To determine the magnitude of the thermogenic response to a massive long-term overfeeding, an energy-balance study was carried out in nine lean, young Cameroonian men participating in a traditional fattening session: the Guru Walla. Food intake, body weight, body composition, activity, and metabolic rates were recorded during a 10-d baseline period and over the 61-65 d of fattening. Total energy expenditure (TEE) was measured by using doubly labeled water during the baseline period and the final 10 d of Guru Walla. Cumulative overfeeding consisted of 955 +/- 252 MJ (chi +/- SD) mainly as carbohydrate. Body-weight increase was 17 +/- 4 kg, 64-75% as fat. Metabolic rates increased but TEE did not. However, when accounting for the reduction in physical activity, substantial thermogenesis was observed but its amplitude was not greater than that observed under less extreme carbohydrate-overfeeding conditions. If luxuskonsumption does exist, it is not related to the magnitude of the cumulative overfeeding.