“The best way to lose weight, believe me, is to eat less,” Boris Johnson said as he defended the government’s food strategy after salt and sugar tax proposals were ignored.
With that “trust me,” the Prime Minister hit on a nerve for serial dieters: Which parts of the vast panoply of advice should we follow to ensure our health and happiness?
Along with the recent introduction of calories to restaurant menus, it can feel like a shame to give up food altogether.
For Professor Tim Spector, an epidemiologist at King’s College London, famous for his work on identical twins, as well as diet and the microbiome, all of the above represents a step backwards in public understanding of how humans react to and process food.
“For the past 100 years, we’ve been obsessed with calories, and it’s really taken our mind off things,” says the 63-year-old author of The Diet Myth and Spoon-fed. He worked hard to change that way of thinking.
When The Diet Myth was published in 2015, few people had any idea of the role that the estimated 100 trillion microbes in our gut play in our digestion. Spector’s work has put kefir in our fridges and kimchi in our jars. Through Project Zoe, the world’s largest nutritional study, he encouraged us all to join in and analyze our unique gut, blood lipid and blood sugar responses.
Today, however, his number one myth is that calories are a useful way to monitor our diet. Not only are calorie estimates often less accurate than one might hope, but Spector’s twin studies have shown that humans vary wildly in the amount of energy they extract from a given food.
Per diems for men and women, says Spector, are not based on hard data. So I ask him: what should we be aiming for? Even asking the question, he says, lends credence to the idea that there is a perfect figure. “If there were only 1,900, would that make a difference? No, it wouldn’t.
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 industry of low calorie shakes and Weight Watchers and stuff.”
So what other food myths do we swallow, according to Professor Spector?
Myth: Exercising to lose weight
Exercise requires energy, but our metabolism adapts to this loss by storing more energy as fat the next time we eat.
Our body is programmed to keep our biology stable, known as homeostasis, so if our energy levels are drastically altered with much more exercise and less food, our metabolism will respond by slowing weight loss and eventually by regaining it very quickly when we resume normal activity and eating – this is what we see in yo-yo dieters regaining all the weight they initially lost. “To say that exercise alone is a good way to achieve a long-term healthy weight is pure nonsense,” says Professor Spector.