As long as you get the sleeve instead of gastric bypass, there shouldn't be a problem. My mom got the bypass and because it shortens the intestines, you absorb fewer calories so you tend to lose more weight. With the sleeve, if you feel like you are losing too much weight, all you would have to do is adjust the types of foods you are eating and lean towards higher calorie foods and you would be fine. I have actually never heard of anyone becoming too thin from either surgery unless they develop post-op anorexia. Post op anorexia is super rare because instead of obsessing about food after your surgery, it kind of become in consequential.