The majority of foods contain some protein. Both animal and plant sources provide protein in varying amounts and qualities.
Many people rely on animal proteins to meet their protein needs. Animal sources of protein include fish and shellfish, poultry, game and game birds, red meat, offal, eggs and dairy products. These foods provide varying amounts of protein as well as other nutrients, vitamins and minerals. Some animal sources of protein may also contain unhealthy amounts of saturated fat.
Fish and shellfish
Fish contains 40-60 per cent of its calories as high quality protein.
Oily fish, such as salmon, mackerel, herring and sardines, is a rich source of the healthy omega-3 fatty acids and most fish contains useful amounts of some vitamins and minerals. Shellfish, including molluscs such as clams, mussels and oysters, and crustaceans such as crab, lobster, crayfish and prawns, is also a rich source of protein, containing approximately [5 per cent of its calories as high quality protein. It is low in saturated fat and total fat; it also contains the omega-3 fatty acids that offer protection against heart disease.
Replacing red meat in the diet with fish and shellfish provides high quality protein while reducing the amount of saturated fat consumed. Steaming, poaching and grilling are preferable cooking methods for fish, and shellfish should be thoroughly cooked to minimize the risk of food poisoning.
The meat of domestic fowl, such as chicken, turkey and duck, contains approximately 60 per cent of its calories as high quality protein. Poultry is a healthier option than red meat and is low in saturated fat and total fat. A high proportion of the fat in poultry is unsaturated and so does not raise blood cholesterol levels – most of the fat can be eliminated if the skin is removed. Skinless chicken and turkey breasts contain around 5 per cent fat and are recommended for people who need a low-fat diet; duck and goose are fattier birds. Poultry is also a rich source of most B vitamins, which are needed for a healthy nervous system. Since many chickens and turkeys are factory-farmed and need to be treated with drugs to prevent the spread of disease, it is advisable to choose free-range birds where possible.
Game and game birds
The nutrient and energy value of game varies greatly because the term covers a wide range of livestock, from small birds such as pheasant and quail to larger animals such as deer. Generally, however, game and game birds are excellent sources of high-quality protein, containing approximately 30-35 per cent protein. Wild game is considered to be healthier than farmed meat because the animals live in a natural environment and do not build up the fat reserves found in farmed animals. When compared with untrimmed meat from farm animals, game and game birds are lower in fat and calories; they are also rich in B vitamins and iron. Another advantage of wild game is that any risk of contamination by antibiotics, artificial growth hormones or pesticides is minimal. Reared game, however, is not always free from these chemicals. Venison is a very lean meat and makes a good substitute for beef. Be careful to remove any lead shot from wild game as you prepare it for cooking.
Beef, lamb, mutton and pork are red meats that contain approximately 50 per cent of their calories as high quality protein. In the West, most people derive the majority of their protein from eating these meats – a factor implicated in some health problems. For example, many red meats are high in saturated fat, a high intake of which contributes to increased levels of cholesterol in the blood and a higher risk of heart disease. For this reason, it is helpful to trim the fatty tissue in beef, lamb and pork. Red meat is, however, a useful source of the blood-strengthening nutrient iron and, unlike the iron in protein sources such as grains, the iron in red meat is readily-absorbed by the body. Lean meat, carefully prepared and cooked using healthy methods, and eaten in moderation (a maximum of two or three times a week), can still be part of a healthy diet.
Any edible parts of an animal, apart from the flesh, are classed as offal; these include the liver, kidneys, tongue, brains, heart and stomach (tripe). Offal is a source of high-quality protein, containing about 20 per cent of its calories as protein, and is rich in the B vitamins as well as iron and zinc. However, organs such as liver, heart and kidneys can be high in cholesterol, and should be avoided by people on low-cholesterol diets. Liver is not recommended forbecause of its high vitamin A content; it is thought that high doses of vitamin A may cause birth defects.
Eggs and dairy products
Eggs, milk and the range of dairy products made from milk (including cream, cheese, yoghurt and butter) are a source of high quality protein. The protein content varies with the individual products, but ranges between 20 per cent for milk to 34 per cent for eggs and up to 49 per cent for some cheeses. These foods are also a rich source of vitamins and minerals, particularly calcium. However, they can also be high in saturated fat so low-fat produce should be favoured (except for children under the age of five, who need the energy provided by the extra calories). For people who are intolerant of, or prefer to avoid, dairy products from animal sources, a wide range of dairy alternatives made from plant proteins is available.
Many people rely on animal sources for most of their protein, believing that plant foods do not supply sufficient protein. This is not the case, however, and a daily diet that includes protein from a variety of plant sources, including nuts and seeds, grains and pulses, vegetables and mycoproteins (made from fungi), can provide the body with an appropriate intake of good quality protein. Vegetable sources of protein also tend to contain beneficial complex carbohydrates. Because of concerns about the health risks of saturated fat and contamination with pesticides, growth promoters, drugs and antibiotics, cutting down on meat consumption is thought to be desirable in terms of health. People who are reluctant to cut down on meat in their diet because they enjoy its taste may enjoy meat substitutes made from some plant proteins.
Grains and pulses
Although individually most types of grain andprovide low quality protein, they can be combined to make high quality protein. Combining proteins from different food groups – pulses with grains, for example – means that if one food contains low levels of some amino acids, the shortfall can be made up by high levels in another food group. Some grains and pulses supply protein of a quality close to that supplied by meat; these are the cereals, quinoa, amaranth and brown rice and soya beans.
Soya beans are a particularly good example of high quality protein supplied by a plant source. They contain 54 per cent of their calories as protein of a quality comparable to that of animal foods. They are very nutritious, providing desirable polyunsatur ated fats, fibre, vitamins, iron and other minerals. Soya beans are a versatile food; they can be used in recipes requiring beans and are also processed to make a range of other foods. The beans can be ground to make milk; the milk can then be used to make alternative dairy products and a bean curd called tofu. This product is high in protein, low in saturated fats and cholesterol-free (although it does tend to absorb a lot of fat – around 15 per cent – when fried).
Tofu can be substituted for meat in many recipes, including soups, stir-fries, casseroles and burgers. As with meat-based processed foods, processed meals and products made with tofu may contain high levels of saturated fats and additives, so these should be kept to a minimum. A meat substitute called textured vegetable protein (TVP) is also made from soya. It is usually fortified with iron, zinc and vitamin B12 and is a good source of protein, but, again, many TVP products contain added saturated fats and salt. Other soya products include soya flour, soya sauce and soya bean oil.
The consumption of soya products has been linked with a number of health benefits, mainly to a reduced risk of heart disease and a lower incidence of breast cancer. Asian women, who traditionally consume much greater quantities of soya protein (and less animal protein) than Western women, have significantly lower rates of breast cancer.
Most vegetables provide about 10 per cent of their calories as protein, with the percentages varying from 11 per cent for potatoes to up to 49 per cent for spinach. They are also rich in vitamins, minerals and fibre and are an important part of a balanced diet. In addition, vegetables contain substances called phytochemicals that are believed to have immune-boosting properties that help in the tight against diseases such as heart disease and cancer. Although the quality of protein supplied by vegetables is much lower than that supplied by animal protein, it is improved if vegetables are combined with other plant proteins. A mixed vegetable stir-fry or casserole with a serving of rice or quinoa, for example, provides a high quality protein meal. Vegetables should be eaten raw or lightly cooked to preserve their vitamin, mineral and fibre content.
Nuts and seeds
Most nuts and seeds provide approximately 10-20 per cent of their calories as reasonable quality protein. They are also a rich source of fibre, essential fats, B vitamins, vitamin E and some minerals. Their protein quality can be improved if they are eaten as part of a meal that includes grains, such as rice or quinoa, and pulses, such as lentils or chickpeas.
Commercially produced mycoprotein (the protein produced by fungi) is used to make a range of meat substitute products. It is sold in the form of mince or cubes and often used as a substitute in dishes requiring beef and chicken. Mycoprotein is a good source of protein (gram per gram as much as a whole egg); it is also low in fat and relatively high in fibre. Processed foods based on mycoprotcin are also available; these include sausages, burgers, pies and other dishes. However, they may be high in saturated fat and additives.