Do low-GHG-emission diets lead to higher nutritional quality and positive health outcomes? A systematic review of the literature
This study evaluates the links between diets and health in relation to greenhouse gas emissions by reviewing 16 studies, comparing a total of 100 dietary patterns. The researchers examine how diets with reduced greenhouse gas emissions (GHGE) affected the subjects in the studies in terms of nutrient intake and health outcomes.
The main conclusion of the paper is that it cannot be assumed that lower GHGe diets will improve nutritional quality and health outcomes.
The study tried to assess if: 1) low-GHGE dietary patterns are associated with reduced cardiovascular disease and cancer incidence or mortality 2) low-GHGE dietary patterns are associated with reduced saturated fat, sugar or salt consumption and lastly if 3) low-GHGE dietary patterns are associated with increased micronutrient consumption. In a later stage they used the results to assess whether associations between GHGE and health/nutrition outcomes vary by level of meat consumption in the low-GHGE dietary patterns.
A number of dietary comparisons/scenarios were made across all studies (up to 158) based on the 100 original dietary patterns. Noteworthy is that the studies reviewed used dietary data from countries in which the majority of the population was likely to follow a Western diet and so the data cannot be seen as representative in a global perspective. The review found that the lower-GHGE diet, characterized by lower levels of meat, was shown to be linked to lower levels of saturated fat and salt (true for 68% - N.B. from a total of 84 dietary scenarios). It also showed that 70% of the lower-GHGE dietary patterns included in the studies had a higher than average sugar intake (of a total of 55) and that 88% had lower micronutrients intake (out of 158). The results thus clearly indicate micronutrients as a key area for concern in advocating reduced-GHGE diets.
When it comes to risk of non-communicable disease, such as cardiovascular disease and cancer, an inconsistent relationship between reduced GHGE and positive health outcomes was shown. In the paper it is explained that: “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. Cardiovascular disease risk was assessed by only two studies, and within these this disease was higher in low-GHGE diets in four out of five scenarios”.
In conclusion, even if lower-GHGE patterns show no consistent relationship with reduced nutrients, lower GHGE diets cannot be assumed to lead to improved overall nutrition and health. If sustainable diets are promoted in policy, this paper suggests that they should be promoted in ways that ensure sufficient micronutrients and reductions in sugar intake.
To evaluate what is known about the relative health impacts, in terms of nutrient intake and health outcomes, of diets with reduced greenhouse gas emissions (GHGE).
We systematically reviewed the results of published studies that link GHGE of dietary patterns to nutritional content or associated consequences for health.
We included studies published in English in peer-reviewed journals that included data on actual and modelled diets and enabled a matched comparison of GHGE with nutrient composition and/or health outcomes.
Studies included used data from subjects from the general population, who had taken part in dietary surveys or prospective cohort studies.
We identified sixteen eligible studies, with data on 100 dietary patterns. We present the results as dietary links between GHGE reduction and impact on nutrients to limit (n 151), micronutrient content (n 158) and health outcomes (n 25). The results were highly heterogeneous. Across all measures of 'healthiness', 64 % (n 214) of dietary links show that reduced GHGE from diets were associated with worse health indicators. However, some trends emerged. In particular, reduced saturated fat and salt are often associated with reduced GHGE in diets that are low in animal products (57/84). Yet these diets are also often high in sugar (38/55) and low in essential micronutrients (129/158).
Dietary scenarios that have lower GHGE compared with average consumption patterns may not result in improvements in nutritional quality or health outcomes. Dietary recommendations for reduced GHGE must also address sugar consumption and micronutrient intake.
Payne C. L.., Scarborough P., Cobiac L. (2016) Do low carbon – emission diets lead to higher nutritional quality and positive health outcomes. A systematic review of the literature. Public Health Nutrition.
See the full paper here (requires journal access).
See also three similar review studies (as highlighted by the authors of this paper):
- Joyce A, Hallett J, Hannelly T et al. (2014) The impact of nutritional choices on global warming and policy implications: examining the link between dietary choices and greenhouse gas emissions. Clin Ophthalmol 8, 2501–2506.
- Hallström E, Carlsson-Kanyama A & Börjesson P (2014) Environmental impact of dietary change: a systematic review. J Cleaner Prod 19, 1–11.
- Auestad N & Fulgoni VL (2015) What current literature tells us about sustainable diets: emerging research linking dietary patterns, environmental sustainability, and economics. Adv Nutr 6, 19–36.
While some of the food system challenges facing humanity are local, in an interconnected world, adopting a global perspective is essential. Many environmental issues, such as climate change, need supranational commitments and action to be addressed effectively. Due to ever increasing global trade flows, prices of commodities are connected through space; a drought in Romania may thus increase the price of wheat in Zimbabwe.
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