If a person were to take in 0 calories (so no macronutrients) but took in sufficient micronutrients, in what ways has this been found to effect the body?
It’s not ideal but the body will cannibalize itself before allowing itself to die. The problem with this is that muscle mass (including heart tissue) may be used along with fat stores to keep alive. Look up Angus Barbieri for an extreme example showing it’s possible under the right conditions. He was under close medical supervision and started out extremely obese.
How can you have fat soluble vitamins without the actual fat to allow it to be in solution? Hard to be without any calories and still consume vitamins, since vitamin sources will have calories and you can never remove them all.
Besides, ideally you’d need food to have an optimal gut microbiome so as to allow better absorption of nutrients. If you’d like, there is a “fast mimic diet”, which proposedly has many if the benefits of fasting without limiting micronutrition.
Edit: fast mimicking diet