Metabolic adaptation

Metabolic adaptation is the drop in energy expenditure during dieting beyond what the loss of body weight would predict.^{1Norton and Baxter, The Complete Reverse Dieting Guide, p. 18.} A smaller body needs less energy to function and move, but adaptation reduces expenditure further.^{1Norton and Baxter, The Complete Reverse Dieting Guide, p. 18.} Basal metabolic rate, non-exercise activity thermogenesis (NEAT) and, to a lesser extent, exercise energy use fall with calorie restriction.^{1Norton and Baxter, The Complete Reverse Dieting Guide, p. 18.} The reductions in basal metabolic rate and NEAT often exceed what weight loss alone explains; Norton and Baxter describe a typical basal metabolic rate response as about 15% below prediction.^{1Norton and Baxter, The Complete Reverse Dieting Guide, p. 18.}

Exercise also takes less energy after dieting, even when body weight is accounted for: dieters wearing weighted vests to replace lost weight still used less energy for the same exercise than before.^{2Norton and Baxter, The Complete Reverse Dieting Guide, p. 21.}

In practice

• After a long diet, a client’s maintenance calories are usually lower, so returning straight to their previous intake can overshoot maintenance.^{3Norton and Baxter, The Complete Reverse Dieting Guide, p. 7.}
• The reduction can persist: in a study of contestants from a televised weight-loss competition, measured metabolic rate remained about 500 kcal a day below prediction six years later.^{4Norton and Baxter, The Complete Reverse Dieting Guide, p. 19.}