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Prof Alta Schutte, one of the speakers at a recent CNE Event, spoke about “Adipose Tissue: A Fascinating Endocrine Organ”, which proved to be most insightful.
Fat in the body
Until the mid 1990s everyone thought of body fat as an inert stored substance, rich in energy, but very inactive. In 1994, researchers Friedman and Coleman discovered a defective gene in obese mice which responded to leptin injections. As is well know, everyone immediately hailed the hormone leptin as the solution to all obesity and leptin injections became a “magic bullet to cure obesity”.
Read: Leptin - the answer to obesity?
The problem was that the only obese individuals (humans and rodents) who responded to leptin injections were those who had an inborn or relative leptin deficiency. As was later realised with ongoing research, the vast majority of people who suffer from obesity do not have a leptin deficiency, but suffer from what could be called “leptin resistance”.
This means that their leptin receptors don’t respond to leptin injections because they already have an overabundance of leptin in their bodies, which their cells cannot use! Unfortunately unscrupulous practitioners still promise instant weigh tloss and subject their overweight patients to very expensive leptin injections.
An overlooked discovery
What researchers and the public tended to overlook at the time when leptin was discovered, was that body fat is not just a passive depot for energy storage, but a hormone-producing organ that can have a number of effects on metabolism.
Read: 5 body trouble spots
In addition, two different types of body fat were identified, white adipose (fat) tissue and brown adipose tissue. According to Prof Schutte, these two type of body fat differ considerably:
a) White adipose tissue (WAT)
This kind of fat is made up of cells that consist of a single large droplet of fat and very few mitochondria (the powerhouses of the cell). But these white fat cells can produce hormones that regulate insulin sensitivity and satiety (how full you feel).
White adipocytes are efficient at storing excess fat in the body and are able to release energy to the body during periods when the food supply is cut off.
b) Brown adipose tissue (BAT)
This kind of fat is made up of cells that consist of many little drops of fat and contain many mitochondria (powerhouses of the cell). Brown fat cells are richly supplied with blood vessels and nerves. They produce a substance known as “uncoupling protein 1".
Read: Brown fat cells may combat obesity
The most important characteristic of brown adipocytes is that they release chemical energy from fatty acids to produce heat. Unfortunately our stores of brown adipocytes decrease with age – at the age of 20 humans have about 50% cold-activated BAT, but at age 50 to 60 years we only have about 10% cold-activated BAT.
Some researchers are of the opinion that when we’re young we tend to be lean, have small white fat cells and plenty of brown fat cells, and then at a certain age, we switch over to white fat cells and lose our brown fat cells. This scenario would help to explain why people tend to gain weight exponentially as they grow older.
Transforming WAT into BAT
Researchers did not pay as much attention to brown fat, until recently when there was a resurgence of interest in trying to find ways of activating adult brown adipose tissue (adult BAT) to help with weight loss and combat obesity. It is now believed that to involve BAT as an anti-obesity agent, we need to find out how to stimulate the number of brown fat cells in the body and also to increase their activity.
Read: Shivering produces calorie-burning brown fat
Methods of stimulating BAT number and activity include cold exposure (which may not be too popular with patients!), stimulation of the sympathetic nervous system and increasing thyroid function. Some researchers have even suggested that WAT (white adipocyte tissue) could be transformed into BAT (brown adipose tissue) to stimulate weight loss.
Although these aspects of brown fat cell manipulation sound highly exciting and may have great potential, the research into BAT has only just restarted, and we will have to wait and see what scientists achieve in this field.
Next week we will have a closer look at WAT, which influences practically every aspect of human metabolism.
References:
- Schutte A (2015). Adipose Tissue: A Fascinating Endocrine Organ. Paper presented at the Nutritional Solutions CNE Event, 16 April 2015, Johannesburg.
- Tam CS et al, 2012. Brown adipose tissue: Mechanisms and potential therapeutic targets. Circulation, 125: 2782-279.
Read more:
Understanding the different kinds of fat in our diet
Lower indoor temperatures increase fat burning
Image: Fat and thin from Shutterstock
