The claim that some obese individuals are ”carbohydrate sensitive” seems to be related to insulin sensitivity and glucose tolerance. The quality of the carbohydrate in the diet is also critical.
In this study, the lean rats did much better on the high carbohydrate diet and the obese rats did better on both the high fat and the low carbohydrate diets over the high carbohydrate diet.
However, the lean rats on the lower carbohydrate diets experienced reduced insulin sensitivity.