The authors' interpretation of negative metabolic changes resulting from the irregular timing of food intake raises several questions that are extremely important to clinical nutrition today. First, what are the characteristics of persons who eat irregularly, and what proportion of the general population do they make up? The answers to these questions are not yet known, and Farshchi et al (8, 10) did not report the usual eating patterns of their subjects. Second, if irregular eating frequency is indeed prevalent, how much does that irregular frequency contribute to obesity compared with other eating behaviors that may also influence energy intake (11)? Third, is the specific time of day that food is eaten important? With respect to this question, the potential for breakfast food consumption to reduce total daily intake (12) and the capacity for smaller evening meals to aid in weight loss (13) have both drawn renewed interest of late.
A major hurdle to overcome before these 3 important questions can be answered is that of the poor validity of energy intake records, particularly those from overweight persons (14, 15). This problem is illustrated nicely by carefully examining the energy intakes reported by Farshchi et al for obese (8) and lean (10) women: these intakes were approximately the same at baseline (8.37 MJ/d in the lean women and 8.47 MJ/d in the obese women), even though the obese women clearly had higher energy requirements (15, 16). A comparison of those reported intakes with the energy requirements for women of average height (1.65 m) who are in the same body mass index range and who have a low physical activity level (1.4–1.6; see Table 5-30 in reference 16) shows that the average underreporting by the obese women may have been 22–27%. Farshchi et al suggest that the obese women may have consistently underreported their energy intakes in both phases of the study. However, the degree of underreporting is known to increase with energy requirements (15, 17) and, possibly, with eating frequency (7). Thus, the implication is that the effect of an irregular eating frequency on ad libitum energy intake may have been underestimated by Farshchi et al (8, 10), particularly in the obese women, because there was a small increase in energy intake with increased eating frequency during the irregular eating protocol. In addition, whereas irregular eating frequency was associated with a significant increase in energy intake in the obese but not the lean women studied earlier, the group differences in reported energy intakes between the 2 eating regimens were similar (0.40 MJ/d in the lean women and 0.34 MJ/d in the obese women). The significance of the findings in one study but not of those in the other may have been due to the fact that the reported energy intake variances differed between the 2 samples, which reflects the difficulty of obtaining consistently valid self-reports of energy intakes. This problem is not by any means unique to the studies of Farshchi et al but instead is found among nearly all studies in which free-living energy intakes are measured (18).
Two last issues raised by Farshchi et al (8) are whether the effects on metabolism of eating regularity are independent of or mediated by energy intake, and, if there are independent effects, what mechanisms contribute to these effects.
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