I believe the human body has a fat lag effect. Which means the certain body fat increasing or decreasing activities will not take effect until a 3-4 weeks later, while this period does depend on the individual.
SO,
for the eater: don't be too glad when you've eaten a huge amount of food and see no added fats to your body within a few days.
for the exerciser: don't be too discouraged when you've exercised a huge amount and see no decrease of fat within... immediately =]