I've done nothing but gain weight since my colectomy. I thought that this surgery would have the silver lining of no more weight worries. Nope, my small intestine has been as efficient as ever. I even wound up enrolling in a medical weight management course in order to lose some weight. The small intestine is where the nutrients are absorbed, not the colon.
The secret? There is none. Healthy choices and small portions. A real eye opener to find out how small your portions should be to maintain a healthy weight. Keep the activity level up. Exercise alone will not get you to lose weight, but it keeps your metabolism from dropping when you reduce the calories. Eating sweet, salty, and fatty foods just tells your brain you want/need more. You need a 3500 calorie deficit to lose one pound.
Bottom line, you cannot eat the same at age 40 as at age 20.