Side Bar The Glycerol Story is it a carb

Glycerol (1,2,3 -propanetriol) is a nutrient that has gotten some attention in the bodybuilding magazines as a supposed "plasma expander" and is hocked as having some ability to increase the fullness of muscles.

It's also added to MRP bars for its mild sweet taste and gives the bar good texture similar to fat. Glycerol is used in the food industry to improve moisture, palatability and as a sweetener.

Over the past few years, there has been a great deal of confusion over exactly what glycerol is and what it is not. Is it a carb? A fat? Can it increase performance? First, let's get to the basis of what glycerol is as it's defined chemically. Glycerol is an integral component of the triglyceride molecule. As most people who have taken a basic nutrition or biology course will tell you, glycerol forms the backbone of the triglyceride molecule, which is one of several ways the body transfers fat around in the body.

Most people also know that high triglyceride levels are a risk factor for heart disease. Does that make glycerol a fat? Not exactly! If you break up a triglyceride, you will get three free fatty acids and glycerol (hence the reason it's called the back bone of a triglyceride).

Now that you've liberated glycerol from the clutches of fatty acids, what does glycerol become? A fat? A carbohydrate? Or maybe it really doesn't fit into any neat category. This is where things have gotten messy and why there is so much rampant confusion, leading some less than ethical supplement companies to make wild claims about glycerol.

So what exactly is glycerol you ask? If you go by how chemistry books define carbohydrates and glycerol, you'll see that fitting glycerol into the carbohydrate category is not going to happen. I won't bore you with the details, but you won't find glycerol defined as a carbohydrate in any biochemistry textbooks (Lehninger, A.L., 1993).

Glycerol is defined as a naturally occurring trivalent alcohol. Similar to carbohydrates, glycerol oxidation yields 4.32 kcals per gram. So even though the number of calories in carbohydrates and glycerol are the same, structurally, they aren't the same. Besides, proteins and carbohydrates have a similar caloric value also, but they sure as heck are not the same!

So if glycerol is clearly not a carb, what about the people making a big deal out of its conversion to glucose? Does glycerol act like a carb from its conversion to glucose (blood sugar)?

The big question is whether or not glycerol contributes to the formation of glucose, via a process called gluconeogenesis. The basic answer is no! For example, if you starve yourself for 3-4 days, then glycerol might contribute a bit to glucose production (about 22% of total glucose production).

But if you don't starve yourself on a regular basis - and no one should if they can avoid it - glycerol contributes much less than 5% of total glucose production (Baba, H., et al., 1995).

When the body is starved for both calories and carbohydrates, under the right conditions, it will convert certain non-carbohydrate substrates to glucose, such as glycerol, certain amino acids, etc., but this is not major source of carbohydrates (glucose) under normal conditions. Under normal conditions, like when a person is eating normally (i.e. not starving themselves) you can consume enough glycerol to fill an elephant, but you don't get large changes in blood glucose and insulin.

For instance, in a study published in the "European Journal of Applied Physiology," on six healthy, non-obese men - 32 years of age on average -during exercise to exhaustion on a cycle ergometer (73% of V02max). The men either ingested glucose, glycerol or placebo. The ingestion of glucose (1 gram per kg body weight, equal to 70 grams for a 150 lb person) 45 minutes prior to exercise produced a 50% increase in plasma glucose, as well as a 3-fold increase in plasma insulin at zero minutes of exercise.

On the other hand, glycerol consumption (1 gram per kg body weight) 45 minutes prior to exercise produced a 340-fold increase in plasma glycerol; but resting levels of plasma glucose and insulin did not change (Gleeson, M., et al., 1986).

Is there any use to glycerol in the diet? Possibly. A Dr. Jose Antonio suggests that substituting glycerol for high-glycemic carbohydrates could minimize the plethora of health problems associated with eating cookies and cakes and other very high GI foods. As Dr. Antonio points out, "glycerol has little if any effect on resting plasma glucose and insulin at rest even after taking whopping doses."

Is glycerol a legitimate ergogenic aid? Because of glycerol enables you to retain more fluid, some scientists theorize that taking exogenous glycerol might help performance. This is based on the fact that if you keep yourself well-hydrated, then you'll be able to train harder and longer, particularly in hot environments.

Some studies have found mild improvements in endurance athletes given glycerol (Wagner, D.R., 1999; Montner, P., et al., 1996.) but studies have been mixed with some finding no effect. As with all science, there isn't a unanimous consensus on glycerol's effects. Some sports nutrition companies sell glycerol to bodybuilders as a "plasma expander" as glycerol can pull fluids into the vascular system temporarily and may enhance the pump you feel in the gym or when stepping on stage.

So far, the feedback on such a strategy is mixed with many bodybuilders reporting a crushing headache after ingesting large amounts of glycerol.

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