How is acupuncture helpful for weight reduction?

Not really. There aren't good randomized control studies that show accupuncture causes weight loss. To achieve weight loss, you have to expend more calories than you take in. Weight loss takes work. There is no magic bullet to lose weight - not pills, not herbs, not accupuncture. If there was an easy way to do it, everyone would be thin. It's all about diet and exercise.
Appetite suppressio. I have a number of patients that i treat with auricular (ear) acupuncture every week. They all stay physically active and are mindful of what they eat. Most are in the military and were in danger of losing their career due to their weight and body fat. All are now well within standards. The ear acupuncture helps a person to know when they are satiated and also helps with cravings.