I like to make fun of recommendations to avoid evening/nighttime meals for reasons of metabolism, as they typically avoid the realities of 24-hour energy accrual and expenditure. It strikes me as more likely that in the instances where a morning calorie emphasis seem to help, the praise is likely owed to various aspects of breakfast reducing hunger throughout the day. “Magic Metabolism,” on the other hand, isn’t high on my list of potential variables.

But I’ll admit when it seems like I’m wrong, and Morris’ paper “The Human Circadian System Has a Dominating Role in Causing the Morning/Evening Difference in Diet-Induced Thermogenesis” looked like it had some mind-changing potential.

The paper posits that there is a meal-dependent metabolic effect associated with morning food and provides a likely mechanism in Circadian Rhythm. What we call "Circadian Rhythm" is a host of connected processes that almost certainly evolved to help us deal with day/night cycles. The processes occur in almost every tissue. Included in those tissues are gastric organs and nerves, and in the processes are aspects of metabolism.

The current study’s specific culprit was Diet-Induced Thermogenesis (DIT). Probably better known as the Thermic Effect of Food (TEF) or Specific Dynamic Action (SDA), DIT is one of the three primary prongs of total metabolism, the other two being the resting metabolic rate and energy expended as a part of physical activity. DIT is basically the metabolic “cost” of digesting and distributing nutrients, with an extremely rough calculation of its effects coming in at about 10% of caloric intake. Breaking it down by macronutrient, DIT can be as low as 5% for fats and as high as 35% for protein.

RELATED: Adaptive Thermogenesis — The Beauty and the Beast of The Biggest Loser

If DIT is in fact a variable we can control through a choice on whether/how to distribute our calories across the day, it could be the example of magic metabolism claimed in so many fitness tip listicles. Provided of course, the effect’s magnitude was meaningful.


Interestingly, the study revisited a 1993 paper (Romon, cited below) that found DIT varying by meal-timing. Essentially, the earlier paper found that breakfast has an increased “calorie cost.” This follow-up aimed to refine the earlier study’s results and to look more at the effects of shift work. For applicability’s sake, I’m going to ignore the shift-work facets; the paper is available for free online if you’d like to dig into these aspects.

Morris’ research team (a Boston-based crew comprised of folks from Harvard and/or Brigham and Women’s Hospital) created a well-controlled study of 13 healthy individuals ranging in age from 20 to 49 years of age. Each participant received identical meals at 8 AM and 8 PM, as well as pre- and post-meal measurements via indirect calorimetry that measured breath composition to determine metabolic rates. If you’re familiar with my earlier article on The Biggest Loser, this study wouldn’t fall victim to the same uncertainties as the TBL paper.

Just as the 1993 study found, there Boston team recorded a measurable Circadian-related effect: DIT was higher after breakfast than it was after dinner. In this instance, the subjects’ respective DIT rates were ramping up more in response to the breakfast than they were the dinners by a difference of about 44%.

MORE: Mixing Macros — How to Use Macronutrient Combinations to Improve Your Physique

Now how does that 44% translate into absolute terms? Not quite as impressively. The researchers concluded that DIT was about 0.11 kcal/minute greater during morning meals, i.e., over the 90 minute observation span morning meals burned an extra 10 calories. Even if we hypothesize that this effect might stretch out over a longer period of time (and other studies suggest it actually peaks after one hour), doubling the period to three hours only offers about 20 additional calories burned after breakfast. It’s hard to see how a difference so small (less than one percent of daily caloric intake for the general elitefts readership) can offer much for the lifting community.

Recalling the 1993 study, this is a great example of how aspects of research seem to come and go in cycles. Though the ’93 study didn’t break things down into calories, some quick back-of-the-envelope math (or back-of-the-business card, in my case) shows there was a roughly 30 kcal absolute difference in DIT between meals occurring and 9:00 AM and 1:00 AM, as measured over a six-hour period. It’s easy to see why this result didn’t warrant a great deal of replication.

As a dietary intervention, this study doesn’t give us much to go on—the kcal difference in DIT is so small it could easily be lost in rounding. As a lifestyle intervention it’s conceivable that this small difference could add up over time and make for a meaningful change, provided dietary consistency in all aspects of consumption.  Getting back to the introduction, whatever short-term weight loss results can be associated with shifting calorie intake to the morning is probably associated with satiety/hunger aspects and not with metabolic changes.


  • Morris, C. J., Garcia, J. I., Myers, S., Yang, J. N., Trienekens, N. and Scheer, F. A.J.L. (2015), The Human Circadian System Has a Dominating Role in Causing the Morning/Evening Difference in Diet-Induced Thermogenesis. Obesity, 23: 2053–2058. doi: 10.1002/oby.21189
  • Romon M, Edme J, Boulenguez C, Lescroart J, Frimat P. Circadian variation of diet-induced thermogenesis. Am J Clin Nutr 1993;57:476-480.