Is intermittent fasting effective for weight loss?

Intermittent fasting diets deliver benefits for weight reduction and cardiometabolic risk factors that are comparable to continuous energy restriction (CER), reports a study.

Alternate day fasting (ADF) provides additional improvements to CER in overall weight, anthropometric measurements, lipid, and systolic blood pressure measures. This benefit, however, is not present in other intermittent fasting strategies.

“Our network meta-analysis showed similar benefits for various intermittent fasting strategies and CER in cardiometabolic risk compared with ad-libitum diets,” the investigators said.

This systematic review and network meta-analysis included 99 randomized clinical trials (RCTs) involving 6,582 adults. These studies were searched from Medline, Embase, and central databases from inception to 14 November 2024. Of the participants, 720 were healthy, and 5,862 had existing health conditions.

Compared with ad-libitum diet, all intermittent fasting and CER diet strategies resulted in reduced body weight. ADF, compared with CER, was the sole intermittent fasting strategy that led to reductions in body weight (mean difference, –1.29 kg, 95 percent confidence interval [CI], –1.99 to –0.59; moderate certainty of evidence). [BMJ 2025;389:e082007]

In addition, ADF resulted in a “trivial reduction” in body weight relative to both time restricted eating (mean difference, –1.69 kg, 95 percent CI, –2.49 to –0.88) and whole day fasting (WDF; mean difference, –1.05 kg, 95 percent CI, –1.90 to –0.19; both with moderate certainty of evidence).

Similar estimates were seen in trials with short duration (<24 weeks of follow-up; n=76), but moderate-to-long-term trials (≥24 weeks; n=17) only delivered weight reduction benefits in diet strategies compared with ad-libitum.

Cardiometabolic risk factors

Comparisons between intermittent fasting strategies showed ADF to reduce total cholesterol, triglycerides, and nonhigh-density lipoprotein (non-HDL) compared with time-restricted eating. However, time-restricted eating led to a small increase in total cholesterol, low-density lipoprotein, and non-HDL cholesterol relative to WDF.

Intermittent fasting, CER, and ad-libitum diets demonstrated no significant differences in HbA1c and high-density lipoprotein levels.

“Additional high quality RCTs with extended durations beyond 52 weeks are needed to elucidate the long-term effects of these dietary strategies, with greater emphasis between intermittent fasting diets, and their impact on cardiometabolic health and cardiovascular outcomes across diverse populations,” the investigators said.

The current findings support those of previously published meta-analyses. A study by Cioffi and colleagues assessed intermittent fasting (combining WDF and ADF) vs CER in 11 trials of adults with overweight or obesity and found no significant improvement for weight loss. [J Transl Med 2018;16:371; JBI Database System Rev Implement Rep 2018;16:507-547]

In the present network meta-analysis, ADF was the only intermittent fasting strategy that effectively reduced weight relative to CER. This was potentially due to the easier adherence to ADF as opposed to a continuous diet strategy. [Obes Sci Pract 2016;2:293-302]

“The hypothesized improvement in cardiometabolic health through a fasting diet approach derives primarily from extensive animal model studies,” according to the investigators. [Cell Metab 2014;19:181-192; Cell Metab 2014;20:991-1005; Science 2016;354:1008-1015]

“Such studies have noted that fasting states can encourage the use of fat stores, with a preferential reduction or browning of adipose tissue mass, improved insulin sensitivity, and reduction in inflammation and oxidative stress,” they added.