Intermittent Fasting + Resistance Training: 1st 8-Wk Human Study to Provide Modest Evidence of Benefits During Cuts

You have heard me argue based on theoretical considerations before that "intermittent fasting" is probably best used during cuts, not during "bulks" - the results of the study at hand, even though they may not show stat. sign. inter-group differences, support this suggestion.
You will be surprised, but the latest article Tinsley et al. (2016) published in the European Journal of Sport Science is indeed the very first study to investigate the effects of time-restricted feeding (TRF) "on nutrient intake, body composition, and strength" when they are combined with a standardized resistance training regimen.

That's too good to be true? Well, wait until you've learned more about the methodology and results, but it is indeed cool that someone finally studied the effects of what the majority of people think of if you talk about "intermittent fasting" (that's in contrast to scientists who often think of alternative day fasting when they hear "intermittent fasting, the benefits of which I have discussed only recently, read more).
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The subjects were recreationally active, but probably less active than the average SuppVersity reader (because they hadn't been following a consistent RT programme over the previous three months). The study was a randomized controlled 8-week trial that did or didn't involve time-restricted feeding (TRF, 4h eating, 20h fasting window) and identical resistance training (RT) programs:
"The RT programme for both groups consisted of three nonconsecutive days per week of training performed at the gym of the participant’s choice. Participants alternated between upper and lower body workouts. The upper body workout consisted of barbell bench press, seated row machine, dumbbell shoulder press, lat pulldown machine, dumbbell biceps curls, and triceps extension machine. The lower body workout consisted of barbell squat or hip sled machine, lunges with dumbbells, leg curl machine, leg extension machine, and calf raise machine.

Participants who were unfamiliar with the RT exercises were instructed regarding the proper execution of each exercise. Participants were also instructed to utilize a weight that elicited muscular failure after 8–12 repetitions and to adjust the weight as necessary to meet this criterion. Four sets of each exercise were performed and a 90- second rest period between sets was assigned (Tinsley. 2016; my emphasis).
The variables the scientists tracked were, as previously mentioned, the subjects' individual nutrient intakes (as reported in a repeated four-day dietary record) and changes in body composition (X-ray absorptiometry using a "Hologic Discovery W" device for whole-body scans; muscle size was assessed by ultra-sound measurements) and muscular strength (assessed by obtaining the 1-repetition maximum (1-RM) using the hip sled and barbell bench press exercises).
How long did they fast? 20h? Isn't that too much? With a feeding window of 4 hours (at any time between 4PM and midnight | as in Kelly, 2007), the TRF(=IF) regimen in the study at hand is significantly shorter than that in the average IF-dieter who will probably use 6-8h fasting windows... whether the results would be fundamentally different for these shorter fasting windows of 16-18h would have significantly changed the outcome is questionable, also because the subjects fasted only on non-workout days and were allowed to eat ad-libitum on the three days on which they performed RT. Thus, further research is obviously warranted (see bottom line for suggestions).
The reasons that the results are still relevant and worth reporting are (a) they are the first of their kind and (b) it is unlikely that the effect of intermittent fasting is different for people with different training status. What may difference is the baseline response to resistance training, but that's the same for both groups (you can also argue that the response will change over time which is why it is great that the study lasted eight, not just two weeks).

IF cuts energy intake, but not body fat? True, if we focus on statistically sign.

As you can see in Figure 1, the TRF reduced energy intake did, as SuppVersity readers will have expected the reduction in daily energy intake of the subjects by ∼650 kcal per day (see Figure in the bottom line for information on the "macros") - you can only eat so much in a given time-frame and four hours are not long. What may be more interesting than the reduction in energy intake you've expected based on previous research.
Figure 1: Relative changes in body composition; none reached sign. inter-group diff., d-values indicate effect sizes which show a trend towards fat loss and lean & fat mass gains in the TRF and control group, respectively (Tinsley. 2016).
Against that background, it is quite surprising that the TRF regimen did not significantly affect the total body composition - especially the amount of body fat. In that, it is possible that this was just because the study duration was too short, but eventually 4 weeks of being in a caloric deficit should suffice. Eventually, however, the body fat (total mass and %) reduction in TRF shows that (cf. Figure 1) what's missing is only the statistical significance of the difference (and that's nor really a wonder with only N = 28 subjects in total and thus only n = 14 subjects in each group). This in turn which raises the question(s): (A) Was there a reduction in physical activity in TRF that of which we could assume that it compensated maybe 200-300kcal of the ~650kcal deficit? And (B) how accurate the 4-day food logs reflected the energy intake over the two 4-week periods during which they were recorded.

Similar questions and that criticism of the methodology can be brought forward for the lack of significant difference in the increase in cross-sectional area of the biceps brachii and rectus femoris in the two groups. If we look closely at these values and take the effect size data (values over the bars) instead of the p-values for the absolute gains as our yardstick, there is evidence that the TRF regimen impaired the lean mass gains (+2.3 kg, d = 0.25) and upper and lower body muscular endurance increases (not shown in Figure 1) that were brought about by the standardized resistance training protocol both groups followed for 8 weeks.
The lack of protein in the TRF group (0.88g/kg vs. 1.3g/kg) could be a reason for the lack of muscle gains.
So, the study had no results we can use? Not really, but there's certainly reason for further research, because (a) it would be nice to ascertain that the extent of the caloric deficit was in fact -33% (that's neither unlikely nor unheard of, but it is important enough to ask for a more rigid control) and to (b) evaluate whether the 20h fasting window was simply too large. Especially the last-mentioned follow-up study which ideally should involve a control (no fasting), a 16h- and 18h-fasting window could yield very interesting results, after all studies show that significant protein breakdown will occur only after >18h of fasting and last for ~another 24h before the body starts to react to conserve lean mass (reduced RMR, etc.).

What would be similarly interesting, though, would be having a standardized, prescribed protein intake in both groups. With "only" 72 and 81 g of protein per day in the first and second four weeks, respectively the TRF group consumed not just much less protein than the control group (107 and 97 | that's not sign. less, though due to high inter-personal variation); with only 0.88 g/kg they also consumed way less protein than any reasonable recommendation for resistance trainees [~1.6-2.2 g/kg] would suggest.

Overall, the study at hand is thus the first study to investigate the interaction between intermittent fasting and resistance training. The results appear to confirm what I have repeatedly written in the past, i.e. "intermittent fasting" is great for cutting (and potentially "recomp", i.e. losing fat while maintaining lean mass and thus improving your body composition), not so good for gaining weight, but - for the previously outlined reasons - it is not the study to yield final insights into how good / bad it actually is for these purposes and how it compares to alternate-day-fasting that produced impressive weight or rather fat loss in a very recent study | Comment on Facebook!
  • Kelly, Caleb J. "A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults." The American journal of clinical nutrition 86.4 (2007): 1254-1255.
  • Tinsley, Grant M., et al. "Time-restricted feeding in young men performing resistance training: A randomized controlled trial†." European Journal of Sport Science (2016): 1-8.
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