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Are you not eating enough to lose weight?

Metabolic adaptation delays time to reach weight loss goals

Obesity Society Online. January 27 2022.

When we want to lose weight, our first consideration is the amount of food specially calories we eat. We put ourselves on a restrictive diet with fewer exogenous calories (calories from energy outside our body). The hope is that our body will then begin to break down the endogenous calories (calories we have stored on our body) which will lead to weight loss. It makes perfect sense and mostly is effective. This equation doesn't take into consideration that our bodies don't like to feel deprived. When we take in fewer calories, our bodies consider that may be in danger and enact changes to cellular metabolic mechanisms. Our bodies need a certain amount of calories or energy to sustain ourselves for basic mechanisms that our body does, even at rest. We call this our basal metabolic rate (BMR) or sometimes called resting energy expenditure (REE). This equates to the number of calories we would require even if we were at rest for 24 hours. Standard advice for weight loss is to take in 500 calories less than the BMR. Your BMR can be calculated by a body composition analysis (BCA) machine which considers fat and muscle composition or by using a calculation that includes height, weight, age an activity level. If you ingest fewer calories than your BMR, you will need to use the energy you have stored on your body such as fat in adipose tissue. This simplistic idea is complicated by our body's survival mechanisms that occur when you lose a significant amount of weight. A recent study by the Department of Nutrition Sciences at the University of Alabama at Birmingham concludes that metabolic adaption will slow down weight loss to conserve energy in the setting of food scarcity. Study design

  • 65 premenopausal women, overweight by BMI (BMI 25-29)

  • 36 white women, 29 black women

    • Nonsmoking, normal menstrual cycles, normal glucose, family history of overweight/obesity, no medications

  • 800 calorie diet until BMI 25 reached

  • One group exercised once weekly and one group exercised routinely

  • 64% adhered to the diet

  • 16% weight loss over 5 months

    • BMR retested in a fasted state during the follicular phase of menstrual cycle

    • Average decrease of 46 calories/day less after weight loss

What can we do to counteract this metabolic adaption?

  • Avoid rapid weight loss. Aim for weight loss of 1-2 calories

  • Include weight lifting and avoid excessive cardio exercise

  • Alternate energy intake - Consider intermittent fasting that varies caloric intake

  • Change cardio exercise to zone 2 exercise

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