If the reason for the weight gain is the medication, it has nothing to do with your metabolism. Most drugs that treat mental illness can have weight gain as a side effect, but it's a very individual thing -- a person can gain a ton on one drug in a class of meds and not on another, and another person on the same drug might gain nothing at all. Some drugs are more likely than others to result in weight gain, but that doesn't mean it definitely will or that other drugs that most don't get this side effect on will have anything to do with you. You don't want to talk about limited calories, but you do need to know that first, calories aren't the main factor in weight. They are one factor, but metabolism of food isn't related to medication, it happens to everyone. If you eat foods that metabolize quickly into sugar and you don't quickly burn off the sugar, it will store as fat. Some high calorie foods are not at all tied to weight gain, such as fatty fish like salmon. Not all fat is equal. Eating very low calorie diets can actually leave you with a more permanent weight problem than medication which can be stopped and another tried, as if you starve your body of essential nutrients your body can't function properly. It's also really bad for your mental health, as that is also regulated by the nutrients in food. I really don't know why the drugs have this effect -- it might be metabolism, it might be the sedation, it might be interfering with the natural performance of neurotransmitters that not only regulate the brain but also regulate everything else as well, including digestion. Serotonin affecting drugs are often culprits in weight gain, and serotonin is mostly found in the body in the digestive system, not the brain. There is an old book by a psychiatrist who practices a more holistic form of medicine called The Anti-Depressant Survival Guide that proposes a diet to deal with drug-induced weight gain. While I don't think the diet he suggests is particularly healthful, it might give you some ideas of how to cope with this in a healthier way that helps you understand the connection between nutrition and your long-term health. Meaning, you know, because you don't want to hear about it, that eating too little will leave you malnourished and while you may not notice in the short run you will definitely notice in the long run, so this isn't sustainable and given you are on antipsychotics, assuming you're on them because you suffer from psychosis and not because they're being used as atypical antidepressants, you have to take medication for the rest of your life. So eventually you're going to start eating more because you'll have to or you'll get sick and you'll gain the weight back. I don't suffer psychosis, I have an anxiety problem, and I had this problem on Paxil. I gained 50 pounds on it, and I didn't alter my eating habits a bit and I exercised a whole lot more than you do. It just happened. When I stopped the drug, it destroyed my life, but I did almost immediately lose the weight. It wasn't me, it was the drug. I have been on several other anti-depressants and none of them caused weight gain including other drugs in the same class as Paxil. So the hopeful thing is you and your psychiatrist can find a drug or combination of drugs that work for you but don't cause the significant weight gain. I'd also suggest that unless there are other health problems you haven't mentioned, you're young and can exercise a whole lot more than walking twice a day which will burn off a whole lot more calories. Hope you find the key for you.