Mayo Clinic Q&A: Is intermittent fasting a good idea?

DEAR MAYO CLINIC: My friend swears by intermittent fasting since her recent weight loss. I know it works for some people, but is it actually healthy?

ANSWER: Although it may appear to be a new trend, intermittent fasting has been popular for over 1,500 years. While we know that it works for some people to lose weight, the reality is that whether or not it helps organs such as the heart is still to be determined. Early research presented at a recent scientific meeting suggested that intermittent fasting might be harmful or risky in general. It showed that people practicing intermittent fasting are twice as likely to die from heart disease or die in general than those who don’t practice.

The main problem is that intermittent fasting is not standardized. There are many ways to do intermittent fasting. Over the past few decades, it has been popularized in the UK as “eat whatever you want for five days, then don’t eat for two full days other than fluids and soups.” People were losing weight, and from that point on, people started adapting to fasting in very different ways. Some people will restrict their time for eating to 10 a.m. to 3 p.m., for example. The most common form of intermittent fasting I have seen is that people just skip breakfast.

Whether breakfast is “the most important meal of the day” is still under debate. Skipping breakfast historically hasn’t been something necessarily healthy. It is not fully understood why, but there are numerous studies showing that people who skip breakfast have an increased risk for heart disease and other ailments. Early morning is the time when people have the most heart attacks. Part of the reason for that is the high-adrenaline state that occurs early in the morning. If you match that with no food, no calories at all, that might be the reason why studies show that people practicing intermittent fasting are not necessarily healthier or safer. I think that’s important to keep in mind.

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

When patients ask if intermittent fasting is healthy, the response should be, “It all depends.” If they start skipping dinner, having very light dinners or just trying not to have dinner too late, that’s an excellent way to practice. Or perhaps having a very light lunch or skipping lunch altogether — just not necessarily going for too long with no food.

Studies show that having multiple small meals throughout the day versus just two big meals results in better cholesterol and many other positive changes in the metabolism. So, this idea of not having any food or calories for long periods of time is still under debate. Based on recent evidence, intermittent fasting is particularly unsafe for patients with heart disease. Practicing intermittent fasting can be safer with supervision from your healthcare team.

— Francisco Lopez-Jimenez, M.D., Cardiovascular Medicine, Mayo Clinic, Rochester, Minnesota

Mayo Clinic Q & A is an educational resource and doesn’t replace regular medical care. This Mayo Clinic Q&A represents inquiries this healthcare expert has received from patients. For more information, visit www.mayoclinic.org.