The six calorie health myths making you fat

Been blaming your tight waistband on advancing age? We've got news for you. Photo / Towfiqu Barbhuiya, Unsplash

Do you count your calories? In April, new legislation came into force requiring all large restaurants in England to confess to the calorific content of each of their dishes, publishing the number on the menu. Not everyone agreed with this directive, but the UK has an obesity crisis – surely calorie counts are key to combating it?

Well, perhaps not in the ways you currently think. Last month, a study from the University of Aberdeen, published in the journal Cell Metabolism, caused a stir by dispelling a certain myth. It looked at the time of day people ate and whether it had any impact on metabolism.

Participants were provided with all their meals for eight weeks. All consumed the same number of calories, some weighted towards the morning, and some towards the evening. Their energy expenditure and body composition was then monitored for changes.

The result? “The time of day at which they ate the bulk of their calories made no difference at all to their weight loss or metabolism,” says Alexandra Johnstone, professor of appetite research at the University of Aberdeen. Breakfasting like a king, lunching like a prince and dining like a pauper may not be the best for our waistlines after all.

So what other fallacies have we been swallowing?

Myth 1: A calorie is a calorie is a calorie

A calorie is the basic unit of measurement for the amount of energy in an item of food. According to the NHS, the average man needs around 2500 a day, and the average woman around 2000. So, in theory, 500 calories of cake has the same effect on your weight as 500 of cauliflower, right?

Wrong. Last year, researchers from the University of Toronto concluded that around 20 per cent of calories in almonds pass right through our bodies so that, in the words of principle investigator John Sievenpiper: “a calorie labelled may not be a calorie absorbed”.

In fact, explains Giles Yeo, Cambridge University molecular geneticist and author of Why Calories Don’t Count: “the calorie counts on food labels today are all wrong”. Not all the calories listed on the label will be absorbed by your body: some foods emit fewer calories than others as they pass through you.

Much of what we think we know about calories stems from work conducted in the late 1880s by Wilbur Atwater, an American chemist who spent his career feeding various foods to human volunteers, then measuring the heat of combustion of their resulting faeces using a piece of kit known as a “bomb calorimeter” (“reflect on this next time you want to complain about your job”, suggests Yeo).

Not all the calories listed on a food label will be absorbed by your body: some foods emit fewer calories than others as they pass through you. Photo / Hanson Lu, Unsplash

“In 1900, after a whole lot of burnt poop, Atwater presented his calculations to the world,” Yeo explains. “More than 120 years on, these ‘Atwater factors’ are still the basis for how calorie counts on all food packaging are derived.”

But here’s the catch. “Humans, however, are not bomb calorimeters. We are only able to extract a proportion of the calories locked up in any given food… Protein actually has a caloric availability of 70 per cent, meaning that for every 100 kcals of protein that makes it into the bloodstream, we are only ever able to use 70 kcals. By comparison, fat has a caloric availability of 98 per cent. As for carbs, it depends on whether we are talking about complex (90 per cent available) or refined (95 per cent).”

All calories, it turns out, are not created equal. There has been, says Yeo, no indication that the food industry will change its labels to reflect this research.

Myth 2: Metabolism slows with age

Been blaming your tight waistband on advancing age? Last year, a research team at Duke University published a paper that poured cold water on that theory. The team looked at the average daily calories burned by 6400 people, ranging in age from newborn to 95, as they went about their daily lives around the world.

If you are imagining that the teens and twenty-somethings burn through calories the fastest, you are not alone. But you are wrong. “We can’t blame our metabolism for the weight we gain in middle age,” says Herman Pontzer, study lead and author of Burn: The Misunderstood Science of Metabolism. “The calories we burn each day are incredibly stable all through adulthood, from our 20s up until we hit about 60.”

From our 60s onwards, our metabolism does slow, but only at a rate of 0.7 per cent a year. So there goes that excuse.

Myth 3: We all process calories the same way

Remember that infuriating friend who claims to eat like a horse while maintaining the figure of a rake? Well, it turns out that she may not be fibbing. In 2019, the largest ongoing scientific nutrition study of its kind, led by an international team of scientists including researchers from King’s College London, revealed that individual responses to the same foods are unique, even between identical twins.

The researchers measured how blood levels of markers – sugar, insulin and fat, for example – change in response to specific meals, while tracking data on activity, sleep, hunger and gut bacteria in thousands of participants in the US and UK (60 per cent of them twins).

The results revealed a wide variation in blood responses to the same meals, suggesting that personal differences in metabolism, caused by factors such as the gut microbiome and exercise, are just as important to our health and waistbands as the nutritional composition of our foods. “It depends on who you are, of course,” says Yeo, “and it is not 50/50 exactly, but both aspects play a substantial role.”

The moral of this myth? You may not be able to eat more or, unfortunately, less of the recommended calorie intake before you gain weight.

Myth 4: Low-fat foods are best if you want to slim down

Fats provide more than twice the calories per gram of carbohydrates. So stick the low-fat yoghurt in your basket next time you’re shopping… right? Actually, no.

“What consumers assume is that when something’s labelled low fat, it will be low calorie, but that’s often not the case,” says Johnstone. “Just because it’s low fat doesn’t mean it’s low calorie, that food product will need to contain other macro-nutrients.”

Manufacturers often increase the amount of sugar in their low-fat products to compensate, leading to blood-sugar spikes and cravings. On the other hand, healthy fats, like those in nuts or avocado, help to keep us feeling full for longer. Reach for low-fat alternatives and you may also end up reaching for more snacks later.

Healthy fats, like those in nuts or avocado, help to keep us feeling full for longer. Photo / Tetiana Bykovets, Unsplash

Myth 5: Calorie counting keeps weight off

In July, a survey published in the British Journal of Health Psychology brought a crumb of comfort to those who struggle to ignore the rumblings of our stomach as elevenses approaches.

Over 6000 young adults across eight countries were quizzed about their self-esteem and body-mass index. Researchers then compared three eating styles: intuitive (eating when you feel hungry), emotional (or “eating your feelings”), and restrained (restricting calories to lose or maintain weight). Little surprise that those who ate intuitively tended to have higher self-esteem. They also, however, appeared to have a lower weight.

“The problem with ‘weight-control strategies’, or dieting, is that they typically require you to ignore your physical cues of hunger and satiety,” explains lead researcher Dr Charlotte Markey, from Rutgers University in New Jersey.

“This isn’t a good long-term strategy. Those cues are there for a reason – to keep you alive! This doesn’t mean that people should just eat anything at any time or all the time. But being hungry is miserable and not sustainable.”

In fact, a 2010 study from the University of California found that counting calories can cause the rise of a stress hormone linked to excess abdominal fat. “Cutting your calories increases cortisol,” explained study lead A Janet Tomiyama. “We think this might be one reason dieters tend to have a hard time keeping weight off in the long term.”

Myth 6: Low-calorie foods are best for your waistline

Tempted to reach for that calorie-lite bag of Monster Munch or Quavers as a waist-friendly snack? Not so fast. Ultra-processed foods might be making you fat, in spite of their lower calorie counts.

In 2019, scientists from America’s National Institute of Health published the results of a study in which they fed volunteers three meals a day plus snacks for a month. The first fortnight consisted of a menu made up entirely of ultra-processed foods, while in the last weeks they were offered meals made entirely of unprocessed ones.

The volunteers were always offered twice the amount of food they would need to maintain their weight and the diets had the same amount of fat and carbs, though the processed one had slightly less protein (14 per cent, compared to 15.6 per cent in the unprocessed meals).

What happened? They ate 500 more calories a day on the processed diet, the researchers found: 280 of these came in the form of extra carbs and 220 from extra fat. The amount of protein consumed stayed pretty much constant across the two diets, suggesting something known as the “protein leverage hypothesis” might be at play.

As Yeo explains in his latest book, back in 2005 Australian scientists Stephen J. Simpson and David Raubenheimer suggested that the amount of protein in our diets might be one key to the obesity epidemic. If a diet has less than 15 per cent protein, we will eat more calories in the form of fat and carbs to make up for it. If more, then less fat and carbs (and thus fewer calories) are consumed.

Highly processed foods tend to be low in both fibre and protein, part of the reason why they can contribute to weight gain. And they appear to be addictive. On a processed diet we generally eat more calories.

Diet rules to remember

• Don’t worry so much about when you eat, it’s the daily tally of calories that counts.
• Beware of low-fat foods that replace fat with extra sugar.
• Healthy fats are your friend. Nuts and avocados can help you feel full for longer.
• Avoid highly processed foods. They really will make you pile on the pounds. Eat foods as close to their natural state as possible. They’ll fill you up for longer.
• Don’t fall for the age myth – you can burn calories and lose weight at any age.