Do low-carbon-emission diets lead to higher nutritional quality and positive health outcomes? A systematic review of the literature.

Objective: 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).
Design: We systematically reviewed the results of published studies that link GHGE of dietary patterns to nutritional content or associated consequences for health.
Setting: 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.
Subjects: Studies included used data from subjects from the general population, who had taken part in dietary surveys or prospective cohort studies.
Results: 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).
Conclusions: 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.