Functional nutrition asks a simple question before it gives any advice: why does this person feel the way they do?
Two people can both feel tired at 3 pm. One skipped breakfast and had a large plate of plain rice at lunch. The other sleeps five hours. The food advice that helps each of them is different.
A functional approach looks at blood sugar swings, gut comfort, nutrient intake, sleep and stress together. Then it picks the smallest food changes most likely to help, and checks whether they worked.
What it is not: a replacement for medical care, a list of banned foods, or a promise to cure anything. If symptoms are persistent, severe or new, see a doctor first.