Which intermittent fasting schedule works best?
Alternate-day fasting has the strongest research backing of all IF schedules, both for weight loss and for blood fats. How much you eat matters more than when you eat, so the schedule you can stick to longest wins.
Alternate-day fasting (fasting every other day) has the strongest support of all intermittent fasting approaches for weight loss. On average it leads to about 1.3 kg more weight loss than ordinary calorie cutting, and it also outperforms time-restricted eating (a fixed daily eating window) and whole-day fasting. For blood fats, alternate-day fasting also comes out on top: it lowers total cholesterol, triglycerides and bad cholesterol more than time-restricted eating. Across a broad comparison covering multiple health outcomes, alternate-day fasting ranked first in 64% of cases.
How large is the benefit? If you look purely at weight loss, the strictest calorie restriction (eating very little every day) leads on average to more than 11 kg greater loss than a control group. That far exceeds alternate-day fasting. When total calorie intake is kept equal, intermittent fasting is no better than simply eating less on a regular basis. How much you eat matters more than when you eat.
There is one serious caveat with intermittent fasting: in studies shorter than 24 weeks it appears to work well, but after 12 weeks the results start to fade. That was less apparent with ordinary calorie cutting. This may mean that intermittent fasting is harder to stick to over the longer term. Time-restricted eating also showed, in one analysis, a small rise in total cholesterol and LDL cholesterol compared with whole-day fasting, which makes it a less obvious first choice for people with elevated blood fats.
All forms of intermittent fasting lead to weight loss compared with unrestricted eating. If you choose intermittent fasting, the current body of research gives the most support to alternate-day fasting, both for weight and for blood fats. But if your primary goal is weight loss, how much you eat is still more decisive than whichever schedule you choose.
This answer draws on several combined analyses of dozens of studies. The researchers themselves describe the certainty of the findings as variable: from high (for alternate-day fasting versus continuous calorie restriction) to low (for long-term comparisons with at least six months of follow-up, where certainty was rated low to very low because of risk of bias in the studies). For most other comparisons, certainty was moderate. The overall picture is therefore reasonably consistent but not definitive: the studies differ in design, duration and participant groups, and the long term remains insufficiently mapped.