Hello,
first of all, thank you for the interesting question that many patients ask themselves!
We can't know exactly in advance how each person will react to the antidepressant
There is a diversity of effects: some people will gain a lot of weight, others not at all
Drug-induced weight gain can result either from increased appetite, mainly for high-fat and high-carbohydrate foods (food craving), or from a reduction in resting metabolism, which is responsible for more than 50% of daily energy expenditure.
The brain plays a key role in the feedback control of the system of regulation of energy intake and expenditure
For the second part of the question, there are several antidepressants that have little effect on weight and libido: Bupropion, Desvenlafexine, Duloxetine, and also slightly Escitalopram and Fluvoxamine.
Depending on your other medications, your doctor and pharmacist can discuss which one is best for you to avoid complications, side effects and maximize benefits