>>715941017It technically doesn't improve its caloric value directly, but it does make it substantially easier to digest; meaning we can take up the nutrients within it more readily.
>>715941158There is a marginal loss in both nutrient and calorie content from cooking, but the massive increase in digestibility more than makes up for it, especially since the body has to use more energy to try and break down more difficult to digest foods and does so at a reduced efficiency.
Combine that with the additional food safety from killing bacteria and parasites, cooked meat is sometimes cited by evolutionary biologists as the innovation that catapulted early advanced primates from tool users to thinkers, on account of the massive increase in available energy and time, as foraging and hunting did not fully dominate all active living hours.