This small trial tested the effects of a particular form of intermittent fasting on metabolic markers.
Eleven subjects were randomized to one of two four-day diets. Both diets contained the same number of calories and were comprised of 50% carbs, 35% fat, and 15% protein. Both contained three meals, but the timing differed. On the control arm, subjects ate at 8 a.m., 2 p.m., and 8 p.m. On the test diet — termed eTRF for early time-restricted feeding — the three meals were at 8 a.m., 11 a.m., and 2 p.m. Subjects were not allowed to consume snacks, so the control group experienced a nightly fast of 12 hours (8 p.m. to 8 a.m.) while the eTRF group fasted for 18 hours (2 p.m. to 8 a.m.). Blood was drawn in the morning before breakfast and again at 8 p.m., just before dinner in the control group. Blood glucose levels were continuously monitored.
Figure 1: Study Protocol. Eleven participants were randomized to eat between 08:00 and 20:00 (control arm) or between 08:00 and 14:00 (early time-restricted feeding (eTRF) arm) for 4 days and then crossed over to the other arm after a 3.5–5-week washout period. On day 4, they consumed 3 identical meals that constituted one-third of their daily energy requirements, while undergoing 24-hour continuous glucose monitoring. In addition, blood was drawn in the evening (PM) on day 3 and in the morning (AM) on day 5 to measure serum analytes and gene expression.
As expected, the 24-hour glucose profiles differed significantly between groups. The eTRF group showed continually elevated blood glucose levels between 8 a.m. and 2 p.m., but blood glucose levels remained low and flat overnight between 8 p.m. and 8 a.m. Controls showed greater variation throughout the day but also had a large dinnertime glucose spike that did not fully subside until 2 a.m. (halfway through sleep).
Figure 2: 24-Hour Glucose Levels. Relative to the control schedule, early time-restricted feeding (eTRF) (A) changed the temporal profile of 24-hour glucose levels, as measured by continuous glucose monitoring, particularly in the evening, (B) lowered mean glucose levels while asleep and decreased 24-hour mean glucose levels, and (C) lowered glycemic excursions as measured by Mean Amplitude of Glycemic Excursions (MAGE). Error bars on panel (A) are suppressed for visual clarity. * p < 0.05.
There were some small additional differences in metabolic markers between the two groups, including higher ketone levels in the morning in the eTRF group. While the treatment group also showed higher glucose and insulin levels at 8 p.m., this observation is difficult to interpret, because this group had consumed all three meals by the time of the nightly blood draw while the control group had not yet consumed dinner. Longer studies may determine whether changes in markers related to aging, circadian rhythm, and other factors have clinical significance over time.
In sum, this interesting but preliminary trial shows time-restricted feeding does meaningfully change glucose profile over the course of the day and may change some metabolic markers, even over short periods. Longer studies will help determine whether this different metabolic profile — most markedly distinguished by a greater share of each day being spent at low blood glucose levels — has significant impact on health or disease markers.
Comments on Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans
hi! it is very interestinf what this "small trial" shows for the community!! Thanks for sharing good data !
BUT !!
We would love to share a almost 8 years old " living LAB " of CrossFit- Fasting - CBD , Circadian Rythms and Carbohidrates Cycling
AND ALL THE AMAZING RESULTS!!!
ALL THANKS TO YOU!! CROSSFIT!!!
Consistent with this insight from the study
"Controls showed greater variation throughout the day but also had a large dinnertime glucose spike that did not fully subside until 2 a.m. (halfway through sleep)"
It's becoming clear that the variability in glucose levels (e.g. hypoglycemia-hyperglycemia roller coaster) is a bigger disaster than the average glucose elevation (i.e. AUC).
This is partly reflected in the fact that HbA1c is a relatively poor predictor of disease outcomes (it's better used to identify trends rather than quantify absolute risks)
Hadn't been on the official crossfit website in about 9-10 years now. I see a lot changed. I was curious what the "essentials" were because I always like foundational type articles and this is like the number two "essential" article to crossfit? Some trial study about intermittent fasting. I see some things never change and if Crossfit is still like it was back in the day my comments will be censored out so no bad publicity.
It says, "The proven elements of this broad, general, and inclusive fitness, in terms of both movement and nutrition, are what we term our CrossFit Essentials."
Brian,
The articles are listed in chronological order, not in order of importance. Truthfully, I'd expect one to infer that.
Question is: does the time related to your last meal and when you sleep change glucose levels? Meaning if my fast starts at 9pm and I go to sleep at 930, but don’t break the fast until 3pm next day, do we see similar results?
I think that is one of the aspects they are trying to shed light on but given the structure of the study and the resulting data I believe it is unlikely that they can answer that question currently. My guess is that there would be some variation due to higher blood glucose for the first part of your night but the degree to which that is positive or negative, I would be interested as well.
Also, it appears this study was only lasted 4 days for each participant so I would like to see this study pushed out further to see what those markers look over an extended period of time especially with regards to eTRF.
Good question. I.e. Does circadian rhythm have an effect on glucose levels in the AM during a fast?
Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans
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