Intermittent fasting may help people with Type 1 diabetes control blood sugar

A six-month clinical trial led by researchers at the University of Illinois Chicago suggests that time-restricted eating may help adults with Type 1 diabetes improve blood-sugar control without increasing the risks of severe hyperglycemia, hypoglycemia or diabetic ketoacidosis. The findings, published in Diabetes Care, offer an early indication that adjusting when people eat—not necessarily how much they eat—could become a useful strategy for some adults living with the demanding metabolic condition. Researchers caution, however, that the approach remains investigational and should be attempted only with close guidance from an endocrinologist or other qualified health professional.

The study was led by Krista Varady, a professor of kinesiology and nutrition at UIC and a prominent researcher in intermittent fasting and time-restricted eating. Her team recruited 32 adults from the Chicago area who had Type 1 diabetes and were classified as obese according to Centers for Disease Control and Prevention body-mass-index categories. Type 1 diabetes occurs when the immune system destroys the pancreatic beta cells responsible for producing insulin, leaving the body with little or no endogenous insulin production. Because insulin is essential for allowing glucose to move from the bloodstream into cells, people with Type 1 diabetes must continuously manage insulin replacement, food intake and blood-glucose fluctuations.

Participants were randomly assigned to one of three groups for six months. Those in the time-restricted eating group consumed food only during an eight-hour daily window, from noon until 8 p.m., and were not required to count calories. A second group followed a conventional calorie-reduction strategy, aiming to reduce daily energy intake by 25%. The third group served as a control and made no intentional changes to its eating behavior. Comparing these approaches allowed the researchers to examine whether the timing of food consumption itself might influence metabolic outcomes, independently of a prescribed calorie deficit.

The primary signal emerged from measurements of glycated hemoglobin, commonly known as HbA1c. This blood test reflects the average amount of glucose attached to hemoglobin in red blood cells over roughly the previous two to three months. Unlike a single glucose reading, HbA1c provides a longer-term view of blood-sugar exposure and is widely used to evaluate diabetes management. After six months, participants following the noon-to-8 p.m. eating schedule showed a greater reduction in HbA1c than those in the calorie-counting group. The average decrease was approximately 0.5 percentage points, a change that could be clinically meaningful if reproduced in larger and more diverse studies.

The result is notable because people with Type 1 diabetes face a distinctive set of risks when changing their eating patterns. Restricting food intake can alter the timing and amount of insulin required, while prolonged periods without carbohydrates may complicate glucose management for individuals using injected insulin or insulin pumps. If the body does not receive enough insulin, it begins breaking down fat for energy, producing acidic compounds called ketones. Excessive ketone accumulation can lead to diabetic ketoacidosis, a potentially fatal emergency. Conversely, taking more insulin than required during a fasting period can cause hypoglycemia, which may lead to confusion, seizures or loss of consciousness.

Within the limits of the trial, time-restricted eating did not appear to increase the frequency of extreme high or low blood-sugar events. The researchers also reported no elevated risk of diabetic ketoacidosis among participants assigned to the restricted eating schedule. These safety observations are particularly important because previous research on intermittent fasting has largely focused on people without Type 1 diabetes or on those with Type 2 diabetes, a condition in which the body typically still produces insulin but does not use it effectively. The physiological demands of Type 1 diabetes mean that results from other populations cannot automatically be applied to people who depend on insulin replacement.

Varady described the trial as the first study to examine intermittent fasting in adults with Type 1 diabetes and characterized the findings as promising. The biological mechanisms behind the improvement remain uncertain, and the trial was not designed to establish precisely why the restricted schedule lowered HbA1c. One possibility is that concentrating eating into a consistent daily interval may reduce late-night food intake or improve alignment between meals, insulin dosing and the body’s circadian rhythms. Another is that participants may have experienced modest changes in total energy intake or body weight even though they were not instructed to count calories. The available findings do not establish which explanation is responsible.

The study also addresses an important practical question in nutrition research: whether a dietary intervention can be followed without requiring constant calculation. Traditional calorie restriction asks participants to estimate the energy content of meals and track daily intake, a process that can be difficult to sustain. Time-restricted eating instead imposes a schedule, potentially making it simpler for some people to follow. Yet simplicity does not guarantee suitability. An eight-hour window may be inconvenient for people with variable work schedules, gastrointestinal conditions, pregnancy, eating-disorder histories or other medical needs. For individuals with Type 1 diabetes, any change in meal timing may require careful adjustment of insulin doses and monitoring plans.

The investigators emphasize that the trial is an initial step rather than definitive evidence for broad clinical adoption. Its sample was small, included adults from a limited geographic area and focused on people with both Type 1 diabetes and obesity, so the findings may not apply to leaner adults, children, adolescents or people with different patterns of insulin use. A six-month study also cannot determine the long-term effects of the eating schedule on cardiovascular health, diabetes complications, nutritional adequacy or quality of life. Varady’s team hopes to conduct larger, multisite trials that can test the approach in more varied populations and clarify how it affects insulin requirements, weight, glucose variability and other indicators of metabolic health.

For now, the findings suggest that the clock may be an important variable in diabetes research, alongside calories, carbohydrates and insulin. A structured eating window was associated with improved HbA1c in this small randomized trial, while the study found no apparent increase in severe glucose-related complications. That combination makes time-restricted eating a potentially valuable subject for further investigation, but not a replacement for insulin therapy or individualized medical care. Anyone with Type 1 diabetes considering a fasting or time-restricted eating pattern should first consult a healthcare provider, because safe implementation depends on coordinated decisions about meals, insulin and glucose monitoring.

News Publication Date: Not specified in the provided content

Web References: https://doi.org/10.2337/dc26-1093; https://ahs.uic.edu/profiles/varady-krista/; https://www.cdc.gov/bmi/adult-calculator/bmi-categories.html; https://www.mayoclinic.org/diseases-conditions/type-1-diabetes/symptoms-causes/syc-20353011

References: Diabetes Care, “Efficacy and Safety of Time-Restricted Eating in Adults With Type 1 Diabetes: A Randomized Controlled Trial,” published 17 August 2026