Can young diabetics safely observe Jewish fasts? Insulin pump tweaks can help, Israeli study finds

A first-of-its-kind study has found that more than 70% of young participants completed a 25-hour fast without significant complications when they adjusted their insulin pumps in advance, thus raising the likelihood of success eightfold.

With two major fasts and four minor ones in the Jewish calendar, many people with type 1 diabetes will regularly face a difficult question: Is it possible to observe the fast without putting their health at risk? The new research was conducted jointly by researchers at the Jerusalem College of Technology (JCT) and Shaare Zedek Medical Center. Offering encouraging findings, it showed that advanced diabetes technologies can make it possible for many people with type 1 diabetes to fast safely.

The study, conducted by the diabetes clinic team at Shaare Zedek Medical Center and led by Dr. Floris Levy-Khademi of Shaare Zedek and Dr. Eliyahu Heifetz, a lecturer and researcher at JCT, examined whether automated insulin delivery (AID) systems could enable adolescents and young adults with type 1 diabetes to safely complete prolonged Jewish fasts.

There are two major Jewish fasts commonly observed in the calendar: Yom Kippur (a 25-hour fast, including both food and drink; Tisha B’Av (essentially the same food-and-drink restriction, from before sunset until after nightfall); and four minor fasts (all from dawn to nightfall) – 17 Tammuz, the fast of Gedaliah, 10 Tevet, and the fast of Esther. 

The team decided to carry out the study only for the major fasts, even though some religious young people don’t eat or drink on the minor fasts as well. “They could endanger their health; they mustn’t do it without consulting their doctor,” Levy-Khademi asserted.

Levy-Khademi is the director of Shaare Zedek’s pediatric endocrinology unit, which diagnoses and treats a wide array of hormonal and metabolic conditions in children and adolescents, not only those with type 1 diabetes but also those with puberty disorders, pediatric obesity, and more. Heifetz is a lecturer and scientific researcher at the JCT’s Faculty of Management.

It was published in the Journal of Diabetes Science and Technology under the title “Automated insulin delivery systems are safe during prolonged religious Jewish fasting among adolescents and young adults with type 1 diabetes.”

Fasting despite having an exemption

The purpose of religious fasting is “to gain self-restraint, arouse spiritual consciousness, and better understand the poor and hungry,” they wrote. “Traditionally people with type 1 diabetes were exempted from fasting by the medical and religious authorities, due to a fear of hypoglycemia, hyperglycemia, and dehydration.

“Despite medical recommendations, many individuals with the condition from various religious backgrounds choose to fast; it makes them feel equal, mature and capable of fulfilling their religious obligations.”

The researchers analyzed 109 fasts undertaken by 80 adolescents and young adults with type 1 diabetes on Yom Kippur and Tisha B’Av, in 2023 and 2024. All participants used automated insulin delivery systems that combine an insulin pump with a continuous glucose monitor. The findings showed that 71.5% of participants successfully completed the fast without significant complications.

The mean age of participants was 17.4 ± 4.1 years; 47.5% were male, and the average duration of diabetes was 7.2 ± 4.3 years. A total of 67.6% of participants modified their AID system settings during the fasting period, with the most common modification being a change in the target glucose level, the researchers reported.

“The most important finding of the study is that there were no life-threatening complications among the participants, with no cases of severe hypoglycemia or diabetic ketoacidosis (DKA), the two major complications that raise concerns during prolonged fasting,” said Levy-Khademi.

Another notable finding was the importance of advance preparation and consultation with the patient’s medical team. “About 68% of participants adjusted their pump settings ahead of the fast, either by raising their glucose target or reducing their insulin dosage,” said Levy-Khademi. “Among those who made adjustments, 84.5% successfully completed the fast, compared with just 40% of those who did not.”

Statistical analysis showed that adjusting pump settings before the fast increased the likelihood of successfully completing it eightfold,” she noted. “This is the first study to examine the use of automated insulin delivery systems during prolonged Jewish fasts,” she continued

Heifetz, whose son was diagnosed with autoimmune diabetes as a child and has observed full fasts since age 13, including in the years before today’s advanced technologies became available.

The researchers said that participants’ blood sugar control actually improved during the fast. Participants remained within their target glucose range 80.7% of the time during the fast, compared with approximately 72% during the week leading up to it. The amount of time participants experienced low blood sugar was also relatively limited.

Levy-Khademi explained that “most patients completed the fast successfully, but of the 28.5% who did not, some thought that if they gave themselves less insulin, they would be OK. We told them to be careful, that if they saw their blood sugar was going down significantly, they should stop fasting.

“We monitored them not only during the fast, but also a week before and a week after. We carried out the study because they knew that some religious diabetics were doing dangerous things without consulting anyone.”

The researchers noted that this is the first study to examine the use of automated insulin delivery systems during prolonged Jewish fasts.

“The findings indicate that this technology may enable some people with type 1 diabetes to fast safely, but only with individualized adjustments to their system settings and appropriate medical guidance,” the researchers said.

They didn’t include older people with type 1 diabetes, or those who already had complications of the disease. The team members plan to continue the study next year, focusing on ketones, which are chemical substances that the liver produces when it breaks down fat for energy instead of using sugar because it doesn’t get enough carbohydrates from food.

They cautioned, however, that the findings should not be interpreted to mean that everyone with type 1 diabetes can safely fast.

“The study participants were relatively young and had good glucose control. The decision about whether to fast therefore needs to be made on an individual basis, based on the recommendation of the treating physician and in consultation with the appropriate halachic authority,” the researchers said.