Intermittent fasting offers health benefits, study says. But diet is not for everybody

Kristin Lam | USA TODAY

Show Caption Hide Caption Diets we want to say 'goodbye' to in 2020 New year, new you! But some diets need to stay to stay in the past.

Trading indulgences for intermittent fasting could yield health benefits from lower cholesterol to reduced stress, according to a new study.

The dieting method requires patience, researchers wrote in a review published Thursday in the New England Journal of Medicine, but doctors can help patients reach the scientifically-proven benefits or warn at-risk groups to avoid it.

While intermittent fasting diets vary, the practices of alternating between certain periods of eating and not eating fall into two categories, said co-author Mark Mattson, a neuroscience professor at the Johns Hopkins School of Medicine. One restricts eating to six to eight hours per day and another limits people to one moderate-sized meal two days each week.

The eating patterns can increase resistance to stress and improve blood sugar regulation, while decreasing blood pressure, blood lipid levels and resting heart rates, Mattson wrote. Multiple studies on humans and animals have reported those results, he said, bringing legitimacy to the practice.

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"We are at a transition point where we could soon consider adding information about intermittent fasting to medical school curricula alongside standard advice about healthy diets and exercise," Mattson said in a release statement.

Even so, committing to intermittent fasting for the long periods of time is often difficult, said Dr. Guy L. Mintz, director of cardiovascular health and lipidology at Sandra Atlas Bass Heart Hospital in New York. Some studies show patients eating more than recommended on fasting days and less on feast days, said Mintz, who did not participate in the review.

Mintz also urged certain groups to avoid intermittent fasting, including patients who are not overweight. Most clinical studies have worked with overweight young and middle-aged adults, the study said, so more trials on other ages are required.

"Intermittent fasting may not be a good diet for diabetic patients on medications and/or insulin that could have swings in blood sugar," Mintz said. "Intermittent fasting is not for older patients. Hypoglycemia needs to be watched, which can lead to falls."

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The diet works, Mattson wrote, by changing a person's metabolism similarly to how humans adapt to times of food scarcity. The body uses up its sugar stores, which metabolize quickly, and slowly converts fats into energy.

Scientists have also observed these eating patterns and metabolism changes in natural animal behavior, said Dr. Gerald Bernstein, program coordinator at the Friedman Diabetes Institute of Lenox Hill Hospital in New York City.

"Certain birds will change their beak depending on rainfall, said Bernstein, who did not participate in the study. "The beak of these birds will change to meet the height of the plant growth; less rain, big beak; more rain, small beak."

The changes over time may alter the DNA of a bird, which could explain the benefits of intermittent fasting, said Bernstein.

Other preliminary trials have suggested intermittent fasting for animals can delay the onset of Alzheimer's disease and suppress the growth of cancerous tumors, but the study said further research is required. In the meantime, the authors concluded it is unlikely that intermittent fasting will be practiced widely in the United States.

"A diet of three meals with snacks every day is so ingrained in our culture that a change in this eating pattern will rarely be contemplated by patients or doctors," the study said. "The abundance of food and extensive marketing in developed nations are also major hurdles to be overcome."