The present invention provides, among other things, a site specific way to enhance a natural hormonal response to nutrients entering the small intestine after gastric emptying, thereby providing therapeutic value for obesity or diabetic patients. In one aspect, the present invention provides methods of stimulating the release of satiety hormone in a subject comprising applying a first electrical stimulus to a tissue in the lumen of the gastrointestinal system of the subject contemporaneously with the contacting of L-cells of the tissue with a nutrient stimulus. In another aspect, the present invention provides methods for predicting patient response to a weight loss surgery comprising applying a first electrical stimulus to a tissue of the gastrointestinal system of said patient contemporaneously with the contacting of L-cells of the tissue with a nutrient stimulus, assessing the effect of the electrical stimulus in said patient, and, correlating said effect to said patient's response to a weight loss surgery.