By reducing carbohydrate intake, people with type 1 diabetes may reduce fluctuations inblood glucose, but the evidence in this area is sparse. The aim of this study was to investigate glucosemetrics during a one-week low-carbohydrate-high-fat (HF) and a low-carbohydrate-high-protein(HP) diet compared with an isocaloric high-carbohydrate (HC) diet. In a randomized, three-periodcross-over study, twelve adults with insulin-pump-treated type 1 diabetes followed an HC (energyprovided by carbohydrate: 48%, fat: 33%, protein: 19%), HF (19%, 62%, 19%), and an HP (19%, 57%,24%) diet for one week. Glucose values were obtained during intervention periods using a Dexcom G6continuous glucose monitoring system. Participant characteristics were: 33% females, median (range)age 50 (22–70) years, diabetes duration 25 (11–52) years, HbA1c 7.3 (5.5–8.3)% (57 (37–67) mmol/mol),and BMI 27.3 (21.3–35.9) kg/m2. Glycemic variability was lower with HF (30.5 ± 6.2%) andHP ( 30.0 ± 5.5% ) compared with HC (34.5 ± 4.1%) ( PHF-HC = 0.009, PHP-HC = 0.003 ). There wasno difference between groups in mean glucose (HF: 8.7 ± 1.1, HP: 8.2 ± 1.0, HC: 8.7 ± 1.0 mmol/L,POverall = 0.08). Time > 10.0 mmol/L was lower with HP (22.3 ± 11.8%) compared with HF (29.4 ± 12.1%)and HC (29.5 ± 13.4%) (PHF-HP = 0.037, PHC-HP = 0.037 ). In conclusion, a one-week HF and, specifi-cally, an HP diet improved glucose metrics compared with an isocaloric HC diet.