Dieting May Slow Metabolism — But It Doesn’t Ruin It By Adam Collins, University of Surrey and Aoife Egan, University of Surrey via Natural Blaze
When it comes to dieting, research shows the majority of people will regain some – if not most – of the weight they’ve lost. While there are many reasons why this weight regain may happen, some popular claims online are that it’s because dieting permanently wrecks your metabolism. But while it’s true that dieting slows your metabolism, it also improves your metabolism in many positive ways.
When we talk about metabolism, we’re typically referring to your metabolic rate. This is the number of calories your body burns at rest. Of course, the more activity we do, the more calories we burn. In order to lose weight through dieting, you need to consume fewer calories than you’re using. This forces the body to use its energy stores – like fat – to meet the shortfall. Your metabolic rate will also change as a result.
The loss of lean tissue (muscle) when you diet – which burns around 15-25 calories per kilogram each day – lowers resting metabolic rate, meaning you need fewer calories than you previously did. But the body also deliberately slows down metabolism to preserve energy stores and minimise weight loss.
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When the body senses depleted fat stores it triggers adaptive thermogenesis, a process which further reduces resting metabolic rate – and may stunt weight loss despite strict dieting. Adaptive thermogenesis can kick in within three days of starting a diet, and is suggested to persist way beyond dieting – even hampering weight maintenance and favouring weight regain.
One example of adaptive thermogenesis’s effect was seen in a widely publicised 2016 study which looked at former contestants of US reality TV show “The Biggest Loser”. It showed that participants had a significant decrease in their metabolic rate, even several years after initial weight loss. Participants needed to eat up to 500 calories less than expected daily.
Other studies have also shown metabolic slowing with weight loss, but with much smaller decreases (around 100 calories fewer a day to maintain weight). However, there’s less certainty whether this slowing persists once people are weight stable.
