Eat less, move around more.
100% effective, free, works on every body type and every lifestyle.
About 8 years ago, a friend of mine had decided to get gastric bypass surgery. She asked me to go to the initial appointment with her because she had no family nearby.
The surgeon was one of the top gastric docs in Dallas, and he told her exactly that. He said point-blank that the only way to lose weight is to consume fewer calories. He said the surgery is just a tool for those who cannot make themselves eat less.
She had the surgery anyway. It almost killed her 3 different times with complications, including a bleed that required emergency surgery the day afterwards. But it did work - she's at a healthy weight now.