Protein
Protein is a macronutrient (like carbohydrate and fat). It’s essential for growth and repair of every cell in the body, including muscles, bones, skin, hair, haemoglobin, antibodies, enzymes and hormones. If the diet lacks sufficient carbohydrate, protein can also be used as a source of energy. If we take in too much, the excess can be converted to fat.
So where do we get protein? Most people know that animal foods such as meat, fish, poultry, eggs and milk products are good sources of protein. However, some don’t realise that plant foods such as legumes, wholegrains, nuts and seeds are also excellent sources, with soy beans and quinoa rating as highly as animal foods. Although fruits and vegetables provide dietary fibre and a range of vitamins and minerals, most provide only small amounts of protein.
Amino acids
Proteins are made up amino acids, organic compounds of carbon, hydrogen, nitrogen, oxygen and sulphur. Of the 20 or so amino acids that make up the protein in the foods we eat, nine are called ‘essential’ amino acids, a description related to the fact that we need to get them ‘ready-made’ in foods. The other amino acids can be made within the body, although a couple may be classified as ‘essential’ during the first year of life, or during recovery from major trauma to the body (as might occur after severe burns), when the rate of conversion may not be fast enough to meet the need.
The digestion of protein begins in the stomach where strong acid begins to break down proteins into smaller units. These then pass into the small intestine where enzymes finish breaking them into individual amino acids. These can then be absorbed into the bloodstream and used as required.
Until relatively recently, individual foods that contained all the essential amino acids were considered superior. That included all sources of animal protein. Indeed, in the first textbooks I wrote on this topic, I provided lists of the way different plant-based foods could be combined to deliver an equivalent balance of essential amino acids in one meal.
However, as biochemists unravelled more details about amino acids and the way the body uses them, it became clear there was much more leeway than the older references had described. As long as a variety of plant-foods are consumed over the course of a day’s meals, there is no need to specifically combine particular foods at a single meal.
How much?
Breast milk contains varying amounts of protein, which gradually decrease over the months of feeding. The quantity is not affected by what the mother eats. Its unique variety of proteins include casein, alpha-lactalbumin, lactoferrin, secretory immunoglobulin IgA, lysozyme and serum albumin and these vary over the months, perfectly suited to the baby’s needs. Formula milks generally have more protein and lack the complexity of the amazing types found in breast milk.
Protein deficiency is rare in Australia, with national surveys showing 99% of Australians get plenty of protein from what they eat. However, deficiency can occur in extreme poverty, in frail aged people who do not eat regularly and those who follow some extreme diets. As with most nutrients, more is not better.
Who needs protein supplements?
Protein shakes, powders and supplements have become popular. They’re a boon for those who sell them but unnecessary for most people. Excess protein doesn’t magically build muscle and, once the body’s needs are met, any excess not used for energy can be converted to body fat.
Branched chain amino acid supplements that claim they will build muscle or reduce stiffness are especially popular with athletes and body builders. The Australian Institute of Sport notes they are made from processed animal feathers/fur/hair or skin, or purified from plant proteins, or fermented by genetically-modified microorganisms that convert sugars to amino acids.
Much of the hype stems from laboratory studies of cell cultures. Human studies that use a valid placebo for comparison show little effect.
Active athletes almost always eat more food than most people, and get more than enough protein. The best way to build muscle is to exercise and the best foods to provide fuel for muscles are healthy carbohydrates such as wholegrains, legumes, milk or fruit. The first three will also supply protein.
Vitamin supplements
For most people, the best sources of most vitamins are the foods from five food groups: vegetables; fruit; wholegrains; legumes, nuts, seeds, fish, eggs, poultry and meat; milk products. Those foods can supply vitamins A, E, K, C and the eight members of the B complex.
Few foods contain vitamin D, but it’s easily obtained from the action of sunlight on the skin. Exposing forearms to the sun for about 15 minutes a day will provide enough. Vitamin D is stored in the body and these stores can see people in most parts of Australia through days that are too cold to bare your arms.
If you take vitamin supplements your body doesn’t need, most of them end up going down the toilet. That can be a good thing as some could be harmful in excess.
There are exceptions and, as I’ve written before, many frail aged people fail to absorb vitamin B12 and need a supplement (taken by mouth is fine).
Anyone who can’t eat for any reason, including those with an eating disorder, also need a good multi-vitamin-mineral supplement. Unfortunately, that can be hard to find as many multivitamins have hundreds of times the recommended dietary intake (RDI) of some vitamins, and very little of others.
In winter months, sales of vitamin C soar as people believe it will help ward off colds, even though years of careful research fails to back this. Exceptions have been noted only in some small trials in skiers and soldiers on subarctic exercises, which were published 60 years ago! A small positive result in reducing the severity of a cold by 8% has also been reported, but such a possible minor improvement is subject to poor definitions of what is a ‘severe’ cold.
If you do decide to take vitamin C, avoid chewable tablets. Whether they contain sugar or not, their acidity is a major dental hazard and can damage tooth enamel. Dentists also warn that brushing your teeth after chewing something so acidic can worsen the acid damage. Instead, rinse thoroughly with lots of water.
In general, if your diet is low in vitamins, the solution – where possible – is to fix the diet. A diet that lacks vitamins also lacks other nutrients that won’t be helped by supplements.
Dr Rosemary Stanton OAM
