The objective of the present study was to determine the effects of a long-term moderate-fat diet (30 % energy from fat) v. a low-fat one (20 % energy from fat) on metabolic risks. The study was a randomised, prospective 14-month trial on overweight and obese patients (eighty-nine overweight and obese men and women). The intervention was a moderate-fat diet (30 % energy) or a low-fat diet (20 % energy). The main outcome measurements were change in body weight, waist circumference, LDL-cholesterol, HDL-cholesterol, total cholesterol, TAG, and systolic and diastolic blood pressure. Forty-five subjects on the moderate-fat diet and forty-four subjects on the low-fat one were studied. Characteristics of all randomised participants were similar in both groups. After 7 months, the moderate- and low-fat diets had similar effects on cardiovascular risks. The moderate-fat diet was more successful after 14 months in reducing weight ( − 5·0 (sd 2·5) kg in the moderate-fat group v. − 1·2 (sd 1·1) kg in the low-fat one; P < 0·0001), waist circumference ( − 5·5 (sd 2·4) cm in the moderate-fat group v. − 2·3 (sd 1·3) cm in the low-fat one; P < 0·0001), and other cardiovascular risk factors as well (LDL, TAG, total cholesterol and systolic blood pressure). In conclusion, a moderate-fat energy-restricted diet in the long term might have more beneficial effects on weight maintenance and cardiovascular risk factors compared with a low-fat diet. Better dietary adherence with the moderate-fat diet may be the reason for its successful effects.