Diabetes Blood sugar
Intermittent fasting can help diabetics regulate blood sugar levels and lose weight, a clinical study has shown. © unsplash+

Obesity is not the only negative consequence of an unhealthy diet and lack of exercise. More and more people develop an insulin resistance – with the result that blood sugar levels remain permanently high. Type 2 diabetes is the diagnosis in this case, which frequently triggers cardiovascular diseases, including heart attacks and strokes. Patients in an advanced stage of the disease may eventually have to get insulin injections every day. There is still a lack of precise data about the prevalence of this metabolic disease in Austria. There are estimates of case numbers totaling up to 800,000, which corresponds to about nine percent of the population. Experts agree, however, that there will be a sharp rise in the number of people suffering from this disease, which is also a consequence of lifestyle.

“Weight reduction plays an essential role in the treatment of type 2 diabetes. Very often, losing weight can lead to an improvement in the glucose metabolism,” explains Harald Sourij, Professor for interdisciplinary metabolic medicine at the Medical University of Graz. This is the reason why, in a recently completed project funded by the Austrian Science Fund FWF, he and his team investigated a form of dieting that has become increasingly popular in recent years: intermittent fasting, which usually involves eating every other day without restriction, while eating little or nothing on the days in between.

Patients with advanced disease

“We were interested in knowing whether this type of dietary intervention works and is also safe for patients with diabetes who are already injecting insulin,” says Sourij, describing the research issue at hand. “Critics of this form of dieting often express the fear that people following the diet might develop a dangerous hypoglycemia on fasting days.” Unsurprisingly, there is a lack of clinical study data on intermittent fasting. Hardly any of the numerous forms of dieting – not even those offered specifically for people with diabetes – come with solid data on the chances of success and safety.

Sourij and his colleagues recruited a total of 46 people for their study. All of them already suffered from an advanced form of the disease and had to take stronger insulin doses. The participants were randomly divided into two groups. One group was given dietary instructions that corresponded to intermittent fasting: they were allowed to eat 500 calories, which corresponds to a normal breakfast, until noon on Mondays, Wednesdays and Fridays. After that, there was no caloric intake at all until the morning of the following day, which was subject to no restrictions. At the same time, insulin therapy was adjusted to the dietary rhythm according to a simple regime. The control group, on the other hand, received only counselling on dietary recommendations for diabetics.

Clear results after three months

During the three-month study period the two groups were closely monitored. Laboratory parameters on blood glucose, lipid metabolism and organ functions were regularly recorded and insulin therapy was adjusted if and when necessary. At the same time, all study participants wore glucose sensors that continuously collected high-resolution data on blood glucose levels. In that way the team could monitor not only whether the specified fasting intervals were adhered to, but also whether the eating regime had a positive or negative impact on the glucose levels.

Evaluation after three months showed clear results: “The average sugar levels improved significantly in the fasting group. In addition, the subjects lost an average of just under five kilograms of body weight,” reports Sourij. “In contrast, blood sugar and weight levels remained largely unchanged in the control group.” The results also dispelled fears that the diet could harm patients. “It was paramount for us that we were unable to detect severe hypoglycemia in any of the test subjects. We now know how to adjust insulin dosage and that it is safe,” adds Sourij. For those suffering from diabetes, this provides a valid diet option that many people find easier to cope with than continuous calorie reduction. It is advisable, however, to seek medical assistance when engaging in the process. 

Losing weight for the long term

The data for the project were already collected two years ago. The study participants were given another checkup this year in order to determine the long-term effects of the diet, which revealed another positive result: “The two-year data show that weight reduction can still be observed in the subjects of the fasting group. Hence, the success was definitely long-term in nature.” The researcher is now planning a follow-up study which will include exercise as a factor. As Sourij explains, “We want to investigate how weight loss from intermittent fasting can be fostered further by exercise – and how exercise affects not just sugar and insulin levels, but also the motivation of people with type 2 diabetes.” The study “Intermittent Fasting in Type 2 Diabetes”, which was conducted between 2020 and 2023, received EUR 335,000 in funding from the Austrian Science Fund FWF.


Obermayer A., Tripolt NJ, Pferschy PN et al.: Efficacy and Safety of Intermittent Fasting in People With Insulin-Treated Type 2 Diabetes (INTERFAST-2)-A Randomized Controlled Trial, in: Diabetes Care 2023

Tripolt NJ, Hofer SJ, Pferschy PN et al.: Glucose Metabolism and Metabolomic Changes in Response to Prolonged Fasting in Individuals with Obesity, Type 2 Diabetes and Non-Obese People-A Cohort Trial, in: Nutrients 2023

Personal details

Harald Sourij is Professor and Head of the Trials Unit for Interdisciplinary Metabolic Medicine and Deputy Head of the Clinical Division of Endocrinology and Diabetology at the Medical University of Graz. Earlier in his career, he held the position of Senior Clinical Researcher at the Diabetes Trials Unit at the University of Oxford in the UK (2011-2014).