Different food items will have different absorption rates for the nutrients they contain when passing through your stomach, upper & lower intestine. For example, an apple may contain a small amount of iron absorbed at a rate of 20%, while a steak may contain significantly more, with an absorption rate of 80%.

These absorption rates can also vary widely from person to person, based on the flora in your gut, the drugs you ingest, your diet, and also certain DNA (eg. most East Asians never developed specific lactose related digestive abilities [1]) and ancestry can significantly alter this too.

For example, my grandfather had issues with high iron absorption, thus he would regularly donate blood to get rid of the excess iron in his bloodstream. Neither I nor my immediate family share that issue, but he made dietary choices based in part on avoiding iron rich food (like the iron enriched cookies I used to eat, mmm).

TL;DR: Your body & the food you eat are very complex things to understand, and we understand the tiniest sliver about it. Highly processed food likely misses important nutrients you need.

1 - https://ghr.nlm.nih.gov/condition/lactose-intolerance#statis...

But how much fast food has paid attention to those things? That Soylent is not perfect does not mean it's not better than the likely alternative.

Food like this that's specifically tuned to your own metabolism would be fantastic of course, but just getting some healthy stuff into you instead of whatever the vending machine sells, is already an enormous improvement for a lot of people.