A plant-based diet: good for us & for the planet
Author | Dr Rosemary Stanton, Nutritionist
Most people are aware of the vital roles that vegetables, fruits, wholegrains and nuts can play in a healthy diet.
And yet, meat eaters get prickly and many doctors and dietitians tack warnings onto any discussion of vegetarian diets. Are fears of nutritional adequacy for plant-food based diets valid? A series of papers produced by the Medical Journal of Australia (and available free here) provide relevant evidence.
I’m not a vegetarian but I acknowledge the wealth of evidence supporting the healthfulness of plant foods. In my current work, I’m also aware of their vital role in reducing our ecological footprint. And as a lover of good food, I don’t understand why we neglect so many great tasting plant foods.
So how does the evidence stand up? In a general sense, a well-planned plant-based diet turns out to be associated with a lower incidence of heart disease, bowel cancer, type 2 diabetes and obesity.
For Australians, the bowel cancer aspect is particularly relevant because it’s a disease where we get a gold medal. It’s the second largest cause of cancer deaths (responsible for about 80 deaths/week) in Australia and affects both men and women, young and old. The World Cancer Research Fund’s band of experts (none of whom has any conflict of interest) now rate the evidence as ‘convincing’ that red meat increases the risk of bowel cancer. Some plant foods, by contrast, are protective.
The MJA papers show that we can also drop our warnings about deficiencies of protein, iron and zinc. The following outline debunks some common fears about plant-based diets:
Amino acids and protein
When writing textbooks in the 1970s, I spent hours poring over lists of amino acids in foods, adding up data to find combinations of plant foods that would equal the protein in meat. Modern biochemistry shows the body can take the amino acids from foods over a day or more and we can stop fussing over which seed goes with which cereal. Eating a variety of foods over the day will ensure an adequate protein intake and we can stop worrying on this issue.
Warnings about iron and zinc deficiency are ubiquitous and certainly relevant in countries where people struggle to find enough to eat. In Australia and other western countries, vegetarians can relax because they are no more likely to suffer iron deficiency than meat eaters.
About 40% of the iron in meat is in a form known as haem iron. It’s true that haem iron in meat, poultry and seafood is absorbed better than the non-haem iron in plant foods and eggs. However, those who need more iron absorb more non-haem iron with absorption increasing as high as almost 60% absorption during pregnancy. Old studies checked iron absorption after only a single meal taken by meat eaters.
Zinc is found in abundance in grains, legumes and nuts, but many nutritionists have been concerned about competition for absorption caused by levels of compounds called phytates in the plant foods. Here the news is also good because of the way we prepare our foods. Adding yeast to breads, soaking legumes and roasting nuts decreases the effects of phytates.
The one relevant warning for plant-based diets is vitamin B12. This vitamin is found naturally only in animal products – although that does include dairy products and eggs. Those who avoid all animal foods will need a supplement or one of the soy foods with added B12.
Dr Rosemary Stanton is one of Australia’s best known nutritionists, with an Order of Australia Medal for her services to community health. As well as authoring many scientific papers, Rosemary has written 33 books on food and nutrition, over 3,500 articles in magazines and newspapers and has been appearing regularly on television and radio over the last 45 years. She is an ambassador for Meat Free Mondays Australia.