People have subscribed to intermittent fasting for centuries, opting to omit eating for a whole host of reasons, from religious observance to political protest.
One of the newest explanations for intermittent fasting is for health optimization.
Some people believe that bypassing a traditional schedule of three meals a day can help them lose weight, boost their energy and even improve their focus.
But is that actually the case?
Jennifer Schriever, MD, offers an expert physician perspective on this emerging trend. Dr. Schriever, a family physician at Sanford Health who specializes in obesity medicine and long-term weight management, appears on the latest episode of AMA podcast “Health vs. Hype,” which is produced in partnership with iHeartRadio.
"Health vs. Hype" takes on medical misinformation, viral health trends, DIY medicine, and common health myths to help listeners understand what’s real, what’s risky, and what’s backed by science. Host Trace Dominguez fact-checks popular health claims, explains how medical misinformation spreads, and reveals the real-world consequences of getting it wrong.
Sanford Health is part of the AMA Health System Member Program that provides enterprise solutions to equip leadership, physicians and care teams with resources to help drive the future of medicine.
Weight management is a long-term process
"We try not to use the word ‘diet’ because it has kind of a negative connotation, and it's something that you do temporarily," Dr. Schriever said. "In my practice treating patients for weight management, I'm trying to create and help you improve your lifestyle in a way that you feel good in the process, lose weight [and] have more energy. I don't want to have a plan that you graduate from or finish. This is something that we might continually have to adjust and manage over time. Even people on intermittent fasting are … going to have to adjust and adapt something over time."
Intermittent fasting can seem to work at first
"Your body will start to shift from burning blood sugar or glucose to using your stored energy, so your fatty tissue, during those fasting periods," Dr. Schriever said, detailing what the medical research shows about patients who are in a “fasted” versus a “fed” state.
"As one starts intermittent fasting, depending on how they approach it, many will have less calorie intake,” she said. “A person might cut out that meal and not replace that nutrition later in the day. So then you're reducing your caloric intake and that can contribute to some early onset of some initial weight loss, so then that makes you feel successful."
"In really good studies," Dr. Schriever continued, "where they compare people who are doing intermittent fasting and those doing caloric restriction, there really isn't any significant difference in weight loss. There's no significant difference in heart health or other metabolic markers. When it comes down to intermittent fasting, if your caloric intake remains the same, you aren't going to see that weight loss, you aren't going to see the metabolic changes or the other reported benefits."
Learn more with the AMA about what doctors want patients to know about healthy eating.
Research doesn’t support intermittent fasting claims
There is "not very clear evidence for living longer, healthier lives in humans" due to intermittent fasting, Dr. Schriever said. "Cancer prevention and mortality is something that can be widely advertised, but there's very limited data. [There are] no high quality studies that show intermittent fasting can prevent cancer nor improve your treatment. Are there studies that are ongoing to look at this? Absolutely. But nothing convincing currently."
Intermittent fasting doesn’t boost cognitive health
"Like most of the studies for intermittent fasting, there is some possibility of improvement in cognitive benefits, but these are very short-term studies and it isn't consistent across populations," Dr. Schriever said. "The high quality meta-analysis data doesn't show any benefit ... so fasting is not any better than a fed state. It's very neutral in healthy adults in general."
"The best evidence for improving your cognition is still back to exercise and adequate sleep," she said. "We're just not finding significantly long enough studies or even significant data that fasting in whatever form is superior to just a healthy diet."
Intermittent fasting comes with a lot of risks
"Anyone with a history of eating disorders really should be cautious about considering it," Dr. Schriever said. "Anyone with diabetes should do it cautiously and not without medical supervision. Anyone who is older … I'd be worried about because we want to watch their nutritional intake.
"I'd be really cautious [for] anyone with lower muscle mass," she added. "Anyone with any signs of insulin resistance should really do it [intermittent fasting] in a supervised fashion."
By not eating a meal or only eating during a limited time frame, "you have a shorter time frame to get your nutrients in," Dr. Schriever continued. "You might become vitamin deficient or might struggle to get enough protein in to keep your muscle mass up. … Depending on how your insulin response is and blood sugar response is, you might have lower blood sugar and just really feel foggy or not well. And also, that can disrupt sleep."
Intermittent fasting "can sound great, but it still takes some insight in knowing what you're eating and what does that do for your body, and are you including things that are important to maintain your muscle mass, your bone density, your basal metabolic ravte—and even to live longer, healthier," she said.
"If you're just focusing on that this is a great plan for weight loss and you're not improving your nutritional choices, you're not going to see the long-term benefits of what we're looking for as we improve our lifestyle, which is improved heart health, less disease, less cancer risk, and living longer and healthier and [having] more energy. It's really not a great plan just isolated by itself."
Find out more about the bottom line for patients on the new U.S. dietary guidelines.
