Most people tend to rank different foods in their minds on a scale of how much good, or harm they do when eaten. Over the last few years many of these perceptions have been dispelled and many foods, originally thought of as being good for you such as butter and eggs, are now viewed with […]
Most people tend to rank different foods in their minds on a scale of how much good, or harm they do when eaten.
Over the last few years many of these perceptions have been dispelled and many foods, originally thought of as being good for you such as butter and eggs, are now viewed with some caution because of their cholesterol content.
However, one widely held food myth persists. It involves protein and the general belief is that it is marvellous stuff and that you just can’t get too much of it. Foods high in protein such as meat and fish are put on a pedestal and treated as being special. Many people still believe that it is essential to include meat in their diets, oblivious to the fact that millions (possibly billions) of people live happily, and very healthily, on a meat-free diet.
All nutritionists know that foods vary in the amount of protein they contain and that the quality of that protein varies considerably from food to food. A considerable amount of research has established what constitutes a high quality protein and what constitutes a low-quality protein.
All proteins, including those found in food and in our bodies, are made up of combinations of amino acids. There are 24 different amino acids which act like building blocks. They combine in millions of different ways to produce larger protein molecules from which our cells and tissues are formed.
Of the 24 amino acids, 8 are termed essential, which means that they must be present in our food. All of the other 16 amino acids can be produced within the body. If any one of the essential amino acids is deficient from the diet, then the body can only grow at the rate determined by the supply of that amino acid, hence it can be termed the Limiting Amino Acid.
It is the presentation of amino acids supplied in any foodstuff that determines the quality of that protein. Eggs and meat are termed first-class proteins because they supply a complete profile of amino acids in roughly the right proportions for our body’s needs. This is perhaps not surprising since these foods are animal tissues themselves.
However, simply because a foodstuff is the best of its type, does not mean that the food itself is essential to the diet. As it happens, a more than adequate amino acid profile can be fairly easily achieved by eating a good, varied vegetarian diet. If eggs and dairy products are included then the diet will provide a plentiful supply of amino acids.
All foods have different amino acid profiles and when they are combined together in a varied diet, the supply evens out so that none of the essential amino acids are deficient.
Perhaps this sounds rather too easy but the facts are clear. Protein deficiency is extremely rare in our society, despite the fact that many people pay little attention to their health and diet. We all tend to eat excess protein and this ensures that no amino acids are deficient. Any excess amino acids supplied (and there tends to be a great excess in Western diets) are simply broken down and used as energy as any carbohydrate would be.
As far as our requirements for protein are concerned, there are several different estimates according to different official bodies such as the World Health Organisation and the UK Department of Health. Usually the level quoted is based on the percentage of calories in the diet that should come from protein.
This generally varies between 4.5% and 8% and 6% would seem to be a safe level. The UK Department of Health recommendation is given in grams and is 36gms for women and 44gms for men. A recent study of intakes of protein in the UK reveals that on average, men consume 85gms of protein and women 62gms.
Of course this table of averages suggests that vegetarians, and especially vegans, should be concerned about their protein intake because such a high proportion of protein is usually derived from dairy products, eggs and meat. However, in reality, vegetarians usually consume a varied diet that introduces far more protein in the form of nuts and pulses, including Soya. Also, it is important to remember that the average diet supplies, for example, a man with 85gm of protein, whereas he actually only needs 44gm, so there is a lot of lee-way.
Whilst food labelling is generally quite clear, care needs to be taken with the food charts in some textbooks. Some of them give protein percentages of foods in their dry state to allow for easy but theoretical comparison between foods. Thus spinach may appear to be 50% protein so you might assume it would provide 50g of protein in 100g (3oz). However, this is not actually the case. Fresh spinach actually only supplies 3.3gm of protein in 100mg (3oz), because it is 96% water.
High protein foods such as meat and cheese are eaten in relatively small amounts. Bread actually supplies more protein in the diet because of the large amount consumed.
If it is true that it is difficult in our society to have a protein-deficient diet, then the next question must be “is it possible to eat an excess of protein?”
Many nutritionists believe that it is. Excess protein needs to be processed by the body to break it down into carbohydrates and the waste product urea. This in itself may not do much harm but it does require vitamins and minerals to fuel the process and this may divert them from other important tasks.
Eating excess protein may mean that the other important components of the diet are being ignored. Complex carbohydrates, fibre, essential fatty acids and vitamins are all rich in vegetable materials and high protein diets often exclude these valuable nutrients. A good example of this is the English breakfast. It contains high levels of protein (and fat) in the eggs, bacon and sausages, but where is the fibre!
Some studies have indicated that high protein diets may be associated with certain diseases. One trial showed that diets high in animal protein supply a high level of lysine (an essential amino acid), which is linked to an increased risk of atherosclerosis. Another study found that vegetarians who were fed with 250mg of beef showed a rise in total cholesterol level of 19% and an increase in systolic blood pressure of 3%. Another concern is highlighted in a study which showed that calcium, magnesium and phosphorous excretion rises when protein intake is increased. This can be interpreted as an indicator that women concerned about osteoporosis should not eat excessive amounts of protein.
Finally, a large study in America that examined numerous diets over a period of several years found that high intakes of red meat were linked to an increased risk of bowel cancer. Diets low in meat or containing only white meat and fish appear to carry a lower risk.
It seems then that the average person in the UK should not be concerned about inadequate protein intake. In fact, it would be better for the health conscious ones to check that they are not consuming excessive levels of protein, particularly if in doing so, they are excluding the essential nutrients found in vegetables from their diet.