Is Intermittent Fasting Healthy?

Gastroenterologist Dr. Shilpa Ravella shares six things to know about this popular weight-loss trend.

If you’re hearing more people tout the benefits of so-called intermittent fasting, you’re not alone. The weight-loss trend — which calls for drastically reducing your calorie intake a couple of days a week — is everywhere these days, with fans in both health bloggers and personal trainers as well as celebrities like Beyoncé and Dwayne “The Rock” Johnson.

Dig a bit deeper and you’ll find current research in mice that suggests the practice may have slimming and endurance benefits for humans, but more and longer-term research is required.

However, it’s not advisable for everyone, such as pregnant women or those taking medication, says Dr. Shilpa Ravella, a gastroenterologist at NewYork-Presbyterian/Columbia University Irving Medical Center and an assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons. Here, she sheds light on the practice, which has existed for centuries.

Health Matters: What is intermittent fasting?
Dr. Shilpa Ravella: It’s really a way to decrease calories at certain times of the day or week. There are many different ways to do this. For example, you can have an intermittent fast that involves eating whatever you want for five days and then eating a lot fewer calories on two days out of the week. So, about 500 calories on two days and then regular meals the rest of the week. You can also fast every other day, for example, eating 500 calories every other day.

Is it healthy?
Fasting has actually been around for thousands of years and can improve health. From an evolutionary perspective, our habit of eating three meals a day and then snacking, eating while watching TV at night, and having all of these different foods during the day is pretty abnormal. For much of human history, our access to food was very sporadic. Believe it or not, we have fat tissue with energy reserves that can support the body for a week if we’re unable to have access to food.

There have been human and animal studies that have shown that fasting for just two to five days each month can reduce biomarkers (a measurable indicator of some kind of biological state or condition) for things like diabetes, cancer, and heart disease. It lowers insulin as well as a hormone called insulin-like growth factor, or IGF1, which is linked to cancer and diabetes. When you lower insulin and IGF1, cells get out of growth mode and enter a state of maintenance. This maintenance can help with the aging process and decrease disease risk factors. There are also studies that have shown that fasting can help improve symptoms in patients with autoimmune disease, for example.

You’ve talked a bit about the benefits. Any cons?
If you’re going to consume fewer calories, you want to make sure that you eat a very healthy diet to avoid malnutrition. This includes eating fruits, vegetables, whole grains, nuts, and beans. Just smaller portions, basically. And remember to stay well hydrated.

If you’re doing an intermittent fasting program where two days out of the week you’re eating 500 calories, it is not a license that on five days out of the week you can eat a lot of junk food or whatever you want. It’s important to eat a varied diet with lots of fresh fruits and veggies.

Dr. Shilpa Ravella

Are there people who shouldn’t try it?
Fasting is not appropriate for pregnant women or people with diabetes, who run the risk of low blood sugar, especially if they’re taking insulin or oral medications. People with other conditions requiring a lot of medication should avoid intermittent fasting as should those who are malnourished or underweight. People with malabsorption issues and nutritional deficiencies may run into problems when attempting intermittent fasting. It’s important to take a look at each individual’s medical problems before determining if intermittent fasting is appropriate. Before embarking on an intermittent fasting program, it’s important to work with a physician and a nutritionist.

Are there different ways you can incorporate intermittent fasting into your lifestyle?
If folks can’t do two days of fasting, they could always try time-restricted eating. I practice a version of it. I’m not terribly strict about it, but I try to consume all of my calories within about nine hours during the day. I then have sort of an extended fast after that until the next day. Some data says that if you consume all calories within eight or nine hours, that can have positive health effects and counteract certain disease processes, including lowering cancer risk and maintaining a healthy weight. The reason being, you’re giving your digestive system a break for a certain amount of time, which allows the body to go into that “maintenance phase,” which triggers cell regeneration.

Is there anything else people should know before they begin?
I really think the key is the quality of your diet. That is the most important thing — beyond intermittent fasting — that your diet is full of fruits and vegetables, whole grains, and all of that. If you adopt a healthy, plant-based diet, it is one of the most remarkable things that you can do to change your life.

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Dr. Shilpa Ravella is a gastroenterologist at NewYork-Presbyterian/Columbia University Irving Medical Center and an assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons, where she directs the Adult Small Bowel Program, managing the gastrointestinal evaluations and medical care of adult intestinal and multivisceral transplant patients. Dr. Ravella offers an integrative approach to patient care with a focus on optimizing nutrition. She has written for a variety of national media, including The Atlantic, Discover Magazine, Slate, PBS, and TED-Ed.