Cutting Carbs After PM HIIT Workouts Will Make You Cross the Finish Line Before Anyone Else: 3% Faster Time Trial, 9% More Power and Twice as Much Fat Mass Lost in 7 Days

Don't be a fool. Simply eating no carbs in the PM is not going to yield the same results. It's all about timing it correctly with your workouts... workouts? Yes, bad  news: you got to get off the couch, bro; workout daily: one light, one HIIT day.
I've written about the adaptational response to "training low", i.e. doing endurance training on a low carbohydrate diet previously. In January, this year, for example, I have reported the results of a study from the French National Institute of Sport that showed that strategically cutting carbs in the PM and thus "sleeping low" will trigger game-changing Performance gains in only 3 weeks (read the article).

Now, the scientists go one better: In their latest study, Laurie-Anne Marquet and colleagues investigated the effect on an even shorter timescale - a timescale that is short enough to consider "sleeping low" as a possible  pre-competition strategy... well, assuming that it would work its performance-enhancing magic within as little as the 7 days, during which the subjects' in Marquet's study followed the "no carbs after your workout" (="sleep low" | SL) prescription the researchers copied from their own previously discussed study.
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Overall, 21 endurance-trained male cyclists (mind the typo about the # in the abstract of the original study, in case you read it; the summary says 11, not 21, which is the correct number) volunteered to participate in the study. All were healthy, aged between 18 and 40 years, and training at least 12 h/week, having at least 3 years of prior training. Their mean (±SD) age was 31.2 ± 7.1 years, their mean body mass was 71.1 ± 5.6 kg, their mean maximal oxygen consumption (VO2max) was 64.2 ± 6.0 mL/min/kg, and their mean maximal aerobic power (MAP, W) was 342 ± 38.3 W.

To isolate the effects of the dietary / carbohydrate modulating intervention, the subjects who trained
according to their habitual training program, initially (1st week) ate according to their usual dietary habits, documenting their food intake via a daily food diary. These diaries were then compared to the prescribed carbohydrate pattern in the 2nd week, which set their CHO intake at 6 g/kg per day.
Figure 1: Graphical overview of the study design; CHO: carbohydrates; HIT: high‐intensity training session; LIT: light intensity training session; SL: Sleep‐Low; CON: Control; MAP: Maximal aerobic power (Marquet. 2016).
After the dietary standardization and the pre-test at the end of this period, the subjects were randomly assigned to two different groups undertaking the same one-week training program.
The study used pre-bed protein shakes, a strategy to build muscle.
Nightly protein shakes, glycogen depletion and lean muscle mass: In contrast to what some people may expect, the no-carbs before bed strategy did not lead to measurable decreases in lean mass. Whether and to which extent that was a result of the protein shake both groups consumed before bed cannot be answered without doing another study. What I can tell you based on previous research, however, is that this, i.e. having a protein shake "before" (not necessarily right before) bed, is a very promising strategy to maximize net protein retention (see "12-Week Study: 25g Bed-Time Protein Almost Doubles Size & Increases Strength Gains" | more).
The built-in and significant difference between the group can be found in the nutritional guidelines according to which all subjects consumed the same amount of 6g/kg CHO, in total, but periodized their carbohydrate intake differently over the day. Specifically,...
  • the control group trained with a high CHO availability (control group, CON group, n = 9) with an even spread of CHO intake over the day and between training sessions,
  • the "sleep low" (SL) group (n = 12 | mind the typo in the scientist' abstract) trained with a CHO intake that was periodized within the various days in a way that no CHO was consumed between the high-intensity interval training sessions (HIIT) held
Practically speaking: The subjects in the "sleep low" group were thus doing truly fasted or, rather, glycogen depleted low-intensity cardio in the morning of each of three of the six otherwise identical workout days.
Figure 2: 20km cylcling times and mean power output in pre- and post-test (Marquet. 2016).
Against that background, it is all-the-more surprising that the subjects saw both: significant reductions in their time-trial times (-3.32%) and improvements in their average power production during the workouts (+9.17%). What is not surprising is that the data in Figure 1 indicates that these power improvements occurred specifically in the latter part of the workout, i.e. when the glycogen stores are running out and the training effect from training low in the AM shows.
Table 1: Rating perception of effort (RPE) during the 20 km cycling time-trial every 5 km (Marquet. 2016).
In contrast to what you would expect, the scientists did not detect a significant difference between group and pre and post tests for the substrate oxidation, markers of lipid oxidation and stress markers - or, more specifically there was ...
  • no decrease in CHO oxidation in the SL group and 
  • no increase in FAT oxidation in the SL group
  • no increased cellular damage in form of lipid oxidation, and
  • no significant difference in the subjects' stress response (plasma catecholamines),
... in the high-performing "sleep low" aka "SL" group. Now, there's a (small) catch, though, that should be mentioned in spite of the lack of statistical significance: the scientists observed a small increase in the subjects' rate of perceived exertion during the light AM sessions (+13%), as well as the post-intervention time trial (+10%) in the "sleep low" group. Moreover, the last-mentioned increase is more or less identical to the increase in average power production during the post-test on day 7. Accordingly, it is questionable if one should call this already non-significant effect a "catch", at all.
Brad Schoenfeld's 2014 "Fasted Cardio"-study falsifies the myth of superior long-term (4 week) fat loss in non-glycogen-depleted non-athletes on a moderate energy deficit (more). It does not exclude, however, that the glycogen-depleted subjects of the study at hand could see increased fat loss in the short or long term.
"And the subjects got ripped, right?" Not exactly. While the statement from the headline is 100% accurate, the total fat loss was (and this is not surprising in view of the study duration) marginal: statistically significant −395 ± 491 g in the SL and statistically non-significant −151 ± 363 g in the control group.

The reason that it is still worth mentioning is that previous studies suggested that doing AM cardio on empty would not increase fat loss (even over longer periods of time). So, how can we consolidate these conflicting results? Well, while further research appears necessary, I could imagine that both, the advanced training status of the subjects' in the study at hand and the fact that they were actually glycogen-depleted and not, as the subjects' in Schoenfeld's seminal paper (Schoenfeld. 2014), "only fasted", so that, if anything, their liver glycogen may have been lowered | Comment!
  • Marquet, Laurie-Anne, et al. "Periodization of Carbohydrate Intake: Short-Term Effect on Performance." Nutrients 8.12 (2016): 755.
  • Schoenfeld, Brad, et al. "Body composition changes associated with fasted versus non-fasted aerobic exercise." Journal of the International Society of Sports Nutrition 11.54 (2014). Previously discussed, here!
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