Intermittent fasting is a time-based feeding protocol that cycles between periods of fasting and eating. It can be helpful for weight loss, as a 2019 study in Current Obesity Reports revealed. Other research has also shown that intermittent fasting has benefits like "increased stress resistance, increased longevity, and a decreased incidence of diseases, including cancer and obesity" (via New England Journal of Medicine).
"Time without food allows the body to reset, leading to decreased insulin, blood sugar levels, and catabolism — the breakdown of stored energy." Nicole Grant, registered dietitian and resident dietitian for Zero Fasting, told Health Digest. It’s important to keep insulin levels on the lower side; if insulin levels are too high, it can lead to organ damage, decreased natural insulin production, and even type 2 diabetes (via Healthline). "The amount of insulin circulating in our blood lowers between meals," Dr. Melanie Boehmer, outpatient dietitian at Lenox Hill Hospital in New York, explained to Health Digest. "If you think about it, it makes sense that fasting for a period may decrease the amount of insulin release."
Nevertheless, each intermittent fasting program has its pros and cons. "It’s more important to look at the diet overall, including total calories, macronutrients, and the foods you are eating," Dr. Gretchen San Miguel, medical director for Medi-Weightloss Corporate, told Health Digest. Let’s take a look at the different types.
The circadian rhythm diet
The circadian rhythm diet, or body clock diet, is a form of time-restricted eating (TRE) that syncs meals with your internal clock. Eat during daylight, in a window of 12 hours or less; fast for the remaining 12 or more hours. "The argument is that our body has evolved to be in sync with the day/night cycle, i.e., a circadian rhythm," Dr. Melanie Boehmer, outpatient dietitian at New York’s Lenox Hill Hospital, told Health Digest. Advocates believe eating with the body’s "natural rhythm" helps it function best.
"The benefits of intermittent fasting are based upon following the body’s natural metabolic circadian rhythms," Dr. Pamela Peeke, assistant professor of medicine at the University of Maryland and author of The Hunger Fix, told Health Digest. "By following TRE during optimally metabolic times, you reduce blood sugar, improve lipids and reduce inner abdominal fat."
In the morning, insulin sensitivity (which is important for efficiently processing carbs) is highest. It decreases by night, prepping your body for rest and cell repair. Unfortunately, many eat most of the day’s carbs late in the day. "TRE works if you consume most of your healthy carbs up to 3 p.m.," said Peeke.
The 14:10 intermittent fasting method
All time-restricted eating can reduce overall caloric intake, which in turn, creates a calorie deficit and allows for weight loss. However, a 2021 study published in Nutrition & Diabetes has shown that the 14:10 method provides optimal weight loss, especially when a person finishes eating in the early evening and then fasts for 14 hours.
"This [14:10 method] is an easier entry point to those interested in the incorporation of a time-based feeding protocol as the 10-hour window is a bit better for people to adhere to," Dr. Melanie Boehmer, outpatient dietitian at Lenox Hill Hospital, told Health Digest. And at least one earlier study, which was published in Cell Metabolism, has shown that 14:10 plan led not only to weight loss, but "healthier body composition, lower blood pressure, and decreased levels of cardiovascular disease-promoting lipids."
Dr. Pam Taub, a cardiologist at the University of California, San Diego’s School of Medicine and one of the study’s authors, told NPR, "When you go into a fasting state, you start to deplete the glucose stores in your body and you start to use fat as your energy source." This process is called ketosis, and it "can lead to a good amount of weight loss," Satchidananda Panda, another study author explained.
The 16:8 intermittent fasting method
A very popular, if not the most popular, intermittent fasting plan is the 16:8 method, or the Leangains method. "I always recommend the 16:8 method, which is where you eat your daily caloric amount in an eight hour window then you fast for 16 hours," James Hickey, personal trainer and nutritionist, told Health Digest. This is fairly easy for beginners, as you can eat from 11 a.m. to 7 p.m. and then fast — mostly when you are sleeping — from 7 p.m. to 11 a.m. the next day. "It basically comes down to you skipping breakfast, which is an easy change for someone who is just starting off on their fitness goals," said Hickey.
Although there’s no specific "diet" you must follow while on the 16:8 plan, Medical News Today advises sticking with healthy foods. This is especially true if you’re trying to reduce your health risks or lose weight. During the hours you eat, focus on including whole grains, lean protein, fruits and veggies, and healthy fats.
The Warrior Diet (20:4)
The Warrior Diet, or the 20:4 method, is an intermittent fasting protocol developed by Ori Hofmekler and summarized in his book of the same name. This method includes eating plant-based foods and eliminating unhealthy foods. "The goal is to reduce flours and processed sugars, and replace them with fresh raw fruits and vegetables," Dr. Allen Conrad, a Pennsylvania-based chiropractor and certified strength and conditioning specialist, told Health Digest. Popularized by Hofmekler, this diet also calls for restricting your eating window to four hours, and fasting for 20 hours. "By fasting during the day, the goal is to help eliminate the dependence on processed foods that are a staple of the average American diet," said Conrad.
"In these longer fasts, mTOR [a type of protein] is also suppressed, which allows for autophagy — the process that many of the longevity benefits of fasting are attributed to," Nicole Grant, registered dietitian and resident dietitian for Zero Fasting, explained to Health Digest. Nevertheless, reducing your eating window to only four hours a day can be problematic when nutritional needs aren’t factored into consideration (via Health). As with any diet, consult your doctor to see if this type of fasting is appropriate for you.
The OMAD method of intermittent fasting
The focus of the OMAD (one meal a day) intermittent fasting method is not on when you don’t eat (23 hours a day) and rather on what you do eat for your one meal. And that is, well, anything. Eating a single meal per day reduces daily caloric intake, which usually results in weight loss (via Good Housekeeping). "The body is constantly kept guessing and has to adapt to the constant change," Shana Hussin, registered dietitian nutritionist and author of the book, Fast to Heal, told Health Digest. This can, of course, "bring about results," according to Hussin.
However, OMAD is hard to maintain and can pose problems. "If [people are] not counting calories, they’re probably only eating around 1,000 calories. If it’s that low, it would be hard to get all your nutrients in. I’d almost recommend taking a supplement just to be careful," Krista Varady, a nutrition researcher at the University of Illinois at Chicago, told Discover. And as registered dietitian Jaclyn London revealed in Good Housekeeping, there’s not much data to support the OMAD method, and it is "scarily similar to a disordered eating practice."
If you are struggling with an eating disorder, or know someone who is, help is available. Visit the National Eating Disorders Association (NEDA) website or contact NEDA’s Live Helpline at 1-800-931-2237. You can also receive 24/7 Crisis Support via text (text NEDA to 741741).