Intermittent Fasting: Should You Try It?

Intermittent fasting is in the news a lot—but what exactly is it? Does it work for weight loss? Is it safe? These are the answers you're looking for.

plate with fork and knife resembling a clock for intermittent fasting conceptWestend61/Getty Images

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, including Christianity and Islam, Judaism, and Buddhism, according to an article in The Journal of the Academy of Nutrition and Dietetics.

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?

With intermittent fasting, 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 of intermittent fasting?

These are the four intermittent fasting approaches people most 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 suggests 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 the 5:2 method, except that you don’t get any calories for those two non-consecutive days per week.
  • The Warrior Method: People who use this method condense their eating into just four hours per day. The other 20 is spent fasting. This method 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 people who fast, and low insulin levels allow your body to more easily access stored fat for energy. This can lead to weight loss.
  • Cellular repair: During intermittent fasting, 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 by prolonging the health of the nervous system.

woman sitting at home eating lunch and looking out the windowOliver Rossi/Getty Images

Are there other benefits of intermittent fasting?

As research expands, scientists and doctors are beginning to learn more about the possible benefits of intermittent fasting. Intermittent fasting may be most popular for short-term weight loss, but other benefits could occur.

  • Increased weight loss: A study in the journal Obesity Review suggests intermittent fasting can help people lose up to 8 percent of their weight in as little as three to 12 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 impact the risk of heart disease, research in the journal Nutrients suggests.
  • Slow aging: With lower inflammation and cell damage, intermittent fasting may also reduce signs of aging and extend longevity.

Is intermittent fasting safe?

The research is still relatively new, but several studies—such as this one in Behavioral Sciences—have found the approach to be safe for the majority of healthy, well-nourished individuals. Just remember that it’s always a good idea to consult with your doctor before beginning any diet or new eating pattern.

Who shouldn’t do intermittent fasting?

Going without calories for long periods of time isn’t wise for some groups, such as:

What’s more, research suggests some women may not experience the same benefits as men when intermittent fasting. One study in Obesity Research 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 in humans.

What are the challenges?

Hunger can be an issue for some people, research in Behavioral Sciences suggests. Others may feel ill or tired as they shift to this new eating pattern. With time, however, they often feel better.

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 intermittent fasting or if you aren’t ready to try that lifestyle, you might be interested in one of these 29 tiny diet changes that can help you lose weight.

Sources
  • The Journal of the Academy of Nutrition and Dietetics: “Intermittent Fasting and Human Metabolic Health”
  • Journal of Translational Medicine: “Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males”
  • EatStopEat.org: “Intermittent Fasting Revolution”
  • The Journal of Nutrition, Health, & Aging: "Comparison of intermittent fasting versus caloric restriction in obese subjects: A two-year follow-up"
  • The Journal of Clinical Investigation: “Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man”
  • The American Journal of Clinical Nutrition: “Alternate-day Fasting in Nonobese Subjects: Effects on Body Weight, Body Composition, and Energy Metabolism”
  • Translational Research: “Intermittent Fasting vs Daily Calorie Restriction for Type 2 Diabetes Prevention: A Review of Human Findings”
  • American Journal of Physiology: Cell Physiology: “Mitochondrial Degradation by Autophagy (Mitophagy) in GFP-LC3 Transgenic Hepatocytes During Nutrient Deprivation”
  • Ageing Research Reviews: “Caloric restriction and intermittent fasting: Two potential diets for successful brain aging”
  • Obesity Review: “Intermittent Versus Daily Calorie Restriction: Which Diet Regimen Is More Effective for Weight Loss?”
  • American Journal of Clinical Nutrition: “Resting Energy Expenditure in Short-Term Starvation Is Increased as a Result of an Increase in Serum Norepinephrine”
  • Translational Research: “Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings”
  • Free Radical Biology and Medicine: “Alternate Day Calorie Restriction Improves Clinical Findings and Reduces Markers of Oxidative Stress and Inflammation in Overweight Adults With Moderate Asthma”
  • Nutrients: “Intermittent Fasting in Cardiovascular Disorders—An Overview”
  • Cell Metabolism: “Fasting: Molecular Mechanisms and Clinical Applications”
  • Behavioral Sciences: “Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects—A Narrative Review of Human and Animal Evidence”
  • Cell Metabolism: “Fasting: Molecular Mechanisms and Clinical Applications”
  • Journal of Abnormal Psychology: “Fasting Increases Risk for Onset of Binge Eating and Bulimic Pathology: A 5-Year Prospective Study”
  • Obesity Research: “Glucose Tolerance and Skeletal Muscle Gene Expression in Response to Alternate Day Fasting”
  • PLOS One: “Gonadal Transcriptome Alterations in Response to Dietary Energy Intake: Sensing the Reproductive Environment”
  • Behavioral Sciences: “Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects—A Narrative Review of Human and Animal Evidence”
Medically reviewed by Elisabetta Politi, CDE, MPH, RD, on June 08, 2020

Kimberly Holland
Kimberly Holland is a lifestyle writer and editor based in Birmingham, Alabama. When not organizing her books by color, Holland enjoys toying with new kitchen gadgets and feeding her friends all her cooking experiments.