Why am I not losing weight in a calorie deficit?
A short-term plateau in a deficit usually comes down to water retention, systematically underestimated calorie intake, or adaptive thermogenesis — not a "broken metabolism".
Water and glycogen mask fat loss
Body weight fluctuates by one to two kilograms (2.2–4.4 lb) a day through water retention, glycogen stores, and gut contents. Phases of higher carbohydrate intake, more salt, or intense training all trigger short-term water retention (Heymsfield et al., 2011). Actual fat loss only becomes visible as a trend averaged over two to four weeks.
Underestimated calorie intake
In a widely cited study, Lichtman et al. (1992) showed that people who described themselves as diet-resistant underestimated their actual calorie intake by an average of 47 percent. Liquid calories, cooking oil, and toppings are the items most consistently missed when tracking.
Adaptive thermogenesis
Over the course of a longer deficit, total energy expenditure drops — partly through reduced NEAT (unconscious everyday movement) and partly through a slight decrease in resting metabolic rate (Müller et al., 2016). In effect, your measured deficit quietly shrinks.
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- Lichtman, S. W., et al. (1992). Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. NEJM, 327(27). PubMed
- Müller, M. J., et al. (2016). Adaptive thermogenesis with weight loss in humans. Obesity, 24(1). PubMed
- Heymsfield, S. B., et al. (2011). Voluntary weight loss: systematic review of early phase body composition changes. Obes Rev, 12(5). PubMed