What macronutrients actually do
Learn · Nutrition basics · Explainer, Typed Supps
The three main nutrients do different jobs. Getting the balance right changes how easy a diet feels.
Stage by stage
- Protein (Substrate + satiety): Building material, most filling per calorie, and 20–30% of it is burned just digesting it.
- Fat (Hormones + vitamin transport): Needed for steroid hormones and to absorb vitamins A, D, E and K. Sustained very low intake causes problems.
- Carbohydrate (The anaerobic fuel): The only fuel usable without oxygen, so it is indispensable above about 70–75% of max effort.
- The ratio (Changes feel, not arithmetic): Composition shifts satiety and what you keep. The energy total still decides the direction.
What the evidence supports
- Protein is the most satiating macronutrient per calorie — strong evidence. Consistent across appetite and ad-libitum intake studies.
- Protein has a substantially higher thermic effect than fat or carbohydrate — strong evidence. Well quantified: roughly 20–30% versus 0–3% for fat.
- Very low fat intake impairs hormone production — moderate evidence. Reasonable evidence at sustained intakes below about 15–20% of energy. Not a concern at ordinary intakes.
- Carbohydrate is required for high-intensity performance — strong evidence. Follows directly from it being the only anaerobic substrate.
Timing
Protein spread across 3–4 meals suits how long the synthesis response lasts. Fat and carbohydrate timing matter far less than most plans imply.
Time to effect
- Days: Hunger and energy respond to a ratio change.
- Weeks: Effects on body composition become measurable.
Common myth
“Macros matter more than calories.” In reality: Calories decide the direction; macros decide what you lose and how sustainable it feels. Both are real, and they are not the same claim.
In the glossary
Sources