Comparison of Low, Moderate and High Carbohydrate Diet on Insulin Requirements and Metabolic Control in Type 1 Diabetes

The scientific basis for dietary recommendations in type 1 diabetes is almost lacking, with the current recommendations being based on type 2 diabetes studies. Therefore the overall purpose of this study is to improve the current evidence for dietary recommendations to people with type 1 diabetes. Study aim: To compare how a strictly low carbohydrate diet, a moderately low carbohydrate diet and a traditional diabetes diet (with higher amounts of carbohydrates) affect insulin requirements and metabolic control in individuals with type 1 diabetes. Carbohydrate intake is 50-60% of the total energy intake in the traditional diabetes diet, 30-40% in the moderately low carbohydrate diet and 15-20% in the strictly low carbohydrate diet with a minimum of 50 g carbohydrates/day. A diet with less than 50 g carbohydrates/day is usually called very low carbohydrate diet or ketogenic and will not be tested in this study. Those who wish to participate and meet the inclusion criteria (and none of the exclusion criteria) will be randomized to one of the three diets. The duration of the intervention is 6 months after which the participants will be able to choose their own diet for another 6 months. The main study visits are at baseline (screening and study start), 3, 6, 9, and 12 months. Shorter visits will be at 3 and 6 weeks. The participants will meet with a study nurse, dietitian and doctor. They will attend two carbohydrate counting courses before the start of the intervention in order to be able to match their insulin to the amount carbohydrates they eat. Participants will receive written materials about their diets with menus and recipes for better adherence to the diet. The primary endpoint is the change in insulin requirements within and between groups (for secondary endpoints please see relevant section). For assessing the different endpoints the participants will provide blood, urine and feces samples for lab analyses as well as register their insulin use, blood glucose, diet, physical activity and any blood ketones or hypoglycemia electronically or in written forms. Continuous/flash glucose monitoring (CGM/FGM) will be also used. Dietary assessment and adherence will be based on 3-4 day food diaries before every scheduled study visit.

Inclusion Criteria: * To have had type 1 diabetes for at least 1 year * Age \>=20 years old Exclusion Criteria: * Cardiovascular disease NYHA class IIIB or more * Kidney disease \> stadium 3 * Liver disease, alanine aminotransferase (ALAT) ≥ 2 µkat/L, * BMI \< 18.5 kg/m\^2 * c-peptide ≥ 0.3 nmol/l * Pregnant/breastfeeding women, women that plan to get pregnant during study period * Other circumstances, which, according to the examiner, make it difficult for an individual to participate.