Economic theory regarding household fertility decisions has long recognized precautionary demand for children, such that households in a high-mortality environment respond to the risk of children not surviving to adulthood by increasing their family size. We test whether such an effect exists in response to nutrient deficiencies. Using survey data on a sample of 5,966 households in Vietnam, we find that a 10% increase in calorie availability decreases the likelihood that they had a child by 0.8%. Protein, potassium and thiamin also have significant effects. These findings provide initial evidence of an economic link between nutrition and fertility.