- Intermittent fasting is an eating strategy that some research suggests could aid in weight loss.
- New research from the University of Illinois Chicago used data to debunk common myths about intermittent fasting.
- Dietitians say commonly believed claims about intermittent fasting often require more nuance.
While some eating strategies, like the Mediterranean diet, have broad support, others remain the subject of scrutiny and, at times, conflicting (and inaccurate) information.
Researchers at the University of Chicago Illinois believe intermittent fasting is one of them.
In a new article published in Nature Reviews Endocrinology on June 19, they sought to debunk what they concluded are common “myths” about the eating plan. These myths include intermittent fasting’s role in causing unhealthy diets, eating disorders, affecting lean muscle mass, and fertility issues.
Even the term “intermittent fasting” is misleading, says one registered dietitian.
“The diet sounds like it involves fasting intermittently — at irregular intervals — but most protocols require you to fast regularly,” says Destini Moody, RD, a registered dietitian with Garage Gym Reviews.
The new report’s authors included research on two types of intermittent fasting: alternate-day (switching between days of consuming a limited number of calories and days of eating as they please) and time-restricted (eating as desired during a four—to 10-hour window).
While the authors who conducted the latest study concluded both types were safe and that four commonly held ideas were untrue, Healthline spoke with additional health experts to discuss the latest research.
They provided more nuance to better explain the researchers’ reasoning behind their conclusions and expanded on the latest science to help debunk 7 commonly believed myths about intermittent fasting.
Myth: Intermittent fasting affects sex hormones
The authors cited research, including a 2024 study of 90 adults living with obesity, that indicated intermittent fasting did not negatively affect sex hormones. The study also suggested that it may decrease testosterone and increase SHBG levels in people with PCOS, improving the condition.
On the latter point about PCOS, one dietitian says the new research is promising (but cautions it’s early).
“Preliminary findings on using intermittent fasting as a strategy for women with PCOS to regulate hyperandrogenism are promising,” says Allie Echeverria, MS, RD, LD. “Androgens are male sex hormones. Women naturally also have androgens, but women with hyperandrogenism have excessive levels.”
Generally, dietitians and research, including a 2021 review, indicate that calorie restriction that prompts under or malnutrition can harm fertility, specifically estrogen.
Moody says intermittent fasting’s effects on sex hormone levels are “contingent on the fact that the dieter is still taking care to eat sufficient calories within their eating window.”
Moody adds that a sign of undernutrition and eating disorders is the loss of a menstrual cycle, which can be detrimental to reproductive and overall health.
Overall, one dietitian calls the current evidence far from conclusive.
“it is very important to note that there is still very limited evidence on both female and male sex hormones being affected by intermittent fasting,” says Courtney Pelitera, MS, RD, CNSC, a registered dietitian with Top Nutrition Coaching. “Many of the trials completed have small sample sizes, often less than 100 people and during a shorter duration of time.”
Myth: Intermittent fasting causes excessive muscle mass loss
Researchers cited studies that suggested that people lost the same amount of lean muscle mass regardless of whether they were fasting or following another diet. For instance, a 2022 meta-analysis of randomized trials compared people who restricted calories each day and those using intermittent fasting. The data suggested that 75% of weight loss could be chalked up to fat tissue, while the remaining 25% was lean mass, regardless of the diet strategy.
The new report’s authors added that resistance training and higher protein intake could help lower the odds of lean muscle mass loss.
“Any healthy weight loss diet that provides adequate protein and strength training will help to preserve lean muscle mass,” says Pelitera.
Myth: Intermittent fasting will affect your diet quality
Authors suggest that intermittent fasting does not cause unhealthy diet quality. Authors cited one review of randomized control trials published in 2024 that indicated that intake of the following indicators of diet quality did not change in people adhering to shorter eating windows (4 to 6 hours) and longer ones (8 to 10 hours):
- Fiber
- Protein
- Cholesterol
- Total fat
- Carbohydrates
- Sugar
- Saturated fat
- Fiber
- Sodium
- Caffeine
What might this mean? It’s currently unclear, Moody says.
“If it means the person had a poor diet prior…then intermittent fasting is unlikely to make their diet worse — it simply changes the time period in which they consume their nutrient-poor diet,” Moody says.
“Furthermore, if the person’s diet is nutritious before IF, one could agree that starting fasting is unlikely to steer them toward poor diet choices,” she says. “While researchers are correct in debunking this myth, it must be stressed that those going into intermittent fasting with a poor diet can’t expect the practice of IF to improve diet quality on its own.”
Myth: Intermittent fasting can cause eating disorders
Of the four claims made by researchers, dietitians arguably stressed the need for the most caution with this one.
Researchers cited a 2023 systemic review and a 2019 doctoral thesis. The latter followed 86 people for four weeks and suggested that intermittent fasting didn’t cause eating disorders.
The authors suggested that healthy adults who used intermittent fasting tended to report fewer food cravings, binge-eating behaviors, weight concerns, and anxiety about appearance. People with a history of eating disorders were screened out. The authors wrote — and the dietitians we spoke with also noted — that participants generally started from a low risk of developing one in the first place.
“Short-term studies suggesting intermittent fasting doesn’t cause eating disorders are limited in scope,” says Emily Van Eck, MS, RDN. “Eating disorders typically develop over longer periods than these studies cover. The study cited is only four weeks long.”
As for the reports of body image and weight concerns?
“[It] is hardly surprising,” Van Eck says. “The act of following a diet plan eases anxiety about food and body size. Many who later develop an eating disorder were able to stick with some — if not many — diets for a short term before their eating disorder developed.”
Myth: Intermittent fasting can “cure” type 2 diabetes
A 2023 randomized control trial suggested that intermittent fasting might help people with type 2 diabetes achieve remission, which goes against the idea that the disease is chronic and lifelong. However, Van Eck says more research is needed.
“The study mentioned here was only three months long and, therefore, does not provide any significant information about people’s ability to stick to this regimen long term or their ability to improve their blood sugar long term,” Van Eck says.
That said, doctors, health organizations, and dietitians generally agree that weight management is a crucial component of diabetes management (but there’s not enough conclusive evidence to support the idea that it’s a “cure”).
Additionally, IF has shown improvements in reducing insulting resistance and improving insulin sensitivity along with improving blood sugar parameters.
“We know that weight control and weight loss can help with the management of type 2 diabetes,” Pelitera says. “Intermittent fasting often leads to calorie restriction, which results in weight loss. As far as reversing the disease, there are many different things that would factor into this [and it is] far more complicated than a specific eating window. Quality of diet and increased [intake] of fruits and vegetables would be the first place to start. Adequate hydration, fiber, and consistent regular physical activity are going to play major roles as well.”
Myth: Intermittent fasting can lead to long-term weight loss
A small randomized control trial of 90 people with obesity compared people who did not count calories but followed time-restricted eating from noon to 8 p.m. to a control group who ate for 10 or more hours per day.
Another group of people in the study restricted calories by 25%. Only 77 people completed the one-year study.
The data indicated that the time-restricted plan produced more weight loss than the control but was not more productive than restricting calories in a racially diverse group.
However, dietitians say that more than a one-year assessment period is needed to draw conclusions about the link between long-term weight loss and intermittent fasting.
“The study cited is small and not very well designed, so one should take the findings with a grain of salt,” Moody says. “That said, it is very possible that IF can lead to long-term weight loss. However, this is the most likely if the fasting is accompanied by comprehensive nutrition education and the supervision/regular counseling of a registered dietitian.”
“If weight loss is to be sustained long term, knowing how to adjust one’s diet to prevent weight regain once IF ceases is critical,” she adds.
Myth: Intermittent fasting is safe for everyone
The new report concludes that intermittent fasting is generally safe, but dietitians emphasize the need for nuance.
Van Eck pointed out that intensive weight loss could increase the risk of all-cause or cardiovascular mortality in people with Type 2 diabetes.
Moody and Pelitera also advised people living with type 1 or 2 diabetes to seek medical advice, regardless of the recent study that suggested that intermittent fasting could “reverse” type 2 diabetes.
“These patients were in a clinical setting under constant monitoring by scientists where safety could be assured,” Moody says. “Otherwise, dangerous lows in blood glucose and other medication-related dangers can occur.”
Moody also advises against following intermittent fasting if you are:
- Pregnant
- Lactating
- Under 18
- Take prescription medications that require regular food intake
- Have a history of eating disorders
Pelitera does not recommend IF to people with kidney disease or who have other conditions that require appropriate levels of specific nutrients, such as sodium, potassium, and phosphorus.
Takeaway
Intermittent fasting is a dietary plan that involves eating during specific windows.
Several myths are commonly believed about the safety and efficacy of intermittent fasting.
These myths included that intermittent fasting could cause adverse effects on sex hormones (and fertility), muscle mass loss, unhealthy diet, and eating disorders.
Intermittent fasting is not safe for everyone, including people with certain conditions or who are pregnant or lactating.
Intermittent fasting research is still limited and hasn’t been conducted in large populations over a long term. It’s wise to speak with a healthcare professional about whether this diet is best for you before beginning.
