Do you mean let the dog gourge till full then fast for a day or feed a set meal then fast ?
Ive found when a dog is working 3-4 days a week in the winter its a job to keep the weight on so dont do it any more .The theory behind the fast is to clear the gut and bowel out and also watch the weight in summer.
It does produce better toned dogs ,though,as their bodies learn to burn excess fat faster.
If you are working your dog hard 3-4 days a week no matter how much or often you feed him he won't keep weight on. Unlike us, dogs eat till full and then cache their food to return later to fe