There is no substitute for a balanced diet.

Powders, liquids or pills cannot substitute for solid food and
yield permanent, healthful results (if God had meant us to live
on supplements, we would have been born with a blender in our
mouths instead of teeth). A balanced diet should consist of 2500
to 3000 calories a day (more depending on athletic activities)
split up into proper proportions of protein (23 to 30%), fat (20
to 25%) and carbohydrates (45 to 55%). Note, that while the
"zone" diet, recommending 30% protein, 30% fat and 40%
carbohydrate, is currently getting a lot of publicity, that
level of fat is probably not appropriate for the over 50
metabolism. These nutrients should come from a variety of foods
spread throughout the day. In fact, it is important to eat often
to spur your metabolism. If possible, five small meals a day
(compared with two or three) would result in both decreased
transit time (going to the bathroom more often) and increased
metabolism (burning calories more quickly since your body knows
it will be fed again soon).