Although type 1 diabetes (T1D) has traditionally been considered a disease associated with a lean phenotype, it is estimated that up to 2 out of 3 people living with T1D are overweight or obese, factors linked to an increased risk of complications in these patients. The available evidence regarding nutritional strategies for weight loss in T1D is very limited, and clinical trials are needed to determine how to effectively and safely promote weight loss in this population. In recent years, low-carbohydrate diets and several intermittent fasting protocols have demonstrated efficacy in promoting weight loss both in patients with type 2 diabetes and in patients with obesity without diabetes. This study will evaluate the efficacy of moderate carbohydrate restriction, time-restricted eating, and standard calorie restriction for weight loss in adults with T1D and overweight/obesity.
T1D treated with intensive insulin therapy (multiple daily insulin injections or continuous subcutaneous insulin infusion systems)
HbA1c 6.5-9%
BMI ≥ 25 and ≤ 45 kg/m2
Active prescription and use of CGM
Pregnancy, pregnancy planning, or breastfeeding
Forms of diabetes other than T1D, or T1D duration < 1 year
Previous cardiovascular events (acute myocardial infarction or stroke), heart failure, unstable coronary artery disease, chronic kidney disease with estimated glomerular filtration rate ≤ 30 mL/min/m², cirrhosis, or presence of active cancer
Unstable diabetes, episodes of glycemic decompensation (diabetic ketoacidosis) or severe hypoglycemia (level 3) within the past year.
Parallel
Moderate carbohydrate restriction
BehavioralParticipants will follow a diet with moderate carbohydrate restriction (25-30%), together with 25% caloric restriction
Early time-restricted eating
BehavioralParticipants will follow a standard diet with an 8-hour early eating window, starting no later than 10 a.m. (16-hour fast), together with 25% caloric restriction
Standard calorie restriction
BehavioralParticipants will follow a standard diet with 25% caloric restriction
Change in percent body weight
Measured by a calibrated digital scale
Change in glycated hemoglobin
Fasting blood samples. Glycated hemoglobin will be assessed by HPLC
Change in continuous glucose monitoring (CGM) parameters
Parameters measured by CGM, including time in range, time below range, mean glucose, standard deviation of glucose, coefficient of variation of glucose, time above range, time in tight range, glucose management indicator
Change in absolute body weight (kg)
Measured by a calibrated digital scale
Change in body mass index (BMI)
Calculated as kg/m2
Change in gut microbiota
Gut microbiota composition and diversity, assessed by 16S rRNA
Change in DNA methylation
Measured by methylation array (Illumina)
Change in inflammatory parameters
Fasting blood samples, including several parameters (e.g., C-reactive protein, interleukin 6, interleukin IL-10, interleukin-1β, TNF-alpha)
Change in adipokines and gastrointestinal hormones
Fasting blood samples, including several parameters (e.g., leptin, adiponectin, GLP-1, GIP)
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