How plausible is it that alien life may contain nutrition and vitamins that affect our biology in a way that is not possible with the current chemicals and vitamins that exist in nature? Like say if colonists went to another planet and happened upon a plant that when consumed overtime causes your nails to grow faster.
Looking at various effects that alien life could have, and evaluating their plausibility based on the complexity of the molecular structures involved:
- Poisons: highly likely. There are a number of extremely simple molecules that interfere with human biochemistry in ways that render it non-functional, such as hydrogen cyanide. The odds of alien biochemistry producing one or more of these is quite good.
- Energy sources: reasonably likely, though you'll probably get drunk as a result. There are four families of molecules that the human body can use for energy: alcohols, sugars, fats, and proteins. Of these, only alcohol has a structure simple enough that alien life is likely to, by chance, produce it.
- Psychoactive drugs: mostly unlikely. Most such substances are complex structures, highly tuned to affect Earth-based nervous systems. See, for example, nicotine (a neurotoxin that, when consumed by humans rather than the insects it targets, merely causes interesting effects). The one exception, as noted above, is alcohol, which is highly likely to be found on other planets.
- Development-altering effects: extremely unlikely. Human biochemistry generally does not use simple molecules for internal signaling. For example, human growth hormone is a chain of 191 amino acids; the odds of an alien plant happening to produce something that would trigger the same receptors is infinitesimal.
- Eat alien plant and die: yes
- Eat alien plant and get drunk: maybe
- Eat alien plant and get high: no
- Eat alien plant and grow outsized hands: not a chance
Our biology evolved based on the nutrients available in our environment. Any alien flora or fauna that gave us an additional nutritional advantage would be a concentration of nutrients already available on Earth. However, we are constantly discovering new compounds in places like the Amazon that have an effect on our physiology. Perhaps your alien species is a natural proton pump inhibitor (aka Prilosec) and eating it cures heartburn.
At its simplest, what you're talking about is not radically different from the ethnic dietary requirements already found on earth. Ethnicities with longtime regional backgrounds in have adapted to the diet available in their region. Although radical dietary changes in real life tend to revolve around deficiencies, such as a Western European trying to get by on an Inuit diet, it's easy to see how such a change might be beneficial instead. Just make the effects are also plausible. People are unlikely to grow a foot if hair per day, for instance, whatever their diet.