This article is based on the food eaten in Metal Gear Solid 3: Snake Eater.
Eating food replenishes stamina. How much stamina Naked Snake has affects how quickly he recovers from injury. The greater it is, the faster he heals. Having low stamina (less than 50%) causes Snake's hands to shake while holding weapons. Snake's grip and oxygen (O2) meters are limited to his current stamina; both meters will run out faster if Snake's stamina is low when hanging or diving. Also, his stomach will start to rumble, alerting guards to his location. Both of these effects increase as his stamina gets lower. Some rare foods, such as the Tsuchinoko, are extremely rare, however, when eaten will cause the player to recover large amounts of Stamina, and in the Tsuchinoko's case, will make the player recover all of it. If the player captures animals alive, a grid can be seen on the animal's portrait indicating that it is placed inside of a cage. For plants, hornet hives, and animals that have been killed, the food type subtitle will have the "R." prefix, meaning "Raw."
Naturally occurring foods (i.e. everything but rations, instant noodles, Calorie Mates, and the Hive of Pain Hornets) can spoil over time. Spoiled items should be discarded, as eating spoiled food will give Snake food poisoning that may be cured with digestive medicine or by making Snake vomit. However, many enemies, if they find spoiled foods that Snake has thrown, will eat them and get food poisoning themselves. This strategy can be very helpful in defeating The Fear. If the player eats a certain type of food for the first time, a cinematic will appear in the survival viewer where Snake is eating the food in question.
In the HD collection, capturing any animal for the first time will result in the trophy/achievement "Can I keep it?" being unlocked, a reference to a typical phrase being uttered when someone finds an animal and wants to keep it as a pet. Trophy/Achievements for capturing all foods of a specific type, or eating a food of a specific type, are covered in the articles below. Achieveing the Markhor rank will also result in the achievement/trophy "King of the Jungle" being unlocked.
Feeding a guard rotten food will cause the guard to have a severe stomachache to the point Snake can walk pass the guard and the guard will be too occupied with the pain to notice him.