9 intermittent fasting health benefits - and possible side effects or risks
- Intermittent fasting is when you only eat in a certain time window, such as from 10 AM to 6 PM.
- Intermittent fasting benefits may include weight loss, improved heart health, and lower blood pressure.
- Potential risks of intermittent fasting include muscle loss, headaches, and hunger.
Intermittent fasting has become a popular approach to weight loss, playing off the idea that we didn't always have food available 24/7, and that our daily snacking habits are feeding the ever-growing obesity epidemic.
Like most diets, the research on intermittent fasting is ongoing. But preliminary studies, in both humans and animals, show promise for several benefits that go beyond just weight loss.
"Research continues to be done, and so far intermittent fasting has been shown to reduce inflammation, improve insulin sensitivity, [and] lead to improvement in glucose, blood pressure, and cholesterol which can prevent the progression of chronic diseases," says Veronica Contreras, DO, an urgent care physician with AltaMed Health Services.
Here are nine benefits of intermittent fasting, important risks and side effects to consider, and tips for getting started.
1. Could help with weight loss
Numerous studies have found that intermittent fasting may help people lose weight. For example, a 2015 systematic review of 40 studies found that, on average, study participants lost 7-11 pounds over a span of 10 weeks.
However, it's unclear if intermittent fasting is any better than basic calorie restriction. For instance, a 2017 study found that a group who fasted every other day (by cutting 75% of their calories) lost no more weight than a comparison group who simply reduced their calories by 25% every day.
Another 2021 study found similar results that alternate-day fasting did not lead to greater fat loss than good, old-fashioned calorie cutting.
Note: The majority of studies that explore intermittent fasting's weight loss benefits are small and short. That's why most experts agree that more research is needed to determine whether this different approach to dieting is safe and sustainable.
2. May reduce inflammatory pain
When your body is in a fasted state, it means that your glucose reserves are next to empty, which may help reduce painful inflammation, says Andrew Wang, MD, a professor of immunobiology at Yale School of Medicine.
To understand how, it's important to address what intermittent fasting does to your body. When you fast for long, extended periods of time, your body ends up using all of its glucose - the main source of fuel that keeps you going - and enters a process called ketosis, where it burns ketones for fuel and energy, instead.
The idea is that your body produces less inflammation when burning ketones compared to glucose, which may explain why some studies have found diets that promote ketosis also alleviate inflammatory pain.
Though, more research is needed to determine if intermittent fasting should be implemented as an effective tool for patients with inflammatory conditions.
3. May prevent dementia
When we age, our organs are prone to chronic inflammation called "inflammaging," says Wang.
Chronic inflammation can contribute to cognitive decline and dementia potentially due to plaque buildup in the brain. Fasting may help to counter this by reducing inflammation, Wang says.
Research in animals suggests fasting can slow the development of Alzheimer's. While the research has not yet been conducted in humans, a 2019 study found that intermittent fasting can slow cognitive decline and improve the symptoms of Alzheimer's disease in mice.
4. Could help boost cognitive functioning
The cognitive benefits of fasting may not be restricted to the elderly. A small 2016 study tested amateur weightlifters after a 48-hour fast and found that the fasting improved "mental flexibility," which the researchers defined as participants' ability to quickly and efficiently switch between tasks.
5. May regulate blood sugar levels
Intermittent fasting may also help regulate blood sugar levels, which is important to protect against diseases associated with glucose intolerance like type 2 diabetes.
Glucose intolerance occurs when your body can't control how much sugar is in your blood, which can lead to dangerously high blood sugar levels.
Blood sugar increases when you eat, so it naturally falls when you fast, Wang says.
That may explain why a small 2019 study of men at risk for type 2 diabetes found that intermittent fasting helped improve glucose tolerance.
Important: If you have diabetes, consult a doctor before fasting, as it can increase the risk of diabetic ketoacidosis for those who use insulin or other medications to treat their diabetes.
6. Could improve heart health
While research on this topic is limited, Wang says it is reasonable to assume that intermittent fasting boosts heart health by reducing inflammation and protecting against diabetes - which are both risk factors for heart attacks and strokes.
A small 2012 study tested Muslims with a history of heart disease who fasted intermittently for Ramadan. After their fast ended, there was an improvement in their 10-year coronary heart disease risk score and a reduction in other heart risk factors like lipids profile, systolic blood pressure, and weight.
7. May lower blood pressure
Another cardiovascular benefit of intermittent fasting is that it may reduce blood pressure.
A small 2018 study found that men with prediabetes who fasted for 18 hours a day for 5 weeks had reductions of roughly 10 points in both their systolic and diastolic blood pressure.
However, the study was presented as a proof of concept, and larger studies are needed to better understand the role of intermittent fasting on blood pressure.
Note: For more ways to reduce blood pressure, read our guide on how to lower blood pressure.
8. Could facilitate cell repair
When your body encounters toxins or has damage, it repairs its cells through a process called autophagy. During autophagy, your cells break down damaged portions, and recycle those materials into new, healthier substances.
While human research in this area is limited, intermittent fasting has been shown to boost autophagy in animals. A 2018 MIT study on mice found that intermittent fasting can make cells more adept at regenerating. Contreras says this is promising for a possible similar response in humans, especially those who use intermittent fasting to eliminate late-night snacking, which can inhibit autophagy.
"If you eat late at night you raise your glucose levels and insulin while you are sleeping, which doesn't allow autophagy to occur," Contreras says. "Intermittent fasting has shown to activate these pathways to remove or repair damaged molecules."
9. May help prevent cancer
Having healthy and optimal autophagy may help suppress tumor growth, while having dysregulated autophagy may contribute to cancer development, according to a 2018 medical paper.
So, it should come as no surprise that scientists are studying whether intermittent fasting may help prevent cancer or slow its progression when it is used alongside cancer-fighting treatments like chemotherapy.
"Although research is still being done, there are studies in patients with certain cancers suggesting that it can suppress tumor growth and in some cases prevent regression," Contreras says.
Side effects and risks
In general, intermittent fasting is safe to try if you are relatively healthy, says Contreras. That's because you're still getting all the nutrients and calories that your body needs, just compressing your consumption into fewer hours of the day.
However, intermittent fasting has been linked to muscle loss. In addition, certain people should proceed with caution when it comes to intermittent fasting since they have more nuanced nutritional needs. Contreras says you should speak with your doctor before starting if you are:
- Under age 18
- Pregnant
- Breastfeeding
- Have struggled with eating disorders in the past
- Are over 65
- Have type 2 diabetes
In fact, that's a good idea for anyone who has never done intermittent fasting, since a doctor who is familiar with this approach can help you make sure you're still getting all the nutrients needed to stay healthy.
That doesn't mean starting intermittent fasting will be easy, especially at the beginning. Contreras says you may experience the following symptoms when you start fasting:
- Hunger
- Irritability
- Headaches
While these typically aren't risks to your health, you should contact a doctor or call 911 immediately if you experience lightheadedness, dizziness, or changes to your alertness.
Insider's takeaway
If you're looking to improve your health and maybe lose some weight, intermittent fasting may be an enticing option. However, since research about intermittent fasting is still ongoing, it's best to speak with a healthcare provider about whether this approach is right for you.
"If someone is considering intermittent fasting, it really has to be personalized individually," Contreras says. "They should consult with a physician who is knowledgeable about intermittent fasting."
The specifics of intermittent fasting will depend on your lifestyle and guidance from your doctor, but it's important to develop a plan that works for you.
"The method by which you decide to fast should [be one that] you can continue to do it long term, which fits your lifestyle and your goals, and where you have the support necessary to achieve this," Contreras says.
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