What is protein?
Protein is the shared building material of muscles, enzymes, hormones and immune cells. It may look like the preserve of sports products, but it is in fact a basic need at every age and in every way of eating.
Short answer
Protein is a basic macronutrient made up of building blocks called amino acids, involved in the body's repair, growth and defence functions, and providing about 4 kcal per gram. A commonly used general reference for adults is about 0.8 grams per kilogram of body weight a day; for people who exercise regularly the requirement is usually judged to be higher. Working out an individual amount is a dietitian's job.
Amino acids: the letters of the alphabet
Proteins are formed when about twenty different amino acids combine in various sequences, rather like building words from letters. Nine of these amino acids are essential: the body cannot make them and has to take them in from food. During digestion protein is broken down into amino acids, and the body reassembles those building blocks according to its own needs. The chicken or the lentils you eat do not become muscle directly; they are first broken into letters and then turned into the words the body is writing that day.
What does protein do in the body?
The role of protein is not limited to building muscle. Repairing tissue, producing enzymes and many hormones, running immune cells, transporting substances in the blood and renewing hair, nails and skin all require protein. In energy terms it provides about 4 kcal per gram, but the body prefers to use protein as building material rather than as fuel. Protein foods are digested relatively slowly, and their contribution to fullness is usually more marked than that of the other macronutrients.
How much protein?
The general reference value commonly used for adults is about 0.8 grams per kilogram of body weight a day; for a 70 kg adult that corresponds to roughly 56 grams a day. This is a lower reference intended to meet the basic needs of a sedentary adult; higher ranges are discussed in the literature for people doing regular strength training, for older adults and for those recovering from illness. In situations such as pregnancy, breastfeeding or kidney disease the requirement differs, and the calculation should be made individually with a dietitian or doctor. The values here are meant to give a starting idea.
Sources: animal and plant
Animal sources such as meat, chicken, fish, eggs and dairy products carry all the essential amino acids in balanced proportions. Plant sources such as pulses, grains, nuts and seeds also provide strong protein; although some individual amino acids may be low, plant sources varied across the day complement one another, and lentils meeting bulgur is a classic example. In budget terms eggs and dried pulses are among the most accessible options, and this subject is covered in detail in the budget-friendly plan guide.
Protein matters more as we get older
Protein needs are usually associated with athletes; one of the periods in which the subject is most critical, though, is later life. From around middle age muscle mass tends to decline gradually, and when the process accelerates it can lead to sarcopenia, a picture in which loss of muscle is accompanied by loss of strength and balance. Muscle loss affects daily life directly through the risk of falls, restricted movement and general quality of life. Research indicates that adequate protein intake in older adults, and particularly the combination of that intake with strength exercise, gives two factors working together to slow muscle loss; some expert groups discuss intakes above the general reference for this age group. In a period when appetite falls and meals get smaller, spreading protein across every meal also gains importance. When planning the diet of an older relative it is worth discussing this balance with a doctor and a dietitian, and taking as a model the gradual approach set out in the guide to starting exercise.
Spread it through the day, and do not overdo it
Spreading protein through the day rather than piling it into one meal is a more sensible approach, both for digestive comfort and for how efficiently the body uses it: eggs or cheese at breakfast, and pulses, meat or yoghurt at other meals. On the other hand, more is not automatically better: protein well above requirement brings no extra benefit and simply becomes surplus energy. Protein powders are supplements rather than foods; a healthy adult's needs can usually be met from food, and it is sensible to seek expert advice before deciding on a supplement.
Frequently asked questions
Can someone eating a plant-based diet get enough protein?
Yes; when pulses, grains, soya products and nuts and seeds are varied, a plant-based routine can meet protein needs. Support from a dietitian makes the planning easier.
Is it essential to take protein straight after training?
The old idea of a 30-minute window has softened in the current literature; the day's total protein intake and its distribution appear to matter more than minutes.
Does too much protein damage the kidneys?
There is no strong evidence that reasonably high intakes harm healthy kidneys; in people with kidney disease, however, protein amounts should be adjusted under medical supervision.
How much protein is in which food?
Approximately: one egg 6–7 g, 100 g of chicken breast 25–30 g, a bowl of boiled lentils 8–9 g and a bowl of yoghurt 5–6 g. The protein line on labels is also a reliable source.
This guide draws on the general reference values in the World Health Organization's reports on protein requirements and on the protein information in clinical nutrition sources.