Protein
Protein is the macronutrient made of amino acids that the body uses to build and repair tissue, including muscle; it supplies about 4 kcal per gram and is the one macronutrient with a daily target worth tracking.
Protein does three jobs that matter to anyone tracking food. It supplies the amino acids that repair and build muscle, it is the most filling macronutrient per calorie, and it costs the body more energy to process than carbohydrate or fat.
Requirement versus useful intake
These are different numbers and conflating them causes most of the confusion. The recommended dietary allowance — around 0.8 g per kilogram of bodyweight for adults — is set to prevent deficiency in a sedentary population. It is a floor, not an optimum.
People who lift weights, and especially people doing so in a calorie deficit, do measurably better at roughly 1.6 to 2.2 g per kilogram. Above that range the evidence for further benefit thins out quickly.
Quality and completeness
Protein sources differ in their amino acid profile and how well they are digested. Animal sources and soy are complete on their own. Most plant sources are lower in one or another essential amino acid, which matters far less than it is made to sound: eating a variety of legumes, grains and dairy across a day covers it without any effort at combining foods at a single meal.
Why it is the macro to track
Hit your calories and your protein and the other two sort themselves out. Miss protein in a deficit and you lose more muscle than you needed to.
Sources
- 1.Protein and amino acid requirements in human nutrition (WHO Technical Report 935) — WHO, FAO and UNU
- 2.Protein supplementation and resistance training: a systematic review and meta-analysis — British Journal of Sports Medicine
Related reading
- Vegetarian protein worth the calories it costs
Ranked by calories per gram of protein, not by grams per 100 g. Which vegetarian sources are efficient, which are not, and how to build a 130 g day.
- Protein per kilo: where the number comes from
Why 1.6 to 2.2 g per kilogram, what to do if you carry a lot of body fat, and how the target changes between a deficit, maintenance and a surplus.
- How much protein do you actually need per day?
The RDA is a floor, not a target. What the evidence supports for people who train, how to reach it on Indian food, and why it is the one macro worth counting.
- What macros are, and which ones are worth counting
Protein, carbohydrate, fat and alcohol, what each supplies, and why calories plus protein is the two-number system most people should actually use.