Popular Intermittent Fasting Diets May Not Provide the Health Benefits Many Expect

Time-restricted eating has gained popularity in recent years, but a recent study suggests that intermittent fasting, while effective for weight loss, may not live up to the hype in terms of broader benefits.

The small German study found that participants who were placed on two different eating schedules with time restrictions lost weight, but did not experience any improvement in blood glucose, blood pressure, cholesterol or other key cardiometabolic markers.

Participants included 31 overweight or obese women. One group ate between 8 a.m. and 4 p.m. and the other group ate between 1 p.m. and 9 p.m. over a two-week period, maintaining their typical caloric intake, according to a news release.

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The findings, which were published in the journal Science Translational Medicine, suggest that the widely touted cardiometabolic benefits of intermittent fasting may be a result of eating fewer calories rather than meal timing, the researchers say.

Participants also showed a change in their circadian rhythms (sleep/wake cycles) when placed on time-restricted feeding schedules, but the associated health impacts are unknown.

The study had some limitations. Some researchers have questioned the importance of the study due to its small size.

“It has very little power to detect any difference, considering how gentle the intervention is,” Dr. Jason Fung, a Canadian physician, author and researcher, told News Digital. He also noted that participants fasted for 16 hours a day instead of the normal 12 to 14 hours.

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Lauren Harris-Pincus, a registered dietitian nutritionist in New Jersey, agreed that the findings could be due to the fact that there was no intentional calorie restriction and reiterated that the sample size is “pretty small.”

“As a registered dietitian, I only recommend time-restricted eating when it is carefully planned and moved earlier in the day,” Harris-Pincus, who was not involved in the study, told News Digital.

“Only one in 10 Americans consume the recommended amount of fruits and vegetables, and 93% do not meet fiber goals. Restricting the eating window requires more careful meal planning to ensure adequate macro- and micronutrient intake.”

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The expert also warned that skipping breakfast so you can eat later can result in lower intake of “nutrients of concern” in the American diet, including calcium, potassium, fiber and vitamin D.

Looking ahead, the researchers said more studies are needed to explore the effects of time-restricted feeding over longer periods of time. It also remains to be seen how the combination of calorie restriction and time-restricted feeding may affect the results. Future research could also explore how different populations may respond.

“I only recommend eating on a restricted schedule when you plan carefully and shift to earlier in the day.”

Dr. Daryl Gioffre, a gut health specialist and celebrity nutritionist in New York, noted that the study did not take into account critical factors such as chronic stress, sleep quality, medications, hormonal status and baseline metabolic health.

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“All of this can significantly mitigate fat loss and cardiometabolic improvements,” Gioffre, who was also not involved in the research, told News Digital.

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“Cortisol, the body’s main stress hormone, is naturally highest in the morning, which overlaps with one of the fasting windows studied,” he continued. “If stress is high, cortisol alone can block fat burning, disrupt blood sugar regulation, and mask cardiovascular improvements, regardless of calorie intake or eating window.”

Gioffre agreed, however, that more and more research shows that intermittent fasting (when done correctly and maintained over time) can improve insulin regulation, reduce inflammation, promote fat loss and contribute to better cardiovascular health.

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“These are results that simply cannot be captured in a brief, stress-blind study like this,” he added.

News Digital reached out to investigators for comment.