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| The great strength of the study, the leeway the subjects had in terms of what and how much they would eat would, is also an important weakness because it would require a much more thorough monitoring of their food intake to appropriately interpret all the results of this pilot study. |
The authors of a recent 10-week human study on 'time-restricted feeding', scientists from the University of Surrey, do now suggest that the changes you have to make to your dietary template don't have to be as extensive as the classic 16h/8h or 18h/6h fasting/feeding windows.
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- The subjects in the intervention group were required to delay their breakfast by 90 minutes and have their dinner 90 minutes earlier, while
- the subjects in the control group simply ate their meals as they would normally do.
So, the diets didn't change? Not to an appreciable extent. Yes, the subjects in the intervention group ate less, but the difference is relatively small (see Figure 1) and 3/7 reported eating ‘less healthily’ via increased consumption of convenience foods (and snacks) due to time restrictions on food preparation. In view of the fact that the only other reported dietary change was a reduced consumption of alcohol in 5 out of 7 subjects in the intervention group, it is not clear what exactly triggered the tissue-specific weight reduction (=pure fat loss) the Antoni et al. observed.
The researchers themselves speculate that the reduction in energy intake was mainly a result of "reduced evening social opportunities", but ascribe the overall effect to a better (=metabolically favorable) alignment of food intake and circadian rhythm.
Speaking of alignment... I think that it's important to point out that the subjects actually restricted their 'feeding window' more drastically than the scientists had intended. Instead of the planned 180 minutes, the subjects cut the time in which they allowed themselves to eat by 235 minutes; thus ending up with a time-restricted feeding scheme that mirrors the classic 16/8h.
The allegedly "modest contraction of the eating window" the scientists obviously think of as one of the benefits of their protocol was thus at least no more modest than that of a classic IF regimen and not that far off of what the scientists label an "extreme temporal restriction".
In the actual study, the subjects reduced the size of their feeding window even more, i.e. from 743 +/- 32 minutes to 517 +/- 22 minutes per day (that's - 235 minutes! | P < 0·001; n = 7 ). A simple change that constitutes a 30% reduction compared to their habitual eating habits but differed from the feeding window of the control group (~660 min) by only 16%.The researchers themselves speculate that the reduction in energy intake was mainly a result of "reduced evening social opportunities", but ascribe the overall effect to a better (=metabolically favorable) alignment of food intake and circadian rhythm.
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| The real (vs. planned) feeding window of the study at hand was significantly less "moderate" that the scientists had planned and came very close to the allegedly extreme feeding windows of classic intermittent fasting. |
The allegedly "modest contraction of the eating window" the scientists obviously think of as one of the benefits of their protocol was thus at least no more modest than that of a classic IF regimen and not that far off of what the scientists label an "extreme temporal restriction".
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| Figure 1: The reduction in daily energy intake (large graph) could well explain the reduction in body fat (a) and marginal improvement in glucose (b), but it doesn't explain either why the reduction in body fat (a) occurred in the absence of changes in body weight or the unexpected increase in glucose in the control group (Antoni 2018). |
- reduced the subjective measures of appetite and subsequently decreased the food and snack intake (especially in the evenings) in 4 out of 7 subjects in the intervention group,
- significantly reduced the subjects' initially high body fat levels from 36% to 34% in the absence of changes in body weight (the authors point out that "the consistency of the observed reduction in adiposity [...] suggests [...] a true treatment effect"),
- normalized the blood glucose levels which were persistently elevated among the participants in the control group and induced modest changes in other metabolic disease risk markers, including trends in favor of a reduction in LDL-cholesterol,
- left the distribution of energy intake unaffected, meaning that it did not trigger increases or decreases in the amount of energy consumed early, in the middle, and late in the day.
Against that background, it is only mildly surprising that 57% of the subjects (remember that's 4 out of only 7 people *rofl*) said that they could not have maintained the new meal times beyond the prescribed 10 weeks. So, even if the results can be confirmed in future larger-scale studies I am not very optimistic as far as the idea of solving our problems with obesity and metabolic syndrome by reducing people's feeding windows - even if the reductions are small and (in theory) easy to implement.
Why do we see fat loss in the first place?
The study was neither intended nor designed to answer this question, but the scien-tists seem to believe that the mechanism for the health benefits of the ~4.5h reduced feeding window was a combination of (a) an improved alignment of energy intake and the endogenous circadian cycle, (b) additional benefits due to an increased length of the daily fast (Longo 2014), and the (probably related) reduction in energy intake that has been observed in previous, often signi-ficantly more restrictive / invasive time-restricted feeding studies, as well (LeCheminant 2013; Gill 2015; Tinsley 2017).
Bottom line: The last-mentioned resistance of the majority of the subjects to actually implement this small, but effective way of time-restricted feeding in the long run is only one of several factors that warrant a careful evaluation of the reliability and practical relevance of the study results.The study was neither intended nor designed to answer this question, but the scien-tists seem to believe that the mechanism for the health benefits of the ~4.5h reduced feeding window was a combination of (a) an improved alignment of energy intake and the endogenous circadian cycle, (b) additional benefits due to an increased length of the daily fast (Longo 2014), and the (probably related) reduction in energy intake that has been observed in previous, often signi-ficantly more restrictive / invasive time-restricted feeding studies, as well (LeCheminant 2013; Gill 2015; Tinsley 2017).
Even though the title of the press release has it right and "[c]hanges in breakfast and dinner timings can reduce body fat", it is by no means clear that an appropriately powered follow-up study conducted with a less diverse group of subjects (body fat levels ranged from ~45% to ~22% in both groups and there was one male subject in the intervention group in an otherwise exclusively female study population) will also find significant changes in body fat % and glucose levels and/or detect significant reductions in the hitherto only non-significantly reduced levels of LDL.
A larger-scale study with a more rigorous dietary control (in the study at hand even subjects who didn't return all their food logs were included in the final analysis) could also help us get to the bottom of the paradoxical lack of weight loss that would imply that the subjects lost fat and gained muscle mass and the pronounced increase in fasting glucose in the control group, which is the actual reason for the significant difference in glucose levels between control and treatment group.
It's not clear when the corresponding study will be available. What is clear, however, is that the authors "are now going to use these preliminary findings to design larger, more comprehensive studies of time-restricted feeding" (from the press release) - and guess what: the SuppVersity is where you'll read about it first... in the meantime, enjoy some N=1 self-experimentation ;-) | Comment!
- Antoni, Rona, et al. "A pilot feasibility study exploring the effects of a moderate time-restricted feeding intervention on energy intake, adiposity and metabolic physiology in free-living humans." Journal of Nutritional Science. (2018).
- Gill, Shubhroz, and Satchidananda Panda. "A smartphone app reveals erratic diurnal eating patterns in humans that can be modulated for health benefits." Cell metabolism 22.5 (2015): 789-798.
- LeCheminant, James D., et al. "Restricting night-time eating reduces daily energy intake in healthy young men: a short-term cross-over study." British journal of nutrition 110.11 (2013): 2108-2113.
- Longo, Valter D., and Mark P. Mattson. "Fasting: molecular mechanisms and clinical applications." Cell metabolism 19.2 (2014): 181-192.
- Tinsley, Grant M., et al. "Time-restricted feeding in young men performing resistance training: A randomized controlled trial." European journal of sport science 17.2 (2017): 200-207.