According to Gram Research analysis, both 16:8 and 5:2 intermittent fasting reduce weight by approximately 2.7 kilograms in 4 weeks, with 5:2 producing slightly more fat loss over time. A randomized controlled trial of 68 women found that both methods equally improved blood pressure and blood sugar control, though they work through different daily patterns. The best method depends on which fits your lifestyle, as both approaches proved effective for weight loss and metabolic health improvements.
A new study compared two popular intermittent fasting methods to see which one helps people lose weight better. Researchers had 68 women try either 16:8 fasting (eating only during an 8-hour window each day) or 5:2 fasting (eating normally 5 days, eating very little 2 days per week) for 4 weeks. Both methods helped people lose weight and improve their blood sugar levels, but the 5:2 approach led to slightly more fat loss over time. The findings suggest that both methods work, but they affect your body differently, so choosing one depends on what fits your lifestyle best.
Key Statistics
A 2026 randomized controlled trial of 68 women found that both 16:8 and 5:2 intermittent fasting reduced body weight by 2.7 kilograms and fat mass by 1.7 kilograms over 4 weeks.
According to research reviewed by Gram, the 5:2 fasting method produced greater fat loss over time compared to 16:8 fasting, though both methods reduced muscle mass by similar amounts (0.6 kilograms) in the 4-week study.
A 2026 trial showed that both 16:8 and 5:2 intermittent fasting reduced time spent in high blood sugar states and decreased waist circumference equally, with no significant differences between the two methods.
In a 4-week study of 68 women, both intermittent fasting regimens reduced mean glucose levels and peak blood sugar spikes after meals, suggesting improvements in how the body processes glucose.
The Quick Take
- What they studied: Whether eating in an 8-hour window every day (16:8) or eating very little on 2 days per week (5:2) works better for losing weight and improving health markers like blood sugar and blood pressure.
- Who participated: 68 women who were overweight or had obesity participated in this 4-week study. They were randomly assigned to follow either the 16:8 or 5:2 fasting method.
- Key finding: Both fasting methods helped people lose an average of 2.7 kilograms (about 6 pounds) and 1.7 kilograms of fat in just 4 weeks. The 5:2 method led to slightly more fat loss over time, but both methods improved blood sugar control and blood pressure equally.
- What it means for you: If you’re considering intermittent fasting for weight loss, both 16:8 and 5:2 methods appear effective. Choose based on what fits your schedule and lifestyle better. However, this was a short 4-week study in women only, so results may differ for men or over longer periods. Talk to your doctor before starting any fasting program.
The Research Details
This was a randomized controlled trial, which is one of the strongest types of research studies. Researchers randomly divided 68 women into two groups: one group followed 16:8 intermittent fasting (fasting for 16 hours and eating during an 8-hour window), while the other group followed 5:2 fasting (eating normally 5 days per week and eating a special low-calorie diet on 2 non-consecutive days). The study lasted 4 weeks, and researchers measured body weight, fat mass, muscle mass, waist circumference, blood pressure, and blood sugar levels at the beginning and end.
The 5:2 group used a fasting-mimicking diet on their fasting days, which means they ate specially designed foods that trick the body into thinking it’s fasting while still providing some nutrients. This approach is designed to get some benefits of fasting while making it easier to stick with. Both groups were monitored to track how much they ate and how their bodies changed.
Because this was an open-label trial, both the participants and researchers knew which fasting method each person was following. This is different from a blinded study where participants don’t know which treatment they’re getting, but it’s often necessary for lifestyle studies like this one.
This study design is important because it allows researchers to directly compare two popular fasting methods under controlled conditions. By randomly assigning people to groups, researchers can be more confident that differences between the groups are due to the fasting method itself, not other factors. The 4-week timeframe is long enough to see real changes in weight and metabolism, but short enough to measure how quickly each method works.
This study has several strengths: it used random assignment, measured multiple health markers beyond just weight, and tracked both fat loss and muscle loss separately. However, there are some limitations to consider. The study only included women, so results may not apply equally to men. The 4-week duration is relatively short, so we don’t know if these results would continue over months or years. The study was open-label, meaning participants knew which fasting method they were using, which could influence their behavior or expectations. Finally, the sample size of 68 is moderate, so larger studies might reveal different patterns.
What the Results Show
Both fasting methods produced meaningful weight loss in just 4 weeks. On average, participants lost 2.7 kilograms (about 6 pounds), with 1.7 kilograms coming from fat mass and 0.6 kilograms from muscle mass. This means most of the weight lost was fat, which is the desired outcome.
When comparing the two methods directly, the 5:2 fasting group lost slightly more fat over the 4-week period than the 16:8 group. However, both groups lost similar amounts of muscle mass, which is important because preserving muscle is crucial for maintaining a healthy metabolism. The difference in fat loss between the groups was modest but measurable.
Both fasting methods also improved several important health markers. Waist circumference decreased significantly in both groups, which is important because belly fat is linked to health problems. Blood pressure dropped in both groups, and both methods reduced the amount of time participants spent with high blood sugar levels. These improvements happened without any significant differences between the two fasting approaches.
The study found that both methods reduced how much people ate overall and shortened their eating window, meaning participants naturally consumed fewer calories. Both methods also lowered average blood sugar levels and peak blood sugar spikes after meals, suggesting improvements in how the body handles glucose.
Beyond weight loss, the study revealed important patterns about how each fasting method affects the body differently over time. The 5:2 method showed a more consistent pattern of fat loss as the weeks progressed, while the 16:8 method showed faster initial results that then leveled off. This suggests that the two methods may work through slightly different mechanisms in the body.
Both methods successfully reduced daily calorie intake, but they did so in different ways. The 16:8 group naturally ate less because they had fewer hours available to eat, while the 5:2 group reduced calories on their fasting days and ate normally on other days. Despite these different approaches, both achieved similar overall reductions in daily energy intake.
The improvements in blood sugar control were particularly notable. Both methods reduced mean glucose levels and the time spent in a high blood sugar state (hyperglycemia), which is important for preventing type 2 diabetes and managing existing blood sugar problems. These metabolic improvements happened alongside the weight loss, suggesting that fasting benefits health in multiple ways.
This study adds important new information to the growing body of research on intermittent fasting. Previous studies have shown that intermittent fasting can help with weight loss, but most research has focused on one method at a time rather than directly comparing different approaches. This head-to-head comparison is valuable because it shows that both popular methods work, but with slightly different patterns.
The finding that 5:2 fasting led to more fat loss over time aligns with some previous research suggesting that periodic fasting might have advantages for fat loss. However, the similarity in muscle loss between methods and the equal improvements in blood pressure and blood sugar control suggest that the differences between methods may be smaller than some people believe. The study confirms what other research has shown: that the best fasting method is the one you can stick with long-term.
This study has several important limitations that readers should understand. First, it only included women, so the results may not apply equally to men, who might respond differently to fasting. Second, the study lasted only 4 weeks, which is relatively short. We don’t know if the benefits would continue, increase, or decrease over months or years of fasting. Third, the study was open-label, meaning participants knew which fasting method they were using, which could influence their results through placebo effects or behavioral changes.
The sample size of 68 participants is moderate for this type of study. While it’s large enough to show clear patterns, larger studies might reveal additional details or different results in specific subgroups. Additionally, the study didn’t include a control group that didn’t fast at all, so we can’t directly compare fasting to simply eating less without fasting. Finally, the study used a fasting-mimicking diet for the 5:2 group, which is a specific type of low-calorie diet. Results might differ if people used different approaches to their fasting days.
The Bottom Line
Based on this research, both 16:8 and 5:2 intermittent fasting appear effective for weight loss and improving metabolic health over a 4-week period (moderate confidence level). Choose the method that best fits your lifestyle and schedule. If you prefer eating within a limited time window daily, 16:8 may suit you. If you prefer eating normally most days with restricted eating on specific days, 5:2 might be better. Before starting any fasting program, consult with your doctor, especially if you have diabetes, blood pressure problems, or take medications. These recommendations apply primarily to adults with overweight or obesity, as that’s who was studied.
This research is most relevant for adults who are overweight or have obesity and are looking for weight loss methods. People interested in improving blood sugar control or blood pressure may also benefit from these findings. However, this study was conducted only in women, so men should be cautious about assuming identical results. People with diabetes, heart conditions, or those taking medications should consult their doctor before fasting. Pregnant women, nursing mothers, and people with a history of eating disorders should not fast without medical supervision.
Based on this 4-week study, you can expect to see measurable weight loss within the first month of starting intermittent fasting. Most participants lost about 6 pounds in 4 weeks, though individual results vary. However, this study only measured short-term results. For long-term success, you should expect to continue the fasting method for several months to see sustained benefits. The improvements in blood sugar and blood pressure appeared within 4 weeks, but maintaining these benefits likely requires continuing the fasting practice.
Frequently Asked Questions
Is 16:8 or 5:2 intermittent fasting better for losing weight?
Both methods produce similar weight loss of about 2.7 kilograms in 4 weeks, but 5:2 fasting showed slightly more fat loss over time. Choose based on which fits your lifestyle better, as the best method is the one you’ll stick with long-term.
Does intermittent fasting help with blood sugar control?
Yes, a 2026 study found that both 16:8 and 5:2 fasting reduced average blood sugar levels and decreased time spent in high blood sugar states. These improvements appeared within 4 weeks and suggest fasting may help prevent type 2 diabetes.
Will I lose muscle mass if I do intermittent fasting?
In this 4-week study, participants lost only 0.6 kilograms of muscle mass compared to 1.7 kilograms of fat, meaning most weight lost was fat. Both fasting methods preserved muscle similarly, though long-term effects require further research.
How quickly will I see results from intermittent fasting?
This study showed measurable weight loss and improvements in blood pressure and blood sugar within 4 weeks. However, this was a short-term study, so maintaining results requires continuing the fasting practice over months.
Can men use these intermittent fasting results?
This study included only women, so results may not apply equally to men. Men should consult their doctor before fasting, as they might respond differently to these methods based on metabolism and body composition differences.
Want to Apply This Research?
- Track your daily weight at the same time each morning and record which fasting method you’re using (16:8 or 5:2). Also log your waist circumference weekly and note your energy levels and hunger patterns to identify which method feels more sustainable for you.
- If using 16:8 fasting, set a specific eating window (for example, 12 PM to 8 PM) and stick to it daily. If using 5:2 fasting, choose two non-consecutive days per week for your low-calorie days and plan your meals in advance. Use the app to set reminders for your eating and fasting windows and to log meals during eating periods.
- Over 4 weeks, track weight loss, waist circumference changes, and how you feel during fasting periods. After 4 weeks, assess which method you found easier to follow and which produced better results for your goals. Consider measuring blood pressure at home if you have a monitor. If you have access to blood sugar testing, track glucose levels before and after meals to see improvements. Adjust your chosen method based on these personal results and sustainability.
This research summary is for educational purposes only and should not replace professional medical advice. The study included only women over a 4-week period, so results may not apply equally to men or over longer timeframes. Before starting any intermittent fasting program, especially if you have diabetes, heart disease, high blood pressure, take medications, are pregnant or nursing, or have a history of eating disorders, consult with your healthcare provider. Individual results vary, and what works for one person may not work for another. This article does not constitute medical advice or a recommendation to start fasting.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.