Are you trying intermittent fasting? Here's what doctors want you to know

LOS ANGELES (KABC) -- Intermittent fasting has become a popular way to diet, with approaches that range from skipping food for certain hours each day to fasting for entire days at a time.

While research shows this eating pattern can help some people lose weight and may offer other health benefits, doctors say it may not be for everyone.

Experts say intermittent fasting focuses less on what people eat and more on when they eat.

Registered dietitian Tara Collingwood described the approach simply: "You eat only a particular number of hours for the day."

More than 13% of Americans have tried intermittent fasting, and many say they have turned to it either intentionally or even without realizing they were eating that way.

"I have done fasting and I think it's really a great thing," Rhonda Roebuck said.

"There are days where you're busy and you don't eat lunch, so unintentionally intermittent fasting," Daniel Tamae said.

One common form of intermittent fasting is known as time-restricted eating, or TRE. While it can help people cut back on how much they consume, new research from Germany found that it does not improve metabolic health.

Collingwood said the timing of meals can matter.

"If someone is going to eat later in the day, that tends to be a little bit worse for your metabolism and for your risk of disease," she said.

A study by the American Heart Association concluded that eight-hour time-restricted eating is linked to a 91% higher risk of cardiovascular death.

And while experts say some longer fasting periods - not eating for four days or more - may enhance cognition, shorter fasting appears ineffective, especially for those with cognitive decline.

Roebuck said fasting can feel more risky as people age.

"As you get older, you could get diabetes...Fasting could be really difficult for certain people," she said.

Questions also remain about long-term weight loss. Collingwood said the long-term effects of intermittent fasting are still unknown and stressed the importance of monitoring overall calorie intake.

"It's the reduction in calories that causes the weight loss, not necessarily eating in a shorter period of time," she said.

Some research on fasting and cancer is also emerging. A 2025 small study in the British Journal of Cancer suggests that eating normally for five days and restricting intake for two days might slightly slow the progression of metastatic breast cancer.

Tamae, a chemistry professor who has researched the field, said there is a scientific basis for studying the connection.

"Some tumors are driven by glucose metabolism. So there is, you know, there are some rationale behind it," he said.

Other studies involving cancer patients have found that intermittent fasting may help reduce some side effects of chemotherapy, and numerous active studies on intermittent fasting are ongoing.

Before you try it, doctors say check with your physician first, especially people who are diabetic or who have other specific health risks.