Influence of Diets Differing in Macronutrient Composition on Metabolic Regulation During Exercise in Adults with Type 1 Diabetes

<b>Aim:</b> To compare the effect of consuming three isocaloric diets that differed in macronutrient composition on substrate oxidation and glucose regulation during sustained submaximal exercise in adults with type 1 diabetes (T1D). <b>Methods:</b> In a randomised, crossover design, 12 adults with T1D (n = 4 female, age: 46 ± 15 years, HbA1c: 55.9 ± 7.8 mmol/mol) consumed three isocaloric diets over seven days: (i) HCLFLP (high-carbohydrate [48%], low-fat [33%], low-protein [19%]), (ii) LCHFLP (low-carbohydrate [19%]), high-fat [62%], low-protein [19%]), and (iii) LCLFHP (low-carbohydrate (19%), low-fat [57%], high-protein [24%]). On the morning of day eight, participants undertook 45 min of cycling (≈60% V.O_2peak) whilst fasting. Venous-derived plasma glucose and free fatty acids (FFA) were measured throughout the trial period. Indirect calorimetry was used to determine rates of substrate oxidation during exercise. Data were analysed via repeated measures ANOVAs with <i>p</i> ≤ 0.05 accepted as significant. <b>Results:</b> During exercise, rates of lipid oxidation were higher (1.2-fold, <i>p</i> = 0.030) and carbohydrate oxidation lower (0.8-fold, <i>p</i> = 0.030) in LCHFLP versus HCLFLP. Concentrations of FFA after exercise were higher in LCHFLP compared to HCLFLP (by ≈22%, <i>p</i> = 0.019). Overall time spent in euglycaemia was higher (HCLFLP: 55.6 ± 43.9, LCHFLP: 87.3 ± 28.7, LCLFHP: 95.2 ± 7.9%, <i>p</i> = 0.003) and hyperglycaemia lower (HCLFLP: 44.4 ± 43.9, LCHFLP: 12.7 ± 28.7, LCLFHP: 4.8 ± 7.9%, <i>p</i> = 0.003) in both LC diets relative to HC. No differences in any measured biomarkers were observed between the two LC diets. <b>Conclusions:</b> One-week consumption of isocaloric diets that differed in their macronutrient composition shifted patterns of energy metabolism during a standardised bout of moderate intensity exercise performed in the fasted state in adults with T1D.