Low-Carb Diets Help T1D Adults Stay in Range During Exercise

What Was Studied and Why It Matters

Managing blood sugar during exercise is one of the trickiest challenges for people living with Type 1 diabetes (T1D). Physical activity can cause unpredictable swings — both highs and lows — making it difficult to stay in a safe glucose range. Researchers wanted to know whether what you eat in the days before exercise could make a meaningful difference in how your body handles blood sugar during a workout.

This 2025 study, published in the journal Nutrients, tested three different eating patterns on 12 adults with T1D to see which diet best supported stable glucose control during moderate cycling exercise.

How the Study Worked

Participants followed each of three diets for one week at a time, in random order. All three diets contained the same number of calories — only the balance of nutrients differed:

• High-Carb Diet (HCLFLP): 48% carbohydrates, 33% fat, 19% protein
• Low-Carb, High-Fat Diet (LCHFLP): 19% carbohydrates, 62% fat, 19% protein
• Low-Carb, High-Protein Diet (LCLFHP): 19% carbohydrates, 57% fat, 24% protein

On the morning after each diet week, participants cycled for 45 minutes at moderate intensity while fasting. Researchers measured blood glucose, fat levels in the blood, and how the body was burning fuel throughout the session.

What the Findings Show

The results were striking. People following either of the two low-carbohydrate diets spent significantly more time with their glucose in a healthy range during exercise compared to those on the high-carb diet:

• On the high-carb diet, participants spent about 56% of exercise time in a healthy glucose range — and 44% of the time running too high (hyperglycemia).
• On the low-carb, high-fat diet, time in range jumped to about 87%, with only 13% of time spent in hyperglycemia.
• On the low-carb, high-protein diet, results were even better — roughly 95% time in range, with less than 5% in hyperglycemia.

The low-carb diets also caused the body to burn more fat for fuel during exercise, which is a more stable energy source that doesn't require as much insulin management. Importantly, neither low-carb diet triggered more low blood sugar episodes than the high-carb plan.

What This Means for Real Patients

If you have Type 1 diabetes and struggle with blood sugar spikes during or after exercise, this research suggests that reducing carbohydrate intake — even for just one week — may help your body stay in a healthier range during workouts. Both low-carb approaches (whether higher in fat or protein) performed similarly well, giving you flexibility based on personal preference.

Of course, any dietary change should be discussed with your diabetes care team, especially since carbohydrate reduction affects insulin dosing. Consistent glucose monitoring remains essential — whether you use a CGM or traditional fingerstick testing, having reliable supplies on hand matters. MDS Diabetes carries a wide range of monitoring and insulin delivery supplies to support your routine, whatever diet approach you choose.

Bottom Line

Adults with Type 1 diabetes who followed a low-carbohydrate diet for one week spent far more time in a healthy blood sugar range during moderate exercise than those on a high-carb diet — without an increased risk of low blood sugar. Talking to your care team about your pre-exercise nutrition could be a meaningful step toward safer, more confident workouts.