When we eat certain foods and the body feels warmth, it feels like body has gained some heat energy from this food. Is this true?
Let us not call the heat that is gained by the body as energy gained. We actually spend our (vital) energy to get our body heated by the process of digestion and then burning the sugar (the product of digestion) with the help of oxygen that we breathe into heat for maintaining all the actions and reactions in the body.
Doing a few sets of Pranayama before each meal aids digestion thereby conserving vital energy.