Person eating cereal after intermittent fasting

What is intermittent fasting?

Written on February 3, 2023 by Gillian (Gigi) Singer, MPH. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Table of contents

About intermittent fasting

A Harvard publication explains that intermittent fasting (IF) “is a diet regimen that cycles between brief periods of fasting, with either no food or significant calorie reduction, and periods of unrestricted eating. It is promoted to change body composition through loss of fat mass and weight, and to improve markers of health that are associated with disease such as blood pressure and cholesterol levels” [1].

Healthline notes that “IF has become very popular, and some studies have shown IF to be effective for weight loss. However, there is a lack of long-term studies and studies with conflicting results” [2].

“Many diet and exercise trends have origins in legitimate science, though the facts tend to get distorted by the time they achieve mainstream popularity,” says Roger Coller, senior editor of the Canadian Medical Association Journal, “Benefits are exaggerated. Risks are downplayed. Science takes a back seat to marketing. One needn’t look any further than the emerging trend of intermittent fasting for a prime example” [3].

Does intermittent fasting have any benefits?

In a clinical trial from 2020 that included adults classified as overweight or obese, “time-restricted eating was associated with a modest decrease (1.17%) in weight that was not significantly different from the decrease in the control group (0.75%)” [4]. This study showed that 65% of the weight loss was actually lean body mass (muscle mass) [4].

Other than weight loss, the goal of IF is called metabolic switching, which is when “fasting triggers the body to switch its source of energy from glucose stored in the liver to ketones, which are stored in fat… Ketogenesis, or the increase of ketones in the bloodstream, initiates activity in a variety of cellular signaling pathways known to influence health and aging” [5].

Disordered eating and intermittent fasting

A study by Kyle T. Ganson, PhD, MSW from the University of Toronto, discovered clear patterns tying IF with disordered eating in young men and women from all over Canada [2].

In women, Ganson reported binge eating, vomiting, compulsive exercise, and laxative use. In men, Ganson observed mostly compulsive exercise. As a whole, “Participants also reported fasting for an average of 100 days in the past 12 months” [2].

Scientific recommendations

The authors of an article from 2020 “suggest that clinicians who prescribe intermittent fasting encourage their patients to adopt a gradual, phased-in schedule in consultation with a dietitian or nutritionist” [5].

Further research

The same article referenced above questions the long-term effects in humans of intermittent fasting. They also say that more “Studies are needed to determine whether this eating pattern is safe for people at a healthy weight, or who are younger or older, since most clinical research so far has been conducted on overweight and middle-aged adults. In addition, research is needed to identify safe, effective medications that mimic the effects of intermittent fasting without the need to substantially change eating habits” [5].

Talk to a healthcare provider for weight loss via Everlywell

Instead of doing crash diets or fad diets, talk to a healthcare provider about the best way for you to approach fitness and/or weight loss.

Everlywell offers access to telehealth for weight management online, which can connect you with a qualified healthcare provider. You can discuss your weight loss goals based on your availability from the comfort of your home.

Weight loss: keto vs. intermittent fasting

Does intermittent fasting work?

How long should you do intermittent fasting?


  1. Diet review: Intermittent fasting for weight loss. The Nutrition Source. URL. Published May 17, 2022. Accessed January 30, 2023.
  2. Citroner G. Intermittent fasting linked to disordered eating, compulsive exercise. Healthline. URL. Published November 11, 2022. Accessed January 30, 2023.
  3. Collier R. Intermittent fasting: the science of going without. CMAJ. 2013;185(9):E363-E364. doi:10.1503/cmaj.109-4451. URL.
  4. Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity. JAMA Intern Med. 2020;180(11):1491. doi:10.1001/jamainternmed.2020.4153. URL.
  5. Research on intermittent fasting shows health benefits. National Institute on Aging. URL. Accessed January 30, 2023.
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