Despite exercise being brilliant for our health, research shows that its role in weight loss is minimal. Photo / Getty Images
Two nutrition experts bust the common myths that people subscribe to when trying (but failing) to shed the weight.
What do I have to do to lose weight? It’s a question many of us will have considered. However, for anyone who has tried to shift the scales, it’s often not that simple – daily trips to the gym and calorie-cutting may have proved fruitless.
Despite more than a century of research into calories and body weight, there is still confusion on how to achieve weight loss and where there is advice, it is often based on science that has been extrapolated “far beyond what a study actually demonstrates”, says nutrition and metabolism scientist Dr Kevin Hall.
Food Intelligence, his new book with health journalist Julia Belluz, cuts through the myths about nutrition to provide clarity on what works, so that people “can look a bit more critically at the next book that’s telling them the secret to weight-loss success”, he says. Here are some of the most prevalent weight-loss myths – and what actually works instead.
“Recently, I was talking to a friend who had put on weight and she was saying that she just doesn’t have time to go to the gym,” Belluz says. “I was thinking, it’s not the exercise that is the problem – it is the overconsumption of food.”
Despite exercise being brilliant for our health – for building and maintaining muscle mass, protecting our heart from disease and even reducing our cancer risk – research shows that its role in weight loss is minimal.
Hall has seen this first hand during his time studying the contestants in the US TV show The Biggest Loser, where people competed for seven months to lose the greatest percentage of their body weight in return for US$250,000 ($432,000).
“What we observed was that when they were in this crazy competition and doing an enormous amount of unsustainable exercise [often at least three hours of vigorous workouts per day], when it came to weight loss, there was no correlation between the folks who did the most exercise and [those who] lost the most weight,” he says. “It was primarily how much they cut calories in their diet.”
Separate research, which saw people complete supervised exercise sessions, confirmed this finding and highlighted that exercise was particularly ineffective at helping women lose weight. “There are almost as many women who gain weight in the process as lose weight,” Hall says. It’s thought that this finding, at least in part, is due to the body adapting to a higher activity level and restricting the overall number of calories it burns. “Men tend to do a little bit better – there is weight loss, on average, but it’s not an impressive amount – they’re losing a few pounds,” he says.
“When people start an exercise programme and they don’t see the numbers falling on the scale, they question what they are doing it for. The answer is, you shouldn’t be doing exercise to lose weight. You should be doing it to improve your overall health and functionality and to be able to enjoy life to its fullest, not for weight loss.”
What works instead: Switching your focus
While exercise won’t fuel dramatic weight loss, it helps in successfully maintaining a lower weight, according to Hall. Research from The Biggest Loser showed that those who maintained an active lifestyle were less likely to pile the pounds back on, though the reasons for this are not yet fully understood, he notes.
“You shouldn’t be looking on the scale to see how your physical activity is affecting your weight loss,” he adds. “However, it’s going to help you maintain the weight loss that you’ve been able to achieve.” In other words, exercise won’t obliterate fat but it can help keep the fat off.
Like many of us, Belluz had long blamed her slow metabolism when her weight increased – the idea that her body was burning fewer calories than it should, meaning that eating a typical amount of food caused her to gain fat.
In a bid to confirm her suspicions, she spent 24 hours in a chamber fitted with an array of metal pipes that measured exhaled gases from her breath – the most accurate way of calculating metabolism. Results showed that the number of calories her body burned was completely normal for her age, sex, weight and height. “I fell prey to the myth in trying to understand my previous weight struggles,” she says.
“The idea of slow metabolism being the causative agent of obesity was really derived by asking people of different sizes to track how much they’re eating,” Dr Hall explains. In an infamous study, participants all reported their calorie intake as lower than it actually was, but obese people underestimated their calorie intake much more than leaner people.
The researchers, who didn’t know that there was this bias, concluded that obese people were eating more or less the same number of calories as thinner people, so a slow metabolism must be to blame for their larger size.
“It was only later, when we had accurate but expensive methods for measuring metabolism, that we realised that people with obesity actually burn more calories than leaner people, on average,” Hall adds. “But still, the myth persists: ‘I have obesity because of my slow metabolism.’ For the vast majority of people, a slow metabolism isn’t the main reason that they’re struggling with their weight.”
In fact, during his time working on The Biggest Loser, he found that people who were the most successful in losing weight also had the greatest slowing of metabolism. “We think that the slow metabolism and the weight loss are both responses to whatever lifestyle changes you’re able to make,” he adds.
What works instead: Hiding or getting rid of ‘treat foods’ from your home
While a slow metabolism “is not a causative factor” of weight gain, another factor outside our control is to blame, according to Hall and Belluz: the food environment.
“The food environment is about our social interactions and social norms, what’s available to us, how it’s being advertised, what our friends are doing, how we’re being influenced by others, the products that are available,” Hall explains. “All of those things have changed quite dramatically since the 1970s.
“[There has been an] explosion of variety and portion sizes have increased, in addition to food becoming so much cheaper and more convenient. No one’s arguing against many of those things, we all like to have choices, convenience and tasty options to have.”
However, easy access to high-calorie and hyper-palatable foods is undoubtedly driving the obesity crisis, the pair argue.
“We hope people take the blame off themselves,” Belluz says. However, there are tactics that people can use at home to control the food environment as much as they can. Hall has taken to hiding unhealthy food in his basement, so that it’s not easy to access, while Belluz limits how much she keeps at her house.
The 3500-calories-per-pound (450 grams) rule has formed the bedrock of weight-loss advice for decades.
“That idea came from a very basic scientific question, which was: how many calories are stored in a pound of human fat tissue? It turns out to be pretty close to 3,500,” Hall says.
However, that finding was extrapolated to the point that advice is issued – from the likes of the NHS as well as the National Institutes of Health in the US – suggesting that cutting 500 calories per day from your diet will consistently lead to a weight loss of one pound per week, he notes.
People may be able to lose a few pounds following this rule, but it will soon stop being as effective, as the body fights against weight loss, Hall says. “The point is you can’t create that deficit over and over again.”
“There were good intentions behind coming up with some sort of rule to tell people, but when that rule is based on inaccurate evidence, it ends up having really bad unintended consequences,” he adds. “It suggested that if you just cut a little bit of calories out of your diet and just waited long enough, then you should be able to lose any amount of weight.”
What works instead: Being honest with yourself about your calorie intake
Unfortunately, scientists haven’t yet come up with a foolproof metric to give to those hoping to shift the scales. “Even if we did have an accurate rule of thumb, most people can’t track their calorie intake very well,” Hall says. Research shows that people underestimate how much they’re eating by around 1000 calories per day, he explains.
However, other dieting experts recommend multiplying your weight in pounds by 11 for the lower end of your calorie intake and by 12 for the higher end. For example, this would mean that an average woman, weighing 159lb (72kg), could eat between 1750 and 1900 calories per day to lose weight. As a person’s weight decreases, so does the calorie range needed to continue achieving weight loss. However, this calculation is also just a rough guide.
Three macronutrients provide most of the fuel that our bodies need: carbohydrates, fat and protein. Both carbs and fat are frequently shunned in the name of dieting but, on its own, this won’t change the number on the scales.
“You can change carb and fat intake by a huge amount,” Hall says, but if calorie intake isn’t reduced, this approach won’t help with weight loss. In other words, you need to eat fewer calories to lose weight and following a low-carbohydrate or low-fat eating pattern alone won’t achieve this – unless you’re eating less food overall.
Hall showed this in a study of 19 obese people who followed a calorie-controlled diet that was either very low in fat or in carbohydrates. Both groups lost nearly identical amounts of weight, although those on the low-fat diet lost marginally more – 40g per day (around the size of a large strawberry).
“When we presented people with minimally processed diets that varied in carbs and fat, almost everybody lost weight on both of those diets,” Dr Hall says. But it was the calorie-intake differences that dictated the differences in body-fat changes and loss of weight.
“People do have tremendous success on low-carb [and low-fat] diets,” Belluz notes. “But when it comes to weight loss, on average, it doesn’t seem to be the thing to focus on.”
What works instead: Cutting out ultra-processed foods
Hall’s ongoing research shows that diets high in ultra-processed foods (UPFs) encourage us to overeat excessively. He has recently tracked participants exposed to different diets, including minimally processed and ultra-processed, and allowed them to eat as much or as little as they want while sticking to these groups of food.
When following a high-UPF diet, participants consumed 1000 calories more per day and gained around 1kg per week. “That’s the only diet we’ve seen that causes people to spontaneously increase the number of calories they’re eating and gain weight and gain body fat,” he says. It therefore makes sense to limit the proportion of UPFs in your diet, to prevent overeating.
Eating enough protein can aid weight loss because it can help with staying full for longer. However, the vast majority of people are already eating enough protein and the proliferation of high-protein foods – which are often UPFs – aren’t necessary for getting trimmer, according to Hall.
“The public is getting a hint of truth,” he says. “If you’re a bodybuilder or extreme athlete and you want to optimise your performance, the very first thing you should be doing is looking at your training regimen and supporting that with enough protein.”
However, the average person being sold these high-protein products probably believes that they are not eating enough protein and that they need to buy them to harness the benefits, which “is misguided”, he says.
“What we see again and again is focus on a single nutrient removed from other things in food,” Belluz notes. “Now, it’s protein and glucose. In the past, it was fat versus carbs.
“You often miss the forest for the trees – the big picture about what you should actually be eating and how your diet should look. If you’re relying on protein-boosted pancakes [as your source of protein], it’s probably not a healthy diet in the first place.”
What works instead: Eating more vegetables
“The evidence on optimal nutrition has been clear and consistent over decades,” Hall and Belluz write in their book. “It’s boring by this point. Eat more vegetables – along with fibre, legumes, whole grains and fruits. Limit sodium, sugar, saturated fat and junk foods.” Sometimes the simplest, most obvious methods are the most effective.