Obesity is a major health issue in Western society. In the Netherlands every fifth person suffers from obesity and every third person is on a weight-reducing diet. The Montignac method is a very popular diet. The diet is claimed to be a nutritional science. The method is based on several hypotheses about the metabolism of carbohydrates and fatty acids: carbohydrates with a low glycaemic index are preferred, carbohydrates are not to be eaten in combination with fatty acids, fruit is propagated but must not be combined with other components. The scientific literature refutes the hypotheses of Montignac regarding the metabolic effects of carbohydrates and fatty acids. As a method to lose weight, the conventional recommendations of caloric restriction, less intake of saturated fatty acids and more physical activity should be preferred to the Montignac diet.