How our Bodies Adapt to Weight Loss

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There are multiple competitive sports that would consider low body fat along with higher amounts of lean body mass an advantage to performance. Gymnasts, wrestlers, and bodybuilders are just some examples of athletes who have a high demand on physique for performance. Studies have shown that weight loss and low calorie consumption typically results in numerous metabolic adaptations.

Thyroid hormone (T3) helps to regulate our metabolic rate. Increased levels of T3 are associated with a higher metabolism. Low calorie intake and low body fat are linked to a decrease of T3, ultimately decreasing metabolic rate (the number of calories we burn throughout the day).

Leptin is produced in adipocytes (fat cells) and helps control satiety levels. Higher circulating leptin  means greater satiety, or feeling "full". When individuals follow a low calorie diet for a prolonged period of time and/or lose body fat, leptin levels will decrease, making it difficult for an individual to feel "full."

Ghrelin is another hormone that plays an important role in our metabolism that essentially stimulates appetite. When intake is low, we are fasting, or we just have not eaten in a few hours, Ghrelin levels rise to promote food intake, aka hunger increases!

We also see changes in energy expenditure in a calorie deficit. TDEE is our total daily energy expenditure and it is made up of our basal metabolic rate (BMR), exercise activity thermogenesis (EAT), and thermic effect of food (TEF). With weight loss, we see a decrease in TDEE meaning, we are burning less calories throughout the day.

Basal metabolic rate- the amount of calories our bodies require while at rest
Exercise activity thermogenesis- the amount of calories burned during exercise activity
Thermic effect of food- the amount of calories required to digest and process foods we eat.

 These responses are our body's way of reacting to what it perceives as a "starvation" state. Our bodies do not know when we are starving versus when we are restricting calories with the goal of weight loss. Because of this, our bodies will try to survive by promoting food consumption, decreasing metabolic rate, and making fat loss more difficult.

Researchers recommend slow weight loss to help slow the effects of these metabolic adaptations.


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Resource: Trexler, E. T., Smith-Ryan, A. E., & Norton, L. E. (2014). Metabolic adaptation to weight loss: Implications for the athlete. Journal of the International Society of Sports Nutrition, 11(7). doi:10.1186/1550-2783-11-7

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