Thinking about trying intermittent fasting for weight loss? A new review of nearly 100 studies suggests one approach—alternate-day fasting (ADF)—may be more effective than others.
ADF involves alternating between days of normal eating and days of either complete fasting or consuming as little as 500 calories.
The method outperformed other intermittent fasting strategies and traditional calorie restriction for weight loss, researchers reported in June in The BMJ. But experts cautioned that the benefits may not last long-term.
Here’s a closer look at what the study found.
Intermittent fasting, which involves restricting eating to specified windows, has gained popularity in recent years as a way to drop pounds.
But it’s unclear whether it’s more effective for weight loss than simply reducing calories, or which of the various intermittent fasting strategies produces the best results. Previous meta-studies haven’t adequately answered these questions, noted the authors of the new research.
To fill the gap, the researchers pulled 99 randomized clinical trials that compared the effects of non-restrictive diets, calorie-restrictive diets, and intermittent fasting strategies, including ADF and two others:
- Time-restricted eating, which involves setting aside a certain number of non-fasting hours—often eight—in 24 hours
- Whole-day fasting, a plan in which people eat freely on some days and fast on a certain number of days of the week (often two)
Researchers discovered that, compared to time-restricted eating, ADF improved heart health markers, resulting in lower levels of total cholesterol, triglycerides, and non-high-density lipoprotein.
When it came to weight loss, intermittent fasting and calorie-restricted diets had a small edge over unrestricted eating plans. ADF emerged as the only intermittent fasting method to beat out calorie cutting, and it also came out on top when compared to time-restricted eating and whole-day fasting.
But, importantly, the differences were “trivial,” the authors noted, with ADF failing even to reach the clinical threshold of at least 4 pounds of weight loss for people with obesity. The benefit of ADF was also seen only in studies lasting fewer than six months.
Because of that, Rekha B. Kumar, MD, an associate professor of medicine at Weill Cornell Medical College and Head of Medical Affairs at Found, told Health that she doesn’t think the study proves that ADF is the superior weight loss strategy.
ADF may not be the clear-cut weight loss winner, but Kumar noted that it does have attributes that could make it a more effective strategy than some other diets.
For one, ADF doesn’t involve many rules, which could make it easier to continue with. “For some people, having a clear-cut ‘fast or feast’ structure makes it easier to stick with compared to tracking calories daily or following shorter fasting periods,” dietitian Erin Palinski-Wade, RD, author of 2 Day Diabetes Diet, told Health.
Additionally, ADF’s more intense but less frequent calorie restriction could prevent the metabolism slowdown that often happens once the body gets used to continuous calorie cutting. With ADF, “you’re more likely to maintain your resting metabolic rate and continue losing fat over time,” Palinski-Wade said.
If you’re interested in giving ADF a try, Palinski-Wade suggests that you:
- Start gradually: Consider easing into ADF by limiting calories to 500 on fasting days rather than not eating anything.
- Prioritize nutrition: On eating days, focus on nutrient-dense foods, such as whole grains and beans, to prevent deficiencies.
- Stay hydrated: Drink plenty of water, tea, or black coffee on fasting days.
- Monitor your body: Watch for signs of excessive fatigue, dizziness, or other health issues.
- Seek support: Work with a registered dietitian or healthcare provider for guidance and accountability and to ensure you meet your nutritional needs.
And if you find that ADF isn’t for you, move on to a weight loss plan that aligns with your preferences. Above all, “the most important factor is long-term adherence and finding an approach that fits your lifestyle, preferences, and health needs,” Palinski-Wade said. “The best diet is one that is safe, sustainable, and enjoyable.”
