You have no doubt heard that the most recent dietary guidelines as drawn up by the U.S. government suggest that “moderate” or “healthy” drinking for women is one alcoholic beverage a day. Men are allowed two.

Why is that?

First, let's define some terms. One “drink” in this case refers to 12 ounces of beer, 5 ounces of wine or 1.5 ounces 80-proof spirits. Note that your mileage will vary with higher proof whiskeys, “light” beers and pre-packaged drinks such as wine coolers.

Also, we hasten to point out that the Centers for Disease Control and Prevention does not recommend that individuals who do not drink alcohol start drinking for any reason.

When it comes to alcohol consumption, what matters at the end of the day (or night, in most cases) is how much alcohol your body has absorbed, and how quickly it did that. Two people can drink the same amount of booze and end the evening with very different blood alcohol levels because of differences in their metabolism. And that's where the gender differences come into play.

Women generally carry more body fat than men, as they are designed in part to nourish unborn children and babies, a privilege that men do not share. A man's body is 15 percent body fat on the average, whereas women tip in at 25 percent. The difference in men is made up in muscle, and muscle tissue absorbs alcohol faster, leaving less of it to soak in the blood stream and rack up those blood alcohol levels.

Although most any women will swear otherwise when asked, women carry around less water than men. The research indicates that men's bodies are around 60 percent water, and women clock in at about 55 percent. Consequently, women will, as a general anatomical rule, end up with a more highly concentrated, less diluted alcohol level in their bloodstream when compared to a man who has imbibed the same amount.

Dive a little deeper into the biochemistry and you learn that women have lower amounts of two key enzymes (alcohol dehydrogenase and aldehyde dehydrogenase) that are used in alcohol metabolism. These compounds break down alcohol in the liver and stomach before it even makes it to the bloodstream. As a result, more alcohol is left in women's blood and everything is processed more slowly.

Finally, women's systems are simply more fragile where alcohol is concerned. One study has shown that women may be at a greater risk of developing alcoholic liver disease than men, even when consuming less alcohol. The fairer sex is also more inclined to die from cirrhoses and develop alcoholic hepatitis than men, with indications that estrogen is an agent of increased liver damage.