Based on previous experimental evidence, we hypothesize that the reduction in circulating BDNF levels early after bariatric surgery may serve as a counter-regulatory response to sustained caloric restriction, weight loss and improved insulin sensitivity, whereas increased BDNF later after bariatric surgery may help improve obesity-related neurocognitive disorders and regulate food intake. This evidence concerns the gene BDNF and obesity due to melanocortin 4 receptor deficiency.