Summary:
In adults with type 1 diabetes, a high-carbohydrate, low-fat, low-protein (HCLFLP) diet
significantly improved substrate oxidation and glucose regulation during sustained submaximal exercise compared to low-carbohydrate, high-fat, low-protein and other isocaloric diet variations over seven days, though it was associated with no significant adverse side effects reported.
| PICO | Description |
|---|---|
| Population | Twelve adults with type 1 diabetes (4 females), mean age 46 ± 15 years, average HbA1c 55.9 ± 7.8 mmol/mol, undergoing sustained submaximal exercise. |
| Intervention | Seven-day consumption of a high-carbohydrate (48%), low-fat (33%), low-protein (19%) isocaloric diet (HCLFLP). |
| Comparison | Seven-day consumption of alternative isocaloric diets differing in macronutrient composition: low-carbohydrate, high-fat, low-protein (LCHFLP) and other variations. |
| Outcome | The HCLFLP diet significantly enhanced glucose regulation and substrate oxidation during exercise, compared to other diets, with no reported increase in adverse side effects. |
Clinical Context
Exercise presents unique challenges for individuals with type 1 diabetes, as insulin deficiency fundamentally alters metabolic fuel selection and glucose regulation during physical activity. The interplay between dietary composition, insulin therapy, and exercise metabolism creates complex management scenarios that affect both performance and safety. Low-carbohydrate diets have gained popularity for glycemic management in diabetes, but their effects on exercise metabolism remain controversial. During sustained exercise, the body typically relies increasingly on carbohydrate oxidation as intensity rises, and substrate availability influences both performance capacity and glycemic stability. Dietary macronutrient composition over days prior to exercise can substantially alter muscle glycogen stores, fat oxidation capacity, and hormonal responses to activity. This crossover study systematically evaluated how different macronutrient distributions affect metabolic responses during standardized submaximal exercise in adults with type 1 diabetes.
Clinical Pearls
- A high-carbohydrate, low-fat, low-protein diet improved glucose regulation during sustained submaximal exercise compared to low-carbohydrate alternatives in adults with type 1 diabetes.
- Substrate oxidation patterns during exercise were significantly influenced by the preceding week’s macronutrient composition, highlighting the importance of dietary periodization for active individuals with type 1 diabetes.
- The seven-day dietary adaptation period was sufficient to produce measurable differences in exercise metabolism, providing a practical timeframe for pre-exercise dietary optimization.
- No significant adverse effects were reported with any dietary pattern, supporting the safety of dietary manipulation for exercise optimization in this population.
Practical Application
Clinicians advising physically active patients with type 1 diabetes should consider macronutrient timing and composition relative to exercise goals. For sustained endurance activities, a higher carbohydrate intake in the days preceding exercise may optimize both glucose stability and substrate availability. Patients following low-carbohydrate dietary patterns should be counseled about potential implications for exercise performance and glucose regulation during activity. Individualized approaches may involve periodizing carbohydrate intake around training or competition while maintaining lower carbohydrate consumption during rest periods. Exercise physiologists, dietitians, and diabetes educators should collaborate to develop comprehensive plans addressing both glycemic management and athletic performance goals.
Broader Evidence Context
This study contributes to ongoing debates about optimal dietary composition for individuals with type 1 diabetes engaged in regular physical activity. While low-carbohydrate approaches have demonstrated glycemic benefits in sedentary settings, their applicability to active populations requires nuanced consideration. The findings align with sports nutrition principles emphasizing carbohydrate availability for endurance performance while adding diabetes-specific insights about glucose regulation. Prior research has shown that exercise itself creates complex glucose dynamics in type 1 diabetes including both hypoglycemia during activity and hyperglycemia from counterregulatory responses. Understanding how dietary composition modulates these responses provides additional tools for optimizing both safety and performance.
Study Limitations
- The small sample size of 12 participants limits statistical power and generalizability of findings.
- The seven-day dietary intervention period may not reflect longer-term metabolic adaptations to sustained dietary changes.
- The submaximal exercise protocol may not reflect high-intensity or prolonged exercise scenarios where metabolic demands differ substantially.
- Individual variability in insulin regimens and dosing adjustments during the dietary interventions was not detailed.
- Real-world dietary adherence outside controlled research settings was not assessed.
Bottom Line
A high-carbohydrate, low-fat, low-protein diet improves glucose regulation and substrate oxidation during sustained submaximal exercise in adults with type 1 diabetes compared to low-carbohydrate alternatives. Clinicians should consider dietary macronutrient periodization when advising physically active patients with type 1 diabetes about optimizing both glycemic control and exercise performance.
Source: McCarthy, Olivia Mary, et al. “Influence of Diets Differing in Macronutrient Composition on Metabolic Regulation During Exercise in Adults with Type 1 Diabetes.” Read article here.
