The secret life of calories: How to lose weight and be healthier

New Zealand is one of the fattest nations on Earth and a Cambridge University geneticist says we should recognise not all calories are created equal. So what should we be eating? By Eleanor de Jong.

Obesity expert Dr Giles Yeo cycles to and from work each day, runs five kilometres on Saturdays and goes long-distance cycling on Sundays, purposefully searching out hills to push himself. But even then, the University of Cambridge geneticist hasn’t avoided the creep of “middle-age spread”.

In addition to his 20 years as an obesity researcher in Britain, Yeo is also a presenter on the BBC’s popular show Trust Me, I’m a Doctor and BBC Horizon, where his investigations are critically acclaimed.

In 2018, aware of his gradual weight gain, Yeo agreed to adopt a vegan diet for a month and have it documented by the show. Despite veganism having a thoroughly unsexy reputation at the time, the evidence behind it being effective for weight loss is strong.

After a month of tofu, pulses and greens, the effectiveness of the regime seemed indisputable when Yeo lost 4kg and lowered his cholesterol by 12 per cent. Returning from his weigh-in, he celebrated by grabbing a packet of cheese and onion crisps at the train station. That night, he ordered his usual king prawn jalfrezi, naan bread and egg pilau rice at his local curry house, followed by a steak for Saturday-night dinner, roast pork, crackling and goose-fat potatoes for Sunday dinner and a multitude of creamy desserts and wines.

Within five days of quitting veganism, Yeo had regained 50 per cent of his previous weight loss. “That was a shock,” he says, speaking to the Listener from his home in Cambridge. “It was really depressing.”

If even a world-leading obesity expert can’t keep the weight off, what hope is there for the rest of us? “Diets only work if you are actually on the diet,” says Yeo. “When I stopped being vegan, the calorific density of the food I was eating had changed so drastically that the weight was simply flooding back – it’s really, really difficult.”

The yum factor

A few years ago, Yeo took a test that found white rice gave him a blood-sugar spike shortly after eating it. Yet the knowledge hasn’t deterred him from pairing it with rendang curries and chicken stir-fries. “I hate brown rice!” he laughs.

It is a good example of the psychological finding that even with access to expert knowledge on how to stay healthy and lose weight, humans still have cravings, favourite foods and indulgences they struggle to resist.

Here, our biology betrays our best intentions by making it biologically hard to say no to plentiful, calorie-rich foods, and then holding on vice-like to the extra weight we put on.

Following his vegan experiment – and five-day weight gain – Yeo became a “flexitarian”, meaning he eats vegan lunches every day of the working week, and at least two vegan dinners a week. The pints and crackling have stayed, as have the curries, naan bread, alcohol and occasional pudding. By no interpretation is it a diet of deprivation.

Yeo’s love of food is reminiscent of TV chef Nigella Lawson, and large chunks of his latest book, Why Calories Don’t Count, are devoted to joyfully detailing his favourite recipes and indulgences. Many readers are now begging him to publish a cookbook.

His Twitter feed is filled with food escapades, such as when he recently took a detour from a London conference to Chinatown to pick up some Peking duck, or a selfie of him red-faced at a backyard barbecue, captioned, “Yeeha! Scorcher of a weekend evening, so piece of cow on the barbie, cold beer and we’re good to go!”

Yeo’s attitude is both personality driven and deeply intentional. In countless studies, food has been shown to light up the dopamine-rich, pleasure-seeking regions of the brain, sending saliva rushing to the mouth in the anticipation of the joyous job of mastication.

Food can also be an expression of, and connection to, culture – it is one of the reasons Yeo still prefers his white rice – a comfort at the end of a hard day, a bonding or mating ritual, an expression of love or sustenance to power through arduous challenges. Yeopoints out that UK long-distance runner Sir Mo Farah eats nearly 4000 calories a day when in training.

In a culture that is increasingly telling people the food they love is “clean” or “dirty”, or that they should face moral condemnation when they eat too much of it, Yeo is fighting back against “food shaming” by using science to prove that eating is deeply human – and so, too, is struggling to stop.

Fuller for longer

Surprisingly, many of the diets on offer today – Atkins and ketogenic diets, for example – do work, but for the simple reason that the diets are all mainly plant-based and high in fibre and protein.

The evidence for the effectiveness of the low-carb, high-protein diet goes back to 1863, when William Banting ditched bread, beer and potatoes and wrote a booklet, Letter on Corpulence, Addressed to the Public, detailing his weight-loss success.

The Atkins diet of the 1970s built on Banting’s weight-loss discovery, as have the majority of successful diets since, simply under different names, with different celebrities attached and often bizarre variations in “rules”.

In simple terms, calorie for calorie, meals high in protein make people feel fuller and satiated for longer, meaning they are less likely to reach for a second helping or a sugary snack when cravings hit.

As a macronutrient, protein is far more complex than carbohydrates or fat, Yeo writes in Why Calories Don’t Count, offering a “challenge” for the body to break down. “Unlike fat or carbohydrate, which are composed entirely of differing proportions and configurations of carbon, hydrogen and oxygen, protein contains (in addition to carbon, hydrogen and oxygen) a significant amount of nitrogen,” he says. “Although the human body can store carbon, hydrogen and oxygen or pretty much oxidise it completely, any nitrogen that is not used (as part of protein) has to be excreted.”

What this means is that while carbohydrates and fats can easily be stored as fat if not burnt off, the amino acids of protein cannot. Therein lies their powerful weight-loss potential. An increase in proteins is also often coupled with a reduction in carbohydrate consumption.

This is why all calories are not created equal – some are simply more nutritious and valuable to your body, and weight-loss, than others.

Although a few tablespoons of prawns and a few slices of rye bread have the same number of calories – about 120-150 – the high-density protein of the prawns does not carry the weight-gain potential of the bread and will contribute to you feeling less hungry and eating less at your next meal. Win-win. “Put simply, a calorie of protein makes you feel fuller than a calorie of fat or carbs,” says Yeo.

“There is actually plenty of evidence to support the effectiveness of diets ‘high’ in protein for weight loss – at least in the short term. The issue is there is no general consensus as to what constitutes a ‘high’ protein diet.”

The World Health Organisation (WHO) recommends protein should contribute 10-15 per cent of your daily intake, which largely reflects the current status quo, with both the UK and US populations consuming 16 per cent.

Using these guidelines, that equates to about 64g of protein a day for women and 88g a day for men.

Although that may sound small, the reference is to pure protein. A 100g rib-eye steakcontains about 19g of protein and 211 calories. “That would mean that chewing your way through a full 300g rib-eye would still only get you 57g of protein,” Yeo writes.

The leanest and most expensive beef cuts reward the eater with higher quantitiesof protein, with 100g of raw beef fillet containing 23g of protein and 5.5g of fat, which is 141 calories. This is why the quality of your food also counts – it rewards in greater nutritional density.

Although there is more protein per gram of fillet compared with rib-eye, fillet steaks are typically served in 200g portions, which would be 46g of protein. This is two-thirds of the daily requirement for women and not difficult to increase if they are pursuing weight loss.

Foods with 20 per cent or more protein are classified as “protein-enriched” and include lean white meat such as chicken and fish. Other protein options include eggs, nuts, dried lentils and tofu.

“My point is that 88g is actually quite a bit of protein, equivalent to a 450g rib-eye, 14.5 eggs or nearly a kilogram of lentils,” Yeo writes.

“And it is important to note, for all you vegetarians and vegans out there, it is the amount of protein rather than their source that is crucial to satiety, which means that a range of protein sources can contribute to satiety, including dairy, meat, poultry, cereals, fish, peas, pulses and legumes.”

A diet containing 10-15 per cent protein is advised by the WHO to maintain weight – not lose it – so a diet aiming for a higher intake may be advised if weight loss is the goal.

Because there is no definition of what a high-protein diet is, Yeo does not commit to a protein “target”, but does say that most research papers that assess its effectiveness tend to include all diets that have more than 16 per cent of the calories from protein.

The evidence for protein’s effectiveness is, at this point, robust.

“In a review paper that summarised the main findings of 14 studies comparing ‘high’ protein with at least one other macronutrient, 11 found that high protein significantly increased subjective ratings of satiety,” Yeo writes, meaning your diet shouldn’t leave you feeling hungry.

When it comes to red meat, Yeo suggests using whole cuts such as steak, which can be cooked quickly, rather than mince, as the further away food is from its natural state, the more calorific it becomes. Mincing meat then cooking it alters the collagen protein it contains, making it easier to chew and digest. The same applies to slow-cooked stews and casseroles; if they are heated through three or four times, it increases the caloric availability each time, he says.

Feast on fibre

As with protein, fibre slows down digestion in the gut, making it work harder and burn more calories to extract it. “Dietary fibre is actually a plant-derived carbohydrate; it is the part of plant-based food that humans cannot digest,” writes Yeo.

The wonders of fibre were discovered by British surgeon Denis Burkitt in the 1960s,while undertaking field work in Uganda. He found the fibre-rich diet of the local people – low in red meat and animal fat, but high in fibre-rich foods such as colourful fruits and vegetables, leafy greens, tubers, beans, nuts and whole grains – resulted in a relative absence of modern Western diseases such as colon cancer, type 2 diabetes and heart disease.

Back then, as now, Britons consume about 18g of fibre a day, far below the 50g Burkitt recommended as part of a high-fibre diet.

“We now know, from multiple epidemiological studies, that significantly increasing the fibre content of our diet either decreases the risk of, and in some cases protects against, a number of different non-communicable diseases,” Yeo writes.

One such study, based on data from the European Prospective Investigation into Cancer and Nutrition (Epic) study, involved 519,978 participants from 10 European countries. It found a 40 per cent reduction in cancer risk when low-intake populations doubled their fibre intake. “Crucially,” writes Yeo, “more is better in this case, with fibre intakes higher than 35g a day appearing to be even more effective at reducing disease risk.”

A recent review of 58 clinical fibre trials, encompassing 4635 people, found a 15-30 per cent decrease in cardiovascular-related stroke, type 2 diabetes and colon-cancer deaths, as well as a decrease in the incidence of all these diseases, when comparing the highest-fibre consumers with the lowest.

The case for adding more fibre to your diet – as much as three times more than you’re likely to be currently eating – is sound, Yeo says.

Food double standard

With the innovation of meat-free, ultra-processed foods, such as the Beyond and Impossible plant-based burgers, the simplicity of labelling all such processes “bad” is becoming more complicated, Yeo says.

“What will surprise many is that the grains that we eat every day, from which humans get the majority of their calories, are also processed.” Yeo cites such standard foodstuffs as rice and wheat, but also yogurt, which was first eaten in 5000 BCE in Mesopotamia.

“So, although the term ‘processed food’, as used today, is associated with a whole host of negative connotations, the processes of cooking, food preservation and separation were critical to our ability as a species to survive and to thrive.”

Cooked food, for complex reasons, also increases the calorie count of what we eat. For most of human history, food has been scarce and energy-intensive to gather, meaning the more calories the better.

But in the modern world, where food appears to grow in supermarkets, we’re now demanding the opposite. This is one reason the raw diet works – a stick of celery clocks in at only five calories when raw, but rises to 30 after cooking.

Although processing food is ancient, ultra-processed food, which Yeo describes as “foods that have been processed beyond what is ordinary or proper” – think oat milk, cheap chicken nuggets, packet soups, soft drinks and mass-produced packaged breads and buns – takes it many steps further.

“In recent years, the term ‘ultra-processed’ has become synonymous with unhealthy fast-food options, high in sugar, fat and salt, that are blamed for the obesogenic environment we find ourselves in today,” he writes.

“Ultra-processed food is the opposite of ‘clean’, the antithesis of ‘real’. Yet ultra-processed plant-based milks are unashamedly marketed as healthy. What makes one ultra-processed food item different from another? What makes some suited to be condemned and legislated against, while others remain respectable, eminently Instagrammable even?”

Often, the difference comes down to good or bad PR, Yeo says. “The milk we get from the supermarket is pasteurised, so milk is actually a processed food.

“Most of the plant-based milk options, with the exception of coconut milk, because of all the machinations that are required to convert quinoa or oat extract into a facsimile of milk (how exactly do you milk a quinoa?) are actually classed as ultra-processed.”

Adding to the complexity is that although some ultra-processed foods are at the forefront of modern health experiments – the Impossible burger, for example – the vast majority remain astoundingly unhealthy, especially when they make up the bulk of a person’s diet.

“Diets that include a lot of ultra-processed foods are intrinsically nutritionally unbalanced and intrinsically harmful to health,” says Carlos Monteiro, a professor of nutrition and public health at the University of São Paulo in Brazil, who is credited with inventing the term “ultra-processed”.

In the UK, 65 per cent of calories eaten by primary- and secondary-school children come from ultra-processed food or drinks. In most Western countries, ultra-processed foods account for 50 per cent of the calories in a standard diet, with the three highest consumers in Europe, led by the Netherlands.

New Zealand is not far behind as the seventh-highest consumers of ultra-processed foods in the world.

This is really concerning, says Yeo, because each percentage point increase in the availability of ultra-processed calories in an average household is associated with an increase of 0.25 per cent in obesity prevalence within that country.

Rates in the developing world are also rapidly catching up with the West, with the added problem that ultra-processed eating is often a status symbol for the newly emerging middle class.

The chemical, man-made processes that ultra-processed foods undergo to reach their consumer-friendly form are routinely so extreme they strip the food of any flavour. Huge quantities of additives such as salt, fat and sugar become necessary to make the food palatable, let alone delicious.

“Ultra-processed foods are typically higher in salt, sugar and fat, and lower in fibre, which is what makes that lovely ‘protein of chicken origin’ nugget oh so moreish, and also oh so very calorically available,” writes Yeo.

“It is easy to eat and even easier to extract the calories. Compare that with eating a piece of chicken breast, even if it has been battered and fried, where you can control the amount of seasoning and fat that goes in.”

Studies are also finding that ultra-processed foods encourage your body to eat more, as much as 500 calories in one sitting. It is thought the lack of protein in these foods make the body go into overdrive in an effort to secure this vital resource.

Even when matched calorie for calorie – as in a 2010 cheese-sandwich experiment by Sadie Barr and Jonathan Wright from Pomona College, California – wholefoods come out on top. Subject participants ate two sandwiches, both of 600 calories, but one was classified as a “wholefood sandwich” of wholegrain bread and real cheddar cheese, while the other used ultra-processed cheese and white bread.

“Even though the sandwiches contained exactly the same number of calories, the body has to spend nearly twice the number of calories to metabolise the wholefood sandwich compared with the processed sandwich,” wrote Yeo of the study. “Put another way, eating the processed sandwich means you absorb 10 per cent more calories than if you had eaten the wholefood sandwich.”

Studies have found humans biologically struggle to resist foods stuffed with fat and carbs. A 2018 Yale University study suggested this might be a result of our first food – breast milk – being loaded with them, resulting in our brains associating the two with growth, comfort and pleasure. However, apart from breast milk, fat and carbs rarely occur together in high quantities in nature – macaroni cheese is a human construction. Ultra-processed foods can hijack your efforts to stay slim in a multitude of ways. “There does appear to be a biologically plausible mechanism to explain why our response, as humans, is to overeat in this contemporary environment rich in ultra-processed foods that are high in fat and carbs,” Yeo writes.

At this point, simply dropping ultra-processed foods from the diet is near impossible for most people, Yeo says. Instead, he advocates for pragmatism.

“It really annoys me when experts tell people, ‘Just replace that chocolate bar with a banana,'” Yeo says. “It’s stupid, because sometimes you need a chocolate bar, and other times you need a banana. What I want is a better kind of chocolate bar loaded with nuts. And there is no way they need to be in petrol stations and at supermarket checkouts – that’s pure manipulation. If you want a chocolate bar, you should have to walk to the chocolate aisle to get it.”

Hungry genes

Yeo is ethnically Chinese, meaning he is at a greater risk of developing diabetes, among other weight-related diseases. “The interesting thing is that your fat cells and my fat cells can expand to different amounts,” says Yeo. “So, East Asian people, me, South Asian people, Indians, Pakistanis, don’t have to gain much weight before they get metabolic disease – they just don’t. My risk factor, as ethnically Chinese, is 23 or 24 in terms of body-mass index (BMI), while for Europeans, it is more like 25, 26 or 27.”

When people consume too many calories and don’t burn them off – the universal explanation for weight gain – the extra weight is stored in the body’s fat cells, which expand or decrease “like balloons” depending on how much fat you’re storing.

When fat cells reach their capacity, any additional fat then begins to form on organs such as the liver, increasing the risk for obesity-related “modern” illnesses.

Frustratingly, looking in the mirror or even at a set of scales won’t tell you this. A skinny person of Indian origin with a small beer belly may be at greater risk of developing diabetes than a large Māori person who looks heavier but is actually healthier. This makes it difficult for the “average Joe” to know when they are getting into dangerous territory with their weight.

“I think the answer will come down to genetic and other types of tests, but we’re not there yet; maybe in 10 to 15 years’ time,” says Yeo. “I think the easiest way at the moment is to look at your parents, should they be alive. But even if they’re not alive, what did they die of? What shape were they in, what diseases did they have? They are a picture of the future you, to some degree. So that is still far more predictive than simply your body weight.”

In addition to ethnic weight differences, individual feeding behaviours are governed by more than 1000 different genes, dictating such things as how hungry you feel, how much food you want to eat, when you feel full and how happy that food makes you feel.

These complex genes all speak to each other, and even a slight mutation or abnormality can lead to imperfect communication between the belly and brain – and, possibly, help explain your lifelong struggle to say no to banana bread slathered with butter. “At this point you have to ask, is how much we eat really a choice?” Yeo says.

Why are we so fat?

According to the WHO, 1.9 billion adults 18 years and older are now classified as overweight, with more than 650 million of them obese.

In New Zealand, one in three adults are classified as obese, making us one of the fattest nations on Earth, while for children the figure is about one in 10. Children living in the most socio-economically deprived areas of the country are 2.7 times more likely to be obese as children living in the least-deprived areas, while the rate for adults is 1.8 times.

Obesity is not evenly distributed in this country. According to the 2019/2020 New Zealand Health Survey, the prevalence of obesity among adults differed by ethnicity, with 63.4 per cent of Pacific, 47.9 per cent of Māori, 29.3 per cent of European/Other and 15.9 per cent of Asian adults obese.

This is important, because Māori and Pacific people are also more likely to live in deprived suburbs and regions. Local and international research has repeatedly found that the prevalence of highly calorific food outlets such as takeaways and drive-throughs is five times greater in low socio-economic regions.

In real terms, this means that a child walking home from school in South Auckland is five times more likely to encounter a KFC than a child in wealthy suburbs such as Ponsonby or Remuera. Predictably, children, as with adults, have great difficulty saying no to treats placed right in front of them, particularly ultra-processed treats high in fat, salt and sugar.

Adding to this geographic and income disadvantage, studies have found that highly calorific, ultra-processed food is about a thirdcheaper in supermarkets.

Combined with gene inheritance, which determines 40-70 per cent of your body weight – the fluctuation in those numbers is influenced by the environment you live in – what size you end up often has very little to do with your best intentions of being bikini-ready by Christmas.

“Body weight is not a choice,” Yeo says emphatically. “Most policymakers still think obesity is a result of personal choice and bad habits, when in large part, for biological and non-biological reasons, it isn’t.

“We need to try and help people make the healthier decision by fixing the built environment around them. If we don’t fix the environment, if we don’t make the healthy choice the easier, more convenient, cheaper choice, then we’re not going to fix the problem.”

As with many in the middle-class Western world, Yeo and his wife spent lockdown nurturing a sourdough starter and cooking slow, thoughtful meals. But for millions in the UK – and New Zealand – the pandemic has highlighted disturbing rates of food insecurity, with at least 10 per cent of families unsure how they’re going to provide their next meal. Early evidence suggests these numbers have as much as doubled since the pandemic hit in early 2020.

In terms of weight loss, Yeo points out that the rules are fairly straightforward: more plant-based foods, protein and fibre, and less sugar, fat and carbs. But there’s a catch: “You need to give people realistic and pragmatic solutions, rather than say, ‘Please have more carrots and hummus.’ It’s fine advice if you have hummus in the fridge, but not everybody is going to have hummus and carrot sticks in the fridge – ever – and I think that’s part of the problem.”

It is why the moralising judgments over “clean” and “dirty” food angers Yeo so much. When you’re time poor, cash poor and have never had any education on nutritious eating, there’s no such thing as good and bad food, there’s just food. The cheaper it is and the more calories it contains for immediate fuel, the better. “Human beings are designed to eat food efficiently, and very easily store it as fat,” Yeo says. “But it takes a long time to burn off, because that’s how we have evolved to survive. It will take you 60 seconds to eat a Mars bar, which is 240 calories, but always half an hour to burn it off.”

This simple example highlights why it is so easy to gain weight – even over a single weekend – and so extremely difficult to lose it again. Fat is potential energy and the body is biologically resistant to parting with its fuel. From an evolutionary standpoint, starvation, pregnancy or war could always be around the next corner.

Yeo understands that, for myriad reasons, picking up a frozen pizza at the supermarket is going to be a more appealing choice for many people than buying the ingredients for, say, an organic vegetarian frittata with a rocket and pomegranate-seed salad.

“If you require a frozen pizza because you’re in a rush, or you like frozen pizza, or that’s what the kids want to eat – there can be a million valid reasons why you want it. What I want to change is: can you pick a better frozen pizza, something with more protein and fibre?” Yeo says.

“I am not saying that frozen pizza is ever going to be better for you than other types of food, but if you need a frozen pizza, can we give people the tools to pick a better frozen pizza? And I think if we do that, we’re being more pragmatic and realistic about people’s lives.”

Tricking the brain

There are few government-led interventions that have been successful in lowering obesity rates, but Yeo, whose lab is funded by the UK government, has – somewhat reluctantly – shown his support for the tax on sugary drinks. He says that in response to the tax, many companies lowered the amount of sugar in their beverages so they would not face financial penalties.

In multiple studies since, consumers were found to barely notice the difference in taste. This is positive news.

On a personal level, Yeo has found his flexitarian diet to be sustainable in the long run. A change in home insurance also inspired him to track his fitness, as his insurance company offered an annual £200 ($400) rebate if he stayed physically active.

“Humans are like magpies, we like shiny new things, so anything – be it technology, publicity, whatever – that nudges you every so often into making healthy decisions can be effective.”

But the most important way to make a difference to obesity rates is to tackle the eating habits of kids, especially those in high-risk areas of the country. This should become a passion for any government serious about obesity, Yeo says, particularly one like New Zealand, whose well-being goals and poverty-reduction aspirations he praises.

Although many middle-class schools now have market gardens and healthy-food initiatives, these same policies are often absent in lower-income schools and homes – the very places most in need of intensive healthy-eating support.

For some, weight-management medications may become more mainstream in the future, with five now approved by the US Food and Drug Administration. Hormone therapy to “weaponise” gut hormones is also beingtrialled in the UK, Yeo writes, and the initial findings are promising.

Beginning more than a decade ago, scientists at Hammersmith Hospital in London, led by professors Tricia Tan and Sir Steve Bloom, have been conducting trials infusing patients with the hormones GLP-1, oxyntomodulin and peptide YY individually.

Each hormone on its own could modestly reduce food intake, Yeo writes, and over the years the team has systematically tried different doses and combinations. They are now at the stage of trialling an infusion of all three hormones in a single mixture.

“While the treatment is still in the testing phase, it appears that this hormone infusion can indeed mimic gastric bypass, at least partially, and make the brain think it is full so patients actually eat less, about 30 per cent less in a single meal,” says Yeo.

The biggest hurdle for hormone therapy is to make the infusions longer lasting. They currently need to be injected before each meal, but once a week would be ideal. The “holy grail” involves delivering the concoction in pill form.

“But because of the pesky acidic cauldron that is the stomach, that is a long way off yet,” Yeo writes. “Nevertheless, these results are very exciting indeed and represent really significant progress in obesity therapeutics.”

However, if Yeo could wave a magic wand and change one thing about the modern food environment, it would be far simpler than this. “What I would do overnight, if I could, is subsidise healthy foods, fruits and vegetables. We need to make the healthier choice the cheaper, more convenient choice. So, if you’re trying to feed yourself, the healthier decision is cheaper. That would be more equitable for all.”

Tellingly, at the end of Why Calories Don’t Count, Yeo includes some of his own recipes, including for meals that would make traditional diet followers baulk: crispy-skin duck pancakes, Chinese black beef brisket and beef short-rib rendang.

The recipes are decadent, impressive, and “good for entertaining”. They are also based around wholefoods, high in protein and fibre and packed with flavour.

And this is why calories don’t count, at least not to this geneticist. “We don’t eat calories,” Yeo says. “We eat food.”

A menu of diets

Obesity expert Dr Giles Yeo gives his summary of the benefits and drawbacks of recent dieting trends.

1. Ketogenic diet

A high-fat, moderate-protein, very-low carbohydrate diet, at the “extreme end” of carbohydrate-restricting diets on offer. Ketogenic diets have been around in a clinical setting since 1921, when they were used to treat children with epilepsy. Yeo says most people cannot manage the recommended 80 per cent daily fat intake, which he calls “an extreme level of fat unpalatable to many”.

2. Paleolithic diet

“There was no single paleolithic diet, because there were no single paleolithic people,” Yeo writes. “The reality is we are not eating what our ancestors did, because we can’t. Those foods simply no longer exist. Almost everything that we eat today is a product of many generations of domestication.” Yeo labels the backstory of paleo “quite nonsensical”, and trying to adopt it today “fantastical”.

Yeo says the diet does work as a weight-loss strategy “for some” but largely because it follows basic rules: it’s high in lean meat and seafood, as well as fruit and non-starchy vegetables, and it avoids cereals and grains and starchy root vegetables. It’s a low-carbohydrate diet, by another name.

3. Carnivore diet

An extreme diet that is effective in the short-term for weight loss, but not healthy in the medium or long-term. No one has conducted studies into the long-term safety of the carnivore diet, Yeo says, and labels “this particular fad diet a bad idea”.

4. Alkaline living

It works in the short-term for weight loss, “in spite of its nonsensical nature, barely able to stand up to casual scrutiny”, Yeo says. Why? “As it turns out, because meat and most other animal-based products are labelled as ‘acidic’, an alkaline diet is pretty much plant-based by another name.”

5. Sirtfood diet

One of the selling points of this diet, developed by two British nutritionists, is that singer Adele credits it for her 2020 weight loss, and it allows chocolate and wine, “which I must admit, is undoubtedly appealing”, Yeo says. “Most of the recommended ‘sirt foods’ are plant-based, coupled with calorie restriction, making it a weight-loss strategy for some, wrapped up in some ‘sciency’ explanation to make it more compelling.”

6. Raw diet

“Eating raw food – a salad, basically – means you will be absorbing fewer calories, which is why a raw-food diet is so effective for weight loss,” says Yeo.

7. Mediterranean diet

Studies have shown as much as a 30 per cent reduction in cardiovascular disease – the most common cause of death in the world – for those following this diet, compared with those on a low-fat diet. It gets a solid tick from Yeo for its health and weight-loss benefits.

8. Vegetarian/vegan diets

Plant-based and high in fibre and protein – another tick from Yeo – these diets are easily incorporated into a flexitarian menu for the long-term. Yeo recommends avoiding specialist “vegan products”, many of which are expensive and lack fibre and protein and are at the mercy of intensive marketing drives. Researching specialist vegan meals, rather than trying to recreate meat meals with vegan products, is also recommended. Yeo does not like vegan cheese or replacement meat products such as quorn.

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