A mega sweep of pooled studies has confirmed that the health and environmental impacts of different foods are inextricably linked – and how just one extra food serving can make a difference.
Westernised diets have become increasingly harmful to people’s health and the planet, leading to calls for a radical overhaul of the flailing food system.
Poor diets account for nine of the top 15 risk factors for disease globally, while agricultural practices have multiple destructive environmental impacts through greenhouse gas emissions, land clearing, freshwater exploitation and pollution of ecosystems and waterways.
To explore this, Michael Clark, from the University of Oxford, UK, and colleagues set out to quantify how one additional serving of different food groups is related to health and environmental outcomes.
Their findings are published in the journal Proceedings of the National Academy of Sciences.
“We thought that this approach might be tangible to individuals because it examines the potential effect of small changes to current dietary patterns,” says Clark.
Food groups were fruits, vegetables, legumes, nuts, olive oil, eggs, fish, chicken, dairy, potatoes, processed and unprocessed red meat, refined and whole grain cereals and sugar-sweetened drinks.
Ultra-processed foods, trans-fats and added sugar were not included due to lack of dose-response meta-analyses on these groups.
The researchers focussed on five outcomes with the largest health burden (heart disease, type 2 diabetes, stroke, colorectal cancer and total mortality) and five environmental impacts (greenhouse gas emissions, land use, water use, and acidification and eutrophication from nutrient pollution).
First, they scoured 19 meta-analyses that tracked dose response data on diet and health outcomes from tens of millions of people, controlling for confounding factors such as age, weight, sex and history of smoking.
Each food had similar health impacts across the board. Specifically, nuts, vegetables, legumes, fruits, minimally processed whole grains and fish were associated with lower mortality and/or disease risk.
Conversely, processed and unprocessed red meat was strongly associated with disease risk across all five health outcomes, while dairy, egg and chicken didn’t have a broad impact. Sugar-sweetened drinks were linked to increased risk of heart disease, diabetes and stroke.
Exploring the environmental outcomes of these food groups, the authors turned to two meta-analyses of life cycle assessments that included 742 agricultural systems and 38,000 farms.
This analysis found that unprocessed meat had the biggest impact across all indicators and that minimally processed plant foods and sugar-sweetened drinks had the lowest environmental effect on all outcomes.
The researchers then used radar plots to combine the data and “examine which foods might be win-wins for health and the environment, which might be lose-loses, and which might be beneficial for one outcome but detrimental for the other”, says Clark.
They found that foods with the highest environmental impacts also tended to have the worst health effects, and this was most striking and consistent for red meat, processed or not.
The only deviation from this was sugar-sweetened drinks, with poor health outcomes but low environmental impact.
Ranking the foods on each outcome also revealed that producing a serve of red meat had 10 to 100 times greater impact on the environment than plant food sources.