Energy balance

Reducing total dietary fat intake to less than 30% of energy leads to a small but consistent reduction in body weight, BMI, and waist circumference in adults not intentionally trying to lose weight.

If you reduce your total fat intake to 30% or less of your daily calories, you can expect a small but real reduction in body weight (about 1.5 kg) and waist size over time, even if you aren't actively trying to lose weight. This effect is consistent in adults and children, though the magnitude is modest. The key is consistency over months or years, not short-term drastic cuts.