According to a 2024 survey conducted by the International Food Information Council (IFIC), 12 percent of 1,022 Americans practice intermittent fasting, which has been shown to have numerous benefits. These include: improving cognitive abilities, cardiovascular health, physical fitness, and eliminating symptoms of diabetes and obesity.
However, some research and personal experience suggests that intermittent fasting can have negative consequences. Newsweek discussed this with Varady and Maria Fox, who claims to have lost 50 pounds in seven months thanks to intermittent fasting.
Intermittent fasting does not lead to a poor diet
In a new commentary in Nature Reviews Endocrinology, UIC scientists debunk several common myths. The scientists based their conclusions on clinical trials. After reviewing the findings, they found that intake of sugar, saturated fat, cholesterol, fiber, sodium, and caffeine remained unchanged during fasting compared to before fasting. In addition, the percentage of energy from carbohydrates, proteins, and fats also did not change.
— Eating within eight hours naturally creates a 300-500 calorie deficit, resulting in weight loss. Eating healthy foods is important, but it’s the calorie deficit that causes weight loss, Varady said.
Intermittent fasting does not affect sex hormones
Varady says this is the most common misconception. She explained that many people believe that intermittent fasting can disrupt reproductive hormones.
—It’s simply not true. Multiple human studies have shown that sex hormones (estrogen, testosterone, progesterone, sex hormone-binding globulin (SHBG)) do not change after a year of intermittent fasting in men and women, Varady said. “This misconception stems from poorly controlled animal studies conducted in species very different from humans, such as rats. “These animal studies should not be used to inform what happens in human populations with intermittent fasting.”
Intermittent fasting does not cause eating disorders
Varady has been studying intermittent fasting for 20 years and is often asked whether this form of diet is safe. For most people, it is.
“However, people with a history of eating disorders should not use this method because it can exacerbate those problematic eating behaviors,” Varady said.
Intermittent fasting does not cause excessive loss of lean muscle mass
Research shows that people lose a similar amount of lean muscle mass when losing weight, regardless of whether they fast or follow another diet.
— Resistance training (i.e. lifting weights) causes the body to build more muscle. But the body needs a higher protein intake in order to use it to build new muscle, Varady said.
How Intermittent Fasting Helped Maria Fox Lose Weight
Fox, a former police superintendent, found himself at a crossroads in 2020. Weighing 215 pounds, his life was a cycle of unhealthy habits.
“My routine consisted of skipping breakfast, snacking on ultra-processed foods throughout the day, and frequently consuming wine and snacks after work,” Fox told Newsweek. The long hours meant she relied on fast, ready-made meals, and despite an intense exercise regimen designed to burn calories, stress rendered her weight-loss efforts ineffective.
The turning point came in October 2020, when Fox, who had been laid off from her job due to burnout, discovered Lumen, a wearable device designed to measure, track, and analyze metabolism. Armed with this tool, she began incorporating fasting into her routine, gradually increasing the length of her fasts from 12 to 14 to 36 hours. She also committed to eating a balanced diet during her eating windows, completely eliminating processed foods, sugars, and alcohol.
“I think the biggest problem is that people focus on duration, rather than starting from a simple point and extending the fast,” the 53-year-old told Newsweek. She emphasized the importance of gradual changes, as guided by Lumen, to help the body adapt without taking drastic measures. Fox also stressed the importance of different fasting practices, especially for women, who should consider their monthly cycle when planning their fasts because of their different nutritional needs throughout the month.
Initially, Fox was concerned about the effects of fasting on muscle mass and the heart. However, she soon realized that these fears were unfounded.
— We live in a society where ultra-processed foods are considered healthy. I think people should talk to their doctor and get blood tests to make sure everything is OK before they start fasting. We were a people who feasted and fasted as hunter-gatherers; I think humans are wired to deal with that. We are very good at storing fat for a rainy day, says Fox.
Fox’s life has improved significantly since adopting her new lifestyle. After suffering a mental breakdown that led to her being laid off from her job in 2020, she wrote the book “Crisis to Comeback: A Roadmap for Health Transformation After Burnout,” which chronicles her recovery.
“Fasting significantly reduces stress levels without the cortisol spikes of not eating, which allows the body and immune system to focus on fighting infections,” Fox explained to Newsweek. She has rarely been sick in the past four years, and when she has, she has recovered quickly.
“I believe fasting is key to strengthening the immune system,” she concluded, crediting it for improving mental clarity, energy, sleep and overall health.
Text published in the American magazine “Newsweek”. Title, lead and subtitles by the editors of “Newsweek Polska”.
