• A recent analysis indicates that intermittent fasting achieves weight reduction comparable to traditional calorie counting.

  • However, a specific type of intermittent fasting called whole-day fasting was slightly more effective at reducing weight than calorie counting.

  • According to experts, having similar outcomes from various dieting methods provides more flexibility for those seeking weight loss solutions that fit their lifestyle.

Recent studies confirm that intermittent fasting can be as beneficial for losing weight and improving cardiometabolic risk factors as diets that limit daily calorie intake.

A comprehensive review involving around 100 randomized clinical trials comparing intermittent fasting (IF) with conventional calorie restriction (CR) revealed that both strategies offer similar health advantages. This study, released on June 18 in The BMJ, emphasizes the effectiveness of both dietary methods.

Intermittent fasting is characterized by specific eating and fasting periods, focusing less on the types of food consumed and more on the timing of meals. On the other hand, calorie restriction involves adhering to a predetermined number of daily calories without specifying when those calories must be consumed.

The review covered various popular intermittent fasting methods, including:

  • Alternate day fasting (ADF) which alternates normal eating days with fasting or significantly reduced calorie days.

  • Time-restricted eating (TRE) limits eating to specific hours of the day, often within an 8 to 12-hour window.

  • Whole day fasting, also known as the 5:2 diet, entails fasting for two or three days per week.

All intermittent fasting approaches and traditional calorie restriction resulted in weight loss compared to diets without restrictions. Among the primary methods of IF, only alternate day fasting showed a significant increase in weight loss compared to calorie restriction, although further extensive research is required to confirm these results.

“This data indicates that all three methods generally produce comparable weight loss, which supports the idea that the most effective weight loss strategy is one that aligns with your lifestyle and can be maintained over time,” stated David B. Sarwer, PhD, the director of the Center for Obesity Research and Education at Temple University and a spokesperson for the Obesity Society. Sarwer was not involved in the study.

Although intermittent fasting has surged in popularity over recent years, its benefits for weight loss and cardiometabolic health have shown varying results when compared to more traditional calorie-restricted diets.

While some supporters of intermittent fasting might find these findings underwhelming, experts suggest that having comparable results from different diets allows individuals to choose the method that best suits their preferences and needs.

No definitive ‘best’ diet

The systematic review included 99 randomized clinical trials with over 6,500 adult participants. The average age of these participants was 45, and about two-thirds were female.

A small subset of participants was in good health, but approximately 90% had pre-existing health issues such as overweight, obesity, or type 1 and type 2 diabetes. The average body mass index (BMI) of the participants was 31, categorizing them as obese according to the Centers for Disease Control and Prevention (CDC).

The duration of these trials varied from 3 to 52 weeks, with an average span of 12 weeks, and they differed in quality.

The analysis showed that both intermittent fasting and calorie restriction led to modest reductions in body weight compared to an unrestricted diet. Among the different IF methods, only alternate day fasting was slightly more successful in reducing weight (by nearly three pounds) than calorie restriction.

While this difference may be statistically significant, Sarwer noted that such a minor difference in weight loss might not substantially impact health issues related to weight.

ADF also marginally outperformed both TRE and whole-day fasting in terms of weight reduction, but these differences were not considered significant. Additionally, ADF showed slight improvements in total and LDL cholesterol compared to time-restricted eating.

“There’s no conclusive evidence that one diet is superior for weight loss,” Sarwer added.

“Instead, the ‘best’ diet is one that allows an individual to make manageable, impactful changes in their food choices, eating habits, and physical activity. This diet should minimally disrupt their daily routine and be sustainable over the long term,” he explained.

Who should consider intermittent fasting?

Despite being highly popular, intermittent fasting lacks strong evidence to support its widespread recommendation. However, it has been associated with numerous health benefits, including:

  • weight loss,

  • improved insulin sensitivity,

  • decreased inflammation, and

  • enhanced brain health.

The main issue, however, is not whether IF offers benefits over an unrestricted diet, but rather if it’s more advantageous than calorie restriction. This aspect remains somewhat ambiguous.

A review in 2024 noted that both IF and CR were effective for weight loss and showed similar outcomes for cardiometabolic health, cancer, and neurocognitive conditions. The review also highlighted better adherence rates with IF protocols, indicating that participants were more likely to stick with these diets throughout the study period.

A slightly earlier study from 2022 published in NEJM concluded that for individuals with obesity, time-restricted eating did not offer more benefits than calorie restriction.

Conversely, a clinical trial funded by the NIH and published in April 2025 found that participants practicing a variation of whole-day fasting (a 4:3 schedule rather than the typical 5:2) lost 50% more weight than those following calorie restriction (7.6% vs 5% body weight) over a year. This additional weight loss also led to improvements in cardiometabolic measures such as blood pressure, total cholesterol, and A1C levels.

Another study, released in May 2025, demonstrated that just three months of time-restricted eating resulted in long-term weight loss even after participants stopped following the diet.

Calorie restriction isn’t without its drawbacks either. Although it has been a long-standing method for weight management, it can cause issues like fatigue, nutritional deficiencies, and even depression.

Ultimately, the consensus among experts is that the ideal diet depends on the individual. The most effective diet is the one you can consistently adhere to.

“Fasting diets tend to be simpler to follow because they have straightforward rules compared to starting a Mediterranean diet, for example. Time-restricted diets might particularly benefit those who frequently snack at night,” mentioned Sun Kim, MD, an associate professor of Endocrinology, Gerontology, and Metabolism at Stanford Medicine, who was not involved in the study.

She also advised that individuals with diabetes who use insulin should be cautious with fasting diets, as these may require adjustments in insulin dosage and timing.

Additionally, you should be careful with intermittent fasting if you:

  • are over 65 years of age,

  • have a history of eating disorders,

  • suffer from low blood pressure, or

  • are pregnant or breastfeeding.

Consistency is crucial for sustained weight loss

An important observation from the study was that adherence rates significantly declined as trials progressed.

Studies shorter than 24 weeks reported high adherence rates, above 80%, while those extending beyond 52 weeks generally noted poor adherence. In one particular trial on whole-day fasting, adherence dropped from 74% at six weeks to just 22% at 52 weeks.

This underlines that diet plans should not be one-size-fits-all but tailored to each person’s lifestyle.

“Finding a sustainable lifestyle change is crucial. In our society, many factors encourage weight gain. I always discuss with my patients the importance of adopting lifestyle changes they can maintain over the long term,” said Kim.

According to Sarwer, making small, sustainable adjustments is key.

“I often recommend that people reduce how often they eat ice cream each week or cut down on the portion size rather than eliminating it completely,” he noted.