The best way to gain weight is to increase protein. I lost too much weight eating low carb & wasn’t willing to eat more carbs. I slowly added more protein to each meal until I gained what I needed to & kept it at approximately the same portions to maintain weight.
One bonus of eating more protein is that it keeps hunger away. I did have to increase my insulin slightly for increased protein intake. Though carbs have the most impact, protein effects BG as well.
I had a hard time eating enough protein, so I used protein shakes. The highest protein is in whey isolate protein, not the cheaper hydrolyzed form. The unflavored type is very low carb & makes delicious milk shakes. I use unsweetened almond milk (lactose in milk sends me soaring), two scoops of whey isolate powder, unsweetened cocoa powder & sweetener (I use zero carb stevia powder). Sometimes I add a raw egg & a splash of heavy cream (for more calories). Great when you need a fast, filling meal. Protein powder can also be used in baking.
I’ve tried several brands & like NOW brand the best. It dissolves easily & tastes great. My health food store carries it in bulk.