A 59-year-old man who had always been lean was submitted to overfeeding for two months in preparation for a 3-week expedition through Greenland, during which a considerable negative energy balance was expected. The overfeeding protocol consisted of an estimated energy surplus of 2000 kJ per day and this induced body weight and fat gains of 4.7 and 3.6 kg, respectively. Whole-body indirect calorimetry measurements following 4 and 8 weeks of overfeeding showed that there was no change in the subject's daily energy expenditure. Ad libitum energy intake measured during a buffet-type meal was substantially increased during overfeeding. As expected, the expedition induced a negative energy balance which reduced body weight below the pre-overfeeding level. Daily energy expenditure measured 12 days after the expedition, when the subject had recovered his initial body weight, was decreased by 1.4 MJ/day. The increase in ad libitum energy intake observed during the pre-expedition overfeeding persisted after the expedition. These adaptations tended to persist three weeks and four months after the end of the expedition. These results suggest that both energy expenditure and intake were modified after the expedition to prevent a subsequent body energy deficit.