Slowly the child loses weight. It's initially not very noticeable, but for example - in our case he stayed with his father over the summer and when he came back he was noticeably thin.
The child begins drinking a lot. It starts off with an excessive thirst. Can't go more than an hour without drinking. But ends up with them not being able to do anything, peeing constantly and never being able to quench their thirst. When he came back to us, he was close to this stage. He was constantly eating ice cubes as they melted slowly enough so that he felt like he was constantly moistening his mouth. After about 3 days we took him to the doctors office, where by he went to Hospital.
Fatigue - the child has zero energy and when they are not drinking they can barely move. This was rapid. He came home on a Sunday evening, and by Wednesday morning he looked like pure death.
Ketones in the blood skyrocket. This is incredibly dangerous. When blood sugar rises above about 15 mmol/L (270 mg/dl) things start getting quite nasty. Health is put in jeopardy. Quite often the child will go in to a coma if they get too high.
All of the sugars are peed out. The child's pee will smell very strongly and be a very dark colour if they are anything like my stepson.
It was basically horrific. But as soon as we got him treatment, he bounced back quickly.
We now use a carb counting system supported by a device that tracks is blood sugar and insulin intake. Regulating his insulin is a constant battle as he still thinks he is indestructible, and convincing a 14 year old boy that skipping "a few" shots every day or injecting a guesstimate as he is "too busy to do it properly" is a bad idea is not easy.
Saw this first hand babysitting a kid a long time ago. He kept asking for glasses of water--almost begging for them while at the same time peeing frequently and then wetting the bed. Parents took him to the doctors and the diagnosis came swiftly.
Interestingly enough, your body also raises its level of activity in order to burn calories and maintain weight levels. I believe they've measured a surprising amount of excess calories burned from extra fidgeting when overfeeding people relative to their usual diet.
TL;DR: dietary fatty acids are disassembled and then reassembled into triglycerides which are stored in adipocytes (fat cells) until needed.
Does anyone know where the calories go if it isn't stored as fat? Glycogen stores? Or our digestive system just stops absorbing them?