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Dietary advice explained: protein

Posted on Tuesday 3 December 2019

Protein is usually the focus of our Christmas dinner: the traditional Turkey, or clichéd nut roast for vegetarians. But what is it?

Charlotte Hawkins

Proteins are constructed of amino acids, of which hundreds exist in nature, but twenty are used in human nutrition. Around half are considered "essential", which means the body must get them from food; the others are termed "non-essential", as the body can synthesise these from other amino acids.

While we can survive without eating carbohydrate, we cannot survive without consuming protein. Proteins are the building blocks of our cells. They are used to create muscles, organs, hair and skin. They also are involved in hormone production, our immune response and creation of blood cells. Protein left over after essential bodily functions have been fulfilled can then be broken down and used for energy production.

All foods contain a mix of protein, carbohydrate and fat, but we think of each food group according to which nutrient predominates. For example, our Christmas turkey is considered a protein food, as most of its calories come from protein (the rest being nearly all fat). In fact, meat and fish are nearly all protein and fat as carbohydrate levels are minimal. The proportions depend on the source: white fish, poultry and game tend to be lower in fat and higher in protein than oily fish or beef, pork or lamb, but we consider these all to be protein foods. Eggs and dairy products are naturally higher in fat than protein, and dairy contains significant levels of carbohydrates, but we still consider most concentrated dairy products (such as cheese) as protein foods. The vegan foods that are considered good sources of protein are pulses, which actually contain more carbohydrate than protein, and also nuts, which are higher in fat than protein, but they still contain enough protein to be thought of a good source of this nutrient. Non-starchy vegetables such as broccoli and cabbage are also surprisingly high in protein, although it would be necessary to eat an enormous amount of these to consider them a significant protein source.

Protein-based foods are considered "complete" proteins or "incomplete" proteins. The human body needs particular combinations of amino acids for different functions. The construction of  proteins in the body is a bit like a multi-coloured beaded necklace. If each amino acid resembles a different coloured bead, when a particular amino acid (or coloured bead) runs out of supply, production of the protein chain (or necklace) stops. In reality, there is no neat divide as to what is a complete or incomplete protein, but there are categories that make the concept of protein in human nutrition easier to understand.

So a complete protein is one where the proportions of different amino acids in a given food are similar to those that are needed in the human body to construct chains of proteins. For this reason, it is sometimes referred to as high-quality or highly usable protein. Eggs are a good example of this, as 97% of the protein is considered usable for functions other than energy production. Most animal sources of protein are also considered high quality, but to varying degrees. The proportion of amino acids in pulses is less well suited to the human body: pulses are generally low in the amino acid methionine, and grains are low in the amino acid lysine. Most people have heard that combining pulses and grains (for example, in beans on toast), creates a complete protein, as a deficiency in one is counterbalanced by a fair supply in the other. Nuts are fairly high in protein overall, but are often low in several amino acids, but as long as the foods we eat over the course of a day supply all the essential amino acids, it does not necessarily need to be at the same meal. Eating a varied diet is good for everyone, but for vegans it is especially important to eat a wide range of foods to ensure adequate consumption of all essential amino acids.

It used to be thought that if someone didn't consume animal protein, they would not be able to get sufficient protein to be healthy. In reality, unless someone is eating a very low calorie diet or consumes only a few specific low-protein foods, this is unlikely to be the case. Protein consumption is a bit of a world-wide obsession, although in reality most people in the developed world eat far more protein than they actually need. It has been estimated that we need 0.8 grams of protein per kilo of body weight to be healthy, so an average man may need 55g of protein per day, and a woman around 45g. This is not a lot. For example, a chicken breast contains around 55g protein in itself, a 30g portion of cheddar contains around 10g, and one egg contains around 8g. For vegans, half a tin of baked beans is around 10g, a handful of almonds is 6g and a couple of slices of wholemeal bread is around 2g. It is easy to see how this can adequately be obtained through eating a diet without any animal produce. Indeed, some research has suggested that needing 0.8g per kilo of body weight might be an over-estimate, but it is the figure which the World Health Organisation has settled on as a compromise. Most people in the West eat at least double this amount. At certain times of life, someone may need a little more protein, for example during pregnancy or fighting illness, but the increase is small. Some body-builders feel that they need to consume extra protein to build their muscles, but again, increased protein requirements are likely to be small, and this belief has stemmed more from successful marketing from protein supplement manufacturers rather than nutritional science.

Beyond the use of protein as a building block, as an energy source, protein has both positive and negative qualities. On the plus side, it takes longer to break down, which keeps us feeling fuller for longer and helps to regulate our blood sugar. This has obvious advantages, as a meal high in protein will make us less likely to reach for a sugary pick-me-up only a few hours after a meal, which means we are less likely to consume unnecessary unhealthy calories. Also, foods rich in protein often tend to be high in vitamins and minerals as well, such as B vitamins, zinc and iron. Indeed, the concerns that may be raised over a diet low in protein are often not due to protein deficiency itself, but a deficiency of the nutrients that are present in protein-rich foods.

On the down-side, a diet high in animal protein has been linked to an increased risk of heart disease and cancer. Diets around the world where the diet is based on vegan sources of protein have been linked to a lower risk of these diseases. However, it is important to look beyond the basic statistics. People who eat a diet high in processed red meat products - i.e. the standard Western diet - do indeed have a higher risk of disease, but indigenous populations who have traditionally eaten a diet based on unprocessed sources of these foods - for example, the Kenyan Masai or North American Inuit - do not show a similar risk of disease. Intensive factory farming of animals may also play a role, as the nutrient profile of meat and dairy products from grass-fed animals is very different from the nutrient profile of that from animals fed a grain-based diet, as is the case of farm animals in industrial-style feeding lots.

A further downside of a diet in animal protein is not to do with human nutrition, but  to do with ethical and environmental issues. The ethics of eating animal foods is a complex issue, and not for the scope of this article, but the environmental aspect of using animal-based foods to supply us with our protein is something that should be considered. With the world population at 7.7 billion, and estimated to grow still further, it is not possible to continue to feed the world on a diet based on animal sources of protein. It is now well-known that the intensive farming of animals for meat production is contributing significantly to climate change through deforestation and greenhouse gas production, as well as having a huge impact on the local environment where these animals are reared. Vast amounts of grains are grown at significant environmental cost, not for human consumption, but to feed the animals which will then become or produce our food, which is a hugely inefficient use of energy and resources. In an ideal world, animals would be grazed and eat their natural diet - either foraged foods or grass, but realistically there is nowhere near sufficient grazing land in the world to cater for a population of 7.7 billion with our current level of meat consumption. Many people in the developed world have become conscious of the environmental impact of eating meat and have deliberately cut back, but the meat consumption in developing nations continues to rise exponentially.

There is no easy solution. The use of insect protein has been touted as a way forward, but it would require a huge change in social attitudes to overcome the "yuck" factor. Also, laboratory-grown synthetic meat has been seen as a way of people being able to consume meat without the environmental impact, but many people feel uncomfortable with this, and it also raises a different set of ethical issues.  Changes need to be made on a worldwide level, probably with governmental involvement, as the move away from relying on animal products to supply their protein needs, by a small number of enlightened individuals in the West, will only make a small difference.

However, a small difference is better than no difference. For those of us who choose to eat animal products, we can change our habits by eating more vegetable sources of protein, and also eating lower down on the food chain. For example, this means choosing poultry over beef, or sardines over farmed salmon. We can also practise nose-to-tail eating by including offal in our diet and using meat bones for stock. We can eat more animal products such as eggs rather than the animals themselves, and also make the obvious change of consuming more pulses and nuts rather than animal products at all. As members and supporters of an organisation such as True Food, we can join together to express our concern over the impact of our food production on the environment, as together our voice is louder.

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