Here’s a scenario:
You’re pregnant (Congrats)! You’re eating all the healthy food, that should be enough, right? However after a blood panel is run by your midwife you are surprised to find you are lacking in some key nutrients. This is a pretty common story in real life.

So what is going on?

Bioavailability could be the culprit. Certain nutrients need other specific nutrients to bind to in order to be used by the body. For example: Calcium, which you can see in this link is complicated enough when only considering getting it from dairy foods:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7393990/ .

To make a long story short: It’s not what you’re eating but how you’re eating it that may make the difference.

Another way bioavailability is affected is through gut health (It would be wouldn’t it? Gut health is all the rage nowadays). As it turns out the bacterial composition of the gut does impact how food is broken down. It is no wonder breast milk contains so much carbohydrate sugars that specifically feed infant gut bacteria; maximum absorption means less nutrients are required.

Some science-y stuff on Bioavailability and gut health:
https://www.researchgate.net/publication/249317405_Benefits_of_polyphenols_on_gut_microbiota_and_implications_in_human_health