OBJECTIVE To examine the effect of overfeeding isoenergetic diets enriched in 1-monoglyceride or triglyceride on nutrient oxidation and appetite throughout the day that it was given and the subsequent day's food and energy intake. METHODS Six men [mean (s.d.) weight; 76.89 (7.00) kg, height; 1.77 (0.05) m, age; 26.4 (6.0) y], were each studied twice in a 3 d protocol. On day 1 (maintenance day) they were fed a medium fat (MF) maintenance diet (MF: 40% fat, 47% carbohydrate and 13% protein by energy) calculated at 1.6 x resting metabolic rate (RMR). Subjects entered the calorimeter at 06.30 on day 2 for 49.5 h. On day 2 (manipulation day) subjects consumed a MF diet at 1.6 x RMR with an additional 0.45 x RMR as either 1-monoglyceride or triglyceride. On day 3 (outcome day), subjects had ad libitum access to isoenergetic, isoenergetically dense MF (40 :47: 13, 550 kJ/ 100 g) foods. Subjective hunger and satiety were tracked hourly, during waking hours throughout days 1-3. RESULTS There was no significant effect of diet on nutrient oxidation or balance either during day 2 (manipulation day) or day 3 (outcome day), fat oxidation was similar on both diets. Subjective hunger was not affected by diet on either day with mean values of 34.3 and 35.0 mm (SED 5.2) on manipulation day (day 2) and outcome day (day 3), 35.3 and 40.8 mm (SED 5.2) on the 1 -monoglyceride or triglyceride diets respectively. Day 3 food and energy intake were unaffected by the previous day's dietary treatment, with mean intakes of 15.9 and 15.6 MJ (SED 1.07) on the 1-monoglyceride or triglyceride treatments, respectively. CONCLUSIONS This study suggests that when 1-monoglyceride is covertly incorporated into a diet at unusually high levels, it behaves in a manner that is very similar to triglyceride, in its effects on appetite, feeding behaviour and net nutrient balance.