What’s the single question you’re most likely to be asked, once people find out that you eat a plant-based diet? Of course, it’s
“Where do you get your protein?”
The person asking this question doesn’t realise it, but they’re stuck in 19th century thinking when it comes to protein: they’ve bought into the myth that adequate protein, or ‘high quality’ protein, or even protein per se, can only be found in foods of animal origin.
I’ve dispensed with each of these myths in my previous post, The big fat protein swindle, so I won’t rehash them here. Frankly, I’m bored by those protein questions.
But since nutrition science has long since moved on from the question “are we getting enough protein?” (spoiler alert: we all are, unless we’re eating insufficient calories/kilojoules), in the last few years, researchers from around the world have been grappling with a critical take on the “where do you get your protein?” question:
“Does the source of our protein matter?”
And study after study is answering that question with a resounding “Yes!”: where we get our protein from does matter, if we want to live long, healthy lives.
The most recent puzzle piece to be slotted into the protein jigsaw is a study published on August 26, 2019 in JAMA Internal Medicine, titled ‘Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality’.
It followed over 70 000 Japanese men and women aged 45-74 who were enrolled in the Japan Public Health Center–based Prospective Cohort.
At the beginning of the study, participants’ dietary habits were assessed in order to calculate their daily energy consumption, and their intake of total fat, saturated fat, monounsaturated fat, polyunsaturated fat, total and refined carbohydrate (including refined carbohydrate), total protein, animal protein and plant protein.
In a cohort study, participants are not given any advice or treatment by the researchers; they’re simply tracked over time, to see how many of them develop the outcome that the research team is investigating.
In this case, the outcomes of interest were all-cause mortality (dying from any cause) and deaths due to cancer and cardiovascular disease (including both heart disease and cerebrovascular disease, such as stroke).
After an average of 18 years of follow-up, over 12 000 of the participants died. Unfortunately, cohort research can be a morbid business – in order to answer their research questions, investigators often have to wait for people to die!
The researchers then compared the dietary intake of participants who died to that of survivors, and found that
“Higher intake of plant protein was associated with lower total mortality. Moreover, substitution of plant protein for animal protein, mainly for red or processed meat protein, was associated with lower risk of total, cancer-related, and cardiovascular disease–related mortality.”
Or in plain language, eating more protein from plants was associated with a longer life. And if you swap even a little of the steak and bacon on your plate for tofu and vegetables, you’re upping your chances of making it to old age and lowering your risk of dying from cancer or heart disease.
Why might this be? The Japanese researchers suggested 2 possible explanations:
- When people eat more protein from animal foods, they inevitably decrease their consumption of other foods. Typically this means eating less carbohydrate-rich plant foods such as grains/cereals, legumes/pulses, vegetables, and fruits, which results in a lower intake of fibre, phytochemicals and micronutrients found in abundance in plants.
- Animal-derived proteins have different amino acid profiles to plant-sourced proteins, potentially leading to differential health effects; for example, intake of plant protein, but not animal protein, has been associated with healthier blood pressure, total and LDL cholesterol, insulin levels, waist circumference, and weight; and plant protein, unlike animal protein, does not elevate levels of the cancer-promoting hormone insulin-like growth factor 1 (IGF-1).
I would propose a third contributing mechanism: the impact of a diet high in animal protein on the gut microbiome. Substantial differences have been observed in the composition of the gut microbiota in vegans and vegetarians compared to omnivores, and the more diverse and stable gut microbial ecosystem found in plant-eaters is now believed to contribute substantially to their decreased risk of cardiovascular disease and diabetes, among other chronic diseases.
No doubt there are many other mechanisms which contribute to the longevity-promoting effects of plant protein, just waiting to be unearthed by researchers.
But the message emerging from nutrition research is clear and consistent: if you want to live a long, healthy life, get more plants on your plate.
So next time someone hits you with the “where do you get your protein?” question, you can let them know: “My protein comes from foods that will help keep me alive and healthy. Where does yours come from?”
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