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By Beth Krietsch Fasting can help some people reduce how many calories they eat - but it's not 'effortless' as some would have you believe Intermittent fasting can help people lose weight - but the research behind purported benefits, like improvements in cognitive health, is sparse. About 15% of Americans followed an intermittent-fasting diet last year, thanks in part to a push from biohackers and health influencers confidently touting it as the key to effortless weight loss. But when you dig into the scientific research, the findings are more nuanced.
Intermittent fasting is a way of eating whereby you only consume food during certain windows of time. Among American consumers, it was more popular than eating low-carb or Mediterranean diets, according to a recent survey. There are many different approaches to intermittent fasting.
With the 16:8 method, you eat during an 8-hour block of time each day and fast for the remaining 16. There's also the 5:2 diet, which involves eating normally five days out of the week, and consuming just 25% of your normal caloric intake the other two days. That often looks like having just one 500- or 600-calorie meal each day.
The general idea is that going long stretches without eating depletes the body's stored sugar, or glycogen, so it burns stored fat for energy. But it's not clear that that's what drives weight loss; a simpler explanation is that some people simply find they have an easier time cutting back on calories - like that pesky snacking habit you can't seem to shut down, no matter how hard you try - when they can only eat during specific windows of time. Does this approach actually help with weight loss?
And does it work better than other approaches? The research suggests it can lead to modest weight loss, but studies generally find it doesn't work any better than normal calorie restriction. And influencers' claims that intermittent fasting is an "effortless" solution to weight loss are overhyped - most people probably would not consider 16 hours without eating to be "effortless" or easy.
The science behind intermittent fasting A 2024 review found that intermittent fasting may be associated with small reductions in waist circumference and fat mass in people who are overweight or obese. And a 2025 review of 99 randomized clinical trials found that intermittent fasting is associated with modest weight loss compared to a normal, unrestricted diet. But aside from some studies that saw some weight-loss benefits with alternate day fasting for short amounts of time, fasting generally didn't lead to any greater weight loss than traditional calorie restriction, which aligns with other research.
Similarly, in a smaller review of 22 randomized clinical trials conducted around the world, researchers concluded that for people who are overweight or obese, intermittent fasting makes little to no meaningful difference in weight loss compared to following standard dietary advice, such as cutting back on calories or eating different foods. The study's lead author even went so far as to say that the existing evidence for intermittent fasting doesn't justify the hype seen on social media. Want to read more more first-person articles like this?
Check out Health Equity, a MarketWatch column about your health Beyond weight loss, intermittent fasting is often held up as a path to better health - from sharper mental clarity and improved insulin sensitivity to a longer life and cellular repair. Some early evidence may support a few of these claims. Research suggests that intermittent fasting may improve blood-sugar control in people with Type 2 diabetes.
And while intermittent fasting isn't going to cure cancer, as some have suggested, a small study of women with advanced breast cancer found that incorporating fasting alongside resistance training during chemotherapy may be associated with slower cancer progression - though the researchers said more studies are needed. But research showing cognitive benefits in humans is sparse, as is that on cell repair and longevity - a category that's particularly hard to study anyway. Animal studies make up a good portion of this kind of research, and without more high-quality studies in people, we can't say whether the findings translate to humans.
None of this means intermittent fasting is useless. If sticking to a clear, defined eating window helps you rein in late-night snacking, cut back on calories and stick to a nutritious diet over a long period of time, intermittent fasting may be a reasonable approach to managing your weight. But for many Americans, it may be best approached with a healthy dose of skepticism.
And for people with certain medical histories, like having an eating disorder, being pregnant or taking a SGLT2 inhibitor, fasting isn't a good idea. Based on the evidence we have, intermittent fasting isn't superior to calorie counting for weight loss, and many claims about longevity and health optimization are far ahead of existing research evidence. It may be a useful tool for some people - but it isn't a magic wand for improving your health. -Beth Krietsch This content was created by MarketWatch, which is operated by Dow Jones & Co.
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