There’s been a ton of research around intermittent fasting over the past few years, but the latest evidence suggests that it can lead to similar weight loss results as a calorie-restricted diet. But intermittent fasting may have an edge in some areas, including helping you lose certain types of fat.
That’s the major finding of a new study published in the journal Nature Medicine. But what kind of fat are we talking about here and how can you approach intermittent fasting safely if you’re interested in going this route? Here’s what the study found, plus what a dietitian wants you to know.
Meet the expert: Scott Keatley, RD, is co-owner of Keatley Medical Nutrition Therapy
What did the study find?
For the study, researchers in Spain did a 12-week eating intervention with 197 people with obesity.
The study participants were asked to follow one of three different fasting strategies:
- Fasting between 5 pm to 9 am.
- Fasting from 2 pm to 10 pm.
- Fasting during a time slot they preferred (most chose between 8 am and 12 pm).
Another group was just given a nutritional education program, which all of the study participants went through, too.
The researchers found that intermittent fasting didn’t seem to have additional benefits over the nutritional education group when it came to reducing visceral fat, which surrounds certain organs in the body.
But the fasting groups had more weight loss, on average 6.6 to 8.8 pounds, compared to the control group. The group that fasted between 5 pm and 9 am had more of a drop in subcutaneous fat (i.e. fat just under the skin) in the belly area.
Why did intermittent fasting lead to greater weight loss compared with a calorie-controlled group?
It’s not clear. However, it could be that study participants simply had less time to eat, which interfered with their normal routine.
In Spain, most people have breakfast between 7 a.m. and 8 a.m., and dinner at 9 p.m. to 10 p.m., creating a 12 to 14 hour window of eating. Intermittent fasting reduced their eating window and may have caused them to simply eat less.
Why did intermittent fasting reduce belly fat better than the calorie-controlled group?
The researchers didn’t detail why this strategy may have reduced belly fat. However, they pointed out that following an intermittent fasting schedule helps people follow a consistent cycle of eating and fasting, which can help to stabilize their biological rhythms.
On the flip side, eating irregularly can interfere with these rhythms and increase the risk of developing obesity, cardiovascular disease, and type 2 diabetes.
Why did fasting lead to more glucose control?
The researchers didn’t determine this, but they theorized that it may have something to do with the consistent eating schedules.
“It’s worth noting that just about any form of calorie restriction tends to lower blood glucose levels, making it difficult to separate the benefits of intermittent fasting from overall caloric reduction,” says Scott Keatley, RD, co-owner of Keatley Medical Nutrition Therapy.
Are the results applicable to people who don’t have obesity?
It’s hard to say. Data has had mixed results on how effective intermittent fasting is for weight loss, usually concluding that it’s about as effective as going on a calorie-restricted diet. But most of the studies on the impact of intermittent fasting on weight loss have been conducted on people with obesity.
That doesn’t mean that this can’t be an effective strategy for weight loss for everyone else, though—the results just may not be as significant.
Are the results applicable to Americans?
It’s also hard to say. The eating habits of people in Spain are very different from those of most Americans. However, intermittent fasting has been show to help people lose weight in other studies.
How should I start intermittent fasting safely?
It’s best to follow a “thoughtful and gradual approach” to intermittent fasting, Keatley says.
If you have any underlying health conditions like diabetes or gastrointestinal issues, he recommends consulting with a healthcare provider to make sure this is a safe method for you. After that, “begin by gradually shifting your meal times to end earlier in the evening, reducing the adjustment period for your body,” he says.
During the eating window, Keatley suggests focusing on nutrient-dense meals with balanced macronutrients, like protein, healthy fats, and fiber, to help sustain your energy levels and tamp down on hunger during fasting hours.
“Hydration is critical, so drink plenty of water, herbal tea, or black coffee during the fasting period to stay hydrated,” Keatley says. “Monitor your body’s response to fasting, paying attention to signs like fatigue, dizziness, or irritability, and adjust as needed.”
Other healthy habits are still important, including exercising regularly, and especially strength training to preserve muscle mass while losing fat. “Finally, prioritize consistency and patience, as improvements in blood sugar regulation and fat loss may take time to manifest,” Keatley says.
Korin Miller is a freelance writer specializing in general wellness, sexual health and relationships, and lifestyle trends, with work appearing in Men’s Health, Women’s Health, Self, Glamour, and more. She has a master’s degree from American University, lives by the beach, and hopes to own a teacup pig and taco truck one day.