Those 10,000 Daily Steps You Tried To Take? A typical adult weighing 150 pounds (10st 7lb) burns about 250 kcal in the process, he explains. This is roughly the equivalent of half a Big Mac. Climbing a staircase uses about 3.5 kcal – less energy than doing a single M&M.
It’s enough to send you back to the sofa defeated. But it shouldn’t be, because as Pontzer makes clear, exercise is vital to your health – it just doesn’t make you thin. “If you start a new exercise program tomorrow and stick to it religiously, in two years you will most likely be almost the same weight as you are now,” he writes. “You should do it anyway! You will live happier, healthier and longer. Don’t expect any significant weight change from exercise alone in the long run. “
So, if it doesn’t stop us from taking an extra trip to the gym every week, what are we going to do? I told Pontzer that the super villain in Burn is the ultra-processed, highly flavored foods in the western diet. While the Hadza stuck to a simple whole food diet, we were seduced by an ever larger selection of technical delicacies. These won’t nourish or fill us up so we can eat more of them.
“I think that’s right when you had to point your finger at something,” he says. “All of the research we’ve done over the past 10 years – not just in my lab, but other people as well – suggests that diet is the culprit here for obesity. It’s not a sloth, it’s the food.
“What is food especially about? Is it sugar Is it fats? No. It is the fact that we make our foods in laboratories and test them in focus groups to make sure you are overeating. That is literally the point of these big industries: to make sure you buy as much as possible. That’s how they make money. Obesity has emerged alongside the availability and development of processed foods. “
Some of us naturally eat more than others, and some eat more ultra-processed foods than others for various reasons. Genes are part of the picture – though maybe not in the way you’d expect.
You may think you have a fast or slow metabolism, but Pontzer suggests that this perception usually translates as: “I feel like I can eat what I want, and beyond that, I never feel tempted or hungry” or “I feel hungry all the time and if I don’t work really hard I’ll overeat”.
He says, “We know your brain handles your hunger, fullness, and satiety, and we know that people are wired differently and the genes that contribute to the variation in BMI [body mass index]They are active in your brain, not in your fat or muscle cells.
“So it’s the way you’re wired, it seems, that’s going to affect how fast you feel your metabolism is up.”
There are also external factors that affect our diet. One is stress. “It makes our brains make decisions about foods that are probably not the healthiest,” says Pontzer. “Comfort food and stress food are real. I suspect if Covid has an impact on people’s waistlines, that’s what it’s about too [as anything]. ”
Reducing the emotional and psychological stress in our lives, as well as the physical stress caused by sleep deprivation, could help combat overeating. While Pontzer was the first to recognize that busy modern life is about long hours in sedentary jobs, it’s easier said than done.
Obesity therefore arises from a complex interplay of biology and socio-economic factors. And once you become overweight or obese, our sophisticated metabolic pathways make it incredibly difficult to shed those pounds. Pontzer points to research such as the pioneering study conducted in the 2010s on obese people who went to weight loss boot camps for the reality TV show The Biggest Loser. After 30 weeks of cutting calories and exercise, even though all participants had lost weight, tests showed their metabolic rates had slowed dramatically – they were in starvation mode, where cells burn energy more slowly while the body works to conserve calories. By the time the researchers checked in 14 of the participants six years after the program, their basal metabolic rates were still lower than expected, and all but one had regained a significant amount of weight. It’s perverse – and depressing – but writes Pontzer, “From an evolutionary point of view, it makes all the sense in the world”.
So it’s time to rethink how our metabolic engines work. But what do we do in the meantime to lower the weight?
Although amused by the modern obsession with eating like our ancestors in the form of so-called paleo diets, Pontzer says we can learn from the Hadza. “They stay thin because they are on a diet that doesn’t include these processed foods. I think 90 percent of it is that simple. “
We often make it harder with diets because we like to believe the stories around them, he says. It is appealing to think that there might be a magic bullet. But there is no such thing.
“Any diet that works works because it reduces calories,” says Pontzer. “There are different possibilities for this. There is no magic. Any diet will work if you stick to it. “
The diet that works best for you depends on “your particular reward system and the variety of foods that satisfy you most with the fewest calories,” writes Pontzer.
On a personal level, we can keep tempting goodies out of reach. At the societal level, the only way to combat obesity is to change our eating environment. Additional taxes on ultra-processed foods could be a possibility. Whole foods cheaper and easier to get, another.
Physical activity remains vital – to regulate our metabolism, including our feelings of hunger and fullness, to protect against all major illnesses, to support longer lives and to maintain weight loss.
When it comes to understanding metabolism better, Pontzer is optimistic that the tide is turning and when public health guidelines are rewritten to make it clear that exercise is not the key to weight loss, he will know that the penny has finally fallen.
Burn by Herman Pontzer (RRP £ 20). Buy now for £ 16.99 from books.telegraph.co.uk or by calling 0844 871 1514