BMI

Organs that control the activities of other distant parts of the body are part of our nervous system or a part of the endocrine (hormone-releasing) system.

While the brain clearly does a lot to spook our willpower and weaken our ‘eat not, want not’ resolve, it is not an organ we normally want to mess around with. The brain works by using chemicals called neurotransmitters to effect its commands. For example, hunger, mood, craving, etc. may all be induced by manipulating the level of these chemicals in specific parts of the brain. We are increasingly aware of this, but our knowledge is still a long way away from being able to encapsulate it in a pill to make us thinner and healthier. 

Take, for example, the case of rimonabant. It was touted as the drug that would kill bariatric surgery. It acts on the cannabinoid receptors in the brain and kills hunger. Advocates said the drug would cause massive weight loss without the risks and costs of surgery.

What happened? The drug has become another footnote in history, after being withdrawn because of the high incidence of degenerative diseases like Parkinsonism and Huntington’s disease. You clearly don’t want to mess with the brain! 

Apart from this, the brain has a part known as the hypothalamus, that houses both the hunger and the satiety centers. The hypothalamus also secretes and stimulates the secretion of a host of hormones that affect body metabolism and composition. Diseases that affect it may cause massive obesity in patients.

If we leave the brain aside, what are the other organs that affect fat loss or fat gain?

Clearly, the pancreas is top dog, with insulin and glucagon controlling all the major pathways of metabolism (like glycolysis and gluconeogenesis). Diseases that affect the pancreas may cause diabetes and weight loss. However, in the condition known as Type II Diabetes Mellitus, the pancreas either stops insulin production or its insulin does not work on the body (resistance). This condition is usually associated with obesity. Clearly, there ismore than one organ, then, affecting body fat levels.

Body fat itself is now given more attention by scientists. Previously thought of as an inert mass of blubber, it is now considered an endocrine organ! The fat that resides around the organs (like the kidneys, intestines, omentum, etc.) and in those love handles is supposed to be metabolically active. Fat produces hormones like leptin and ASP which are now known to be important hormones affecting fat deposition in many ways. Leptin acts to achieve a sense of satiety, and obese patients are often found to be resistant to it, much as they have resistance to its more famous brother, insulin. 

The small intestine, consisting of the duodenum, jejunum and ileum, is an important engine of metabolism. There are nearly 200 hormones, called incretins, that affect metabolism in mysterious ways. The incretins act on the pancreatic islet cells to secrete insulin, thereby helping control diabetes. This effect is more marked following gastric bypass, leading to diabetes resolution. More about incretins in later posts!

The stomach, rather surprisingly, secretes a hormone critical in the phenomenon of hunger. The hormone ghrelin is secreted by the fundus of the stomach, and this helps explain why patients of the sleeve gastrectomy  or the gastric bypass procedure have a marked loss of appetite, resulting in major weight loss (up to 75% of excess body weight).

In summary, there is more to the neural and endocrine control of body fat and metabolism than insulin. The topic of ASP (Acylation Stimulation Protein) is an extremely interesting one that serves to highlight how closely interconnected various disparate organs may be in the regulation of body fat.

This topic is fascinating in many ways, and underscores how oversimplified people’s perceptions of obesity are, when they identify single villains (insulin, for example) or heroes (antioxidants/beta-HCG/acai berries, etc,). The truth is far too complex!