Basal metabolic processes account for approximately 70% of total daily energy expenditure, and excessive calorie restriction induces physiological adaptations that promote weight regain.

Study: The Effects of Continuous vs. Intermittent Caloric Restriction on Fat Loss: A Randomized Controlled Trial

When people eat way fewer calories, their bodies slow down to save energy, making it harder to keep losing weight and easier to gain it back. This study found that people who ate fewer calories continuously lost the same amount of fat as those who took breaks — but lost more muscle and burned less energy overall, suggesting the body adapts to save energy.

Study: Total daily energy expenditure has declined over the last 3 decades due to declining basal expenditure not reduced activity expenditure.

The study found that our bodies burn less energy at rest now than they did 30 years ago, even though we’re more active — meaning our basic body functions use less energy. This matches the idea that when we eat less, our bodies slow down to conserve energy, making it easier to regain weight.

Study: The effects of graded levels of calorie restriction: VIII. Impact of short term calorie and protein restriction on basal metabolic rate in the C57BL/6 mouse

When mice eat much less, their organs get smaller, and that’s why they burn fewer calories — not because their cells slow down on their own. This helps explain why people often regain weight after dieting: their bodies adapt by using less energy.