Researchers tested whether eating all your food within an 8-hour window could improve health in women who were overweight. Some women ate early (8am-4pm) while others ate late (1pm-9pm), but both groups ate the same amount of food. After two weeks, neither group showed improvements in blood sugar control, cholesterol, or other heart health markers. The study did find that eating schedules shifted the body’s internal clock, but this didn’t lead to the health benefits scientists hoped for.

The Quick Take

  • What they studied: Whether eating all meals within an 8-hour window (called time-restricted eating) could improve blood sugar control and heart health markers in women who were overweight
  • Who participated: 31 women who were overweight or obese. They tried two different eating schedules: one group ate between 8am-4pm, the other between 1pm-9pm
  • Key finding: Neither eating schedule improved insulin sensitivity (how well the body handles blood sugar), cholesterol, inflammation, or weight loss compared to normal eating patterns, even though both groups stuck to their eating windows 96-97% of the time
  • What it means for you: If you’re considering time-restricted eating to improve your health, this research suggests that simply eating within a narrow time window may not provide the benefits you’re hoping for—at least not in the short term. The timing of your meals may matter less than the total amount and quality of food you eat

The Research Details

This was a randomized crossover trial, which means each participant tried both eating schedules in different 2-week periods. Half the women started with early eating (8am-4pm) and then switched to late eating (1pm-9pm), while the other half did the opposite. This design is strong because each person serves as their own comparison.

During each 2-week period, women ate their normal foods but squeezed all eating into the 8-hour window. Researchers measured blood sugar control, cholesterol, inflammation markers, and tracked their body’s internal clock using blood samples. They also monitored sleep patterns and physical activity to make sure nothing else changed.

The key feature of this study was that it was ‘isocaloric,’ meaning women ate roughly the same total calories in both conditions. This is important because previous time-restricted eating studies sometimes showed benefits, but it was unclear whether improvements came from eating less overall or from the timing itself.

Most previous time-restricted eating studies didn’t carefully control how many calories people ate, making it hard to know if benefits came from eating less or from the timing. By keeping calories constant, this study isolates the effect of eating timing alone. This is scientifically rigorous and gives us clearer answers about whether the timing itself matters.

Strengths: The study was published in a top-tier journal (Science Translational Medicine), used a randomized design, had excellent adherence rates (96-97%), and carefully controlled for confounding factors like exercise and diet quality. Limitations: The sample size was small (31 women), the intervention was only 2 weeks (too short to see some health changes), and all participants were women, so results may not apply to men. The study also didn’t measure weight loss as a primary outcome, though minor weight loss was observed.

What the Results Show

The main finding was that insulin sensitivity—how well the body responds to insulin and controls blood sugar—did not improve in either eating schedule. The early eating group showed a small increase in insulin sensitivity (0.31 units), but this wasn’t statistically significant, meaning it could have been due to chance. The late eating group showed even less change (0.19 units).

Blood sugar levels, cholesterol, markers of inflammation, and oxidative stress (cellular damage) all remained essentially unchanged in both groups. None of these measures showed clinically meaningful improvements, meaning the changes were too small to matter for health.

Participants did lose some weight—the early eating group lost about 2.4 pounds and the late eating group lost about 1 pound—but this was modest and likely due to a small unintended calorie deficit (about 167 calories per day in the early eating group), not from the eating schedule itself.

The one clear finding was that eating schedules did shift the body’s internal clock. The late eating group’s circadian rhythm shifted about 15 minutes later in their sleep timing, suggesting that meal timing does influence the body’s biological clock, even if it doesn’t improve health markers.

The study found that the body’s internal clock in immune cells (monocytes) shifted about 24 minutes later with late eating, though this difference wasn’t quite statistically significant. Sleep timing shifted more clearly—about 15 minutes later with late eating. These circadian shifts are interesting scientifically but didn’t translate into health improvements. The researchers also confirmed that participants maintained their normal diet quality and physical activity levels, so changes weren’t due to lifestyle modifications.

Some earlier studies suggested time-restricted eating could improve metabolic health, but many of those studies didn’t carefully control calorie intake. This study’s finding that timing alone doesn’t help—when calories are equal—suggests that previous benefits may have come from eating fewer calories overall, not from the timing. This aligns with the general scientific consensus that total calorie intake is more important for weight loss than when you eat.

The study was only 2 weeks long, which may be too short to see metabolic improvements. Some health benefits take longer to develop. The sample included only 31 women, all of whom were overweight or obese, so results may not apply to men or people of normal weight. The study didn’t look at long-term effects or whether benefits might appear after several weeks or months. Additionally, the modest weight loss observed might have been enough to show benefits if the study had been longer or the sample larger.

The Bottom Line

Based on this research, time-restricted eating (eating within an 8-hour window) is not recommended as a primary strategy to improve blood sugar control, cholesterol, or other heart health markers—at least not in the short term. If you’re interested in improving these health measures, focusing on eating fewer calories overall and choosing healthier foods appears more important than when you eat. However, if time-restricted eating helps you eat less overall or stick to a diet, it may still be worth trying. Confidence level: Moderate (this is one study with a small sample, so more research is needed).

This research is most relevant to women who are overweight or obese and considering time-restricted eating for metabolic health. It’s less relevant to people of normal weight or men (since only women were studied). If you have diabetes or other metabolic conditions, talk to your doctor before trying any eating schedule. This research doesn’t mean time-restricted eating is bad—just that it may not provide the specific health benefits some people hope for.

This study only looked at 2-week periods, so we don’t know if longer-term time-restricted eating might eventually show benefits. Most health changes take at least 4-8 weeks to appear, so don’t expect immediate improvements. If you try time-restricted eating, give it at least 4-6 weeks before evaluating whether it’s working for you.

Want to Apply This Research?

  • Track your eating window daily (record start and end times) and measure fasting blood sugar or insulin levels weekly if possible. Also monitor total daily calories to ensure you’re not eating more overall, since the study suggests total intake matters more than timing.
  • If using an app to try time-restricted eating, set reminders for your eating window start and end times. More importantly, use the app to track total calories and food quality rather than focusing solely on the eating schedule. Consider whether the eating window helps you naturally eat less—if not, it may not be the right strategy for you.
  • Over 4-6 weeks, track: (1) adherence to eating window, (2) total daily calories, (3) weight (weekly), (4) energy levels and hunger patterns, and (5) any blood work if available (fasting glucose, insulin, cholesterol). If you don’t see improvements in these measures after 6 weeks, consider adjusting your overall calorie intake or food choices rather than continuing with time-restricted eating alone.

This research suggests that time-restricted eating alone may not improve blood sugar control or heart health markers in women who are overweight. However, this is one study with a small sample size and short duration. Individual results may vary, and time-restricted eating may still be helpful for some people as part of an overall healthy lifestyle. If you have diabetes, heart disease, or other health conditions, consult your doctor or registered dietitian before starting any new eating pattern. This information is for educational purposes and should not replace professional medical advice.