When I was raised by a fat mother, the fat logic went like this: "Going to the gym, being active (read: show up at the location and use a couple machines), will raise your metabolism. This means the calories you already eat are basically slashed in general. So because your metabolism is being raised and your body can "digest and process" calories better cuz exercise, AND you burned EXTRA calories through working out just 'naow', you have a deficit you can fill with a "treat"/extra meal."