The interventions lasted 1 to 18 months and involved the following forms:

Capsules with different polyphenol types (like resveratrol and flavonoids) and concentrations (8 studies)
Green tea extract (4 studies)
Apple juice (1 study).

The dosages ranged from 150 milligrams per day to 5 grams per day. Most of the studies compared polyphenol supplementation to a placebo. Two studies used caloric restriction (250–300 calories) along with supplementation.

The main outcomes assessed were markers of body fat, such as the following:

Waist circumference
Fat-free mass
Body fat mass
Visceral fat area
Visceral adiposity index

All of the studies showed improvements in at least one outcome.

Poly-lean-ols: Can polyphenols reduce body fat? Original paper