Popular weight-loss show “The Biggest Loser” has come in from criticism from many directions since it began showing in the US in 2004. Doctors and nutrition experts have voiced their concerns about the competitive weight loss regimen.

In May 2016, a study funded by the National Institutes of Health was published that had followed 16 “Biggest Loser” competitors over six years after the show finished. It found that although contestants in the study lost an average of 58.3 kilograms (128.5 lbs.), this weight loss came at a cost. By the end of the show, their resting metabolic rate – the number of calories their bodies consumed at rest – had decreased considerably (on average, by about 600 calories a day). This wasn’t particularly unexpected, but what was more worrying is that six years later, participants had regained an average of 70 percent of the weight they’d lost on the show, and their RMR (resting metabolic rate) hadn’t recovered.

A New York Times article interviewed some of the participants and confirmed what many dieters have known for years – losing weight is one thing, but keeping it off in the long term is a much trickier problem. Many people cited this as evidence that “extreme dieting damages your metabolism and makes you more likely to regain weight”. Is this true?

It turns out that if you dig a little deeper, the truth is a little more complicated. For a start, in the “Biggest Loser” study, the researchers didn’t find a correlation between how much each person’s RMR had decreased and their subsequent weight regain. Other research suggests that the speed of weight loss, per se, isn’t associated with how much weight a person puts back on afterwards, and in fact, some of the evidence suggests that more rapid initial weight loss is associated with better maintenance in the long term.
The authors of the “Biggest Loser” study point out that “While most subjects experienced substantial weight regain in the six years since ‘The Biggest Loser’ competition … 57 percent of the participants maintained at least 10 percent weight loss. In comparison, it has been estimated that ∼20 percent of overweight individuals maintain at least 10 percent weight loss after one year of a weight loss program.” In other words, despite the fact that most participants regained weight (and some gained extra weight), the “Biggest Loser” was actually quite successful compared to the majority of weight loss interventions.

Of course, this is a relatively small study (a common problem in nutrition research), so we should avoid reading too much into it on its own. In context with other studies that have been done, though, it points towards some important things to consider about dieting.

Body weight is a bit like a thermostat

How should we make sense of all this? First of all, we should remember that weight gain and loss typically happen because of very, very tiny imbalances between the number of calories we consume, and the number our body expends. Contrary to our intuition, the difference between maintaining a healthy weight or gaining weight might come down to a discrepancy of only 20 calories a day, added up over the course of a few years. That’s less than a biscuit! None of us count our food intake quite that carefully – even with modern smartphone apps that allow us to track the nutritional content of our food.

The way to understand what’s going on here is to think of a thermostat. If we want to control the temperature of a room, we can program the thermostat with a set point. It’ll then monitor the temperature and if it gets too cold it’ll turn the heating up, too hot and it turns the heating down. There’s good reason to think that the body has sophisticated control mechanisms that act a bit like a thermostat that pushes your body back towards your comfortable weight. When your weight drops below that point, your body fights back by burning fewer calories and making you hungrier. The number of calories you expend is related to the number of calories you consume, and vice versa.

 “Nobody keeps the weight off” - is long-term weight-loss impossible?

The evidence has led some people to go so far as to suggest that long-term weight-loss is, if not impossible, then so difficult that almost nobody manages it; but others have a more optimistic outlook and point out that the important thing is for would-be dieters to change their lifestyle in a way that can be maintained.

The idea of a “set point” for body weight can be misleading. It gives the impression that being overweight may be entirely beyond our control; something we’re stuck with. If this were true, we wouldn’t have seen the recent rise in obesity and related problems. The reality is that our weight is the result of a complex combination of factors, some of which can be modified and others that are difficult or impossible to change. Our genetics and history have a role to play – even as far back as what our mothers and grandmothers ate; but the main factor that’s within our control is our lifestyle. It’s certainly true that some people have the odds stacked against them more than others, but wherever our starting point, what we eat and what we do will affect the weight our body gravitates towards.

The verdict? Misleading.

Going back to the original claim, there’s an element of truth to it: losing weight may very well lower your metabolic rate. It’s not so much that “extreme dieting” causes damage though; it’s perhaps more helpful to think of it as a natural adaptation that takes place as your body stubbornly resists attempts to change. Your weight in the past will affect the feedback mechanisms that control hunger and metabolism, with the result that someone who has been obese might have a harder time keeping the pounds off than someone who’s always been lighter; but it’s probably misleading to blame this on the diet.

The take home message here is that whatever you do to lose weight, you’ll have to change your lifestyle if you want to keep it off. And if that new lifestyle is making you miserable, then your chances of sticking with it in the long term are not very good. If you can find new foods and activities that you enjoy, however, you stand a much better chance of success.