The digestive system of people and animals requires both essential compounds for energy and maintenance plus bulk to activate the associated muscular systems to keep the system in good operation. Our digestive systems have evolved to utilize all the elements of currently available foods and one of those elements is bulk and fiber. You might get by a few days on energy pills but would rapidly end up constipated by a longer trial of minimum food. I enjoy eating a good meal well prepared and a good deal of my pleasure is generated in the preparation. The concept of living on flavorless pills is totally repugnant to me and would be dangerous to any normal physiology.

Man, to get the fiber your body needs for your digestive tract to function that pill would be freakin' huuuge!!

I suppose one could take multi-vitamins and wash 'em down with a half gallon of Metimucil followed by a protein shake and survive a month or two...

Come to think of it, this sounds suspiciously like a fast weight loss diet program I once heard about on morning TV.

LifeCaps.net!

In the Star Trek TOS 1968 episode called 'By Any Other Name," aliens from another galaxy assume human bodies and start by taking their meals in a big pill, stealing the Enterprise to travel many years back to their own galaxy eating only these big pills. The Enterprise crew eventually beat them by showing them how good food and other human experiences are and they decide to stay human. Proves that eating real food is pretty fun.

http://amazon.imdb.com/title/tt0708422/synopsis

This already exists, though it's not in pill form but rather as a fluid, called a "meal replacement drink". People who have had abdominal surgury may need to live on this for weeks at a time, as well as elderly people who have difficulty swallowing. It's quick, just shake it up, open it, slam it down in 30 seconds, and you're done. Dry pills are hard to swallow without liquid anyway, so a liquid-mixed-solution is easier to deal with.

A common one is Ensure, though the complete meal replacement is "Ensure Plus". An 8oz bottle of Plus contains 350 calories. To reach a typical 2000 calorie requirement, you would need to drink six bottles a day for about $13. Two bottles in the morning would cover breakfast for about $4.

There are more specialized versions for people with special needs, such as lactose-free, people with diabetes, and increasingly expensive medical versions for people with weird metabolic problems and who can't digest certain substances.

Also, have you ever considered what is used to keep people alive with a "feeding tube"? It's another type of "full daily nutrition" meal replacement liquid, though usually not flavored since it bypasses the mouth and enters the esophagus directly.