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Recently, intermittent fasting (IF) has become a global phenomenon. It is used as a weight-loss strategy and a means to improve overall health and well-being. However, misconceptions about this dietary approach deter some individuals from trying it. Researchers from the Department of Kinesiology and Nutrition at the University of Illinois recently reviewed common myths about IF. Their findings, backed by scientific evidence, clarify the potential health benefits of this diet and dispel widespread concerns.
What is Intermittent Fasting?
Intermittent fasting alternates periods of eating with fasting. There are two main types:
- Alternate-Day Fasting (ADF): This involves minimal caloric intake (500–600 kcal) on fasting days, with normal eating on other days.
- Time-Restricted Eating (TRE): This limits food consumption to a daily “eating window” of 4–10 hours. During fasting periods, individuals may drink water, unsweetened tea, or black coffee without milk.
Scientific studies consistently demonstrate that IF can aid weight loss, improve metabolism, and enhance mood and sleep quality.
Nearly 10% of adults globally have tried intermittent fasting, and its popularity has surged over the past decade. According to a survey by the International Food Information Council, IF ranked as the third most popular diet in 2024, surpassing the Keto and plant-based diets. In the U.S., 13% of Americans choose IF, while mindful eating (18%) and high-protein diets (20%) took second and first place, respectively.
Despite its appeal, several myths persist about this type of eating, including concerns about hormonal imbalances, muscle loss, poor diet quality, and eating disorders.
Myth 1: Negative Effects on Sex Hormones
A common belief is that fasting disrupts the levels of sex hormones, such as estrogen and testosterone. However, studies have found no significant changes in these hormones among men and women practicing time-restricted eating, even after a year. Slight decreases in testosterone (2–15%) were observed in young male athletes, but these reductions did not affect muscle mass or strength.
Interestingly, one group showed positive changes in hormone regulation—women with polycystic ovary syndrome (PCOS). After practicing intermittent fasting for 1–3 months, premenopausal women with PCOS experienced lower testosterone levels and higher levels of sex hormone-binding globulin (SHBG). These changes alleviated associated symptoms, including weight gain, inflammation, and insulin resistance.
These preliminary findings show promise for the use of intermittent fasting as a viable weight loss intervention for women with PCOS, but more studies are needed to confirm this.
Study authors
Myth 2: Excessive Muscle Loss
Contrary to popular belief, intermittent fasting does not lead to greater muscle loss compared to other diets. Research indicates that about 75% of weight lost during time-restricted eating is due to fat reduction, with the remaining 25% attributed to muscle mass loss. However, this muscle loss is comparable to that seen with traditional calorie-restricted diets. Resistance training and adequate protein intake during IF can help preserve muscle mass.
Studies on the effects of intermittent fasting in older adults (65+) have not shown any detrimental impact on muscle health. However, further research is needed to optimize protein intake recommendations for this group.
Myth 3: Intermittent Fasting Reduces Diet Quality
Some worry that restricting eating to a 4–10-hour window may negatively affect diet quality. There are also concerns that individuals might consume more caffeine to boost energy during fasting periods, potentially impairing sleep quality.
However, clinical studies have found no significant changes in macronutrient consumption or overall diet quality among those practicing intermittent fasting. Participants typically reduce daily calorie intake by 200–550 kcal, leading to a 3–5% weight loss without altering the types of foods consumed. This dispels the notion that intermittent fasting encourages unhealthy eating habits.
Evidence suggests that people don’t typically change the types of food they eat during intermittent fasting, they just eat less of those foods.
Study authors
Myth 4: Risk of Eating Disorders
Concerns about IF triggering eating disorders are valid but lack substantial evidence. Notably, nearly all clinical trials on intermittent fasting exclude individuals with a history of eating disorders. Researchers emphasize that people with such a history should avoid IF.
Clinical studies suggest that IF can positively influence eating behaviors. Participants report reduced food cravings, anxiety about weight and appearance, mood-related eating issues, and binge-eating episodes. However, researchers caution against applying intermittent fasting strategies to adolescents. Eating disorders typically emerge between the ages of 12 and 25, with adolescents with obesity being particularly at risk.
Conclusions
The myths about IF highlighted in this study represent just a fraction of the many misconceptions surrounding this dietary approach.
While we understand the reasoning behind these beliefs, we would like to underscore that these myths are not justified by the scientific literature. Intermittent fasting might seem like an extreme diet to some individuals, but the safety profile of these protocols is similar to that of daily calorie restriction, low carbohydrate diets and Mediterranean diets.
Study authors
Researchers stress that IF is merely one tool among many for reducing food intake, managing weight, and improving metabolic health. Evidence-based understanding can help dispel myths and guide individuals toward informed decisions about incorporating intermittent fasting into their lifestyles.
