As the title says, this study looks at whether low-carbon-emission diets (typically those that include less meat, more grains) are correlated with better health.
This is important because
- Climate change is a risk to human health.
- Climate change increases disparities because it disproportionally affects vulnerable populations.
- Diversity allows the human species to survive 🙂
Diets that are better for the planet are better for health. Except if the diet for the planet is not better for health, which is the exploration in this paper.
Here are the hypotheses tested.
- Are low-GHGE dietary patterns associated with reduced CVD and cancer incidence or mortality?
- Are low-GHGE dietary patterns associated with reduced saturated fat, sugar or salt consumption?*
- Are low-GHGE dietary patterns associated with increased micronutrient consumption?
*As with other papers in this category, assumptions about healthy diet are based on a low-fat dietary pattern, which has been challenged as having little to no basis in evidence.
We found highly inconsistent results regarding links between reduced GHGE and reduced content of nutrients to limit. In the cases of salt and saturated fat, the majority of dietary patterns found a reduction in levels of these nutrients in diets with reduced GHGE (twenty-nine of forty-three diets for salt, twenty-seven of forty-one diets for saturated fat). This may be due to the reduction in meat consumption in lower-GHGE dietary patterns. Of the twelve studies that reported salt and saturated fat content of diets, eight analysed diets with reduced levels of meat and dairy. However, the majority of dietary patterns that reported sugar intake showed increased sugar in lower- GHGE diets (thirty-eight of fifty-five diets). The reasons for this are unclear.
As with this paper (Just Read: Nutritional and greenhouse gas impacts of removing animals from US agriculture), there may be greater nuance between carbon and carbohydrates than was previously thought, even among researchers who use the low-fat diet as their basis for healthy eating.
If the low-fat diet is not the healthy standard, how does the impact of increased chronic disease care costs offset the reduced GHGE of higher carbohydrate diets?
In the United States,
- current GHGE from health care are about equal to GHGE emissions from all of agriculture.
- Not all of health care GHGE is due to chronic illness, and
- not all of GHGE emissions in agriculture are due to the sustainability of diets.
- The health care GHGE also does not include overall health impact of chronic illness.
We also found an inconsistent relationship between reduced GHGE and positive health outcomes. Overall mortality was associated with four higher-GHGE diets and four lower-GHGE diets. Cancer was similarly inconsistent, with increased incidence in five reduced-GHGE diets and decreased incidence in seven reduced-GHGE diets. CVD risk was assessed by only two studies, and within these this disease was higher in low-GHGE diets in four out of five scenarios.
Financial support: This review was funded by the Department for the Environment, Food and Rural Affairs (grant number FO0318) and the Biotechnology and Biological Sciences Research Council as a contribution to the European Commission SUSFOOD funding call (proposal number 114: SUSDIET). The funders had no role in the design, analysis or writing of this article. Conflict of interest: None. Authorship: P.S. and L.C. formulated the research questions and study design. C.L.R.P. carried out the study, analysed the data and wrote the article.
Payne CL, Scarborough P, Cobiac L. Do low-carbon-emission diets lead to higher nutritional quality and positive health outcomes? A systematic review of the literature. Public Health Nutr [Internet]. 2016 Oct 15;19(14):2654–61.