Compared with nibbling, neither gorging nor a morning fast affect short-term energy balance in obese patients in a chamber calorimeter.

OBJECTIVE

To test if a diet of 4.2 MJ/24 h as six isocaloric meals would result in a lower subsequent energy intake, or greater energy output than (a) 4.2 MJ/24 h as two isocaloric meals or (b) a morning fast followed by free access to food.

DESIGN

Subjects were confined to the Metabolic Unit from 19:00 h on day 1 to 09:30 h on day 6. Each day they had a fixed diet providing 4.2 MJ with three pairs of meal patterns which were offered in random sequence. They were: six meals vs two meals without access to additional foods (6vs2), or six meals vs 2 meals with access to additional food (6+vs2+), or six meals vs four meals (6+vsAMFAST). In the AMFAST condition the first two meals of the day were omitted to reduce daily intake to 2.8 MJ and to create a morning fast, but additional food was accessible thereafter. Patients were confined in the chamber calorimeter from 19:00 h on day 2 until 09:00 h on day 4, and then from 19:00 h on day 4 to 09:00 h on day 6. The order in which each meal pattern was offered was balanced over time.

MEASUREMENTS

Energy expenditure (chamber calorimetry), spontaneous activity (video) and energy intake (where additional foods were available) during the final 24 h of each dietary component.

SUBJECTS

Ten (6vs2), eight (6+vs2+) and eight (6+vsAMFAST) women were recruited who had a BMI of greater than 25 kg/m2.

RESULTS

From experiment 6vs2 the difference between energy expenditure with six meals (10.00 MJ) and two meals (9.96 MJ) was not significant (P=0.88). Energy expenditure between 23:00 h and 08:00 h ('night') was, however, significantly higher (P=0.02) with two meals (9.12 MJ/24 h) compared with six meals (8.34 MJ/24 h). The pattern of spontaneous physical activity did not differ significantly between these two meal patterns (P>0.05). Total energy intake was affected by neither meal frequency in experiment 6+vs2+ (10.75 MJ with six, 11.08 MJ with two; P=0.58) nor a morning fast in experiment 6+vsAMFAST (8.55 MJ/24 h with six, 7.60 MJ with AMFAST; P=0.40). The total diet of subjects who had a morning fast tended to have a lower percentage of total energy from carbohydrate (40%) than when they had six meals per 24 h (49%) (P=0.05). Subsequent energy balance was affected by neither meal frequency (6vs2; P=0.88, 6+vs2+; P=0.50) nor a morning fast (P=0.18).

CONCLUSIONS

In the short term, meal frequency and a period of fasting have no major impact on energy intake or expenditure but energy expenditure is delayed with a lower meal frequency compared with a higher meal frequency. This might be attributed to the thermogenic effect of food continuing into the night when a later, larger meal is given. A morning fast resulted in a diet which tended to have a lower percentage of energy from carbohydrate than with no fast.