Raw meat is edible, digestible, and nutritious when fresh. You can also cut it, marinate it, salt it, dry it, or bury it and let it ferment a bit. Besides meat, there are plenty of edible nuts, berries, tubers, grains, and leaves. You can make hard things more digestible by pounding them between rocks. Humans are clever dietary generalists and can exploit many types of food sources. Think how the modern apes do.

Even in cooked food, there is matter that is not energetically exploitable. Pre-fire humans would not have eaten food that had negative caloric value because they would starve to death (unless there was a non-nutritive reason, like for medicine). Fire and food processing make it easier to get at the caloric value and takes some of the risks out (parasites, toxins). It allows humans to exploit food sources they might not have bothered with. You can do without fire and modern crops, but it's harder and requires proper ethnobotanical education that would have been collected by experienced elders and passed down to children.