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).