Early time-restricted feeding improves insulin sensitivity, blood pressure, and oxidative stress even without weight loss in men with prediabetes (Sutton et al., 2018)
Tl;dr: 8 prediabetic men, 5 week crossover study. When on eTRF, the only rule was basically dinner no later than 3 pm and no snacking thereafter. It was isocaloric because: 1) studies on meal timing and weight loss have been done; and 2) they wanted to test meal timing specifically, not confounded by weight loss.
Also, I think the results are due to meal timing, not fasting duration per se, because of the studies by Jacobs & Hirsh. In brief, they tested meal timing with similar fasting durations and showed people who ate one-meal-a-day all at breakfast lost more weight than people who ate one-meal-a-day all at dinner. First they showed this in an ad lib context and then again in an isocaloric context. Metabolism is gimped at night.
And literally every other study on this shows the benefits of front-loading food intake relative to skipping breakfast. Your "n-1's" may vary, and I respect that, but science says you might be better off doing it the other way around. According to this study, it took ~12 days to adapt to eTRF.
Best of all, the eTRF group reported lower desire to eat in the evening. TRANSLATION: J & H and "Eco-Atkins" got it right -- if participants reported more satiety in an isocaloric context, then they'll eat less and lose weight in an ad lib context.
Most studies on IF have shown neutral or negative effects (eg, Carlson et al., 2007, Soeters et al., 2009, Stote et al., 2007, and Trepanowski et al., 2017). That may have been due to meal timing. Worse "late Time-Restricted Feeding" (lTRF) has actually ben shown to worsen blood glucose, blood pressure, and blood lipids (eg, Carlson et al., 2007, Stote et al. 2007, and Tinsley et al., 2017). If if were simply a matter of fasting duration, actual time of the feeding window wouldn't matter.
In humans, insulin sensitivity is higher in the morning and we're more likely to store fat at night.
You Krafters are gonna love this: lower insulin response with no change in blood glucose means improved insulin sensitivity!
Feedback from the participants: it took ~12 days to adapt;they would've prefered an 8-hour feeding window than the 6 one that was prescribed (btw, I'm totally fine with that, because I think the results were more due to meal timing than fasting window); at the end of the study but before they knew the results, 8/8 of the subjects said they'd keep doing it if it improved their health.
This study was high quality: "to ensure compliance, participants were required to eat all meals at our research clinic or to be supervised in real-time via remote video monitoring by Skype." Awesomesauce.
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