In this series, we will look at the basics of metabolism and discuss the very well-known science around obesity. Many of the diseases that bedevil humanity flow from obesity, including cancer and Type 2 diabetes, and so understanding metabolism and the causes of obesity is ground zero in the fight for a long life and good health.
One of the many great services Gary Taubes provided in Good Calories, Bad Calories was to read though medical literature from a previous era before a certain kind of medical politics rendered certain ideas less palatable. One such series of books was the 1965 publication of the American Physiological Society titled Handbook of Physiology. Taubes calls on this series to describe a biological process known as lipolysis.
Metabolism, it should be remembered, is really a process of turning big molecules in to small molecules and vice versa, as part of the larger process of turning food into energy. Lipolysis is a part of metabolism. More specifically, lipolysis is a complex biological mechanism for converting triglycerides to free fatty acids so they can be moved in and out of fat cells. A triglyceride is three fatty acids (“tri”) stored on a backbone of glycerol (“glyceride”) and it can be thought of as the stored form of fat energy.
But, a triglyceride is too big to pass through the cellular membranes that provide the barrier between the cell and the blood stream and lipolysis is the chemical mechanism that converts triglycerides into free fatty acids so they can be released from the cell. Esterfication is the process where fatty acids are reassembled back in to triglycerides, so lipolysis and esterification are opposites and this process goes on inside and outside the cells continuous. Fatty acids are assembled into trigylerides, stored, then broken down again and circulated.
A critical thing to know is in the wiki entry on lipolysis:
Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and three fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes. The most important regulatory hormone in lipolysis is insulin; lipolysis can only occur when insulin action falls to low levels, as occurs during fasting.
And, so we are brought back to insulin as a master regulator in fat metabolism. When insulin falls, cells use lipolysis to convert triglycerides in to free fatty acids and send them out of fat cells to power other cells. This empties the adipose, or fat, cells.
By the way, this is a good time to mention that emptying the fat cells can be done by force. Various methods using cold, radio waves, sound waves and other methods are meant to burst the adipose cells and release the triglycerides inside without inducing lipolysis. This allows for the ‘spot reduction’ of fat in areas like the waist. Most of the time, it works to a limited degrees, but the fat will come back if the body needs to store energy in those cells. Fat storage gets back to insulin and carbohydrates.
If you want to know more about this process, including the other hormones that drive lipolysis, here is a pretty good 5 minute explanation: