Intermittent Fasting May Be as Effective as Calorie Restriction for Weight Loss

Health Line

21-06-2025

Intermittent fasting resulted in similar weight loss as traditional calorie restriction, according to a new review.
One form of intermittent fasting, known as whole-day fasting, did yield slightly more weight loss than caloric restriction.
Experts say that the similar results across different diet protocols mean individuals trying to lose weight have more options available to suit their lifestyle.
New research suggests that intermittent fasting is as effective as calorie-restricted diets for weight loss and cardiometabolic risk factors.
A systematic review of nearly 100 randomized clinical trials involving intermittent fasting (IF) and traditional calorie restriction (CR) found that both approaches yielded similar health benefits. The study, published on June 18 in The BMJ, found that IF and CR were equally effective.
IF involves designated periods of eating and fasting and places less emphasis on what you eat than when you eat. By contrast, CR targets a specific daily calorie goal and allows any eating schedule.
The analysis included several of the most common IF protocols, including:
Alternate day fasting (ADF) alternates standard eating days with fasting days or very low calorie days.
Time-restricted eating (TRE) restricts food intake to a daily window, typically 8 or 12 hours.
Whole day fasting, also known as the 5:2 diet, involves two or three weekly fasting days.
All forms of IF and traditional CR produced weight loss compared with no intervention at all — known as an ad libitum, or unrestricted, diet. Of the three primary IF methods, only alternate day fasting resulted in greater weight loss than CR. However, the authors note that longer trials are needed to substantiate their findings.
'This analysis suggests that all three approaches, for the most part, lead to similar weight losses. This is why many of us believe that the best approach to losing weight is finding an approach that matches your lifestyle and is something you can practice for the long term,' said David B. Sarwer, PhD, director of the Center for Obesity Research and Education at Temple University and a spokesperson for the Obesity Society. Sarwer wasn't involved in the research.
IF has grown rapidly in popularity over the past decade, but evidence of its health benefits — namely, weight loss and cardiometabolic measures, such as blood glucose — has been inconsistent compared with more traditional, calorie-restricted diets.
Although proponents of IF may be disappointed by the latest findings, experts say that similar results across diets mean that people have more options to find a method that works best for them.
No clear 'best' when it comes to diet protocols
Researchers included 99 randomized clinical trials involving more than 6,500 adults in the systematic review. The average age of participants was 45, and two-thirds were women.
A small percentage was considered healthy, but the vast majority (about 90%) had existing health conditions, including overweight, obesity, and both type 1 and type 2 diabetes. Participants' average BMI was 31, meeting the standard clinical definition of obesity, which is a body mass index (BMI of 30 or higher.
Trials ranged between 3 and 52 weeks — with an average of 12 weeks — and varied in quality.
The review found that both IF and CR led to small reductions in body weight compared to an unrestricted diet. Among the different IF protocols, only ADF resulted in slightly more weight loss (nearly three pounds) than CR.
Sarwer pointed out that while this may be statistically significant, such additional weight loss would be trivial in improving weight-related health issues.
ADF also slightly outperformed both TRE and whole-day fasting in terms of weight loss, but these findings were not deemed significant. ADF also resulted in slight improvements to total and LDL cholesterol compared to time-restricted eating.
'There is no compelling evidence that there is a 'best' diet for weight loss,' said Sarwer.
'Rather, the 'best' approach is one where the person can make small, yet impactful changes to their food choices, eating behaviors, and level of physical activity that cause minimal disruption to their lifestyle and that they can maintain for the long term,' he said.
Who benefits from intermittent fasting?
Though IF is touted as the diet du jour, there isn't enough compelling evidence to support it yet. Nonetheless, it has been linked to an array of health benefits, including:
weight loss
improved insulin resistance
reduced inflammation
brain health
The key question, though, is not whether IF is beneficial compared to an unrestricted diet, but whether it's better than CR. That's where things are a little unclear.
A 2024 review found that IF and CR were both associated with weight loss and equally effective across cardiometabolic, cancer, and neurocognitive outcomes. However, they noted that IF studies reported greater adherence, meaning people were better able to stick to them for the trial duration.
A slightly older study published in NEJM in 2022 also concluded that among people with obesity, TRE wasn't more beneficial than CR.
On the other hand, in a clinical trial funded by the NIH, the results of which were published in April 2025, participants who did a variation of whole-day fasting (a 4:3 schedule rather than the more common 5:2) lost 50% more weight than CR (7.6% vs 5% body weight) after one year.
The additional weight loss also translated into cardiometabolic improvements, such as blood pressure, total cholesterol, and A1C.
Another trial, published in May 2025, found that just three months of TRE led to long-term weight loss, even after participants stopped the protocol.
CR isn't perfect either. Though it's long been a standard dietary intervention, it can be harmful, leading to fatigue, nutrient deficiencies, and even depression.
For now, experts agree that the right diet solution comes down to the individual. The best diet for you is the one you can stick to.
'Fasting diets are easier to follow because the rules are fairly simple vs trying to start a Mediterranean diet, for example. Some patients who may particularly benefit from a time-restricted diet, for example, are individuals who tend to snack a lot at night,' said Sun Kim, MD, an associate professor of Endocrinology, Gerontology, and Metabolism at Stanford Medicine who wasn't involved in the research.
She also cautions that individuals with diabetes who take insulin should be careful with fasting diets, as they may necessitate adjustments to insulin dosage and scheduling.
You should also be cautious with intermittent fasting if you:
are over age 65
have a history of disordered eating
have low blood pressure
are pregnant or nursing
Adherence is key to long-term weight loss
One final notable finding of the study was that adherence rates dropped precipitously the longer trials went on.
Studies shorter than 24 weeks had high adherence, above 80%, while trials longer than 52 weeks typically reported poor adherence. In one trial involving whole-day fasting, adherence crashed from 74% at six weeks to just 22% at 52 weeks.
These findings reinforce the idea that diet protocols should not be viewed as 'one size fits all' but rather as tailored to each individual's lifestyle.
'I wish there was an easy solution to weight loss. In our society, there are many forces that push individuals toward weight gain. I always discuss with patients about finding a lifestyle change that they can sustain for the long haul,' said Kim.
According to Sarwer, small, sustainable changes are key.
'I'm more likely to suggest that people reduce the number of days a week that they eat ice cream, or reduce the portion size they eat, than to recommend that they stop eating ice cream all together,' he said.