|MadSci Network: Biochemistry|
Although it would be theoretically possible to subsist (to continue living) on instant breakfast powder, it certainly would not be possible to be as healthy as one could be eating a balanced diet of solid foods.
Despite the fact that you might be getting enough calories, fat, protein, carbohydrate, vitamins, and minerals necessary for a person of your age, weight, gender, and activity level, you would still be missing out on a lot of important "non-nutrient" dietary components. These include soluble and insoluble fiber, as well as the "phytonutrients" (carotenoids, flavonoids, etc.) from plant foods. Scientist believe that phytonutrients may be important for the prevention of disease, although they are not sure how important they might be at this point. Besides, a diet without fiber can make a person pretty unhappy after a while.
In my opinion, it's OK to use instant breakfast powders as supplements to a good diet (at most replacing one meal per day) but they should never be the only thing you eat, for the reasons that I've described above.
I hope that this helps.
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