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| When you're alternate day fasting your plate will look as empty or almost as empty as this every other day. |
In the scientific literature, the term "intermittent fasting" is used inconsistently. Often, however, it refers to an every-other-day-fasting-regimen, in which you eat on day A and don't eat (or eat almost nothing) on day B. This was also the case of Juliet D. Gotthardt's latest study, where "intermittent fasting" therefore meant eating an ad-libitum diet (eat as much as you want and when you want) on day 1 and starving on day 2 (Gotthardt. 2015). What the scientists from the
State University of New Jersey already knew was that this would protect male C57BL/6 from weight gain, what they didn't know and wanted to find out was whether the macronutrient content of the diet would modulate this effect..
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Accordingly, 64 mice were purchased from The Jack son Laboratory (Bar Harbor, ME, USA) and fattened up on an ad libitum, high fat diet (HFD; 4.73 kcal/g, 45% fat, 20% protein, 35% carbohydrate; D12451) for 8 weeks (note: this means all mice were already overweight, when the actual "intermittent fasting" began).
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| Figure 1: Energy content (kcal/100g) of the high and low fat diets the rodents were fed over the course of the 4-week experimental phase either ad-libitum or on an every-other-day-fasting regimen (Gotthardt. 2015). |
The mice were then equally divided by bodyweight and transitioned to one of four experimental groups:
- HFD - an ad libitum high fat diet
- IMF-HFD - an every-other-day fasting high fat diet
- LFD - ad libitum low fat diet
- IMF-LFD - an every-other-day fasting low fat diet
The mice in the IMF group were food deprived every other 24-hour period beginning at 9:00 AM (fasting day), 2 hours into the light cycle. On fasting days, all animals were weighed, food in take was recorded, cages were changed.
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| The alternative-day fasting induced a sign. reduction in food intake. |
What's the mechanism, here? As the food intake data on the left shows, the effect is at least partly mediated by a significant reduction in food intake. In other words, just as it has been observed in humans, there's no full compensation for the lack of energy intake on the fasting day. This is intriguing, because the increase in norepinephrine (NE | 50-60%) in the hypothalamus and the expression of NPY in the arcuate nucleus ( 65–75%) in both IMF groups would suggest that the rodents were not immune to the regular compensatory stress response to fasting.
After four weeks, the mice on the IMF-HFD ( 13%) and IMF-LFD ( 18%) had significantly lower body weights than those who continued on the HFD.
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| Figure 2: Body composition as assessed by EchoMRI in all groups at the end of 4 weeks of the diet intervention. Data are represented as means SEM. A: Fat mass (g). B: Lean body mass (g). *** indicates difference from HFD (P .001); * indicates difference (P < .05) from HFD; $ indicates difference (P < .05) from IMF-HFD (Gotthardt. 2015). |
As you can see in
Figure 2, the body fat of the mice was also significantly reduced - in all four groups by 40–52%. The significant lean mass increases I hinted at in the headline, however, were observed only in the intermediate fasting low fat diet group (IMF-LFD | 12–13%).
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| Figure 3: Oral glucose tolerance tests in all groups at the end of 4 weeks of the diet intervention. Data are represented as means SEM. A: Blood glucose (mg/dl) response to an oral bolus of glucose (2 g/kg) over 180 minutes. Values for IMF-HFD and LFD overlap. B: Area under the curve (AUC) of glucose tolerance test (Gotthardt. 2015). |
As
Figure 3 goes to show you, the low fat alternative-day fasting (IMF-LFD) group also had the highest oral glucose tolerance with almost no increase in glucose during the glucose tolerance test. Whether that's due to the increase in lean mass is yet as questionable due to the mere extent of the reduction in glucose AUC. If the latter was simply due to an increase in muscle mass, you'd furthermore expect that the insulin levels of the IMF-LFD rats would have been lower as well. Insulin, as well as leptin, however, decreased to a similar extent in all treatment groups (compared to the high fat diet, obviously).
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| Figure 4: Cause and consequences of the low-fat exclusive increase in dopamine (DA) in the anterior hypo-thalamus of the fasted rodents are two things researchers don't yet fully understand (Gotthardt. 2015). |
What do we make of this study? While I have to admit that the headline suggests that the lean mass increase was a result of the reduced fat intake, a hypothesis that would explain why there should be a mechanistic link between
alternate-day-fasting, low fat dieting and increases in lean mass is not in sight. That's disappointing, but with the low-fat exclusive significant increase in anterior hypothalamus dopamine expression (see
Figure 4) and the previously mentioned extreme increase in glucose sensitivity (cf.
Figure 3), Gotthardt's study provides starting points for future research and it confirms that alternate day fasting does not cost you muscle mass... in this respect
previous human trials showed similar results, by the way.
One thing you have to keep in mind is that the high fat diet (HFD) in the study at hand was after high in fat, but it was not low in carbohydrates. Accordingly, it would be really interesting to see, how a true low-carb diet would have affected rodents - and obviously humans, of whom a 2013 human study by Klempel et al. that used a similarly messed up "high fat diet" (45% fat, 40% carbs, 15% protein) shows that they lose the same amount of weight and body fat on "high" and "low fat" diets. Whether that's a species-dependent difference to the study at hand or a result of "too much fat" in Klempel's diet (25% fat is significantly more than in the Gotthardt study) will yet have to be determined in future studies; studies that will hopefully also use an actual high fat alternate-day-fasting regimen instead of the the high fat + high carb Western diet clone that was used in both, the study at hand, and the previously cited human study by Klempel et al. |
Comment!
References:
- Gotthardt, Juliet D., et al. "Intermittent Fasting Promotes Fat Loss with Lean Mass Retention, Increased Hypothalamic Norepinephrine Content, and Increased Neuropeptide Y Gene Expression in Diet-Induced Obese Male Mice." Endocrinology (2015): en-2015.
- Klempel, Monica C., Cynthia M. Kroeger, and Krista A. Varady. "Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet." Metabolism 62.1 (2013): 137-143.
