Does Intermittent Fasting Work? Yes! Here’s How It May Help With Weight Loss

Fasting has been around for millennia, and it’s an important part of many religions and cultures — for spiritual and health reasons. More recently, intermittent fasting has become a popular way for people to try to manage their weight and improve their overall health. 

But does fasting really work, and is it right for you? Read on to learn the basics of intermittent fasting, including what the benefits are and how to do it safely. 

What is intermittent fasting?  

Intermittent fasting is when you alternate between periods of fasting (not eating at all) or eating very little, and periods of eating normally. There are different approaches to intermittent fasting. These include:

• Time-restricted eating: This is when you eat during a certain window of time (for example, 8 hours) and fast the rest of the day (16 hours). This is the most popular type of intermittent fasting.

• Whole-day fasting (or the 5:2 plan): You fast for 2 days and eat normally the other 5 days. Some modified versions allow you to eat about 500 to 600 calories on the fasting days.

• Alternate-day fasting: You fast every other day (or limit your intake to 500 to 600 calories a day) and eat normally on non-fasting days. 

How does intermittent fasting work for weight loss?

Most approaches to managing your weight focus on what and how much to eat. Intermittent fasting, on the other hand, focuses on when to eat. 

The theory is that going for long periods of time without food reduces your body’s stores of glucose (sugar) for energy. When the body no longer has enough glucose, it starts burning fat for energy. This is called ketosis, and it’s also the goal of the popular keto diet.

It’s not clear how intermittent fasting works for weight loss. It may come down to: 

• Calorie restriction

• An improved response to insulin

• Changes to your metabolism

• Lowered inflammation 

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Or it could be a combo of the above and other effects. 

Does intermittent fasting work for weight loss?

Intermittent fasting can help people lose weight. But there’s no scientific evidence that it works better than traditional, calorie-restricting diets. 

One review of the research found that people who followed intermittent fasting for more than 6 months lost more weight compared to those who followed a traditional diet of restricted calories. But another review found that the two approaches led to similar weight loss.

Importantly, the evidence seems to be stronger for alternate-day fasting and the 5:2 method than it is for time-restricted eating. 

Intermittent fasting, and particularly alternate-day fasting, may have additional health benefits, too, including:

• Reduced visceral fat: Fasting may help reduce excess visceral fat, the fat that’s found in your abdomen. Too much visceral fat has been linked to increased risk of diabetes and heart disease. 

• Improved cardio-metabolic health: Intermittent fasting may improve insulin function, blood sugar levels, and cholesterol levels. These are all important for reducing your risk of diabetes and heart disease. 

But fasting may be difficult for some people to stick to over the long term. More research is needed on the long-term benefits. Ultimately, it may be worth a try to see if it works for you.

Which type of intermittent fasting schedule is best for weight loss?

Alternate-day fasting may lead to more weight loss than time-restricted eating. But again, the research isn’t conclusive. Which type you choose may depend more on what you’re more comfortable with. 

Many people find time-restricted eating the easiest to follow. That’s when you fast for 16 hours and eat normally for 8. For example, you might start eating at 10AM and have your last bite to eat at 6PM. 

But choose the type that best fits your lifestyle and eating preferences. This can take some trial and error. You may try one schedule and decide it’s easier doing it another way. 

Benefits of intermittent fasting for weight loss

Intermittent fasting may have some benefits that make it easier to follow than a traditional weight-management program. These include: 

• You can eat what you want. With other weight-management programs, you often have to limit foods you like (think pasta). With intermittent fasting, you don’t have to follow a specific diet or avoid foods. But you still want to eat a nutritious diet during your non-fasting time. 

• You don’t need to track calories. You don’t have to restrict calories on non-fasting days, so you don’t have to count calories. 

Potential disadvantages of intermittent fasting

Intermittent fasting doesn’t work for everyone. Some people don’t lose weight on it. Or they don’t like the way fasting makes them feel. 

When you first start intermittent fasting, you may experience symptoms like: 

• Headaches 

• Nausea

• Dizziness

• Excessive hunger

• Dehydration

• Irritability

Most of these symptoms go away after a few weeks as you adjust to fasting. When fasting, drink plenty of water or other sugar-free beverages to stay hydrated and help prevent symptoms. 

Is intermittent fasting safe?

For most people, intermittent fasting is considered safe. But it may have some risks for certain groups. Speak with your primary care provider before starting an intermittent fasting regimen if you:

• Are pregnant or nursing

• Are a child or teenager

• Have a health condition like diabetes, kidney disease, or heart disease, or are immunocompromised

• Are an older individual with a history of dementia 

• Have a history of an eating disorder (like anorexia or bulimia)

• Are on certain medications that need to be taken with food

Tips for incorporating intermittent fasting into a weight-loss plan

Intermittent fasting may be hard to follow at first. Not eating for long periods of time may make you feel irritable or have low energy in the beginning. For most people, it does get easier. But it usually takes 1 to 2 weeks to adjust to fasting. 

Here are some tips to help you be successful while following an intermittent fasting plan: 

• Start slow: If you’re doing time-restricted eating, start by fasting for 12 hours instead of 16. Or, if you’re trying the 5:2 plan, start by fasting for 1 day instead of 2. 

• Stay hydrated: When fasting, drink plenty of water or other non-caloric beverages throughout the day. 

• Eat a nutritious diet: On non-fasting days, eat fresh fruits, vegetables, legumes, and healthy sources of protein like chicken or fish. Avoid overly processed foods, fast foods, and sweetened beverages, as these may be high in calories and low in nutritious value. 

• Avoid overeating after fasting: It’s easy to overeat when you’re hungry. Try to eat portions that are typical for you, not oversized. Before reaching for second helpings, ask yourself if you’re truly hungry. 

• Keep busy: This can keep your mind off of hunger. Staying distracted may be harder when you’re home with some downtime. Schedule phone calls or video chats with friends, watch a movie, or go for a walk. 

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Written by:

Margaret Apura, RD, MPH

Margaret has almost 20 years of experience as a registered dietitian with a focus on weight and chronic-disease management. She started her career as a research dietitian at Boston Children’s Hospital.

Edited by:

Laurie Tarkan

Laurie Tarkan is a senior health editor for general health and well-being at GoodRx. She has an extensive background in health journalism, and wrote regularly for The New York Times for a decade.

Reviewed by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

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