There is a specific part of the hypothalamus called the arcuate nucleus. It lacks a blood brain barrier, because the neurons there have a special function to se

There is a specific part of the hypothalamus called the arcuate nucleus. It lacks a blood brain barrier, because the neurons there have a special function to sense blood-born hormones like insulin and leptin. When sensed, the brain interprets this as a "full tank of gas" and suppresses appetite while increasing metabolism. Since theres no blood brain barrier here, these neurons get damaged easily due to things in the blood. When that happens, they don't see leptin anymore, and obesity develops. Fructose and high fat diets have both been shown to cause inflammation here. (hypothalamic gliosis) heres a random selection of many papers http://diabetes.diabetesjournals.org/content/65/3/551.figures-only http://diabetes.diabetesjournals.org/content/65/3/551.figure... We also know that certain viruses show up in obese people (adenovirus36). As the field develops, I would not be surprised if labs demonstrate both viral infection of the hypothalamic ARC and damage by endocrine disruptors there.