Protein: What It Does, How Much You Need and Where It Comes From

Overview

Protein is one of the three nutrients that supply calories, along with carbohydrate and fat, and every cell in the body contains it. [1] Most people in countries with plentiful food get protein from ordinary meals. This page is the starting point for the Amino Acids and Protein library: what protein does, where it comes from, and what the official reference numbers mean. It does not set a personal target. A clinician or registered dietitian can do that for a person.

What protein does

MedlinePlus says you need protein in your diet to help your body repair cells and make new ones, and that it matters for growth in children, teens and pregnant women. [1] Protein in food is broken down into amino acids during digestion, and the body then uses amino acids to build its own proteins. [1][2] Amino acids can also be used as a source of energy. [2] One gram of protein supplies 4 calories. [1] For the step-by-step process, see How Protein Is Digested, Absorbed and Used.

Amino acids in brief

MedlinePlus groups amino acids as essential (the body cannot make them, so food must supply them), nonessential, and conditionally essential (usually not essential, except in illness and stress). [2] Nine are essential: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. [2] The full explanation is on What Are Amino Acids?, and each essential one is covered on Essential Amino Acids.

Where protein comes from

Amino acids are found in animal foods such as meat, milk, fish and eggs, and in plant foods such as soy, beans, legumes, nut butters and some grains. [1] MedlinePlus states that you do not need to eat animal products to get all the protein you need. [1] The NHS lists beans, pulses, fish, eggs, meat and other protein foods as one food group and calls pulses good alternatives to meat. [3] MedlinePlus says the balance of amino acids across the whole day matters more than eating every one at every meal. [1] How foods differ in amino acid content and digestibility is on Protein Quality and Complete Proteins.

What the official numbers say

Reference values are written for groups of healthy people, and they differ by country because expert committees use different data and definitions. These are population references, not personal goals. The table shows adult values only; children, pregnancy and activity levels are on Protein Intake Levels by Age, Sex and Country.

The Health Canada table also gives an acceptable range of 10 to 35 percent of calories from protein for adults 19 and over. [4] A percentage of calories, grams per kilogram and grams per day are different ways to express an amount and should not be mixed. The NIH Office of Dietary Supplements pages could not be read for this page, so US figures come from the joint US and Canadian table on Health Canada's site.

Life stages and activity

Needs per kilogram are higher in infants and young children, and in the second half of pregnancy and in breastfeeding, according to the Health Canada table. [4] For older adults, EFSA concluded the data were not enough to set a separate requirement and that at least the young-adult level is required, while the Nordic Nutrition Recommendations 2023 give 1.2 to 1.5 g per kg for older adults. [5] For people who exercise, the British Heart Foundation describes ranges that rise with activity, around 1.2 to 2 g per kg for intense strength training or endurance athletes. [6] See Protein for Older Adults and Vegetarian or Vegan Diets and Protein for Muscle, Resistance Training and Recovery.

Is more protein harmful?

The European Commission summary of EFSA says an intake of twice the population reference intake can be regarded as safe in adults. [5] The British Heart Foundation says there is no official upper limit but that regularly eating more than 2 g per kg a day can strain the kidneys, especially in people with kidney problems. [6] A 2018 meta-analysis of trials in adults without kidney disease found higher-protein diets did not adversely affect kidney function, with an unclear risk of selection bias in the included trials. [7]

Related

RDA, AI, DV and UL explains what intake references mean in general. Protein Deficiency covers who is at risk of too little.