Type 2 Diabetes and Fasting: How Dangerous Could it Be?

March 15, 2018
Gregory M. Weiss, MD

Fasting sounds like a bad idea for anyone with type 2 diabetes and especially bad for someone taking antihyperglycemic drugs. But, is it really?

 â–º Fasting of any type increases the risk of hypoglycemia in patients with type 2 diabetes mellitus (T2DM) on hypoglycemic medications.

 â–º Even with supervised hypoglycemic medication reduction, weekly supervision and education on hypoglycemia, intermittent fasting increased the rate of hypoglycemia twofold in T2DM

 â–º Severe hypoglycemia is rare in T2DM even if intermittent fasting is undertaken.

Obesity rates and the incidence of T2DM both continue to rise worldwide. Medical treatments and low calorie diets are often employed in both conditions-to help facilitate weight loss and reduce blood sugar. The practice of fasting, consuming a no- or very low-calorie diet on consecutive days or intermittently during the week, has gained popularity but in persons with T2DM could promote dangerous levels of hypoglycemia.

BT Corely and colleagues at the Centre for Endocrine Diabetes and Obesity Research, Wellington Hospital, Wellington, New Zealand point out that dieting and fasting may be even more problematic for T2DM patients who are taking hypoglycemic medication. Few studies, they point out, have been conducted looking at intermittent fasting in patients with T2DM and none have examined the effect of hypoglycemic medications during low- or no-calorie periods on incidence of hypoglycemia.

The authors hypothesized that during a 5:2 intermittent fasting diet in individuals with T2DM on hypoglycemic medication, non-consecutive days of caloric restriction along with diabetes medication adjustment would reduce the overall risk of hypoglycemia to a greater extent than consecutive days of caloric restriction. Findings are presented in a recent issue of Diabetic Medicine.

The Study

37 patients were included in the study with 19 in the non-consecutive day fasting group and 18 in the consecutive day fasting group. The primary outcome measured was number of hypoglycemic events during 12 weeks of observation. The risk of hypoglycemia on fasting vs non-fasting days was considered a secondary outcome.
 

The Results

 â–º 53 hypoglycemic events were observed during 84 observation days involving 15 subjects.

 â–º 59% of subjects had no hypoglycemic events.

 â–º 23 hypoglycemic events occurred over 851 fasting days (1 event per 37 days) while there were 30 events over 2257 non-fasting days (1 event per 75 days).

 â–º No episodes of severe hypoglycemia were observed.

 â–º Fasting conferred a twofold increase in the risk of having hypoglycemia [RR 2.05 (95% CI 1.17–3.52); P=0.013].

 â–º There was no difference in the risk of having a hypoglycemic event between groups [RR 1.54 (95% CI 0.35–6.11); P=0.51].

Implications for Physicians

►Patients with T2DM who desire weight loss can benefit from very-low-calorie diets and supervised intermittent fasting programs such as 5:2 normal calorie to very-low-calorie day regimens.

►T2DM patients choosing to fast can be reassured that even though they are at higher risk for hypoglycemia on fasting days, it is unlikely that they will experience significant or severe hypoglycemic events.

►Any regimen for intermittent fasting in T2DM should be accompanied by a protocol for adjusting insulin doses and calorie intake based on blood sugars.

►Such a protocol is offered by the authors and can be found in the methods section of the complete article (link below).

 

Source: Corley BT, Carroll RW, Hall RM, et al. Intermittent fasting in type 2 diabetes mellitus and the risk of hypoglycemia: a randomized controlled trial. Diabet Med. 2018. Published first online 27 Feb 2018; 10.1111/dme.13595