How cutting actually works
Learn · Body composition · Explainer, Typed Supps
You lose fat when you use more energy than you eat. The rest is just what makes that bearable.
Stage by stage
- The deficit (Intake below expenditure): The mechanism, entire. Every effective approach is a different way of producing this.
- Fat mobilisation (Insulin falls, lipolysis proceeds): Lower insulin releases the brake on fat release. The deficit drives this — not the other way round.
- What you lose (Protein + lifting partition it): 1.6–2.4 g/kg protein and resistance training shift the loss toward fat and away from muscle.
- The pushback (Adaptive thermogenesis): Expenditure drops and hunger rises as you get lighter, so the deficit narrows and needs recalculating.
What the evidence supports
- An energy deficit is required for fat loss — strong evidence. As settled as anything in nutrition science.
- Higher protein preserves lean mass during a deficit — strong evidence. Consistent across many trials, with resistance training amplifying the effect.
- Low-carbohydrate diets produce more fat loss than higher-carbohydrate diets at matched calories and protein — insufficient evidence. Tested repeatedly under controlled conditions and not supported. Differences in free-living studies track adherence and protein, not carbohydrate.
- Intermittent fasting outperforms continuous restriction — insufficient evidence. Comparable outcomes when calories are matched. Useful if it suits you, not superior.
Timing
Timing is an adherence tool, not a metabolic lever. The best pattern is the one you will still be doing in three months.
Time to effect
- 1–2 wks: Scale moves, mostly water and glycogen.
- 0.5–1%/wk: A rate that preserves muscle reasonably well.
Common myth
“Carbs make you fat.” In reality: Trials matching calories and protein find near-identical fat loss across carbohydrate levels. Low-carb helps many people because protein and fat are satiating, so intake falls without effort.
Sources