Knowing that a food is high in protein, calcium, or magnesium can be misleading. You should also consider how much of each nutrient is absorbed. That’s a question of bioavailability: What percentage of a given nutrient, once ingested, becomes available for use in your body?

We want to optimize our diets for both nutrient density and bioavailability. Put another way, we want to eat nutritious foods that are well-absorbed. Animal sources, such as liver and clams, tend to outperform plant sources in both nutrient density and bioavailability. I’ll dig into that later, after we lay a bit of groundwork.

We’ll cover lots of ground in this article: What determines bioavailability, how recommended daily allowances factor in, how foods and supplements compare, how cooking affects nutrition, and a few top sources of essential micronutrients.