Letter to the Editor from Melanson et al (second letter): “Twice as High Diet-Induced Thermogenesis After Breakfast vs Dinner on High-Calorie as Well as Low-Calorie Meals”

To the editor:

We thank Richter and Oltmanns for responding to the concerns raised in our previous letter (1-3). However, we feel that their response did not sufficiently clarify the underlying issues that we raised.

First, we raised a concern that using the pre-dinner resting metabolic rate (RMR) as the baseline to measure the diet-induced thermogenesis (DIT) effect at dinner created an artificially high baseline because of the lingering effect of DIT from the lunch consumed 4 hrs prior. Richter and Oltmanns contend that minimizing the fasting periods between meals “created equal thermogenic conditions prior to dinner.” This does not, however, address the concern we raised. DIT is defined as the increase in energy expenditure (EE) above RMR; thus, we maintain our contention that using the pre-dinner RMR is incorrect and leads to a spurious result. Richter and Oltmanns attempt to defend their approach based on a previous study that used a similar approach to calculate the DIT of dinner (4). However, in our assessment, that study suffered from the same methodological flaw. In that study, the difference between early postprandial EE measured in the morning vs the evening (1.24 ± 0.04 vs 1.18 ± 0.03 kcal/min) was explained almost entirely by the differences in pre-meal EE (1.00 ± 0.04 vs 1.05 ± 0.04 kcal/min) (4). Furthermore, the duration of fasting in that study between meals was 8 hours. The World Health Organization suggests that basal metabolic rate (BMR) be measured after at least a 10- to 12-hour fast (5). Although BMR is more strictly defined than RMR, we suggest that to a longer fasting period is advised for DIT measurements to ensure that the effects of previously consumed food and beverages be removed, and that a true resting state has been reestablished.

Second, we suggested that measuring DIT for only 3 hours after each meal incompletely characterized the DIT response which extends at least 6 hours after consumption of a meal. In their response, Richer and Oltmanns suggest that the patterns in response for the first 3 hrous indicate that this would not have occurred. Further, they contend that extending the measurement period would not have been practical. In response, we argue that robustness in scientific approach should be a more important consideration.

Third, to support their findings, Richter and Oltmanns reference a study where obese women were prescribed isocaloric diets where a larger proportion of the daily intake was to be consumed either at breakfast or dinner; over 12 weeks, the breakfast group lost 8.7 kg more body weight than the dinner group (6). However, no metabolic measurements were made in that study, so to contend this supports their findings is misleading—there is no evidence from that study that differences in weight lost were attributable to differences in DIT at the breakfast or dinner meals. In the study by Jakubowitz et al (6), although there were no significant differences in self-reported intake, it is well known that self-report measures are fraught with error. Indeed the magnitude of difference in weight loss is far greater that what would be expected based on the 25 kcal difference in DIT reported by Richter and Oltmann’s study; clearly, the large differences in weight loss in that study were primarily (if not entirely) due to differences in energy intake.

Richter and Oltmanns’s study is timely and important. However, to answer this question about whether there is a circadian pattern to DIT requires careful consideration of study design. Unfortunately, using metabolic carts to answer this question has several limitations, as Richter and Oltmanns correctly suggested in their response. In light of these limitations, we contend that this question would be better addressed using whole-room calorimetry to study the integrated DIT effects over 24 hours. As an example, in a previous study in Dr. Melanson’s lab, we showed that there was no difference in the 24-hour EE when participants consumed 3 meals vs 6 meals per day (7). Prior to that study, the popular dogma that had become entrenched was that consuming smaller more frequent meals during the day would have a greater effect on DIT and this would be better for weight management.

In closing, we defend our position that the title and the interpretation of the data inflates the metabolic differences between the 2 conditions; the magnitude of difference, even if real, is trivial. Unfortunately, the press releases relate to this study focused on the conclusion that post-meal metabolism is double after the breakfast than the dinner meal. We remain concerned that this conclusion is misleading to the general public.

Disclosure Summary: Dr. Melanson is supported by resources from the Geriatric Research, Education, and the Clinical Center at the Denver VA Medical Center. The contents do not represent the views of the U.S. Department of Veterans Affairs or the United States Government.

Glossary

Abbreviations

BMR

basal metabolic rate

DIT

diet-induced thermogenesis

EE

energy expenditure

RMR

resting metabolic rate