Twenty years ago or so she used to teach that only meat, dairy and eggs could provide “high quality protein” and she felt that people on plant-based diets would be missing out on good nutrition.
I pondered this for a while and asked Assoc Prof Anne-Louise Heath, of the human nutrition department at the University of Otago, whether thinking had changed about the increasingly popular plant-based or vegan diets.
Many people think that protein is all about meat and it’s hard to change the idea that you won’t get enough and it won’t be good enough quality if you don’t eat meat or dairy, but that isn’t true, she said.
“We live in a country that is a major exporter of meat and dairy so we probably get more than our fair share of stories about how essential those foods are. It would be interesting to know if it’s quite as relentless in other countries. Many people like eating meat and dairy and they can be an easy way to get vitamin B12 and calcium, but they certainly aren’t essential.”
In fact there is some protein in most foods apart from some very refined ones such as sugar or vegetable oil, she said.
She explains the science: We need about 20 different amino acids which make up proteins in our diet, but our bodies can make most of those. There are just nine indispensable amino acids that we cannot make and need to get from food.
“So the question is where do you get them from? Well you can definitely get them from plant proteins. However, plant proteins tend to be rich in some of the indispensable amino acids and poor in others so you need to eat a variety of plant foods,” she said.
“In general, New Zealanders eat far more protein than they need, so we’ve got quite a big buffer. So even if you’re vegetarian or vegan as long as you eat a variety of foods and you are maintaining a healthy body weight then you’ll be getting plenty of protein.”
However, for many years vegetarians and vegans thought they needed complementary types of plant protein in the same meal to provide a complete protein mix.
Often these combinations are found in food cultures such as bread and hummus or falafel in the Middle East, rice and dhal in India, corn and beans in the Americas, or our own staples, baked beans on toast or peanut butter on grainy bread.
This idea was made popular by Frances Moore Lappe’s influential 1971 book, Diet for a small planet. She said you needed to “consciously combine” plant proteins to get complete proteins in a vegetarian diet.
At the time people were beginning to be concerned about the environmental impact of meat production, Prof Heath said.
Much of our nutritional information at the time came from rationing during World War 2 (1939-45) when the British government needed to make sure that everyone received their fair share of the limited food available. The amounts of available foods to cover people’s nutrient needs and ensure good health were calculated by scientists and statisticians.
Subsequent research in the past few decades has shown that besides animal-sourced products, soy is also regarded as a complete protein with all the essential amino acids. It has also shown that it is not necessary to “consciously combine” different plant proteins in the same meal.
“As long as you are having a range of proteins during the day you’ll get the amino acids from here and there and your body will happily use them to make into proteins.”
An interesting aside is that the last nutrition survey more than a decade ago showed that in fact our main source of protein was bread rather than meat!
The protein in bread is plant-sourced and comes from wheat which doesn’t have more protein in it than meat, but because people ate so much, often more than once a day, it ended up being at the top of our protein sources, she said.
However, if you only ate one plant food such as just rice or just bread as might happen in a famine, you certainly wouldn’t get enough of the essential amino acids, but you’d also suffer a lot of other nutritional problems from lack of vitamins and minerals as well, she said.
“It’s one of those hypothetical things that virtually never happens and certainly doesn’t happen in New Zealand.”
The nub of the matter is if you are eating enough from a variety of food sources to maintain a healthy bodyweight, there is no problem, she said.