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Intermittent fasting over two days can help people with Type 2 diabetes


Intermittent fasting can help people with Type 2 diabetes lose weight, lower blood pressure and improve blood sugar levels, a rigorous new study has found.

The new research, published Friday in the journal JAMA Network Open, found that intermittent fasting had striking metabolic benefits that surpassed even the effects of prescription medications for people with newly diagnosed diabetes. Here are the findings:

  • Over the course of 16 weeks, people who were assigned to practice intermittent fasting lost more weight and improved their blood sugar control to a greater extent than people who were given metformin or empagliflozin, two commonly prescribed diabetes medications.
  • The research focused on a form of fasting called the 5:2 diet, in which people eat normally for five days a week and then fast for two days, consuming just 500 to 600 calories on their fasting days.
  • After 16 weeks, the fasting group lost an average of 21 pounds, almost double the 12 pounds on average that the people taking metformin lost. Those who were prescribed empagliflozin lost an average of about 12.8 pounds during the study.
  • Previous studies have examined whether intermittent fasting can help people with Type 2 diabetes, but they have been mostly small and did not compare the diet head-to-head with medications.
  • The study involved more than 330 overweight and obese adults who had recently been diagnosed with Type 2 diabetes.

Courtney Peterson, an expert who was not involved in the study, said the results were “exciting.”

“Often times we assume that drugs are more powerful than lifestyle approaches,” said Peterson, an associate professor of nutrition sciences at the University of Alabama at Birmingham. “But here they showed that a lifestyle approach was more effective for lowering blood sugar than putting people on drugs. That’s a very powerful statement.”

The 5:2 diet was first popularized a decade ago by a BBC documentary and a best-selling book, “The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting,” by British physician Michael Mosley, along with co-writer Mimi Spencer.

The new study of the 5:2 diet took place in China, which has more people with Type 2 diabetes than any other country in the world. At least 141 million adults in China have diabetes and half the population is overweight or obese.

The authors of the new study recruited adults with Type 2 diabetes and then split them into three groups. In the first two groups, participants were assigned to take either metformin or empagliflozin. In the third group, participants were taught to follow the 5:2 diet. Women consumed just 500 calories on each of their two weekly fasting days, while men consumed no more than 600 calories — equivalent to about a quarter of their usual caloric intake.

On their fasting days, the participants consumed sparse amounts of food: An egg for breakfast, a couple servings of fruit or vegetables for lunch, and a light salad for dinner. Each meal was paired with a low-calorie meal-replacement drink that contained healthy fats, protein, vitamins, minerals and other nutrients. On their non-fasting days, the participants would eat normally for breakfast and lunch and then have a light dinner with a meal-replacement drink.

Significant and sustained improvements

In addition to losing weight, the fasting group saw their HbA1c, a long-term measure of their blood sugar levels, drop 1.9 percent — significantly more than the groups taking medication. About 80 percent of participants in the fasting group saw their HbA1c fall below 6.5 percent, the cutoff for diabetes, compared to 60 percent of the participants on metformin and 55 percent of the people taking empagliflozin.

Eight weeks after the study ended, the researchers followed up with the participants and found that most of the people in the fasting group had maintained blood sugar levels below the threshold for diabetes, suggesting that the diet “significantly and sustainably improves HbA1c levels,” the authors wrote.

The researchers found that the fasting group also had greater reductions in their waist circumference, blood pressure levels and triglycerides, a type of fat that circulates in the blood, compared with the participants taking medication.

The researchers cautioned that more studies were needed to examine the long-term effectiveness of the 5:2 diet with meal replacements for Type 2 diabetes. But they said their findings suggest that the diet might be a good initial lifestyle intervention for people with early-stage diabetes.

Fasting combined with meal replacements

Peterson said the study was large, rigorous and cleverly designed because it essentially combined two dietary interventions — intermittent fasting and meal replacements — that have been shown to help people with diabetes.

Many studies have found that diets that incorporate low-calorie meal-replacement shakes, soups and bars help people lose weight and lower their blood sugar levels. A number of studies have also indicated that the 5:2 diet helps people improve their blood sugar control.

Peterson said that one downside of the 5:2 diet is that people often see impressive results in the first few months, but that after about six months to a year on the diet, “they start falling off.”

“It does seem to have an advantage in the short term, but in the long term which is a year or more, it doesn’t seem to be better than a standard low-calorie diet,” she added.

She also stressed that more long-term research was needed. But in the meantime, she said that people with newly diagnosed Type 2 diabetes might consider discussing with their doctor whether it is worth trying the 5:2 diet in combination with meal replacement shakes like Optifast, Ensure, Soylent or others.

She noted that while participants in the study did not experience many adverse events on the fasting regimen, about 6 percent of people on the diet reported symptoms of low-blood sugar, which can potentially be dangerous.

“People should absolutely work with their doctor if they want to try this,” Peterson said. “They shouldn’t try it on their own.”

Do you have a question about healthy eating? Email EatingLab@washpost.com and we may answer your question in a future column.



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