Calories in vs calories out isn’t as simple as just eating more/less or exercising more/less. Your body has several mechanisms to counteract the calorie changes you make in your diet or exercise routine.
Base metabolic rate (BMR) is how many calories your body’s cells would burn if you were to lay completely still for an entire day. Contrary to popular belief, healthy people all have similar BMR for their body weight.
Your body will fight back
If you create a caloric surplus your body will try to fight this surplus by increasing base metabolic rate. This means that your body will burn more calories at rest counteracting your weight gain. If you create a calorie deficit your body will decrease base metabolic rates in order to preserve energy reduce your weight loss.
It is important to understand, however, that whenever the body tries to counteract changes you make (a phenomenon known as negative feedback) the change will only be reduced and never reversed ie the changes in your BMR can never cause weight GAIN in a caloric deficit or weight LOSS in a caloric surplus. So if you want to increase BMR you can do so by eating more calories, but that will not help you lose weight. The purpose of this post is to make you aware of how the body “fights back” when you try to lose weight.
So what can you do about this? To quote the study authors:
” stepwise, incremental fashion, utilizing small energy deficits to ensure a slow rate of weight loss. Participation in structured resistance training program
and adequate protein intake are also imperative. More research is needed to verify the efficacy of periodic refeeding and reverse dieting in supporting prolonged weight reduction and attenuating post-diet fat accretion.”
Eric T Trexter. Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr. 2014; 11: 7.