Intermittent fasting is surging in popularity thanks to its ease and health benefits, but fasting has been around for millennia. Fasting for religious purposes has long been practiced among many faiths, from Christianity and Islam to Judaism and Buddhism.
Today, several types of intermittent fasting have risen to prominence within health and nutrition circles as some studies find that fasting, or eating patterns that restrict when you eat food—but not what you eat—may have many benefits. Here’s how intermittent fasting works, what the benefits might be, and whether it’s right for you.
What is intermittent fasting?
Basically, you have a window of time during which you’re allowed to eat, and a (longer) period during which you eat no—or few—calories. During the eating window, intermittent fasters often eat as they normally would; during the hours they’re fasting, they either eat nothing or severely restrict their calories. There are several approaches to intermittent fasting, and the type you choose depends largely on what fits with your lifestyle. Many people try intermittent fasting for a few weeks before determining if it works.
What are the methods?
These four intermittent fasting approaches people commonly use:
- The 16/8 Method: This approach may be among the easiest to adopt. People fast for 16 hours and have an eight-hour window for eating. For example, you could eat every day from 12 p.m. to 8 p.m. After 8 p.m.—until 12 p.m. the next day—you can only drink no-calorie beverages like water, tea, and coffee.
- The 5:2 Method: Also known as alternate-day fasting, this method means that you eat normally five days a week and then fast for 24 hours, allowing yourself just 500 to 600 calories. You pick two days a week to fast—say Monday and Thursday, for example.
- Eat-Stop-Eat: This is the same as 5:2, except that you don’t get any calories for those two non-consecutive days per week.
- The Warrior Method: Fasters who use this method condense their eating into just four hours per day. The other 20 is spent fasting. This is more complicated—nutritionists share what you should know about the Warrior Method before trying it.
What happens to your body while intermittent fasting?
Intermittent fasting may be beneficial because of several chemical and hormonal reactions that happen when your body can’t use food for fuel.
- Increased human growth hormone (HGH): With more HGH, your body may boost fat loss and muscle gain.
- Better insulin sensitivity: Research indicates that Insulin levels are lower for fasters, and low insulin levels allow your body to more easily access stored fat for energy. This can lead to weight loss.
- Cellular repair: During IF, your cells enter a process called autophagy during which they remove protein build-up and dead or damaged cell components.
- Changes to gene expression: This process may impact how your body develops certain conditions and diseases.
Are there other benefits?
Intermittent fasting may be most popular for weight loss, but other benefits could occur.
- Increased weight loss: Research suggests intermittent fasting can help people lose up to 8 percent of their weight in as little as three to 24 weeks—for a 200-pound person, that’s about a pound a week. Unlike typical diets, you may be able to lose weight without counting calories on this plan.
- Higher metabolism: The weight loss may result from an increased metabolic rate. Research suggests intermittent fasting could boost your metabolism by as much as 14 percent.
- Lower risk of diabetes: In overweight and obese individuals, intermitted fasting lowered insulin resistance by 3 to 6 percent. Lower blood sugar and insulin levels can cut your risk of type 2 diabetes.
- Decreased inflammation markers: Inflammation is connected to several conditions and diseases. Reducing inflammation may improve health.
- Improved heart health: Fasting may lower “bad” LDL cholesterol, blood sugar, blood triglycerides, and other factors that increase the risk of heart disease, research suggests.
- Slow aging: With lower inflammation and cell damage, intermittent fasting may also reduce signs of aging and extend longevity.
As research expands, scientists and doctors are beginning to learn more about the possible benefits of intermittent fasting.
Is intermittent fasting safe?
The research is still relatively new, but several studies—such as this one—have found the approach to be perfectly safe for the majority of healthy, well-nourished individuals. It’s always a good idea to consult with your doctor before beginning any diet or new eating pattern, but many folks will be able to safely fast.
Who shouldn’t do intermittent fasting?
Going without calories for long periods of time isn’t wise for some groups, such as:
- People who are underweight
- People with a history of eating disorders
- Anyone with a chronic disease, like diabetes or high blood pressure, without prior approval from your doctor
- Pregnant women
- Breastfeeding women
What’s more, research suggests some women may not experience the same benefits as men when intermittent fasting. One study found that while insulin sensitivity improved in men, it decreased in women. Some women may experience irregular cycles or amenorrhea (the complete stoppage of their menstrual cycle) on intermittent fasting—though more research is needed to confirm this.
What are the challenges?
The 16/8 method is considered among the easiest methods. If you’re thinking of trying intermittent fasting, you may want to experiment with this approach. As that becomes easier, you can graduate to more advanced options—but be sure to consult with your doctor before starting any plan. If you aren’t a good candidate for IF or if you aren’t ready to try that lifestyle, you might be interested in one of these 30 tiny diet changes that can help you lose weight.