The diets of contemporary hunter-gatherers are diverse and highly nutritious, but are rapidly changing as these societies integrate into the market economy. Here, we analyse empirical data on the dietary patterns and sources of foods of three contemporary hunter-gatherer societies: the Baka of Cameroon (n = 160), the Tsimane’ of Bolivia (n = 124) and the Punan Tubu of Indonesia (n = 109). We focus on differences among villages with different levels of integration into the market economy and explore potential pathways through which two key elements of the food environment (food availability and food accessibility) might alter the diets of contemporary hunter-gatherers. Results suggest that people living in isolated villages have more diverse diets than those living in villages closer to markets. Our results also suggest that availability of nutritionally important foods (i.e., fruits, vegetables and animal foods) decreases with increasing market integration, while availability of fats and sweets increases. The differences found seem to relate to changes in the wider food environment (e.g., village level access to wild and/or market foods and seasonality), rather than to individual-level factors (e.g., time allocation or individual income), probably because food sharing reduces the impact of individual level differences in food consumption. These results highlight the need to better understand the impact of changes in the wider food environment on dietary choice, and the role of the food environment in driving dietary transitions.