Intermittent Fasting Increases 24h Energy Expenditure, But Skipping Breakfast Linked to Reduced Metabolic Flexibility

"To eat or not to eat breakfast?" Unfortunately, the scientists geared their research pretty much to this question.

Alright, you all have read my recent Facebook news post about the reduced energy expenditure students reported in a hitherto unpublished paper. Those of you who have (rightly) pointed out that this was at best preliminary evidence (which is, by the way, exactly what I pointed out, as well), will now feel vindicated: Scientists from the German University of Hohenheim report that "when compared with the 3-meal control, 24-h energy expenditure was higher" with a meal-skipping regimen that had a lot of similarity to what many of you will practice and label "intermittent fasting".
The researchers' main interest was yet not to investigate the effects of "intermittent fasting", but to find out whether the timing of meal skipping "impacts these risks by affecting circadian regulation of energy balance, glucose metabolism, and postprandial inflammatory responses" (Nas 2017).

Figure 1: Schematic overview of the study protocol; note: the interventions were isocaloric and had identical nutrient compositions. *Randomly assigned. BSD, breakfast skipping day; DSD, dinner skipping day (Nas 2017)

To this ends, the researchers had 17 participants [body mass index (in kg/m²): 23.7 6 4.6] participate in a randomized crossover trial comprising three isocaloric 24-h interventions (55%, 30%, and 15% carbohydrate, fat, and protein, respectively), to compare the metabolic effects of

• breakfast skipping day (BSD) with the first meal at 1 PM and the last at 7 PM, and
• dinner skipping day (DSD) with the first meal at 7 AM and the last meal at 1 PM

to a conventional 3-meal-structure (smaller meals at 1 AM, 1 PM, 7 PM - total energy and macronutrient intake were identical) on a control day (control).IF can also help with weight loss in the obese: A recent study also confirms the weight loss benefits of time-restricted feeding showing that obese subjects lose 5% weight, and 4% body fat within 12 weeks when they eat only within an 8h window from 10am-6pm (Gabel 2017 | as discussed in the SuppVersity Facebook News).In contrast to the previously mentioned graduate research, the scientists offer some insights into how they determined the energy expenditure and the use of a respiration chamber is an important plus of the study.

Figure 2: Fat (A) and carbohydrate (B) oxidation, as well as total energy expenditure (C) during control (light blue), breakfast skipping (pink) and dinner skipping (dark blue) scenario (Nas 2017).

In fact, there's hardly a better way to reliably assess one's subjects energy and macronutrient balance; in conjunction with blood analyses that determined the postprandial glucose, insulin, and inflammatory responses in leukocytes as well as 24-h glycemia and insulin secretion, Nas et al. produced quite a comprehensive dataset which shows the expected null effect on the AUC of the "hunger hormone" glucagon and its opposing peaks and troughs (see Figure 3, left).

Figure 3: While the Ghrelin pattern was reversed, the AUC, i.e. the total ghrelin release did not differ between breakfast and dinner skipping. Furthermore, a closer look at the sign. increased 4h post levels of IL-6 and interferon gamma on the right-hand side of the graph lets us speculate that the high variance could be a result of the previously discussed influence of breakfast(-skipping) habits w/ habitual breakfast skippers seeing lower inflammatory effects (2017)

As well, as the following more surprising effects, the scientists describe in their latest paper in the prestigious "American Journal of Clinical Nutrition" (Nas. 2017):

• A recent study by Savage, et al. shows conflicting results. In this graduate research, an allegedly likewise isocaloric intermittent fasting diet sign. reduced the energy expenditure (learn more)

  when compared with the 3-meal control, 24-h energy expenditure was higher on both skipping days (BSD: +41 kcal/d; DSD: +91 kcal/d; both P < 0.01), 
• fat oxidation increased, as it was expected in view of the empty glycogen stores and high AMPK levels in the AM on the breakfast skipping diet (BSD), only (+16 g/d; P < 0.001 | don't forget that this won't translate to increased fat loss if the energy balance is identical)
• spontaneous physical activity, 24-h glycemia, and 24-h insulin secretion did not differ between intervention days

So far, so good! While the formerly cited results suggest that it doesn't make a difference whether you skip breakfast or dinner, as long as you skip it (=fast intermittently), the blood analyses spoke a different language. In particular, ...

• the postprandial homeostasis assessment index (+54%) and glucose concentrations after lunch (+46%) were significantly higher on the BSD than on the DSD (both P < 0.05), and 
• a longer fasting period with breakfast skipping also increased the inflammatory potential of peripheral blood cells after lunch.