Last month I discussed some of the issues we’ll need to address to ensure our food system remains sustainable in the face of climate change. I also mentioned one of my Facebook posts on this issue, where one responder accused me of wanting people to eat ‘bugs’. The poster also told me that “if you also listened to science, you would realise that meat is a great source of protein”.
Of course meat is a great source of protein, but to suggest I don’t listen to science is preposterous. I have spent the last 57 years working in this field, including as a University lecturer and remain a Senior Visiting Fellow in the School of Biomedical Sciences at the University of New South Wales.
So let’s take a look at protein. As I have discussed in previous articles, proteins are made up of more than 20 amino acids. Nine (10 for children) are classified as ‘essential’ amino acids because they can’t be made in the body and must therefore be supplied ready-made in foods.
Meat and other animal foods, including milk, cheese, yoghurt, eggs, poultry, fish and other seafood, contain good quantities of all the essential amino acids. With a few exceptions (including soy and chia), many plant foods don’t have ideal quantities of some essential amino acids. In practice, however, that’s not a problem, because an amino acid that may be low in one plant food is easily amply supplied by another.
Over 50 years ago, when I wrote my first textbook on human nutrition, we thought that all the essential amino acids must be consumed in ideal quantities at each meal. For those who chose not to eat animal foods, I therefore listed combinations of various plant foods that would achieve a top blend of amino acids. Some of these combinations have been popular in many cuisines and cultures, possibly because different groups had found over long periods of time that certain foods eaten together led to better growth in children. Examples of the groupings include beans and corn; couscous and chick peas; rice and soy beans; nuts and grains (which gives a tick to peanut butter sandwiches made with wholegrain bread).
These combinations of plant foods remain healthy choices. However, more recent biochemical research has established that we don’t need to supply exact combinations of amino acids at each meal. It’s more a case that the body has access to a ‘pool’ of amino acids over a day or so which we can use to meet specific needs. As long as people have sufficient food and eat a variety of plant foods that contain protein throughout the day, we now know there is no need for protein ‘combining’ at each meal.
It’s only when diets are severely restricted, as occurs with extreme poverty, or an eating disorder, or when someone follows some crazy fad diet, that we see problems from insufficient quantities of particular amino acids.
The amino acids in protein are essential for growth and maintenance of body tissues, including muscle, skin, all body organs, blood cells, haemoglobin (which carries iron) and all enzymes and hormones. The recommended dietary intake (RDI) for protein increases for women as they get older, with the exceptions that needs are highest during lactation and pregnancy. For men, it’s worth noting that the RDI is highest for men over 70.
Whatever your age, the bigger your body frame and the more muscle you have, the more protein you need. That means most athletes need more protein than those who lead more sedentary lives.
A vegetarian diet can easily supply enough protein. For those who prefer it, a vegan diet can also meet the protein needed for health, growth and strength, although a qualified dietitian may need to help with the diet of young children.
Some of the world’s greatest athletes power their bodies with vegetarian or vegan diets. Studies published in high quality scientific journals also show that vegetarian diets could help athletes protect themselves against chronic, degenerative, and inflammatory diseases, and also control their body weight.
A massive market for protein supplements is now targeting budding athletes. Such supplements are rarely needed because the extra food athletes need to fuel their higher levels of physical activity can easily meet their protein needs. Note too that although exercise builds muscle, taking protein supplements without doing extra exercise won’t build bigger biceps, or any other muscle.
Protein supplements can be useful for the frail aged or those recovering from a period of very poor diet.
Australians protein intake
Average consumption of protein at all ages and in both sexes in Australia is well above what most people need, even taking account of possible extra needs as we age or exercise. So the average Australian doesn’t need to fuss over protein.
What about excess protein?
It’s difficult to exceed protein requirements with healthy plant foods because their dietary fibre makes them filling.
A recent summary of 21 experimental human studies and 11 reviews identified some adverse effects associated with long-term high protein/high meat intake: disorders of bone and calcium balance; disorders of kidney function; increased risk of some cancers; disorders of liver function; and progression of coronary artery disease. With red meat, more is not better. That also applies to the sustainability of our food system. But as I wrote last month, less doesn’t have to mean none.
Dangers of extreme diets
Very low carbohydrate diets verge into danger territory on many fronts. Some may emphasise protein, but others recommend getting most of the day’s kilojoules from fat. These versions often recommend fatty meats as their main protein source. Without adequate carbohydrate, the body can use fatty acids and ketones to supply some energy, but a certain level of blood glucose is essential, especially for the brain. In a process known as gluconeogenesis, glycogen stored in the liver and muscles is used to supply glucose. Once this is used, lean muscle tissue can be broken down to release amino acids that can be converted to glucose. The loss of muscle glycogen and its associated water is a major part of the weight loss with low carb diet. The loss of lean muscle tissue also makes future weight gain more likely – but that’s for another story!
Take home message
Dietary guidelines from many countries now recommend giving much greater emphasis to more plant foods in the daily diet. Good plant food sources of protein include legumes (chick peas, soy, lentils and other beans and peas), quinoa, chia, nuts, seeds and wholegrains (oats have as much protein as eggs). All these foods come with other vital nutrients as well as dietary fibre, the dietary component most likely to be low in the average Australian diet.
There’s no need to exclude proteins from animal sources, but meat, in particular, should move away from the centre of the plate.
