As far as fueling rides goes... I have no scientific information to back this up of course, but - that's the only time I eat carbs. I use Larabars and the Kind bars because they are generally gluten/dairy free (you have to read the labels, as they differ between flavors) and are generally low glycemic index with 20g carb/bar or less. Otherwise, I don't eat carbs unless they come from vegetables in my meals. The body is great at adapting to using fat as a fuel source. When I first switched to paleo (not that your husband is doing that, but it is an example of a low carb diet) I had a hard time on my rides and really really needed the carb filled bars. Now, I am not bothered nearly as much, and I don't get those wicked carb cravings after a long ride (30-50+ miles) like I used to. Just my experience.