Is intermittent fasting healthy?

If you’re looking to lose weight, the dizzying array of diets out there can be daunting. Many of them take certain foods or nutrients off the table (like keto) or over-emphasize others (carnivore diet). Still others replace all solid food with juice. 

And then there’s intermittent fasting, which doesn’t actually have you change what you’re eating at all. Instead you just limit your eating to specific times — and that can be very appealing. “People often think, ‘it's much easier if I can just give myself a window and eat during this time,” says Dr. Melissa Shoemaker, M.D., an assistant professor in the department of internal medicine at UT Southwestern Medical Center who specializes in obesity medicine.

Another reason people are drawn to this approach? On top of weight loss, headlines also suggest it has other health benefits — maybe even helping people live longer! But is that all backed by science just b.s.? Here’s what we really know about intermittent fasting. 

“In and of itself, intermittent fasting is not a diet plan,” says Melinda Boyd, R.D., a doctor of clinical nutrition and an assistant professor in the department of nutrition at Cedar Crest College. “It’s just a pattern of eating.” Depending on the protocol you choose, you can eat during certain times of day or certain days, and the rest of the time you should be fasting.

There are three main forms of intermittent fasting:

• Time-restricted eating: The most common approach, you eat how you normally would during a specific time frame each day (the window is usually somewhere between six to 10 hours), then fast (so nothing but water or zero-calorie beverages) the rest of the time. This can also be called 16/8 fasting, which is fasting for 16 hours and eating in an 8-hour window each day.

• 5:2 approach: This is often seen as a more intense approach to intermittent fasting, with normal eating for five days of the week and two fasting days where you eat very little.

• Alternate-day fasting: Think of this one as the most extreme version. You have a normal eating day followed by a very restricted eating day, and keep going back and forth.

Research on intermittent fasting and weight can be tricky to interpret, since there are a lot of things that can influence the results. These include what form of intermittent fasting you’re doing, time of day for your eating window, and the kinds of foods (and how much) you’re eating during your windows, says Shoemaker. What’s more, your genetics and personal biology play a role, too, says Boyd. “There’s so much nuance to it that [interpreting the research] can become really confusing to the average consumer,” she says.

That said, there are some key takeaways to learn. Mainly, yes, intermittent fasting can help you lose weight. When you’re limited to eating only within a certain period, you may end up taking in fewer calories than you would if you didn’t have any timing restrictions. That can put you in a calorie deficit, and, as a result, you can lose weight. But the same holds true for any diet or way of eating that has you taking in fewer calories than what your body is burning. “Intermittent fasting can be helpful, but generally speaking, it's just a way to eat less,” says Shoemaker. 

This is supported by research: According to a recent Cochrane review, intermittent fasting didn’t lead to any greater weight loss than traditional weight-loss methods, like calorie restriction or focusing on better food choices (say, trying to take in more fruits and veggies, or emphasizing more protein). 

“To me, that’s not surprising because cutting calories or watching what you're eating and being mindful of that would still be successful,” says Boyd, who co-authored the review. A 2025 meta-analysis published in BMJ concluded similarly; combined intermittent fasting and calorie restriction led to weight loss when compared to simply eating normally.

One of the things that makes intermittent fasting so appealing is that it gets linked to all kinds of benefits beyond weight loss — things like a longer life, healthier heart, and better blood sugar control. But only some of that is based on facts.

For instance, some research does show a benefit for cardiovascular health. In a small 2025 study published in Nature Communications, researchers had 41 participants either intermittently fast using the 5:2 protocol or continue with their normal diet for six months. The intermittent fasting group lost weight and improved their LDL cholesterol, non-HDL cholesterol, and triglyceride levels — but they didn’t see any benefits to other major cardiometabolic risk factors, including CRP (a marker of inflammation), blood pressure, fasting glucose, or insulin resistance. 

The BMJ meta-analysis also looked at cardiometabolic markers, and concluded that intermittent fasting may offer similar benefits in that realm as regular calorie restriction. That suggests improvement in those markers may be due to weight loss, not necessarily anything specific to intermittent fasting. 

As for everything else you may have heard? “Beyond weight loss and some lipid effects, the evidence in humans is much less impressive than the hype suggests,” says Dr. Luigi Fontana, M.D, Ph.D., professor of medicine and nutrition at the University of Sydney and author of the Nature Communications study. 

Earlier animal studies show that fasting can encourage the use of fat as fuel, lead to less inflammation, and improve insulin sensitivity, but what you see in animals doesn’t necessarily translate to humans. Lab animals live very controlled lives, whereas people have a lot of different things going on, says Fontana. We don’t all eat the same things, or have the same stress or activity levels, for example.

The same thinking applies to another often-touted benefit of intermittent fasting: that it can be a longevity boon. This comes from rodent studies, which suggest it could extend healthspan (how long you live with optimal health) and lifespan (how long you live, period). This is partly because fasting increases resilience to stress and promotes autophagy, or the body’s system for cleaning up and recycling damaged parts of cells. But the research just isn’t there to confirm this holds true in humans. “This is really wishful thinking and an extrapolation from animal studies, not direct human evidence,” Fontana says. “So we need to be very careful. What is seen in mice should not automatically be assumed to occur in humans.”

Then there’s the question of whether intermittent fasting can offer extra benefits for women, particularly as they go through the menopause transition. 

A small 2025 study published in Nutrients split 54 women ages 41-61 into two groups: One combined time-restricted eating with exercise — circuit training that included cardio and strength components — and the other did just the exercise part. After 12 weeks, the researchers found the women in the combination group experienced greater decreases in total self-reported menopause symptoms, including those in the somatic category (hot flashes and sweating, sleep disturbances, and joint and muscle problems) and the psychological domain (including irritability, depressive symptoms, and anxiety).

This sounds pretty great, right? Like many other studies on intermittent fasting, though, this study didn’t look at how intermittent fasting compared with other diet-related weight-loss strategies. “Because there isn't a clear comparison group with diet, we can't really draw any conclusions about time-restricted eating or intermittent fasting,” Boyd says. 

One small pilot study suggested that weight loss itself — not necessarily anything special from intermittent fasting — may improve some menopause symptoms like hot flashes. This is why Boyd suspects “any version of a diet intervention over none would have improvements.” 

It’s also possible there are other things at play here, too. For instance, the women in the time-restricted eating group were able to choose their own windows for eating and fasting. “Perhaps, and only speculation here, they had improved symptoms and quality of life because they felt in control of something,” says Boyd. “At a time where their bodies are essentially doing things out of their control, having control over that eating window may just [offer] the structure and feeling of success that they need to help feel an improvement in symptoms.”

The body of research doesn’t support any overwhelming benefit to intermittent fasting compared to other ways to lose weight. But if you like the freedom around food choices and think it could be an approach you stick with, there’s no reason not to try it. “It really is an individual, case-by-case thing,” Boyd says. 

That said, others may find the fasting windows unpleasant or unsustainable. Here’s why:

• It can be hard to fit into your social life. “One of the biggest challenges is that it's not always conducive to real life,” says Boyd. For instance, if your eating window is between 10:00 a.m. and 6:00 p.m., you might miss weekend breakfasts with your family, going to celebratory dinners with your friends, or attending other evening events that include food.

• It can send the wrong messages around food. “If you're trying to explain to your child why you can't sit down and eat breakfast with them, you risk setting unhealthy relationships with food, if they're looking at you thinking, ‘I have to skip breakfast in order to be healthy or maintain a weight,’” says Boyd. 

• You may be likelier to binge. Intermittent fasting may trigger an increased preoccupation with food during the windows when you’re not eating at all. Then, when you’re allowed to eat again, you may find yourself over-indulging.  

• It can be unhealthy for some people. This approach is likely not a good choice for people with certain medical conditions that need nutrients spread throughout the day, like people with diabetes who take medication to lower blood sugar, says Boyd. Same for people with a history of eating disorders or disordered eating — or even those who frequently seek out different fad diets, says Boyd. “Intermittent fasting hooks them, and it might further enhance those unhealthy relationships with food behaviors.” And athletes or people with fitness goals may want to think twice too, because they need fuel to complete — and recover from — tough morning sessions that often fall into the fasting window.

If it turns out intermittent fasting is a good fit for you and your health goals and you want to give it a try, here are some things to keep in mind:

• Diet quality is huge — regardless of when you’re eating: “It’s important that the foods that you're fueling with in a shorter window are still the right foods,” Boyd says. Make sure to eat a balance of protein, carbs (including fiber), and healthy fat — and to get in your vitamins and micronutrients too. Eating too much saturated fat, ultra-processed foods, or highly-caloric options can still hurt your health even if you only do so during a smaller window. “You can lose weight without obtaining the expected anti-inflammatory and metabolic benefits if the overall dietary pattern is not improving in the right direction,” Fontana says. Not sure what foods to focus on? Weight Watcher’s behavior change science results in 4.7 times greater improvements in diet quality than standard nutritional guidance.*

• Don’t forget to hydrate: Dehydration can cause headaches, lightheadedness, and fatigue, according to Shoemaker. And since you aren’t eating during a big chunk of the day, it can be easy to forget to drink as well. Make sure you’re staying hydrated during your fasting window, with zero-calorie options, like water, black coffee or tea, sparkling water, or other no-calorie beverages.

• Pick an eating window that works for you: “Choose one that best aligns with your busy lifestyle,” says Boyd. This means one that lets you enjoy any social benefits of food — say, eating dinner with your family — and be flexible. Like any way of eating, perfection shouldn’t be the goal.

Intermittent fasting has been promoted for a wide-range of benefits, from improving weight loss to bettering heart health to even extending lifespan. But the research just isn’t there for a lot of those benefits. Yes, it can help you lose weight, but it doesn’t seem to work any better than other approaches to healthy eating, like Weight Watchers. And unlike WW, it doesn’t put any emphasis on choosing nutrient-dense foods or come with expert support and a welcoming community.