What is Protein?
Like carbohydrates and fats, proteins are macronutrients, and are essential to the body. 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 the muscles, hair and nails. Many hormones are also proteins, and, the immune system, digestive system and blood 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 not 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.
However, although this is an issue in developing countries, 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. It is therefore essential to eat a balanced diet to make the best use of all the nutrients in it.
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 slightly more protein than those who lead more sedentary lifestyles—because protein is essential for building and repairing muscle and other tissues, slightly more is needed for those actively trying to develop muscle.
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 necessary. A simple way to think about protein intake is to think about protein-rich foods making up a quarter of your diet, with a further quarter being carbohydrates and the other half being fresh fruit and vegetables.
When we exercise more, our appetites generally increase, so we eat more. However, the ‘quarter protein’ rule still works as a general guideline, because your protein intake will increase proportionately. Of course, if you are doing something that builds a lot of muscle, such as heavy weights in the gym, then you will need to eat more protein. This is why bodybuilders sometimes use supplements.
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 important to be aware of what other nutrients your protein source also contains, such as sodium (salt) or saturated fats. 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.
As meat can also be high in saturated fats, lean cuts of meat are considered to be better because they contain less saturated fat. Meat preparation is also an important factor in balancing protein intake and fats - for example, fried meat products contain protein but higher levels of saturated fats.
More on Fat - Good and Bad.
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.
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.
One large egg will contain about 6 grams of protein.
Eggs are an important source of protein for vegetarians. Boiled and poached eggs are better than fried as they will contain less fat. However a fried egg - if carefully drained after cooking - is still low in fat. Eggs do not absorb fat so most can be easily removed from the surface before eating.
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 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 too).
Other dairy products are also good sources of protein, including cheeses, yoghurt, fromage frais and sour cream. These products can also, however, be high in fat. Low fat alternatives usually have the same, if not slightly more, protein per gram than the full fat versions, but may contain more sugar.
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 fat and salt.
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, which the body needs. 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.
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.
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.
Source: World Resources Institute, www.wri.org/proteinscorecard
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.
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.