Commercialization of smallholder agriculture is widely seen as an essential pathway towards rural economic growth. While previous studies have analyzed effects of commercialization on productivity and income, implications for farm household nutrition have received much less attention. We evaluate the impact of commercialization on household food security and dietary quality, with a special focus on calorie and micronutrient consumption. We also examine transmission channels by looking at the role of income, gender, and possible substitution between the consumption of own-produced and purchased foods. The analysis builds on survey data from 805 farm households in Western Kenya. A control function approach is used to address issues of endogeneity. Generalized propensity scores are employed to estimate continuous treatment effects. Commercialization significantly improves food security and dietary quality in terms of calorie, zinc, and iron consumption. For vitamin A, effects are positive but statistically insignificant. Commercialization contributes to higher incomes and added nutrients from purchased foods. It does not reduce the consumption of nutrients from own-produced foods, even after controlling for farm size, which can be explained by higher productivity on more commercialized farms. Enhancing market access is important not only for rural economic growth, but also for making smallholder agriculture more nutrition-sensitive.