Have you noticed the overweight person in the gym who sweats it out three or four days a week on the treadmill, but never seems to get any thinner? The evidence of our own eyes goes against everything we're told. The weight-loss dictum is that the more active we are, the more calories we burn, and if our calorie intake falls below our calorie expenditure, we will shed the pounds.
In fact, a lack of exercise has far more to do with obesity than the food we're eating, a review by Stanford University School of Medicine has claimed. A national health survey that tracked Americans from 1988 to 2010 found a huge increase in rates of obesity and inactivity, but not in the number of calories being consumed.1
But if that's right, how does it explain the fat guy on the treadmill? It doesn't seem to be that simple: the more we look, the more that direct line between activity and calorie expenditure starts to disappear, as researchers from Baylor University in Texas have demonstrated.
They've been studying two very different groups of eight-year-olds. One is of the Shuar tribe in Amazonian Ecuador, where a typical day includes working on the family farm and foraging for food. The other is more familiar: eight-year-olds from the West who sit in a classroom and then lounge at home in front of a gaming console or tablet.
Not surprisingly, the Shuar children in the Amazon are around 25 percent more active than their counterparts in the West. But here's the kicker: both groups are burning similar amounts of calories every day.2
It works for a while
It could all be down to evolution and the way the body has adapted to burn calories, the researchers think. Our metabolic system is like a cautious spender who budgets carefully and will stop buying the moment their account balance runs low.
The Shuar children are much leaner than typical Western children, and their bodies "know" to stop burning calories so that the essential physiological processes are protected; at least, that seems to be what's happening, the Baylor researchers suggest.
Other researchers have reported a similar phenomenon. A team from City University of New York discovered that strenuous exercise had an immediate effect on weight—but then weight loss slowed and eventually stopped completely, even though the amount of exercise stayed constant.
Diet is the best way to lose weight consistently and for a long period, the researchers concluded.3 But it's a dangerous idea at a time when one in five children is obese as they begin school, and health guardians are trying to counter this obesity epidemic by encouraging children to become more active.
The Baylor researchers point out there are plenty of good reasons to exercise—your cardiovascular system, for one, will thank you—but doing so only to lose weight isn't one of them.
Leading cardiologist Aseem Malhotra agrees. Regular physical activity reduces the risk of a range of diseases, from some cancers to diabetes, dementia and heart disease—but it's not an essential part of any strategy to lose weight.
It's the diet
That's because obesity and weight loss are almost exclusively a response to diet and the type of food we eat, and it's the sugary, high-carbohydrate processed foods that are the main culprit. As the title of one of Dr Malhotra's papers puts it, you can't outrun a bad diet.4
"People are drowned by an unhelpful message about maintaining a healthy weight through calorie counting, and many still wrongly believe that obesity is entirely due to lack of exercise," he says.
And we're not even getting the right message about food. We get our energy from fats and carbohydrates—essentially, sugars—and we're told that to lose weight, we must cut back on fats. But that is simplistic, and often fueled by a food industry that makes its major profits from low-fat foods and drinks. As a result, we eat more carbs, despite the fact that in reality it's the sugars, not the fats, that put on the pounds.
And not only are the carbs responsible for weight gain, the other message is that "a calorie is a calorie." It was coined by the sugar industry in the 1950s, and updated by Coca-Cola in 2013 as "all calories count." In its campaign, Coca-Cola blamed the obesity epidemic on inactivity—and not on its sugary drinks.
But all calories are not created equal. Sugar calories (from carbs) promote fat storage and hunger, and studies have shown that at the country-wide level, the incidence of diabetes goes up by 1 percent for every 150-calorie increase in citizens' daily sugar consumption, while increases in fat or protein had no such effect.5
The health hazards of a processed-food diet could be magnified in people who are insulin-resistant, or alternatively, perhaps people are becoming resistant—a precursor of diabetes—as a result of the diet.
Not enough evidence
The mainstream view still holds to the calorie-control theory. Advocates of exercise point to evidence demonstrating that it's the most effective way to lose weight, as a study by researchers from Massey University in New Zealand concluded.
They had taken another look at 15 trials, involving 556 people who each lost an average of 8 lb (3.7 kg) by exercising for up to 36 weeks. But some of the studies had been poorly designed.
At best, the researchers say there is some evidence that exercise can reduce body fat, but even less that it helps improve metabolic processes such as cholesterol levels and insulin control.6
Another review of 29 trials determined it was "unclear" whether exercise had a significant impact on some characteristics of obesity, such as body-mass index and waist circumference, although it did seem to help people lose weight.7
Dissenters like Dr Malhotra say the evidence isn't conclusive about exercise—and maintain that levels of physical activity haven't changed much in the past 30 years, although obesity rates have skyrocketed.
Researchers have seen this happen in real time in sub-Saharan Africa. Rates of obesity jumped by almost 35 percent in the period from 1992 to 2005, and this coincided with cheap, processed foods becoming much more widely available in the region.8
The emphasis on calorie-counting is shielding the real problem of a diet of processed food—and the World Health Organization agrees, citing a bad diet for causing more disease than inactivity, smoking and alcohol combined.
"We must abandon the myth that lower-fat, lower-calorie products lead to less weight gain. This illusion leads to paradoxical policies that focus on total calories, rather than food quality, so there's a ban on whole milk but sugar-sweetened, fat-free milk is allowed," said Professor Dariush Mozaffarian of Tufts University.
Slim, but sick
It's not just about losing weight and keeping it off. You can still be slim, but as Dr Malhotra put it (see main article), you can't outrun a bad diet.
Dave McGillivray, an organizer of the Boston Marathon who runs the course every year even as a 65-year-old, was diagnosed with severe coronary artery disease six years ago.
McGillivray was shocked. "I've been running all my life. I've done eight Ironman Triathlons and 140 marathons. I've run across the United States. How can I have blocked arteries?" he asked.
The reason was simple. He was eating a fast-food diet and believed that running gave him a free pass to eat what he liked.
"As a runner, I just felt that if the furnace was hot enough, it would burn whatever you put in it. So I would eat anything and everything I wanted," he told the magazine Runner's World in 2018.
He should have spoken with his cardiologist, Aaron Baggish, sooner.
Baggish, director of the Cardiovascular Performance Program at Massachusetts General Hospital Heart Center, said that McGillivray's attitude is typical, especially among runners who jog to get in shape and lose weight.
Overindulgence in simple sugars is "the single most common dietary transgression" of runners, and foods such as white bread, white pasta, white rice and refined sugars get broken down into "bad molecules, bad types of fat, and bad oxidative sugar species" that harm the heart and arteries.