The Mediterranean diet is a way of eating that's based on the traditional cuisines of Greece, Italy and other countries that border the Mediterranean Sea. Plant-based foods, such as whole grains, vegetables, legumes, fruits, nuts, seeds, herbs and spices, are the foundation of the diet. Olive oil is the main source of added fat. Fish, seafood, dairy and poultry are included in moderation. Red meat and sweets are eaten only occasionally.