Feruchemical Weight Loss

I was thinking on my to class about Feruchemy, and when would be good times to store different things. When I got to thinking about storing energy, I realized that you may be able to store stuff you're not currently eating. This would mean that you could store fat, and dehydrate yourself at will. I'm not sure what benefits being dehydrated would give you, other than maybe making a more convincing disguise in some cases, but the first one is obviously useful. You could add some chub to disguise yourself as a rich person, and take off a lot for a poor person. Or, you could just lose weight. Either way, it would be really useful, if it is possible.