Updated: 1 an hour ago Published: 11 hours ago

DEAR MAYO CLINIC: My friend has been swearing by intermittent fasting since her last weight loss. I know it works for some people, but is it really healthy?

ANSWER: Although it seems like a new trend, intermittent fasting has been popular for over 1,500 years. While we know it helps some people lose weight, whether it helps organs like the heart is still unclear. Initial research presented at a recent scientific meeting suggested that intermittent fasting in general may be harmful or risky. It showed that people who practice intermittent fasting are twice as likely to die from heart disease or death in general as people who do not practice it.

The main problem is that intermittent fasting is not standardized. There are many ways to do intermittent fasting. It was popularized in the UK in the last few decades: “Eat whatever you want for five days, then eat nothing but liquids and soups for two full days.” People lost weight, and from there they started to adapt to fasting in very different ways. Some people limit their eating time to 10am-3pm, for example. The most common form of intermittent fasting I’ve seen is people just skipping breakfast.

Whether breakfast is “the most important meal of the day” is still up for debate. Skipping breakfast hasn’t necessarily been healthy in the past. It’s not entirely clear why, but there are numerous studies that show that people who skip breakfast have an increased risk of heart disease and other ailments. Early in the morning is when most people have heart attacks. One reason for this is the high levels of adrenaline that occur early in the morning. Combine that with no food at all and no calories at all, and that could be why studies show that people who practice intermittent fasting aren’t necessarily healthier or safer. I think that’s important to keep in mind.

People who lose weight through intermittent fasting can improve their overall health, but that doesn’t necessarily mean they have to continue intermittent fasting forever. We have to consider many other factors when people skip breakfast or other meals. Stress hormones increase, which can lead to a rise in blood pressure and adrenaline, causing many changes in our system that can actually be more harmful than beneficial.

When patients ask if intermittent fasting is healthy, the answer should be, “It depends.” If they start by skipping dinner, eating very light dinners, or just trying not to eat dinner too late, that’s a great way to practice. Or maybe eating a very light lunch, or skipping lunch altogether — but not necessarily going too long without eating.

Studies show that eating several small meals throughout the day, rather than just two large meals, leads to better cholesterol levels and many other positive metabolic changes. So the idea of ​​going without food or calories for long periods of time is still debated. Current evidence suggests that intermittent fasting is especially dangerous for patients with heart disease. Intermittent fasting may be safer under the supervision of your medical team.

— Francisco Lopez-Jimenez, MDCardiovascular Medicine, Mayo Clinic, Rochester, Minnesota

Mayo Clinic Q&A is an educational resource and is not a substitute for regular medical care. This Mayo Clinic Q&A represents inquiries this health professional has received from patients. For more information, visit mayoclinic.org.