Protein And Nutrition by Jane Thurnell-Read

What Is Protein?

Protein is made up of simpler substances called amino acids. The protein in food is broken down into peptides in the stomach by enzymes, and then in the small intestine into amino acids. Amino acids are small enough to get through the gut wall.

What Does Protein Do In The Body?

Proteins determine the physical and chemical characteristics of cells and so are vitally important. The amino acids from food are used to produce:

• Enzymes
• Some hormones
• Organelles (cellular machinery)
• Muscle (e.g. actin and myosin)
• Structural components of skin and hair (e.g. collagen and keratin)
• Plasma (blood) protein
• Antibodies to fight infection

The instructions for producing proteins come from the genes.

It is possible for the body also to use proteins for energy, but it is not its first choice. Protein is essential for the body, as it is the only type of food that contains nitrogen. Excess protein is converted into fat or glycogen or glucose.

What Are Complete Proteins?

Complete proteins contain all the essential amino acids that cannot be made by the human body. Many vegetarian protein sources are not complete in this sense, unlike meat that has a full complement of the essential amino acids. Vegetarians used to be urged to eat pulses and grains (e.g. baked beans on toast) at the same meal to ensure they achieved that magical complete protein.  Scientists have now established that it is not necessary to eat all of them at the same time, as long as they are all eaten. This change in advice is hardly surprising for early man was an opportunistic hunter and forager and may have gone for long periods with no source of complete protein available.

How Much Protein Is There In Food?

No food is just protein, although some foods have a higher proportion of protein than others. The actual protein content varies depending on growing and rearing conditions, climate etc, so these figures can only be a guide only:

• Meat 20-30 % protein
• Whole grains 10% protein
• Cheese 25% protein
• Cows milk 3% protein
• Nuts 15-25% protein
• Pulses about 7% protein

In practical terms this means:

• 85 grams (3 ounces) of meat has around 23 grams of protein
• 113g (4 ounces) of tofu has approximately 8g of protein
• A quarter litre of milk has approximately 8g of protein
• 39g (1.3 ounces) of peanuts provides 10g of protein
• 385g (13.5 ounces) boiled brown rice provides about 10g of protein

How Much Protein Do I Need?

There are large amounts of variation in the amount of protein people eat. It is difficult to establish the minimum amount of protein people need because there are no definitive deficiency signs apart from growth failure and tissue wasting, which are extreme signs. The UK Reference Nutrient Intake (the amount of nutrient which is thought to be enough for at least 97% of the population) for protein per day is now:

53 to 55 g per day for men
45 - 46.5 g for women
51g for pregnant women
53 to 56g for breast feeding women
28.3 g for children aged 7-10 years

The recommended amounts of protein for adults and children has more than halved in the last 20 years. So the current figure should not be taken as absolutely right.

People who get all their protein from plant sources (such as vegans) may need to increase this slightly (multiplying by 1.1 is the standard advice), as plant proteins can be less digestible, but there are plenty of vegan and vegetarian sources of protein.

Many people seem to eat far too much protein. High protein diets have been seen as a good way of losing weight, but research suggests that the benefits may be temporary. Initially weight loss tends to be great as water is lost from the body with the reduction in carbohydrate. In theory a high protein diet could put a strain on the kidneys. High protein diets have also been linked to bone-density loss.

If you want to lose weight, try eating small amounts of protein throughout the day as this appears to stimulate metabolism, and gives a sense of fullness. It is important to make sure that fat intake is not increased along with any additional increase in protein.

Regular exercisers do not usually need to increase their protein intake: “There is no evidence that habitual exercise increases protein requirements; indeed protein metabolism may become more efficient as a result of training.” (Annual Review Of Nutrition, 2000;20:457-83.)

Copyright 2008 Jane Thurnell-Read High Quality Nutritional Supplements