Fat is caused when you eat a food and it restores your Food% to 100%+.
To avoid getting fat, eat only when the Food% is enough so that the Food you're eating, is not going to take you to or over 100% Food. I.E: DO NOT GO OVER 100% FOOD EVER, OR YOU WILL GET FAT.
To get thinner/skinnier, you have to eat Food that reduces Fat. Currently, Berries are the best for reducing fat and muscle mass. They're easy to obtain, as you can just hit bushes/trees and eventually they will drop.
Different foods affect you differently.
Foods that affect your "Upper Body" will affect the size of your Biceps and Pecs. For female players it has the ability to increase their bust size.
Foods that affect your "Lower Body" will affect the size of your Thighs and Gluteous Maximus.
Foods that affect your "Weight" will add "flab" to all parts of your body. It will also make your waist increase in diameter.
Using the Mabinogiworld Wiki, you can go here, and find out which food is good for gaining or losing fat/muscle mass.
Lastly, foods also increase stats such as HP, MP, Str, Int and Dex; it requires A LOT of that food.
IGN: Brutalitus
