Long-term problems following weight loss surgery depend on which type you have. One of the most common issues, especially with gastric bypass, is "dumping syndrome," in which food moves too quickly through the small intestine. Symptoms include nausea, weakness, sweating, faintness, diarrhea after eating, and not being able to eat sweets without feeling very weak. It can occur in up to 50% of people who had weight loss surgery. But avoiding high-sugar foods and replacing them with high-fiber foods may help prevent it.