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Intermittent Fasting

Anyone searching for new weight loss methods has likely come across intermittent fasting. This eating pattern — based on timing of calorie intake rather than quantity — has become a popular way to lose unwanted pounds.

“At this point, there are probably more books written about intermittent fasting than there are actual medical studies to back them up; however, the studies that have been done show the benefits of intermittent fasting,” says Rachel Kilpatrick, M.D., an endocrinologist at Washington Regional Endocrinology Clinic in Fayetteville.

According to research published in the New England Journal of Medicine in late 2019, intermittent fasting may offer wide-ranging health benefits in addition to weight loss. Clinical trials have shown intermittent fasting to have a positive impact on health conditions such as diabetes, cardiovascular disease, cancers and neurological disorders.

How does it work? After about 12 hours without food, the body has used up all the sugar stored in the liver and, looking for a replacement energy source, begins using ketones stored in fat. This is called the metabolic switch. While an individual practicing any form of fasting likely loses weight simply by consuming fewer overall calories, the metabolic switch also prevents the body from storing fat. Additionally, the metabolic switch activates processes that optimize physiological function, enhance performance, and slow aging and disease.

Dr. Kilpatrick describes several intermittent fasting regimens:

  • Time Restricted Eating: This plan requires fasting for most hours of the day, with calorie consumption restricted to a set number of hours. With a 16:8 regimen, for instance, a person would fast for 16 consecutive hours and then eat normally during an 8-hour window of their choosing. Some followers practice 18:6 or 20:4 regimens. “Studies show this plan is the one most likely to be adhered to long term,” Dr. Kilpatrick says. “It’s important to make sure you stop eating at least 3 hours before bed.”
  • Fasting Mimicking Diet: This describes a low-calorie diet that can simulate fasting.
  • 5-2 Fasting: This regimen requires a 24-hour fast on two non-consecutive days of the week. Then, on the other five days of the week, eating normally.
  • Alternate Day Fasting: Following this plan means fasting every other day and eating normally on the remaining days.

When fasting, drinking water, unsweetened herbal teas and black coffee is allowed. “Dirty fasting” might include as many as 50 calories during the fasting period, such as a nondairy creamer in coffee.

Dr. Kilpatrick encourages taking a gradual, phased-in approach to intermittent fasting. More studies are needed to determine whether it is safe for people with certain health conditions; it is not recommended for women who are pregnant or breastfeeding or for anyone under the age of 18 or with a history of eating disorders. Fasting might also interfere with certain medications. “There is no right answer for any person, and intermittent fasting may not be safe for everyone,” she says. “However, intermittent fasting is an option to help with weight loss and improvement in insulin resistance. Many have found it to be extremely helpful.”

Research on intermittent fasting shows health benefits | National Institute on Aging (