A study designed to settle the debate
Enter the ChronoFast study, led by Prof. Olga Ramich at the German Institute of Human Nutrition and Charité, Universitätsmedizin Berlin. The goal is to isolate the effects of meal timing from the confounding variable that plagues so much nutrition research: calorie intake. The researchers recruited 31 women with overweight or obesity to participate in a randomised crossover trial, adhering to 2 distinct eating schedules for 2 weeks:
- An early window (08:00 to 16:00)
- A late window (13:00 to 21:00)
Crucially, the meals were isocaloric, meaning the total calories and nutrients remained identical across both phases.
Researchers rigorously tracked glucose and fat metabolism through blood samples, 24-hour glucose monitoring, and detailed logs of food intake and physical activity. They also analysed circadian shifts using blood cell data.
The surprising role of circadian rhythms
What the researchers uncovered was unexpected. Time-restricted eating did not deliver the metabolic miracles many had hoped for. Insulin sensitivity, blood sugar levels, and cardiovascular markers remained largely unchanged. Yet, the study revealed something equally fascinating. Meal timing subtly shifted the body’s internal clocks. Participants in the late eating group experienced a 40-minute delay in their circadian rhythms. Their sleep patterns shifted, with later bedtimes and wake-up times.
It’s the calories, not just the timing
So, what does this mean for those who’ve embraced time-restricted eating as a shortcut to better health? Despite expectations based on earlier research, the ChronoFast study found no meaningful changes in insulin sensitivity, blood sugar levels, blood lipids or inflammatory markers. The findings suggest that the benefits observed in earlier studies may have been less about when people ate and more about how much. Unintentional calorie reduction, rather than the magic of a shortened eating window, might have been the real driver of improvements. As Prof. Ramich notes, “Those who want to lose weight or improve their metabolism should pay attention not only to the clock, but also to their energy balance.”
What cyclists should know
For endurance athletes, these insights are particularly relevant. Cyclists often experiment with fasting protocols to optimise body composition and fuel efficiency, but this study makes an important point: timing alone isn’t enough. How much you eat and what you eat remain key. And while shifting meal times might tweak your circadian rhythms, it won’t compensate for a diet that’s out of balance with your energy needs.
