Protein · 4 calories per gram
Protein: The Body's Building Block
Protein builds and repairs every tissue in your body — from muscle and skin to the enzymes and antibodies that keep you running. Here's what the research actually says about how much you need and what happens when you don't get enough.
What Protein Actually Does
Protein is made of chains of amino acids — 20 different building blocks, 9 of which are "essential" because your body can't make them and you must get them from food. Once digested, amino acids are used to build and maintain nearly every structure in your body: muscle, bone, skin, and hair, as well as the enzymes that drive chemical reactions and the hemoglobin that carries oxygen in your blood.[1]
Beyond structure, protein is also used to make:
- Enzymes that power digestion and metabolism
- Hormones such as insulin and growth hormone
- Antibodies that fight infection
- Transport proteins like hemoglobin, which carries oxygen
Muscle Building and Repair
Resistance exercise — lifting weights, bodyweight training — creates microscopic damage in muscle fibers. Both exercise and eating protein independently stimulate muscle protein synthesis (MPS), the process of building new muscle proteins. Combined, they're more powerful: MPS stays elevated for up to 48 hours after a resistance training session as your body remodels and repairs the muscle.[2]
This is why protein timing and total daily intake both matter for anyone trying to build muscle or recover faster: without enough amino acids available, your body can't fully carry out the repair process that makes muscle bigger and stronger over time.
How Much Protein Do You Need?
Baseline (RDA)
The Recommended Dietary Allowance for adults is 0.8 grams per kilogram of body weight per day. This is the minimum intake that prevents deficiency in a sedentary person — it is not an optimal target for anyone trying to build or preserve muscle.[3]
Active Individuals & Athletes
The International Society of Sports Nutrition recommends 1.4–2.0 g/kg/day for people who exercise regularly, in order to maximize muscle protein balance and support recovery. Higher intakes within this range are generally used during calorie restriction to preserve lean mass.[2]
What Happens If You're Deficient
Severe, prolonged protein deficiency is called kwashiorkor — most commonly seen in regions with significant food insecurity, especially in children. It causes swelling (edema, often in the belly and legs), a swollen liver, skin and hair changes, fatigue, and impaired growth.[4]
Milder, more common shortfalls (eating below your needs without full-blown deficiency) are linked with:
- Muscle loss — your body breaks down muscle tissue for amino acids when intake is too low
- Weakened immune function — fewer antibodies and immune cells are produced
- Slower wound healing — tissue repair depends on adequate amino acid supply
- Hair, skin, and nail changes — thinning hair, brittle nails, and skin lesions
- Fluid retention (edema) — low blood protein levels affect fluid balance
Good Sources of Protein
Animal sources provide "complete" protein (all 9 essential amino acids in sufficient amounts); plant sources can be combined across the day to the same effect.[5]