Intermittent Fasting or Low-Cal Diet? Similar HbA1c Drop in Adults With Diabetes

Marlene Busko

July 26, 2018

Patients with well-controlled type 2 diabetes and excess weight had similar reductions in HbA1c after a year of intermittent fasting — fasting 2 days/week and eating normally 5 days/week — versus a consistent low-calorie diet.

Patients in the intermittent fasting group also showed a trend toward greater weight loss, but the difference did not reach statistical significance.

"Intermittent energy restriction is an effective alternative diet strategy for the reduction of HbA1c level comparable to continuous energy restriction in patients with type 2 diabetes, and it may be superior to continuous energy restriction for weight reduction," Sharayah Carter, BND, from the University of South Australia, Adelaide, and colleagues report in an article published online July 20 in JAMA Network Open.

The authors note, however, that intermittent fasting needs to be done with some caution. "For people using sulfonylureas and/or insulin, intermittent energy restriction requires medication changes and regular monitoring, especially in the initial stages," Carter and colleagues write.

"This trial highlights the benefits of caloric restriction," Harpreet S. Bajaj, MD, MPH, a community endocrinologist and research associate at Mount Sinai Hospital in Toronto, Ontario, told Medscape Medical News.

"Some patients may prefer to do intermittent fasting and some patients may prefer to do daily caloric restriction," so treatment should be individualized, said Bajaj, who is also a blogger for Medscape Medical News.

Is Intermittent Fasting More Palatable?

Some patients with diabetes might may find it easier to lose weight if they can eat what they usually do most of the time and fast a couple of days a week, Carter and colleagues speculated.

As they previously reported (Diabetes Res Clin Pract. 2016;122:106-112), a small 3-month pilot study showed that patients with type 2 diabetes had similar glycemic control and weight loss with a continuous low-calorie diet or an intermittent fasting diet.

To extend this work, they recruited 137 adults from the community who had type 2 diabetes and a body mass index (BMI) ≥ 27 kg/m2 but were otherwise healthy. The patients were a mean age of 61 years. They had a mean HbA1c of 7.3% and a mean BMI of 36 kg/m2, and 56% were women.

The investigators randomly assigned participants to a continuous low-calorie diet or intermittent fasting. All patients met with a dietician and received a diet-specific booklet with portion-size advice and sample menus, and they were also given a digital kitchen scale.

Participants in the continuous calorie restriction group were instructed to eat 1200 to 1500 kcal/day (30% protein, 45% carbohydrate, and 25% fat), for a total of 10,300 kcal/week.

Those in the intermittent fasting group were instructed to eat 500 to 600 kcal/day (including a minimum of 50 g of protein) on two (consecutive or nonconsecutive) days of the week and consume their usual diet on the other 5 days, for a total of 11,500 kcal/week.

The participants had scheduled meetings with the dietician every 2 weeks for 3 months, followed by meetings every 2 to 3 months for 9 months. At these meetings the dietician reviewed blood glucose control, weight, and diet checklists to assess dietary compliance.

The patients' medications were managed by the study dietician, endocrinologist, and medical practitioner.

At study entry, most patients were taking metformin (65%), followed by a sulfonylurea (22%), insulin (20%), or dipeptidyl peptidase-4 inhibitor (15%). Few were taking a sodium-glucose cotransporter 2 inhibitor (6%) or glucagon-like peptide 1 (GLP-1) agonist (4%).

Early in the trial, after 38 patients had enrolled, the medication management protocol was modified primarily due to hypoglycemia. The new protocol required that all patients stop taking sulfonylureas and insulin if their baseline HbA1c was less than 7%. In addition, patients with HbA1c between 7% and 10% were instructed to stop taking sulfonylureas and insulin on fasting days and discontinue long-acting insulin prior to a fasting day.

Similar HbA1c and Weight Changes in Both Groups

The drop-out rate was similar in the two groups, with 69% of patients in the continuous energy restriction group and 73% in the intermittent fasting group completing the 12-month intervention.

The mean change in HbA1c at 12 months, was similar in both groups: a decrease of 0.5% and 0.3% in the continuous- and intermittent-calorie restriction groups, respectively. 

The mean weight change was also similar: a loss of 5 kg and 6.8 kg in the continuous- and intermittent-calorie restriction groups, respectively. In addition, there were no significant between-group differences in step count, fasting glucose, lipids, or changes in medication dose.

There were eight hypoglycemic events, with a similar number in each group. The authors note that patients who attended all dietician appointments had greater benefits.  

The results may not be generalizable, the researchers acknowledge, as the patients had well-controlled glycemia and received more frequent contact with a dietician than in usual clinical practice. The patients' changing diabetic medications also make it difficult to interpret this trial.

Nevertheless, Carter and colleagues conclude that "intermittent energy restriction is acceptable for most patients with type 2 diabetes," and safety can be managed with regular monitoring.  

"When patients come in and say, 'I want to do this diet,' we always look at what drugs they are on, and if they are on drugs that can cause hypoglycemia we try to reduce those doses before they try a certain diet," Bajaj noted.  

With newer medications that are less likely to cause hypoglycemia perhaps "it is even safer to help people take up these specific [calorie-restricted] diets," he added. Perhaps "GLP-1 medications that control that hunger/appetite and maybe a combination of things would help improve the sustainability of such an intervention."

The authors have reported no relevant financial relationships.

JAMA Network Open. Published online July 20, 2018. Full text

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