Intermittent fasting doesn't work without eating less

If you've been practicing intermittent fasting primarily for the metabolic benefits, a new study might change how you think about why it works. The ChronoFast trial, published in Science Translational Medicine, investigated whether an eight-hour eating window could enhance insulin sensitivity and cardiovascular health while maintaining the same calorie intake. Researchers followed 31 women with overweight or obesity through two different eating schedules (early window from 8 a.m. to 4 p.m. and late window from 1 p.m. to 9 p.m.), carefully controlling for identical calorie and nutrient intake.

The result? No measurable improvements in insulin sensitivity, blood sugar, blood fats, or inflammatory markers. The only change observed was a shift in circadian rhythms, with participants' internal clocks moving by about 40 minutes based on meal timing. This aligns with what I've always believed about intermittent fasting: it's effective because it spontaneously reduces calorie intake, not because food intake is compressed into a shorter window.

The good news is that most people will naturally eat less when they practice intermittent fasting, which is where the real benefits come from. To be confident it's working, track your calorie intake for a few days and ensure it's actually lower than it would be without the fasting window.

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