All food comes initially from photosynthesizing plants, that make sugar which is converted to proteins, fats and starches/cellulose in plants. Starches can be readily converted back to sugars by the same plants, but cellulose can only be decomposed by microbes in the guts of ruminants and other grazers. Starches and cellulose can also be converted to alcohol by microbes. Other herbivorous animals do not digest the cellulose. Plants are divided into food groups, with different carbohydrates, proteins, and fats. Meat is efficient to eat because it generally contains all amino acids people need in appropriate proportions; individual plant foods contain only some needed amino acids, so mixtures of plants are needed. Animal foods and aquatic foods can also be divided into groups, similar to plant food groups. People can consume about 2,500 Calories per day in modern life styles, but over 9,000 Calories when very active. Daily protein requirements vary with experts, but generally 65 grams per day is appropriate. Different foods were seasonal until preservation and greenhouses developed. Non-food commodities comprise less than one percent of total agriculture production.