Not So Fast: What Intermittent Fasting Will & Won’t Do

First, for any unaware: intermittent fasting (IF) is the practice of fasting during certain periods and not during others. A common method is to eat during a set window of time per day, with an 8-hour window being perhaps the most common choice. Scientists often refer to this by the slightly more helpful term “time-restricted eating“, since well, all fasting is intermittent if you do it more than once. Nevertheless, we’ll stick to the popular term here.

Intermittent fasting has been found to, amongst other things, promote healthy apoptosis and autophagy (in other words: early programmed cell death and recycling—these are good things).

This means that intermittent fasting has anti-aging and anticancer potential. We wrote more about it the mechanism in this article:

Fisetin: The Anti-Aging Assassin ← as the name suggests, this is about a senolytic supplement that does the same thing, not about intermittent fasting per se, but the mechanism is the same and it explains why healthy apoptosis and autophagy is important for these things

If-specific research

It also has anti-inflammatory benefits and decreases the risk of insulin resistance. In other words, intermittent fasting boosts the metabolism while simultaneously guarding against some of the dangers of a faster metabolism (harms you’d get if you instead increased your metabolism by doing intense exercise and then eating a mountain of convenience food to compensate).

Read the science: Intermittent Fasting: Is the Wait Worth the Weight?

Read our prior article: Fasting Without Crashing? We Sort The Science From The Hype

And as for that about insulin sensitivity, see: Improve Your Insulin Sensitivity! ← for many ways to do that, including (but not limited to) IF!

However, not everyone will get to enjoy these same effects. And, ironically, those who are most likely to be trying to lose weight, are least likely to get that benefit:

Why Intermittent Fasting (& GLP-1 Drugs!) Might Not Work For You

The circadian benefit

This is an underrated one, and can be a benefit that stands when some of the others don’t.

For example, remember how we said that people who are most likely to be trying to lose weight are the least likely to get that benefit from IF? Well, researchers (Dr. Olga Pivovarova-Ramich et al.) looked into this, and found that for women in the “overweight” or “obese” category…

❝During the restricted 8-hour eating period, participants were asked to consume their habitual food quality and quantity. Insulin sensitivity did not differ between (−0.07; 95% CI, −0.77 to 0.62; P = 0.60) or within (eTRE: 0.31; 95% CI, −0.14 to 0.76; P = 0.11; lTRE: 0.19; 95% CI, −0.22 to 0.60; P = 0.25) interventions. Twenty-four–hour glucose, lipid, inflammatory, and oxidative stress markers showed no clinically meaningful between- or within-intervention differences. Participants demonstrated high timely adherence (eTRE, 96.5%; lTRE, 97.7%), unchanged dietary composition and physical activity, minor daily calorie deficit (eTRE, −167 kilocalories/day), and weight loss (eTRE, −1.08 kilograms; lTRE, −0.44 kilograms).❞

• TRE = time-restricted eating
• eTRE = early time-restricted eating
• lTRE = late time-restricted eating

Source: Intended isocaloric time-restricted eating shifts circadian clocks but does not improve cardiometabolic health in women with overweight

In other words, for these women in those weight categories, an eight-hour eating window did not improve insulin sensitivity, blood sugar, blood fats, or inflammatory markers when calories and nutrients were held constant.

However!

What meal timing did do is it shifted participants’ internal clocks, with later eating leading to later bedtimes and later wake times.

And this is important, because that does have a big impact on many other aspects of our health, for example:

The Other Circadian Rhythms ← this is about what happens when your body parts clock on and off at the wrong times

Breaking the fast correctly

When it’s time to break the fast, there are considerations, such as:

• Breakfasting For Health: When To Do It
• What Size Breakfast Is Best, By Science?
• What Breakfast Means For Metabolic Syndrome

Want to get intentional with your circadian rhythm?

One of the leading figures in the field of circadian rhythm research is Dr. Satchin Panda, whose work we wrote about here:

The Circadian Rhythm: Far More Than Most People Know

His team’s (free!) app, “My Circadian Clock”, can help you track and organize all of the body’s measurable-by-you circadian events, and, if you give permission, will contribute to what will be the largest-yet human study into the topics covered today, to refine the conclusions and learn more about what works best.

Check out the iOS app here | Check out the Android app here

Enjoy!