Diet Ruins My Metabolism – Myth or Fact?

“You’d be surprise to see how our body can adapt in a relatively short of time” – unknown

A while ago, I wrote about energy expenditure and how it influences our weight loss or weight gain journey. I don’t know if you have ever read anything about how doing a diet ruins our body metabolism or not but I have read some articles about this. Although I think there’s some truth on those articles, the word ‘ruin’ is a bit too strong and misleading. Our body, mind, and habit adjust to many things, including what and how we eat.

I’ve also shared that I’ve been reading an amazing book called The Women’s Book recently and it has taught me many things regarding nutrition, diet, and exercising. One part of the book explains how our body adapt after we perform any kind of diets.

A quick answer: yes, our metabolism adapt after we are in a calorie deficit and lost some weight. Our resting metabolic rate (RMR) becomes lower because it has become more efficient. Also, less body weight means less energy for RMR. However, this change is relatively small and insignificant to reduced our overall metabolism (or overall energy expenditure).

“Individual losing a moderate amount of weight, the total adaptive drop may be no more than 150-250 calories. Of this decrease, perhaps 10-15% is due to the changes in RMR and this amounts to roughly 15-40 calories per day, an insignificantly small number. Even the dieter who experiences a 500 calorie total decrease will still only see the RMR drop making up 50-70 calories per day.” (Mc Donald, Lyle, 2018, The Women’s Book).

So – what is this about slower metabolism while or after dieting?

Some study shows what actually happens is sometimes we tend to move less while we are on calorie deficit. This mean some people simply exercise less and move less overall while on a diet.

Although it is true that our muscular efficiency will increase, especially when we have lost our body fat %, it is also true that the majority of people are less motivated to exercise when they are on a diet.

Another more important aspect that tends to happen is our non-exercise energy is not used as much as before. This means, we walk less from parking lot to the office entrance or choose taking lift instead of stairs – just because we feel more tired due to calorie deficit. A study showed that this reduction in informal movement is the major reason why most people has a lower metabolism rate while dieting.

So, when we read something about this in the future, let us rethink if it’s true or not.

  • Yes, it’s true our body adapt and burn calorie more efficiently when we are dieting
  • Yes, it’s true when we have lost some body fat, our body burn energy more efficiently
  • Yes, it’s also true then after we lose some weight, our RMR will never come back to the previous one as it will be based on our new body weight
  • However, it is also true that we may have burnt less calories simply because we move less. This tho, will come back once our activity is back to normal.


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