’t force everyone to fit into a single size box”

At the time, the discussion was that fibre was important for avoiding cancer. But Eyton’s explanation for its role in weight-loss is interesting: it’s all about how fibre fills you up, stretching your stomach so you don’t feel hungry and stopping other food from being absorbed. She didn’t think it mattered whether food was highly synthetic or wholegrain, as long as it was low calorie, low fat and high fibre. I think that’s really interesting because it brings back how much we’ve developed our knowledge in that area.

Our research of the gut microbiome has revolutionised our understanding of how high fibre diets work: it’s all about the quality of the fibre, not just pouring chemical fibre there. Before, gut microbes were only seen as problematic; they gave you traveller’s diarrhoea or cholera.

Yes. You first wrote about the significance of the gut microbiome and health in The Diet Myth, which essentially argued that we need to ditch restrictive diets, avoid antibiotics and pesticides in our food, and increase our fibre intake if we want to lose weight and stay healthy. You also recommended gut-friendly foods like nuts, seeds, dark chocolate, leeks, onions, garlic and olive oil, or what’s generally thought of as a ‘Mediterranean’ diet.

The F-Plan Diet sold millions of copies, I think it was the best-selling diet book of the decade. But very few people stayed on it long term, basically because the recipes are pretty dire. But it was the first time someone said: ‘don’t drink orange juice.’ Just because it sounds healthy doesn’t mean it is; orange juice doesn’t have fibre, therefore it’s not healthy. So there are a few interesting nuggets in there and it’s a great historical document.

Look how far we’ve come. Now we realise that it’s not just about the quantity of fibre, but the diversity of fibre. It’s about the range of plants you eat. You’re not going to get that from some processed breakfast cereal.

Oh no. I’d very happily live off breakfast cereal for three meals a day. I’ve always thought of Bran Flakes as a health food. Should I be avoiding them?

People like breakfast cereals, but I think that we’ve been brainwashed into thinking that cereal is the standard breakfast, and that’s a bit sad. I appreciate that, if you’re busy, then you’ve got this packet of food that never goes off; you just open it and add milk, and you’re out the door very quickly. But, yes, most of them are really bad for you. In Chile, they’ve banned using cartoons on the packaging of sugary breakfast cereals for that reason. We’re far too lenient on the breakfast cereal market.

Even the vitamins they claim to contain, they don’t actually have or have in such poor quality that they aren’t absorbed. I think people should experiment with other breakfasts. People should be trying to eat real food and going without that sugar high in the morning. Try a high fat breakfast such as yoghurt, eggs or cheese, or skipping it altogether.

Do you personally use full-fat milk, rather than skimmed?

Yes, increasingly. Although I don’t actually drink much milk. I now prefer the mouth feel of the cream, and the flavour of full-fat dairy products. But I also use oat milk for environmental reasons. The fake milks are getting better.

For me, I think that if people pick foods based on their quality and taste, not some arbitrary definition or label, then they’re better off.

Absolutely. You mentioned other countries’ eating habits. That might bring us to The China Study. This book was published by the epidemiologist Colin Campbell (with his son, Thomas) in 2004, and was based on his very extensive epidemiological study of rural eating habits in China conducted in the 1980s.

This book was a huge hit in the US. Basically, this nutrition expert was working for the agricultural board in the US—selling dairy and meat—and got into doing this epidemiological study in China, working out the relationship between what different local populations were eating and rates of heart disease.

Right, because there is no one ‘Chinese cuisine’. The different provinces had very different diets, traditionally.

In the 1970s, when they did the study, China was a very different place. It was poor. Most people ate very little meat and dairy. And they basically had no heart disease, and hardly any cancers. There were no fat people, no diabetics. They were dying of infectious diseases and other problems—occasionally starvation. It was a very different world.

So they studied these different provinces and worked out that the richer ones that were eating more meat and more dairy were getting all the heart disease. That’s where the idea that everyone should be vegetarian for their health came from. The plant-based diet is based on these rules. He was particularly harsh about dairy. Milk and cheese came out very badly in his analyses.

He sold millions of copies of this book, and did a lot to jump-start the vegetarian movement in the US, where it had been very, very small, unlike in the UK. So it was very influential, although when I read and critiqued it, I felt a lot of the data didn’t stand up. In a lot of those regions where they were eating meat, they were also doing other things, so it was very hard to draw the conclusions that he did, but I put this book on the list as it’s interesting on the vegetarian vs. meat eating debate that we have now, and how it’s evolved over time.

“All of us really should be eating less meat and probably less dairy”

Before his study, the vegetarian debate was more about animal welfare; his study made a lot of people realise that it’s also a really good way to avoid heart attacks and cancer. And we now have a third reason to become vegetarian, which is about the planet: 25% of global warming is due to the meat and dairy industry. I think that’s a huge factor for many people who might not have been so worried about the other two factors, and it’s why many young people are turning to vegetarianism and veganism. I think that all the food we eat now has to have some environmental context, which absolutely wasn’t true even when I wrote The Diet Myth five years ago.

The question is, of the three reasons to eat less meat, which one are you most worried about? There’s a chapter in my new book on whether meat is really bad for you, and my general conclusion is that small amounts of really good quality meat is fine for most people. It’s about what else you put on your plate. So I’m not against meat eating, per se. I wouldn’t ban it, but I eat it rarely. That just allows you to have more plants on your plate, which helps the planet and your health.

So, although I think his studies were flawed, he got the debate going, and a whole movement in the US that wouldn’t otherwise have occurred. It’s just a good sign of evolving science; some of what he said was correct, but for the wrong reasons. All of us really should be eating less meat and probably less dairy. Which is tough for me as I do like my cheese, and I’m still struggling with vegan cheese, which was awful although it’s getting better.

Yes, Campbell’s ‘plant-based diet’ is ubiquitous now. It’s really taken off on social media, where I see a lot of influencers using that phrase. But that brings me to one of my anxieties around diet philosophies, which is that evangelising about a plant-based diet, or indeed any restrictive diet, all too easily becomes a cover for disordered eating. Do you worry about this?

Definitely. People have replaced religion with food, and food groups, and food clubs. There’s a general feeling that people want to belong to some group, and eating is very emotive and a public display. You might never discuss your religion with people now, but if you sit down for a meal it’s immediately obvious what your beliefs on food are.

When the plant-based movement began, there were less of them, they were a rare sect. Now it’s a growing movement and they are starting to pressurise people into doing the same. Which does have its place. But I’m worried there are increasing extremists in all these groups that cause problems and, of course, vulnerable people who have eating disorders who will use this.

There are good examples in gluten-free diets. People who don’t need a gluten-free diet might join a group because they feel special if they’re eating particular foods, or because they think they’ve got some intolerances. In those groups, like the plant-based diet, generally if you eat everything else, it’s very safe and healthy. But some other ones, like people who cut out all grains—there’s another book I could have mentioned, The Grain Brain—as an expansion of the gluten free movement, just restrict your diet. You end up with a very narrow range of foods that you can eat. And the food industry has adapted and made ultra-processed versions of these foods which are very bad for you.

So we need to have more flexibility between these groups and realise that everyone’s different. Even within the gluten free and plant-based diets, there are a whole range of options.  I like the word ‘reductionist’: if I eat meat once a month, then I’m not a vegetarian or pescatarian. But I think we need to break down these labels, because they’re restrictive. Or there’s ‘flexitarian’ or ‘progressive eater’, ‘eating for the environment’. These new terms have been forming.

But it’s a big danger that adolescents, particularly, can fall into these narrow groups, often driven by celebrities on Instagram, et cetera. We need to be on our guard, to make sure that people still appreciate the full range of foods.

Well, the concept of reduction, more generally, brings us to our last book, The Fast Diet by Michael Mosley, a food philosophy more commonly known as the 5:2 diet.

Yes. So in 2012, Michael was doing a documentary series about diets, and came across a group of people advocating what was called ‘intermittent fasting’. This means that either every other day, or for two days a week, you will either fast completely or consume only 25% of your normal calories. The rest of the time you just eat normally. The idea was that you reset your metabolism and allow your body to rest. You’re able to lose weight on this diet, because you don’t overeat as much as you might think on the other days. This really caught on.

Michael didn’t invent the diet, he basically took it from other scientists and made it very popular and accessible. I think he’s sold a million copies of that book. And it’s probably the only diet I would recommend, because it doesn’t stop you eating what is good for you, it just alters the way you eat. It’s not what you eat; it’s how you eat. You might eat exactly the same total amount in a week and just rearrange the way you eat it.

I think this was the first time that people actually started to think about the concept of meal timings and other things that might be just as important as the calorie or fat content of the food. People loved the 5:2 diet, and there was a real craze. People are still doing it now, which is a testament to any diet, and the book is still selling. That’s not because it works better than other methods, but because people are more likely to adhere to it after six months.

“Intermittent fasting is the only diet I would recommend”

People say, okay, I’ll do a ‘hungry day’ tomorrow. I’m working flat out and won’t notice it. All of us do that to some extent. It’s just giving you a good rationale about why you should do it. This way of eating has evolved into another form, called ‘restricted time feeding’. There are a number of books on that. Rather than four or five or six ‘meal events’ in a day, you just have two. Most people will lose weight and have a better metabolism. So it was from the idea of increasing the fasting time. It turns out that the longer you fast overnight or during the day, the longer your body is not dealing with food and the better and healthier your metabolism. A lot of that’s coming from gut microbes. Your gut health is better when they have time to recover, heal, tidy up your gut lining, help your immune system. Or that’s the current theory, and increasing data is supporting that.

Our ancestors didn’t eat six times a day and feel faint if they didn’t have a McVitie’s biscuit at 11 o’clock. This is just cultural, learned behaviour.

Having fewer meals sort of makes sense, but it’s the opposite of the diet advice I was given only a few years ago: ‘little and often’.

Thirty years ago it was felt that grazing was better than gorging, and that data has been proven to be wrong. But, again, clearly the food industry doesn’t want to change that. Our snack routine in this country accounts for over 20% of our calories, and it’s not just the calories, it’s also the fact we’re not resting our body, our guts. So the new interesting thing is that if we can work out the best time for us to eat, without actually changing the energy content within the food, we can start personalising the way we eat.

I think if people start to experiment, they can find what suits them. You mentioned breakfast; studies show that if you randomise people to breakfast or no breakfast, but the same amount of food in a day, people overeat a bit if they miss breakfast, but not so much that they over-compensate. Many parents say that their child is not interested in breakfast. Should they force it down? And my answer is, ‘no’. We’ve evolved plenty of mechanisms to tell us when we’re hungry. We don’t need to be forced.

So some people are much better off skipping breakfast. Others are better off eating it. We shouldn’t force everyone to fit into a single size box.

Yes, could you tell me a little more about this idea of personalised nutrition? You said that this is what you’re interested in at the moment.

With the company ZOE, we’re going to launch a product in the UK next year that will allow people to conduct their own experiments and work out their personalised food profiles using an app. Without changing calories or anything, you just work out which of the foods suits you best. We’re working at about 80% accuracy at the moment, and I think the future is personalised nutrition.