Temperature and the Composition of Diets

How climate change affects human welfare depends not only on what food systems produce but on what individuals eat once food is on the table. Using three-day dietary recalls from the China Health and Nutrition Survey matched to county weather in the same three-day window, we show that short-run departures from comfort temperature raise the fat share of energy intake and the probability of a diet whose fat share exceeds the WHO threshold. Heat and cold raise the fat share through opposite margins, though the cold response is smaller and less precisely estimated. Under heat, total energy, carbohydrate, and protein intake fall, while absolute fat intake does not change detectably, so the fat share rises as a composition effect, even as total calories decline. Under cold, absolute fat intake appears to rise more than other macronutrients, an intake effect. A macronutrient decomposition is therefore essential: identical movements in total calories mask very different movements in diet quality, a distinction that calorie- or index-based measures cannot deliver. The responses align with physiological appetite regulation, though our design cannot separate physiology from other demand-side channels. Effects are larger for rural and lower-income households but smaller for those that own cooling and heating appliances. We read individual diet as a behavioral input to health capital through which temperature, and adaptive capacity, shape nutritional inequality.