Newly available evidence confirms that expansion of aggregate food supplies within developing countries themselves is strongly associated with reduced undernourishment. It is not sufficient to rely solely on aggregate economic growth or reductions in poverty incidence to deliver improved food security. But the evidence also shows that higher food prices significantly increase the rate of undernourishment. It is therefore important to stimulate agricultural output without raising domestic food prices. Improvements in agricultural productivity achieve that. But agricultural protection aimed at food self-sufficiency does not, because it operates through an increase in domestic food proces. It delivers benefits to those food insecure people who are not sellers of food. But in most countries their number is exceeded by the food insecure people who are net buyers of food and are made more food insecure by increased food prices. Food self-sufficiency does not imply food security.