Why you can’t keep off the weight you lose

Why can’t I keep the weight off? 

Weight loss can lead to a decline in your resting metabolic rate, or how many calories you burn while resting, Dr Chahal says. In 2016, American researchers published the results of a six-year long study following the former contestants on a weight-loss reality television show, The Biggest Loser. 

During the show, contestants lost an average of 125 pounds each. Six years later, however, researchers found that their resting metabolic rate was far slower than it had been before taking part in the show, meaning that they were burning fewer calories when in a state of rest and would have to work harder (and cut back on more calories) to keep the weight off. The result? They had regained much of the weight lost during the show.

We do not know exactly what mechanism causes weight loss to slow metabolic rate, says Dr Chahal, but the more weight you lose, the more likely your basal metabolic rate will adapt and reduce. Rapid, extreme weight loss makes it even more likely. 

Other changes can also get in the way of maintaining your weight loss. Hormones, for one. Ghrelin, the hunger hormone, will start to increase as you lose weight while leptin, a protein hormone signalling when you are full, will drop. This means you will want to eat. 

“There is also research suggesting that your genes can be involved in weight management as well,” says Dr Chahal. This set point theory states that our genetics, as well as environmental factors and early years experiences, help to establish your body’s weight set point- an innate weight range that your body tries to maintain. Once you fall below this set point, the hormonal and metabolic changes above kick in, explains Chahal. “It’s the body saying: ‘look, I’ve been at this weight for a very long time and now you’ve brought me down to lower weight. I want to try to get back to the original weight.’”

The psychology of yo-yo dieting

Biology aside, there may be psychological factors influencing your weight regain, suggests Dr Chahal. “Sometimes there are psychological triggers to weight gain. If the triggers return, the weight returns with them.” If you tend to reach for junk food when stressed, then a new deadline or looming redundancies at work can push against your weight loss.

Even if your healthy habits are not tied to your mental health, restrictive diets can wear down your resolve and self-control over time. The popular Keto diet – which is high-fat, medium-protein and low-carb – is a good example, says Dr Chahal, because not all calories are created equal. “Fifty kilocalories of carbohydrates in brown bread, for example, will create a different insulin response to, let’s say, 50 kilocalories of protein.”

Calorie for calorie, carbohydrates create a bigger spike in insulin (the hormone that regulates your metabolism). More insulin means your body burns less fat. “This is why the Keto diet became so popular,” says Dr Chahal. But sustaining a no-carbs regime over a long period can be difficult, he explains. Soon enough, real-world routines reassert themselves and carbs re-enter your life.

“It’s not at all surprising that we regain weight. It’s how we’re built,” explains Prof Peter Rogers, a psychologist at the University of Bristol, whose research focuses on human appetite and weight control. “As mammals, we’ve evolved the capacity to store excess energy as body fat. That hedges against the time when it isn’t readily available.” For the privileged in today’s world, however: “Food is all around us. So we have to develop and exert countermeasures.”

Dieting and weight loss has two phases, Prof Rogers explains. At first, you need to significantly reduce the calories you consume, so that your weight drops. Once you find yourself at a healthy weight, you can increase your calorie intake a little. Raise it too much, however, and your weight will creep up again, so you still need to be mindful. This second stage is often the hardest, he suggests, because it is easier to do something dramatic, and with obvious gains for a month, than to do something sensible forever, with no motivating weight loss. This makes it easy to fall into a pattern of losing and regaining weight.  


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