Undernutrition and low dietary quality remain widespread problems in poor population segments, especially among smallholder farmers in sub-Saharan Africa. Hence, the question how smallholder systems can be made more nutrition-sensitive is of particular relevance for research and policy. Recent studies analyzed whether increasing farm production diversity may help to improve nutrition. Most existing studies found a positive but small effect on dietary diversity on average. The underlying mechanisms were not examined in detail. This article tests the hypothesis that the effect of farm diversity on nutrition is small because production diversity is positively associated with dietary diversity obtained from subsistence production but negatively associated with dietary diversity obtained from the market. This hypothesis is confirmed with data from Kenya, using different indicators of production diversity and dietary diversity scores at household and individual levels. The results underline the important role of markets for smallholder diets and nutrition. Hence, strengthening markets and improving market access should be a key strategy to make smallholder systems more nutrition-sensitive.