Alternate-day fasting produces the most weight loss of any intermittent fasting schedule, averaging about 3.4 kilograms (7.5 pounds) more than eating without restrictions. But “most effective” and “best” aren’t the same thing. The schedule that works best for you depends on how much weight you want to lose, how your body responds, and whether you can actually stick with it for months.
A 2025 network meta-analysis in The BMJ, covering 99 clinical trials and over 6,500 adults, directly compared every major fasting approach head to head. The results give us the clearest picture yet of how these schedules stack up.
How the Main Fasting Schedules Compare
There are four widely studied fasting approaches, and they don’t all produce the same results. When each was compared against unrestricted eating, here’s how the average weight loss broke down:
- Alternate-day fasting (ADF): 3.4 kg (about 7.5 lbs) lost on average
- 5:2 fasting: 2.4 kg (about 5.3 lbs)
- Traditional daily calorie restriction: 2.1 kg (about 4.6 lbs)
- Time-restricted eating (such as 16:8): 1.7 kg (about 3.7 lbs)
Alternate-day fasting came out on top in nearly every comparison. It beat time-restricted eating by about 1.7 kg, beat the 5:2 approach by about 1 kg, and even outperformed traditional calorie counting by roughly 1.3 kg. It also produced the largest drop in BMI, with high certainty of evidence. Differences between time-restricted eating and 5:2 fasting were negligible.
One important nuance: while alternate-day fasting led to the biggest drop in overall body weight and BMI, reductions in body fat specifically were smaller than you might expect. The BMJ analysis rated the body fat reduction as “trivial” compared to unrestricted eating. This suggests some of the weight lost comes from water and lean mass, not purely fat.
Alternate-Day Fasting: Most Effective but Hardest to Maintain
Alternate-day fasting involves eating very little every other day, typically around 500 calories on “fast” days, then eating normally on the other days. In an 8-week trial comparing it directly to standard calorie restriction in people with metabolic syndrome, ADF produced significantly greater reductions in body weight, waist circumference, blood pressure, and fasting blood sugar.
The catch is sticking with it. A year-long trial tracking 100 obese individuals found that 38% of those assigned to alternate-day fasting dropped out, compared to 29% in the daily calorie restriction group. That’s a meaningful gap. A broader review of 40 studies found dropout rates across all fasting approaches ranged from 0% to 65%, with no clear evidence that fasting is easier to follow than simply cutting calories every day. If you can sustain ADF, the data favors it. But a plan you abandon after six weeks doesn’t produce results.
The 5:2 Approach: A Middle Ground
The 5:2 diet asks you to eat normally five days a week and restrict calories on two non-consecutive days. On those two days, the typical target is 500 calories for women and 600 for men. If jumping straight to that level feels too aggressive, Cleveland Clinic recommends starting at 900 to 1,000 calories on fasting days and cutting back in increments of 100 to 200 calories over time.
In terms of weight loss, the 5:2 approach lands between alternate-day fasting and time-restricted eating. It produced about 2.4 kg of weight loss compared to unrestricted eating, and the BMJ analysis found no meaningful difference between 5:2 and 16:8 schedules. The practical advantage is that you only deal with two difficult days per week instead of three or four, which can make it easier to plan around social events, workouts, and daily routines.
Time-Restricted Eating: Easiest but Least Powerful
Time-restricted eating, the approach behind the popular 16:8 schedule, means compressing all your meals into a set window each day. You might eat between noon and 8 p.m., for example, and fast the remaining 16 hours. It produced the smallest average weight loss in the BMJ analysis, about 1.7 kg, roughly half of what alternate-day fasting achieved.
That said, when your eating window falls matters. A 3-month clinical trial compared early time-restricted eating (finishing meals earlier in the day) with late time-restricted eating (eating later into the evening), both combined with calorie restriction. The early eating group lost more body fat, had lower fasting blood sugar, and saw greater improvements in blood pressure. Your body processes food more efficiently earlier in the day due to natural circadian rhythms in insulin sensitivity, so shifting meals toward the morning and afternoon offers a metabolic edge over late-night eating windows.
If you choose time-restricted eating, an earlier window (say, 8 a.m. to 4 p.m.) will likely outperform a later one (noon to 8 p.m.), even if the total hours of fasting are identical.
Considerations for Women
More aggressive fasting schedules can affect reproductive hormones. A systematic review examining intermittent fasting in women found changes in several key hormones, including reductions in luteinizing hormone, which helps regulate the menstrual cycle. These shifts may not matter for everyone, but women who are trying to conceive or who notice changes in their cycle while fasting should consider a less restrictive approach, like the 5:2 method or a wider eating window.
Choosing the Right Schedule for You
The data points to a clear pattern: the more restrictive the fasting schedule, the more weight it tends to produce, but the harder it is to sustain. Here’s a practical way to think about it.
If you have a significant amount of weight to lose and do well with structure, alternate-day fasting produces the best measurable results. The key is treating fast days as very low calorie days (around 500 calories) rather than zero-calorie days. This modified version is what most clinical trials actually test.
If you want something sustainable over many months, the 5:2 approach gives you most of the benefits with fewer difficult days. Starting with higher calories on fasting days and gradually reducing them makes the transition much smoother.
If your primary goal is simply to stop overeating and you want the least disruptive change to your routine, time-restricted eating works, especially with an earlier eating window. Just know that its effect on the scale is more modest, and you may need to pay attention to what you eat during your window, not just when you eat.
Across all schedules, the BMJ analysis found that no single fasting method was dramatically superior. The differences between them ranged from roughly 1 to 1.7 kg. That means the gap between the “best” and “worst” fasting schedule is far smaller than the gap between any fasting schedule and doing nothing at all. Picking one you can follow consistently matters more than picking the theoretically optimal one.