16:8 vs 5:2 Fasting: Which Plan Works Better?

A randomized controlled trial published on 28 October 2026 in the journal Obesity put the two most common intermittent fasting plans head to head: daily 16:8 and weekly 5:2. Over four weeks, both groups lost weight and improved on blood pressure, waist size and glucose measures. Weight and fat loss were greater over time in the 5:2 group, while the authors still describe the overall effectiveness of the two plans as similar.

So the short answer to "which works better" is: both worked, 5:2 had an edge on weight and fat in this trial, and the study is too short and too narrow to crown a winner.

The two plans

16:8 is a daily pattern. You fast for 16 hours and eat within an 8-hour window, every day. More on the 16:8 schedule page.

5:2 is a weekly pattern. You eat normally on five days and restrict heavily on two. More on the 5:2 schedule page.

One asks for a little discipline every day. The other asks for a lot of discipline twice a week. People often choose between them on feel alone, which is why a direct comparison is worth reading closely.

What the study did

The trial was run by researchers at The Catholic University of Korea.

Who	68 women with overweight or obesity
How long	4 weeks
Group 1	Daily 16:8
Group 2	Weekly 5:2, using a fasting-mimicking diet on fasting days
Design	Open-label randomized trial
Primary outcomes	Change in body weight and body composition
Secondary outcomes	Waist circumference, blood pressure, dietary intake, glycemic (blood glucose) metrics

One detail is easy to miss. The 5:2 group did not go without food on fasting days. They followed a fasting-mimicking diet, which is a restricted eating plan designed to imitate some effects of a fast while still providing some food. The abstract does not say what the diet contained. That means the trial compared 16:8 with one particular version of 5:2, not with two days of water-only fasting.

"Open label" means everyone knew which plan they were on. With diets there is no real way around that, but it is a limit worth knowing about.

What it found

Across both groups combined, over four weeks:

• Body weight fell by 2.7 kg (95% confidence interval 2.4 to 2.9 kg).
• Fat mass fell by 1.7 kg (1.5 to 1.9 kg).
• Muscle mass fell by 0.6 kg (0.4 to 0.7 kg).

Comparing the plans:

• Weight and fat mass: reductions were greater over time in the 5:2 group than in the 16:8 group. The abstract does not give separate figures for each group.
• Muscle mass: changes were similar in both.
• Waist circumference and blood pressure: both decreased significantly, with no difference between the groups.
• Eating and glucose: both plans reduced eating window duration, energy intake, mean and peak glucose levels, and time spent in hyperglycemia (high blood glucose).

The authors conclude that both regimens improved body weight and metabolic outcomes over 4 weeks. They add that, despite similar overall effectiveness, the two plans showed "distinct temporal response patterns", meaning the changes unfolded differently over the weeks, and they suggest this could one day help match a plan to a person. The abstract does not describe what those patterns looked like.

What it does not show

• It lasted four weeks. Most of the difficulty with any eating pattern arrives later. A plan that does slightly better in the first month is not necessarily the one people are still following after a year, and this trial cannot say which is.
• It included women only. All 68 participants were women with overweight or obesity, in Korea. Men, and people at a lower weight, were not studied.
• There was no non-fasting control group. Both groups fasted. The trial shows how the two plans compare with each other, not how either compares with ordinary calorie cutting or with doing nothing.
• It was open label. Participants knew their plan, which can influence behavior and self-reported food intake.
• The 5:2 arm used a fasting-mimicking diet. A 5:2 plan built on different fasting-day food may not give the same result.
• Some of the loss was muscle. The pooled figures show muscle mass falling alongside fat. The trial was not set up to test ways of limiting that.
• Both groups ate less. Energy intake dropped on both plans, so the trial does not separate the timing of meals from the simple fact of eating less.

What this means if you fast

If you already follow one of these plans and it suits you, nothing here is a reason to switch. Both groups lost weight, both saw waist and blood pressure come down, and both saw lower glucose readings.

If you are choosing, the trial gives 5:2 a small edge on weight and fat over four weeks, with no advantage on muscle, waist or blood pressure. Against that, weigh the thing no trial can measure for you: which pattern you can live with. Some people find a daily window easy to forget about once it is routine. Others would sooner have two hard days and five free ones. How to choose the right fasting schedule for your lifestyle goes through those questions.

Fasting is not right for everyone, and this post is general information, not medical advice. If you are pregnant or breastfeeding, have diabetes or take blood-sugar medication, have a history of eating disorders, take other regular medication, or are under 18, talk to a doctor before fasting.

Tracking either plan with QoFast

QoFast is a fasting tracker app for iPhone and Android, for intermittent fasting and multi-day extended fasts. Its intermittent plans are 16:8, 18:6, 20:4, OMAD and custom, and it shows in real time which phase the app estimates you are in based on hours fasted, with fasting history and streaks to look back on. QoFast gives general information, not medical advice, and is free to download with an optional Pro subscription on the App Store and Google Play.

FAQ

Is 5:2 better than 16:8 for weight loss? In this four-week trial, weight and fat mass reductions were greater over time on 5:2. The authors still describe the overall effectiveness of the two plans as similar, and the study was short.

How much weight did people lose? Across both groups, body weight fell by 2.7 kg over four weeks. Separate figures for each plan are not in the abstract.

Do you eat on 5:2 fasting days? In this trial, yes. The 5:2 group followed a fasting-mimicking diet on fasting days.

Do the results apply to men? The trial enrolled only women, so it cannot say.

Sources

• Kim H, Yun W, Han J, Song Y. "Daily 16:8 Versus Weekly 5:2 Intermittent Fasting for Weight Loss and Metabolic Health: A Randomized Controlled Trial." Obesity (Silver Spring), published online 28 October 2026. DOI: 10.1002/oby.70322. PubMed: 42950885.