A mother's milk provides all a puppy needs up to about four weeks old. It's around this time that puppies can begin to be weaned for a period of one or two weeks. You may be surprised at the amount of food a little puppy needs to maintain its rapidly growing body. Per pound of body weight, puppies need to eat about twice as many calories as normal adult dogs [source: National Academies]. They also need more proteins and fats than adult dogs. Especially for bigger dog breeds, you must be careful that the puppy isn't growing too quickly, because of the stress this can put on bones, joints and organs [source: Becker].
So, what does this boil down to when you're faced with the different varieties of puppy food in the pet store? Experts lend some suggestions to help you decipher what some of the labels mean on these foods. Some puppy food, for instance, isn't specifically formulated for a puppy's diet, but happens to meet the minimum nutritional needs of a puppy as determined by the American Association of Feed Control Officials (AAFCO). At the very least, the food you choose should say on its label that it meets these. But foods that merely say they "meet" these requirements are not as preferable as those that boast balanced nutrition "based on AAFCO feeding trials," or something similar [source: VMRCVM].
Although puppies need a lot of food, you should avoid having food out for them all day so that stay at a healthy weight. You can do this by measuring the food you give them (based on the food label or a vet's advice) and feeding them two to four times a day at regular, consistent feeding times. By the time they're about six months old, you can reduce the frequency to two meals per day.