Many critics claim that Soylent is dangerous since it only contains chemicals we know and understand and some vital chemical may be left out.
Rob refutes this by explaining that we know for a fact many people's diets are already deficient of nutrients we know about. For this reason, swapping to a diet containing every known nutrient is healthier than existing diets which miss known nutrients.
The bacterial ecosystem in the gut is very complex and is trained over time to break down certain types of food.
It's possible that without the intake of a certain type of food, the gut will slowly loose it's ability to digest it in the future.
The concept of "health" is inherently complex and not a fully understood field of science. Adverse effects of a poor diet could take a significant time to show symptoms and effect everyone differently.
This makes it very difficult to run tests on any new food intake system and conclude that it is a safe alternative to normal food.