“The best way to lose weight, believe me, is to eat less,” Boris Johnson said as he defended the government’s food strategy after ignoring proposals for a salt and sugar tax.
With that “believe me”, the Prime Minister struck a nerve for serial dietitians: what parts of the big smorgasbord of advice out there should we follow to ensure our health and happiness?
Along with the recent introduction of calories on restaurant menus, it can feel like we are ashamed to give up food altogether.
For Professor Tim Spector, the King’s College London epidemiologist celebrated for his work with identical twins, as well as diet and the microbiome, all of the above represents a step backwards in the public understanding of how people respond to and process food.
“For the past 100 years, we’ve been obsessed with calories, and it’s really made us think of anything else,” says the 63-year-old author of The Diet Myth and Spoon-fed. I worked hard to change that thinking.
When The Diet Myth was published in 2015, few people had any idea of the role that the estimated 100 billion microbes in our gut play in our digestion. Spector’s work helped put kefir in our refrigerators and kimchi in our bottles. Through the Zoe Project, the world’s largest nutrition study, he encouraged us all to join in and analyze our unique gut, blood fats and blood sugar responses.
Today, however, its number one myth target is that calories are a useful way to monitor our diet. Not only are calorie estimates often less accurate than we might hope, Spector’s studies of twins have shown that people differ greatly in how much energy they extract from a given food.
The daily allowances for men and women, says Spector, are not based on hard data. So I ask him: what should we aim for? Even asking the question, he says, gives credibility to the idea that there is a perfect figure. “If it was only 1 900, would it make a difference? No, it would not. ”
And when people are told to avoid high-calorie foods, Spector says advice can be taken to encourage the consumption of low-calorie drinks and low-fat foods. “That’s why we support this multi-billion-pound diet of low-calorie shakes and Weight Watchers, and all that other stuff.”
So, what other diet myths do we swallow, according to Professor Spector?
Myth: Exercise to lose weight
Exercise does require energy, but our metabolism adjusts to that loss by storing more energy than fat the next time we eat.
Our body is programmed to keep our biology stable, known as homeostasis, so if our energy levels change drastically with much more exercise and less food, our metabolism will respond by slowing down the weight loss and eventually turning it back on very quickly when we go back to normal activity and food – this is what we see in yo-yo dietitians who put back all the weight they initially lost. “To say that exercise alone is a great way to achieve a healthy weight in the long run is total rubbish,” says Prof Spector.