Consult a doctor and/or dietician before making too many radical changes to your diet/exercise.
It starts and ends with food, both before surgery and after.
Consider focusing on food choices and not so much trying to count calories and such. Eating higher quantities of healthy foods will help keep you satiated while limiting glucose/insulin production.
Consider the following:
- Avoid foods with added sugar
- Avoid ultra-processed foods (things with 8-10 ingredients or more)
- Avoid foods made from refined grains
- Avoid artificial sweeteners
It might be hard to do all of those things at once, so just small steps.
Consider the following:
- Drink a lot of water, constantly, throughout the day
- Add more whole-food, plant-based meals.
- This doesn't mean you have to be a vegetarian/vegan, but filling up with plants will give you a full feeling with low calories comparatively.
- Eat different plants each day
- Choose good protein sources (animal or plant-based)
Add little bits of activity, even if you are reclined or stationary. Extra arm movements, leg movements, short walks, if possible. Go slow and easy so you don't injure yourself or over-exert yourself.
No matter how you approach this, it won't be easy. You may get different ideas/instructions from a doctor/surgeon/dietician, so you should follow their instructions if provided. Getting to the surgery can be a long and difficult road, but it is worth it. The more effort and commitment you can give pre-surgery the better you will set yourself up for success after surgery.
Lastly, as mentioned above, reach out for professional help to ensure you are doing things in the safest manner for your physical and mental health. You can get a lot of opinions on the internet, but there is no way for anyone on social media or in a forum like this to know all the details about your, your health, and your lifestyle to give advice that would be 100% right for you. My tips above are suggestions based on what I have done, which was based on a lot of research I've done and on the feedback I've gotten from people I've talked to who have been successful for 10+ years after surgery, but each person's experience is going to be slightly different. I didn't start at the weight you did, so I can't provide experience from that perspective, but in general, making small changes like others have suggested is probably a good place to start.