Why is it so much harder to lose weight than to regain it?
The findings of recent research, published in the journal Obesity, suggest that our bodies actually resist weight loss. While dieting, we reduce our resting metabolic rate, which lowers the number of calories we burn when we are not doing much. The authors of the research warn that keeping weight off requires “vigilant combat against metabolic adaption”.
The study followed 14 participants of the US version of the TV show The Biggest Loser. The researchers found that, after six years, all but one of the contestants in their study had regained weight. On average, they weighed 20st 10lb (131.5kg), compared with the average starting weight of 23st 6lb (149kg) and the 14st 4lb (91kg) at which they finished the show.
Six years is a long time, and being, on average, 2st 10lb (17kg) lighter is not insignificant. But the odds were stacked against the participants. The study showed that, before the competition, the group burned a daily average of 2,600 calories at rest, but this fell to around 2,000 calories a day when it finished. Six years later, instead of creeping back up to its normal level, their resting rate had slowed further to 1,900 calories a day. On average, the resting metabolic rate was 500 calories a day less than you would expect for the age and body composition of the person. So, the contestants had to eat less to stay at their lower weight. While researchers knew that dieting reduces the resting metabolic rate to save energy, this study shows how savagely your body subverts weight loss.
This was a small study without controls, though, and weight loss is influenced by factors such as genetics and hormones. Other studies show that some people are less affected than others. The report on The Biggest Loser participants cites another study showing that obese people who have weight-loss surgery seem to escape this metabolic adaptation. Somehow, the body resets to a new normal weight and the resting metabolic rate doesn’t fall. For the rest of us, being vigilant about what we eat, and building up muscle mass (which is lost with age) through aerobic exercise and strength training are the only ways to fight back.
Your resting metabolic rate determines only a proportion of your energy expenditure. If you burn off more calories than you eat, you will lose weight.Other research suggests that reducing calories by 20% and doing moderate exercise for 20 minutes a day will keep weight off.