When the food matrix does the heavy lifting
Bioavailability is how much of a nutrient is actually absorbed and used, not how much is on the label. Whole foods often deliver nutrients packaged with cofactors that aid uptake: fat-soluble vitamins arrive with dietary fat, and many plant minerals come with vitamin C or organic acids that improve absorption. The matrix can also slow release, smoothing the rise in blood levels.
For some nutrients the food source genuinely wins, which is part of why food-first guidance is common in nutrition.
Cases where the isolated supplement comes out ahead
Sometimes isolation helps. Folic acid in supplements and fortified food is absorbed more completely than natural folate from a mixed meal, and synthetic vitamin B12 in supplements is well absorbed in people with normal stomach function. Inhibitors in food, such as phytates binding minerals, can also make a supplement taken away from meals more available.
This is general educational information, not medical advice. Because the answer depends on the specific nutrient, the individual, and the form, supplementation choices are best made with a qualified professional rather than a single rule of thumb.