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Is alcohol metabolized like sugars? Or something else?
November 13, 2009 8:59 AM   Subscribe

Is alcohol metabolized like sugars? Or something else?

There's a variety of diet books that focus on the theory that in the American diet, carbohydrates and sugars are the primary cause of weight gain and other problems. The Atkins diet is the most well known; Gary Taubes' book Good Calories, Bad Calories also does a thorough job in highlighting scientific evidence that refined carbohydrates and sugars are bad for health. However, none of these books talk about alcohol.

How is alcohol metabolized? Does the body process it more or less like sugar or refined carbohydrates? Does it get converted to glucose relatively quickly and end up causing large changes in blood sugar, insulin, etc? Or does something different happen to it?

(Taubes' book has given me a newfound appreciation of the complexity of metabolism science and the ease by which common wisdom can get mistaken for science. Hoping to find some proper research, not just speculation.)
posted by Nelson to Health & Fitness (12 answers total) 5 users marked this as a favorite
In general, unsweetened wine (red or white) and hard alcohol like whiskey, vodka, etc., will not result in elevated glucose or require an insulin response. In fact, these drinks tend to result in a temporarily lower insulin response, since the liver stops its usual task of putting out glycogen (which triggers insulin release) to converting the alcohol - for a time, anyway. I'm not a doctor or a scientist, but that's my general understanding and experience as somebody with type 1 diabetes. Those drinks have no carbohydrates.

Beer, on the other hand, does contain varying amounts of carbohydrates, which will be converted to glucose and therefore require insulin. A bottle of regular beer has about 12 grams of carbs, I believe, with light beer having less.

Er, so that's not proper research, but it's not speculation, either. Of course, wine and hard liquor sure do contain calories.
posted by chinston at 9:26 AM on November 13, 2009 [1 favorite]

Here's a rundown written in an authoritative tone. I can't verify the science, but it might provide at least some search terms to go on.
posted by restless_nomad at 9:37 AM on November 13, 2009

ethanol itself is worth 7kcal/g, which trumps both carbohydrates and proteins (4kcal/g). So if a drink is 44mL of 80-proof whiskey, the alcohol alone (assuming .789g/mL density) is worth 97kcal.

I'm afraid I don't know the biological pathway which processes alcohol.
posted by d. z. wang at 9:38 AM on November 13, 2009

"Ethanol is metabolized by the body as an energy-providing carbohydrate nutrient, as it metabolizes into acetyl CoA, an intermediate common with glucose metabolism, that can be used for energy in the citric acid cycle or for biosynthesis." -- from Wikipedia

Here's how the process works in humans.
posted by jedicus at 10:11 AM on November 13, 2009

Ethanol is a product of the anaerobic metabolism of glucose. In the human body, ethanol is converted to acetic acid in the liver, which can then be converted to Acetyl-CoA to feed common metabolic pathways. The first stages of glucose metabolism in the human body are also anaerobic, but the end product is pyruvate which can also be converted to Acetyl-CoA. Acetyl-CoA can then feed aerobic metabolism in the Krebs cycle, or can be used as the feedstock for fatty-acid synthesis or creation of glucose.

That's the background, the question of what the liver actually does with the acetic acid product of ethanol is going to depend on layers of regulatory loops that I don't know enough about. If what chinston says is accurate, then it implies that the liver doesn't end up converting the Acetyl-CoA to glucose, or if it does, it ends up storing it as glycogen, rather than dumping it into the blood.
posted by Good Brain at 10:15 AM on November 13, 2009

The Atkins book mentions alcohol several times, actually. I'm not sure if it results in elevated blood glucose, but the reasoning given in his books is that your body will burn alcohol in its system for fuel before it burns other things so it doesn't build up and kill you.
posted by Nattie at 10:31 AM on November 13, 2009

Thanks for all the answers. That Wikipedia article jedicus linked has a lot more biological detail than I can really follow, but what I get from it is "alcohol metabolism is a different process than sugars".

Thanks also for the perspective from Type-1 Diabetes, chinston. When researching this question I found the American Diabetes Association's comments on hypoglycemia (and a potential mechanism), but I couldn't understand if that phenomenon was specific to diabetics or universal.

I realize now I don't really understand carbohydrate metabolism, either, nor how it might cause the various problems hypothesized in the books I mention in the question. Most of Taubes' data is from looking at epidemiological studies, there's very little in it about metabolic mechanisms. So my armchair analysis may not do me much good other than to say "yeah, alcohol is different".
posted by Nelson at 10:39 AM on November 13, 2009

Alcohol can lower blood sugar. As I remember it, the liver is normally supplying some portion of the sugar in the blood. This varies, such as their is a bit of an increase just before normal waking. When you drink alcohol the liver is too busy processing the alcohol to manufacture the sugar and thus it can lead to lower blood sugar levels. While the types of foods and calories you eat can affect your appetite, in the end it is calories in versus calories out and alcohol has a goodly number of them.
posted by caddis at 11:34 AM on November 13, 2009

The goal of metabolism is to extract the energy from hydrocarbon chains and use it to power the chemical reactions of the body. The principle is similar to the way cars burn gasoline (also made of hydrocarbons) to power the engine, but in the body the process is much more convoluted and controlled. A long series of reactions breaks down the hydrocarbon chains and uses the energy to produce ATP, which is the universal fuel of the body.

Here's the process in brief:

1. Ingested carbohydrates are broken down into simple sugars like glucose.
2. Glucose travels through the bloodstream and gets absorbed by cells.
3. Inside of cells, a series of reactions known as glycolysis converts glucose into a chemical called pyruvate, and in the process creates a small amount of ATP and NADH. NADH is a molecular that carries high energy electrons (stolen from hydrocarbons), which will be important later.
4. Pyruvate gets absorbed by mitochondria, where it is broken down by another series of reactions known as the citric acid cycle (aka Krebs cycle) into CO2, producing more ATP and NADH in the process. This is where the CO2 you exhale comes from.
5. The high energy electrons in NADH are used to power the pumping of hydrogen (which is positively charged) out of the mitochondria. This results in a difference in charge between the inside and the outside of the mitochondria (positive on the outside, negative on the inside).
6. Nature doesn't like charge differences, so now all the hydrogen wants back in. It flows through channels in the mitocondrial membrane, and this flow powers the production of even more ATP, not unlike the way flowing water powers a hydroelectric plant.
7. So now we've made a bunch of ATP, but we still have these electrons from NADH sitting around. They're no longer high-energy, because that energy was used for pumping, but they still need to go somewhere. A special complex sticks them onto molecular oxygen (O2), which grabs a few hydrogen cations and forms water. Without oxygen, the electrons build up and the whole long process grinds to a halt. That, in a nutshell, is why we have to breathe.

Alcohol gets converted to pyrvate and enters the process in step 4.
posted by dephlogisticated at 12:37 PM on November 13, 2009 [8 favorites]

To be clear regarding the difference between hydrocarbons and carbohydrates: hydrocarbons are exactly what they sound like. They're a chain of carbon and hydrogen. Carbohydrates are also hydrocarbon chains, but the chains are formed into rings, and the rings have hydroxyl (OH) groups attached all around them. The carbon chains are the important part, energy-wise. The OH groups are just there so that the carbohydrate can dissolve in water. But for the sake of accuracy, replace "hydrocarbon" in the explanation above with "carbohydrate".
posted by dephlogisticated at 1:00 PM on November 13, 2009

There's a really, really excellent lecture by UCSF pediatric endocrinologist Robert Lustig whose subject is sugar (fructose in particular) but which closely compares and contrasts the biochemistry of ethanol, glucose, and fructose metabolism:

I highly recommend it, despite its long running time.
posted by holympus at 6:38 PM on November 13, 2009

Total attribution fail on my part above. I first saw the link on metafilter (there's a surprise):
posted by holympus at 8:21 PM on November 13, 2009

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