Intermittent fasting not more effective than conventional dieting, Rutgers researcher says

Intermittent fasting, one of America’s most popular diet trends, may be no more effective than simply cutting calories for weight loss, a new review of research shows.

Researchers found little to no difference in the amount of weight loss across more than 20 studies comparing intermittent fasting, an eating pattern that cycles between periods of eating and fasting, with traditional dietary advice (which calls for restricting calories or the types of foods eaten).

The findings were published this month in the Cochrane Library, home to evidence reviews that are considered the gold standard for evaluating health evidence.

“From the results of this review, it doesn’t look like intermittent fasting is any better than regular dietary advice,” said Diane Rigassio Radler, a co-author on the study and a clinical nutrition professor at Rutgers School of Health Professions.

The data came from 22 randomized controlled trials involving nearly 2,000 participants across Europe, North America, China, Australia, and South America. Interventions ranged from four weeks to six months long, and looked at participants’ outcomes up to a year later.

In six of the trials, participants were picked at random to either practice intermittent fasting or do nothing. The difference in weight loss between the two groups was so small that it was not considered “clinically meaningful,” Radler said.

People generally need to lose 5% of their body weight to see health benefits. When the research team pooled the results of studies, they found weight loss from intermittent fasting slightly exceeded that of the group that did nothing, but remained below the 5% threshold.

“Anecdotally, people have told me that [intermittent fasting] might work for them, but the reasons for doing these systematic reviews is so that you can pull the evidence and make a stronger conclusion based on facts,” Radler said.

The studies focused on people in the overweight or obese categories as measured by BMI, a calculation of a person’s body fat based on their height and weight. The relevance of the research findings to people in the healthy weight category remains unknown. (While widely used, BMI is often not a good predictor of an individual’s health, as people’s body types can vary widely depending on race, gender, and age.)

The Inquirer spoke with Radler, who is also a registered dietitian by training, about the findings of the study and its implications, in an interview that was lightly edited for length and clarity.

From a physiological perspective, there’s sound science in terms of why fasting might have an edge over just calorie restriction alone.

Number one, it involves calorie restriction. It’s thought to increase fat metabolism. There’s some hormonal stuff going on. It may enhance insulin sensitivity. When you’re fasting, you’re going to be breaking down fatty acids, and those can produce a significant source of energy.

But from the available studies we were able to evaluate, the findings are that intermittent fasting was not really different [in terms of weight loss].

There’s the theoretical framework, and then there’s what happens when you put it into reality.

It’s individualized. It depends on where the patient’s at and what they feel that they want to do.

The cardinal rule of thumb is you create a calorie deficit, and whether that’s with restricted eating or increased energy expenditure (such as through exercise), or a combination of both, you’re looking to achieve calorie restriction over time. Generally, you’re going to probably sustain that for at least 12 weeks, and then look at some outcomes.

We found that people who work with a registered dietitian on a weekly or every other week basis have the most success in terms of achieving weight management.

You have to look at people’s baseline and their other comorbidities if they have any. But generally, we didn’t find that there were adverse effects, according to the studies that measured that as an outcome.

When you fast, there’s a risk of dehydration and risk of low blood sugar, but generally, the studies that measured the adverse effects didn’t find significant differences.

There could be room for more research with a wider diversity of subjects, because most of the studies were in high-income countries. We have to look at some of the cultural differences.

Also, research with longer durations. We were not able to find studies that went out beyond 12 months of outcomes.