What's the primary difference between gastric bypass and lap band?

Main difference: Is that bypass is a bigger operation that redirects the food passage from the stomach to small intestine; whereas lap band is a relatively simpler operation that restricts the stomach volume that can accommodate food.

Band vs Bypass: Many differences. The band is purely restrictive, is the safest, is removable, but has the highest failure rates. Very easy to cheat the band and never lose wt or regain wt after losing. Bypass is restrictive and malabsorptive, is permanent, has the highest average wt loss, is the best operation for someone with diabetes (also great for reflux disease).