You’re right that it has not been studied in diabetic individuals. Let me give you one recent published example of its effects in a non-diabetic population on exercise to exhaustion done at a high intensity. Keep in mind that my comments are related to optimal performance at a higher level, not just doing mild or moderate activity in an average person. From a quick PubMed online search:
Braz J Med Biol Res. 2009 May;42(5):404-12.
Effect of carbohydrate availability on time to exhaustion in exercise performed at two different intensities.
Lima-Silva AE, De-Oliveira FR, Nakamura FY, Gevaerd MS.
Laboratório de Aptidão Física, Desempenho e Saúde, Universidade Federal de Alagoas, Maceió, AL, Brasil.
This study examined the effects of pre-exercise carbohydrate availability on the time to exhaustion for moderate and heavy exercise. Seven men participated in a randomized order in two diet and exercise regimens each lasting 3 days with a 1-week interval for washout. The tests were performed at 50% of the difference between the first (LT1) and second (LT2) lactate breakpoint for moderate exercise (below LT2) and at 25% of the difference between the maximal load and LT2 for heavy exercise (above LT2) until exhaustion. Forty-eight hours before each experimental session, subjects performed a 90-min cycling exercise followed by 5-min rest periods and a subsequent 1-min cycling bout at 125% VO2max/1-min rest periods until exhaustion to deplete muscle glycogen. A diet providing 10% (CHO(low)) or 65% (CHO(mod)) energy as carbohydrates was consumed for 2 days until the day of the experimental test. In the exercise below LT2, time to exhaustion did not differ between the CHO(mod) and the CHO(low) diets (57.22 +/- 24.24 vs 57.16 +/- 25.24 min). In the exercise above LT2, time to exhaustion decreased significantly from 23.16 +/- 8.76 min on the CHO(mod) diet to 18.30 +/- 5.86 min on the CHO(low) diet (P < 0.05). The rate of carbohydrate oxidation, respiratory exchange ratio and blood lactate concentration were reduced for CHO(low) only during exercise above LT2. These results suggest that muscle glycogen depletion followed by a period of a low carbohydrate diet impairs high-intensity exercise performance.
If all of your exercise training and competing is going to be done at a submaximal level (just to finish and not to compete), then this may not apply. However, one last point is that even people with type 2 diabetes will be able to handle some carbs better when doing regular physical activity that depletes some muscle glycogen (the main storage depot for excess carbohydrate consumption), and they may feel less tired and more energetic when eating some carbs during and/or after exercise in particular to speed up muscle glycogen repletion. On rest days, a lower carb diet is certainly better. Sheri Colberg, PhD