Researchers Find Intermittent Fasting Is No Better, or Worse, Than Conventional Dieting
Intermittent fasting, a dietary approach involving restricting eating times, has gained significant popularity. However, a recent rigorous evaluation of the clinical evidence suggests its weight loss benefits may be overstated.
New Research Challenges Intermittent Fasting Claims
A systematic review, considered the gold standard in medical evidence evaluation, found that intermittent fasting produces nearly identical weight loss, quality of life outcomes, and adverse events compared to traditional calorie-counting diets. The review, conducted by researchers from the Universidad Hospital Italiano de Buenos Aires, with collaborators in Chile, Spain, and the United States, analysed 22 randomized controlled trials involving a total of 1,995 participants.
What the Study Examined
The research encompassed several intermittent fasting methods, including time-restricted eating (limiting meals to eight or ten-hour windows), alternate-day fasting, and the 5:2 diet (normal eating five days a week with significant calorie restriction on two days). These techniques were compared to standard dietary advice and, in some cases, no intervention at all.
Across 21 studies involving 1,430 people, the difference in weight loss between intermittent fasting and conventional diets was a mere 0.33 percentage points of body weight. Among four studies tracking a 5% weight reduction, the success rate was virtually the same across all groups.
Limitations and Gaps in the Evidence
While intermittent fasting showed slightly more weight loss – approximately 3.4% of body weight – compared to no intervention in six studies, this fell short of the 5% threshold generally considered necessary for meaningful health benefits. The review also highlighted significant gaps in the existing research.
Notably, ten of the 22 studies relied on self-reported adherence to dietary protocols, a method that Diane Rigassio Radler, a professor of clinical nutrition at the Rutgers School of Health Professions, described as “inherently imprecise.” None of the studies assessed participant satisfaction, examined diabetes outcomes, or extended beyond a one-year follow-up period. 19 of the studies were conducted in high-income countries with predominantly white participants, potentially limiting the broad applicability of the findings.
Currently, most clinical practise guidelines do not specifically recommend intermittent fasting. While the review found no significant safety concerns, the authors emphasize that recommendations remain limited due to the short follow-up periods and low certainty of the evidence.
What Could Happen Next?
Future research could focus on extending study durations beyond 12 months, including more diverse populations, and measuring outcomes that are most important to patients, such as diet tolerability. Clinicians may continue to adopt a patient-centered approach, discussing the evidence with individuals interested in intermittent fasting and supporting them in making informed decisions.
Frequently Asked Questions
What did the review compare intermittent fasting to?
The review compared intermittent fasting to both standard dietary advice and no intervention.
What types of intermittent fasting were examined in the review?
The review examined time-restricted eating, alternate-day fasting, and the “5:2” approach.
Was there a significant difference in weight loss between intermittent fasting and conventional diets?
No, the difference in weight loss was 0.33 percentage points of body weight, which the researchers considered statistically indistinguishable from zero.
Given these findings, what role will individual preferences play in choosing a dietary approach?