What is Protein?

See also: What is Fibre?

Proteins are macronutrients, like carbohydrates and fats. Proteins make up much of the tissue in our bodies, including muscles and organs, as well as hormones and the immune system. Proteins are therefore essential to the body. When we eat, the body breaks down the protein in food into amino acids. These can then be reassembled into the proteins that the body needs.

The body uses twenty different amino acids to make proteins. It can make eleven of these. The other nine are known as ‘essential amino acids’, because it is essential to obtain them from food. Many foods contain protein, but some foods are richer in some of the essential amino acids than others. Usually, therefore, foods need to be combined so that the body receives all the amino acids it needs on a daily basis—part of the reason that we need to eat a varied, balanced diet.

This page explains more about how we use and obtain protein, and which foods are good sources.

How We Use Protein

Protein is the body’s building block.

All of our organs, including the skin, are built from proteins, as are our muscles, hair and nails. Many hormones are also proteins. The immune system, digestive system and blood also all rely on proteins to work correctly.

Protein is therefore essential for development and correct functioning of the body. 

Protein is particularly important for children and adolescents, because they need proteins to build their growing bodies, and develop into adulthood. Protein is also important for pregnant women, who are growing another human (see our page Pregnancy and Wellness for more).

If we do not eat enough protein, our bodies start to break down muscles—the least-essential part of the body—to produce the protein needed for vital organs. Our bodies are good at storing fats and some sugars, but less good at storing proteins. It is therefore necessary to continually replace the protein that our bodies use. Prolonged periods of malnutrition—and particularly a shortage of protein—can result in damage to the immune system, heart and respiratory system, as well as loss of muscle mass.

This is an important issue in developing countries. However, it is seldom a problem in the developed world, where most people probably eat far more protein than they actually need.

A complete picture

Proteins need fuel to work, just like a car needs fuel. Fuel is provided from the carbohydrates and fats in our diet. The production of amino acids in the body is also reliant on other nutrients especially B vitamins and zinc. Your diet therefore needs to contain all these elements to operate effectively—and a balanced diet is generally considered the best way to achieve this.

For more information, see our pages What are Carbohydrates?, What is Fat?, Vitamins and Minerals.

How Much Protein Do We Need?

The amount of protein that we need is dependent in part on our age, weight and levels of activity.

Children and adolescents who are still growing and developing need proportionately more protein in their diets than adults. People who are very active may need more protein than those who lead more sedentary lifestyles. Protein is essential for building and repairing muscle and other tissues, and therefore more is needed for those actively trying to develop muscle, or whose muscles are being worked more often, and therefore need repairing.

Guidelines from sports’ governing bodies generally recommend that athletes should consume around double the recommended daily amount of protein to enable them to build and repair muscle while training. One author even suggested that athletes should consume around 2.2g per kilogram of body weight (so nearly three times the recommended daily amount) (Antonio, J. (2018). High-protein diets in trained individuals. Research in Sports Medicine, 27, 195–203).


The US recommended daily amount of protein is 0.8g per kilogram of body weight.

In other words, to calculate roughly how much protein you need to consume daily, multiply your weight in kilograms by 0.8. The answer is the number of grams of protein you should consume every day.

If you weigh 100kg you should therefore be consuming around 80 grams of protein a day.

Many people on modern diets consume more protein than they really need. However, there does not seem to be any evidence that you can eat “too much” protein, or that eating more is harmful. Excess protein will simply be excreted by the body. A study in Korea also found no link between the level of protein consumed, and overall death rates from all causes.

(Source: Kwon, Y. J., Lee, H. S., Park, J. Y., & Lee, J. W. (2020). Associating intake proportion of carbohydrate, fat, and protein with all-cause mortality in Korean adults. Nutrients, 12(10), 3208)

Choosing Sources of Protein

Most food and drinks contain some protein, but certain types of food are richer in protein than others, and particularly in the essential amino acids.

Animal proteins contain all the essential amino acids. Vegetarians and vegans can obtain what they need from other sources, but they may need to eat a wider variety of food.

The following list includes the food types that contain the most protein. However, it is also important to consider what other nutrients your protein source contains, such as sodium (salt). You may also want to think about the environmental impact of your food choices (see box).


Most meats and poultry are good sources of protein.

A piece of lean meat (beef, pork, lamb or chicken) about the size of a pack of playing cards will contain approximately 20 grams of protein.

However, meats also get a bad press in terms of health. For example, meat can also be high in saturated fats, and therefore lean cuts of meat are considered to be ‘better’ because they contain less saturated fat. However, these links may or may not be genuine: it is hard to create really good studies on food and health because there are so many other factors that can affect the results.

Several studies have also shown a relationship between eating red meat and the risk of developing various chronic diseases.

Governments have therefore advised people to limit consumption of red meat, and particularly processed meats such as bacon or sausages, which are also high in sodium (salt). However, the picture is not that simple. Red meats are probably the richest dietary source of iron, as well as various essential vitamins and minerals, especially vitamin B12 and selenium. Consuming a small amount may therefore actually be good for you—but the key is in that word small.

Too much of anything is bad for you—and that is likely to include meat, whether red or white, and certainly processed.

It is probably also important to consider the quality of the meat that you consume, as well as the quantity: a small piece of high-quality well-reared grass-fed steak is likely to be better for you than the same amount of cheap meat in a hamburger, especially if your burger is processed, with added salt and other ingredients.


Fish is also a good source of protein.

Salmon, trout, mackerel, sardines, pilchards, herring, kipper, eel and whitebait are termed oily fish. Approximately 140 grams of oily fish will contain 20 grams of protein.

Other fish such as cod, plaice, and tuna, and seafood like lobster and crab, are also high in protein but usually in slightly lower quantities. About 150 grams of these fish contain 20 grams of protein. Fish eggs (roe and caviar) are also good sources of protein.

Meat vs. fish: is eating fish healthier?

Government information on nutrition tends to be very ‘black and white’: x is healthy, y is unhealthy (hence the problem about understanding the picture on red meat).

Over many years, fish has been painted as ‘healthy’. Fish oils good, meat fats bad.

However, once again, the picture is more complicated than that.

In actual fact, there appear to be very few health benefits from eating fish. There are also massive problems being caused by over-fishing around the world. Fish-farming brings its own problems, including spreading disease and/or antibiotic resistance to wild populations. Concerns have been raised about the potential impact of heavy metal contamination of fish populations, or the effect of micro-plastics in fish.

The answer seems to be that eating fish is not necessarily bad for you—but you shouldn’t eat huge quantities because those simply cannot be provided sustainably. Small amounts of fish from sustainable sources may be more expensive, but they will not cost the earth, and they may just be better for you.


Eggs are an important source of protein, especially for vegetarians.

One large egg will contain about 6 grams of protein.

You may have heard it suggested that boiled and poached eggs are better than fried as they will contain less fat, or that you should only eat the egg whites because the yolk contains too much saturated fat. However a fried egg is still relatively low in fat. Eggs do not absorb fat so most can be easily removed from the surface before eating. There is also very little evidence that eggs need to be separated to be part of a healthy diet. The few studies that exist suggest that consuming one egg per day has little impact on cardiac health or cholesterol levels, and that eggs are a healthy and cost-efficient food.

See our page: Cooking Fats and Oils to find out which are the healthiest cooking fats and oils to use - for frying an egg and other purposes.

Dairy Products

Dairy products are also important sources of protein.

For example, 200ml (1 cup) of semi-skimmed (2%) milk contains about 8 grams of protein.

Protein comes from the milk itself and not the fat in it. Skimmed and semi-skimmed milk have had much of their fat removed and therefore contain more protein per ml than whole milk (and more calcium). However, being realistic, the amounts of fat in full-fat, semi-skimmed and skimmed milk are actually very small, and also very similar (full-fat milk is 3.7% fat, and semi-skimmed is 1.8% fat). Milk can therefore be a good source of fat-soluble vitamins in a natural and largely unprocessed form.

Other dairy products are also good sources of protein and fat-soluble vitamins, including cheeses, yoghurt, fromage frais and sour cream. These products can also be high in fat, which can put people off. Received dietary wisdom has painted fat as the ‘bad guy’. However, low fat alternatives usually contain significantly more sugar, and are much more processed, than the so-called ‘high fat’ versions. There is therefore growing evidence that eating slightly smaller portions of full-fat dairy products might be a healthier alternative than the ‘low-fat’ or ‘diet’ alternatives.


Beans are a good source of vegetable proteins. These are essential for vegans but also an important part of all well-balanced diets.

Mature soya beans contain nearly 40% protein; soya products such as soya milk and tofu are also good sources of protein. Many other types of beans, including black beans, pinto beans, kidney beans, butter beans and lentils, are all important sources of protein. Peanuts (which are actually beans and not nuts) contain almost 25% protein. Peanut butter is therefore a good source of vegetable protein, although it can contain a lot of other ingredients, especially sugar and oils. It is worth seeking out higher-quality nut butters—which means those with fewer ingredients. The highest quality butters contain only peanuts, with perhaps a little added salt. Less healthy alternatives will contain more vegetable oil and sugar.

Vegetarian and vegan alternatives to meat, like Quorn, also contain proportionately high levels of protein.

Nuts and Seeds

Many nuts and seeds contain protein. They are also a good source of many vitamins and minerals needed by our bodies.

Almonds, cashews, walnuts and pecan nuts are all relatively high in protein, as are sunflower, pumpkin and flax seeds.

Other Protein Sources

Marmite and other yeast extract spreads are high in protein content – about 25% protein.

Whole grains can be significant sources of protein in some diets. They also contain high levels of complex carbohydrates and fibre. Protein-rich whole grains include whole wheat and wheat bran, oats and oat bran, barley and brown rice.

Certain vegetables, especially asparagus, broccoli, Brussels sprouts, cauliflower and avocado, are good sources of protein.


Finally, protein supplements are available. Protein-rich drinks are often made from powdered milk (whey) and soya-based proteins.

Bodybuilders often use protein supplements in this form because they see them as a quick way to build muscle. However, as we have said, most people already consume more protein than they need, and there is growing evidence that supplements of all kinds may be best avoided (see box).

Protein supplements: ultra-processed foods?

Protein drinks are very definitely ‘ultra-processed foods’: foods that our grandparents would not have recognised as food, and which have been excessively processed to break them down into their constituent nutrients before being repackaged.

Protein drinks tend to contain high levels of additives, chemicals and flavourings—and the effects of these have often not been rigorously tested.

There is growing evidence that we should be avoiding these ultra-processed foods in favour of foods that our grandparents would recognise. This approach suggests that athletes may be best simply increasing their dietary intake of protein—perhaps through eating a handful of nuts and having a glass of milk—rather than by using supplements.

There is more about this in our page Ultra-Processed Foods.

Amino acids are also available in pill form, either individually or combining two or more of the essential amino acids. These may be prescribed to people who cannot, for whatever reason, synthesise the amino acids they need from protein in their diet.

For more, see our page on Supplements.

The Environmental Impact of Protein

Agriculture inevitably makes a contribution to greenhouse gas emissions. However, animal farming makes a higher contribution than growing crops. This means that different sources of protein have a different environmental impact. The graph below shows this and makes particularly clear that producing red meat (beef and lamb) has a much greater environmental impact than poultry, and considerably more than vegetable-based sources of protein.

Switching to more plant-based sources of protein, at least for some of your meals each week, may therefore be more environmentally friendly.

For more see - Ethical Food Consumption.

In Summary

Protein is an essential part of the diet, because it is an important building block for the body. However, you probably need to eat less than you think.

Protein is available from a wide range of foods, but not necessarily in equal quantities. Some good sources of protein also contain more saturated fat or salt than others, and may also have more impact on the environment, as well as costing more. It is therefore a good idea to eat protein from a range of sources.