Too much versus too little PROTEIN

Proteins are essential building elements that contribute to the development of the tissues of the human body. They make up between 16 and 19 % of body weight, contain amino acids and enzymes and are endogenous (can be produced by the body itself) or exogenous (taken in through food).

• Amino acids are the building blocks of the proteins from which tissues and organs are made. Protein contributes to the growth and maintenance of muscle mass and to the maintenance of normal bones, and is needed for skin, hair and enzymes.
• Enzymes are protein molecules involved in digesting food, stimulating the brain, maintaining cellular energy and repairing tissue, organs and cells. They play an important role in controlling vital processes in the body by speeding up biochemical reactions.

The body's protein requirement is worked out in terms of quantity and quality, and the human body can produce about 100,000 proteins. If our diet contained no protein, the body would use the amino acids produced by breaking down its own tissue proteins (the process takes place in the liver).

An adult needs on average 1.2-1.5 g of protein/kg of body weight, an amount at which the body does not have to burn its own proteins, but the value varies with age, sex, physical effort or state of health.

From a qualitative point of view, proteins differ in their composition of essential amino acids, which are indispensable for the smooth working of biological processes in the body. The number of amino acids contained in the structure of proteins is about 100, of which 23 are better known and 8 are indispensable. These 8 essential amino acids have to be supplied to the body through food, and a lack of one of them leads to a disturbance of protein synthesis with serious consequences for the body. Amino acids that can be synthesised by the body are called non-essential, and there are 11 of them.

The biological value of proteins comes from the quality, quantity and ratio of the amino acids in their structure.

Where do we get protein from?

While for a long time proteins were confused with meat, eggs or milk, today we know that a range of plant foods are rich in protein: beans, peas, lentils, nuts, peanuts, mushrooms or algae.

Proteins from meat, fish, eggs and milk have a higher biological value, as they contain all the essential amino acids in the optimal ratio. Soya, white beans, peas and cereals contain proteins of average biological value, since the essential amino acids are present in unbalanced proportions. With well-controlled proportions, proteins of this kind can complement one another and together give a high biological value.

Proteins release an amount of energy of 4.1 kcal/g, but for them to be metabolised by the body an amount of energy equal to 60 % of the energy they release is required, which in practice results in energy released of less than 2 kcal/g. This principle is the basis of high-protein diets in weight-loss programmes, which are not recommended, since they produce a range of toxic products of catabolism (uric acid, creatinine, urea, ammonia and other nitrogenous structures) that call on the mechanisms of the body's neutralising and excreting apparatus. Studies show that heat treatment inactivates part of the animal or plant proteins.

There is no natural food consisting only of protein, and the ratio of proteins, lipids and carbohydrates is important for the digestive process.

A lack of proteins in the diet can lead to anaemia, leucopenia, pellagra, exhaustion of the nerve cells, reduced synthesis by the adrenal glands, the pituitary gland, the thyroid gland, the pancreas and the sex glands, a reduction in body mass, a halt in growth in children and disorders of mineral metabolism (osteoporosis): the skin becomes dry, the nails brittle, the hair falls out.

An excess of proteins leads to the body being overloaded with metabolic products, an intensification of the putrefaction process in the gut, an overload on the kidneys and liver and diseases of the bones and joints (gout, degenerative rheumatism, high blood pressure).

Important sources of protein are: soya (35–40 %), cheese (30 %), beans (21 %), meat (18–20 %), fish (18 %), cottage cheese (18 %), nuts (18). %), eggs (12.7 %) – the percentages vary with the type and the origin.