"Our data show that the time of day of food intake makes a difference in humans’ energy expenditure and metabolic responses to meals. In terms of DIT (diet induced thermogenesis), breakfast has a more efficient energetic value for our body than dinner. We clearly show that DIT is 2.5 times higher after breakfast than after dinner. The question arises as to which mechanisms may mediate this effect of reduced DIT in the evening. 2 components of DIT: obligatory and facultative DIT. Obligatory DIT relates to the stimulation of energy-requiring processes during the postprandial period for the digestion, absorption, and processing of nutrients. A certain amount of energy gained from food is consumed for the intestinal absorption of nutrients, the initial steps of their metabolism, and the storage of the absorbed but not immediately oxidized nutrients because these processes require the hydrolysis of adenosine triphosphate. Because various functions of the gastrointestinal tract exhibit circadian activities, it seems likely that the obligatory component of the DIT is increased in the morning. One explanation for the higher rate of DIT in the morning may be rapid morning gastric emptying. The absorption of macronutrients is also subject to circadian regulation, with evidence from rodent experiments for increased intestinal absorption of peptides, lipids, and carbohydrates at the beginning of the active phase compared with the end of the active phase. In contrast to the obligatory component of DIT, facultative DIT is mainly stimulated by the sympathetic nervous system. Thermic effects of intravenously infused glucose can be suppressed by β-adrenergic antagonists. It is conceivable that this component may be elevated in the morning because epinephrine, which increases the metabolic rate and the respiratory quotient, exhibits higher concentrations during this time of day. In this context, our data show a decrease in hypothalamus–pituitary–adrenal axis activity as reflected by circulating cortisol and ACTH concentrations from morning to evening, which is consistent with data in the literature.”
If you’ve followed me long enough, you know I will counter this study with the question of how this impacts total energy expenditure. As far as I know, there aren’t good studies on the impact that meal timing has on total energy expenditure. I do have anecdotal experience that suggests it does have an impact though. Ever since I got into bodybuilding, I’ve preferred consuming most of my daily calories in the morning and afternoon instead of nighttime. On the few occasions where, due to extraneous circumstances, I had to consume the majority of my calories during the nighttime—during a phase where I was trying to maintain my weight consuming a daily caloric intake right at the ceiling of my buffer range—I would notice a spike in bodyweight the next morning. Now, I know what you’re thinking. Couldn’t this just be due to extra food in your GI tract or water retention? Well, I would return to my usual meal timing regimen (consuming most of my daily calories in the morning and afternoon instead of nighttime) the next couple days…and the extra weight would not come off.
Let me be clear. The hierarchy of nutrition is still: kcals >>>> macros >>> food sources >> timing > everything else.
At most, I think this phenomenon of meal timing exerting an impact on total energy expenditure would result in only couple hundred calories of difference, with it probably scaling somewhat directly with the amount of calories as well. This will matter more for those who are trying to get really lean. Many males and females trying to get really lean will need to limit daily caloric intake to 1500-1800 and 1000-1300, respectively. When calories are this low, even a mere 100-200 kcals will feel significant.
Also, this effect is likely blunted if you train in the PM—the body is better at assimilating nutrients peri-workout. And for those who train in the PM, I would never recommend consuming all meals in the AM and early afternoon.