ANSWER: Protein is both a handy energy source and an important building block for the body. The physique of a 70kg adult, for example, contains about 11kg of the organic compound.
Proteins, which are complex molecules made up of amino acids, have many important roles in the body. They form enzymes to help carry out the thousands of chemical reactions in our cells, blood-transport molecules and hormones. They also act as antibodies in the immune system and have structural roles such as providing support for cells and skin.
Protein is found in all living cells, including both animal and plant foods. Foods such as meat, fish, legumes, eggs, nuts and seeds are rich protein sources. Milk, cheese, yogurt and other dairy products, and whole grains, vegetables and fruit, contain smaller amounts of protein.
Human proteins are made from about 20 different amino acids, most of which can be synthesised by the body. However, there are eight essential amino acids that we cannot make and that must be provided by our diet. Interestingly, milk and eggs have an amino-acid composition most similar to our bodies.
A well-balanced vegetarian diet that completely excludes meat can provide the protein needs for growing children. For example, two slices of wholemeal bread (6.4g of protein), a glass of milk (8.5g) and half a cup of yogurt (5-6g) provide the daily protein needs of a child aged four to eight.
For an adult, two slices of wholegrain toast with baked beans and a pottle of yogurt contain about half of our protein needs; a beef or lamb steak and a glass of milk would provide 80% of requirements. An average-sized woman aged 19 to 70 needs about 46g a day of protein, whereas an average man would need 64g.
Legumes are one of the most underappreciated classes of vegetable. Yet legumes such as beans, peas and lentils are a highly nutritious source of protein, folate, potassium, iron, magnesium and fibre. They’re also low in fat and contain no cholesterol, making them a healthy meat substitute.
The need to soak dried beans overnight before cooking runs counter to our fast-food culture, but there are many varieties of tinned beans available. Simply rinse canned chickpeas, lentils, white beans and kidney beans and use them in casseroles, salads and other recipes.
A well-balanced diet containing protein-rich foods such as meat, poultry, fish and/or legumes normally provides enough protein for a healthy adult. Even athletes with tough training regimes can typically meet their protein needs without supplements, according to the Australian Institute of Sport.
The best idea, though, is to include protein- and fibre-rich legumes, such as beans, peas and lentils, if we’re reducing how much meat and fish we eat. It’s easy to boost protein intake with a few simple swaps and additions (see box).
But will the children of our correspondent’s friends be getting all the nutrients they need to grow healthy and strong? In short, if their diet follows the sort of guidelines given here, they should thrive, although one of the main nutritional deficiencies the young are vulnerable to is lack of iron. Legumes, nuts and seeds are rich sources of iron, as is, of course, red meat.
This article was first published in the January 26, 2019 issue of the New Zealand Listener.