(CNN) Guinness, like other Irish stouts, enjoys a seasonal popularity every St. Patrick's Day. It has also been touted as being "good for you," at least by its own advertising posters decades ago.

But can this creamy, rich and filling beer really be added to a list of healthy beverages? Or is its reputation just good marketing? We researched the beer's history and talked to brewing experts and break out the good, the not-so-great and the ingenuity of Guinness.

The good

The original Guinness is a type of ale known as stout. It's made from a grist (grain) that includes a large amount of roasted barley, which gives it its intense burnt flavor and very dark color. And though you wouldn't rank it as healthful as a vegetable, the stouts in general, as well as other beers, may be justified in at least some of their nutritional bragging rights.

According to Charlie Bamforth, a professor of brewing sciences at the University of California, Davis, most beers contain significant amounts of antioxidants, B vitamins, the mineral silicon (which may help protect against osteoporosis), soluble fiber and prebiotics, which promote the growth of "good" bacteria in your gut.

And Guinness may have a slight edge compared with other brews, even over other stouts. "We showed that Guinness contained the most folate of the imported beers we analyzed," Bamforth said. Folate is a B vitamin that our bodies need to make DNA and other genetic material; it's also necessary for cells to divide. According to his research, stouts on average contain 12.8 micrograms of folate, or 3.2% of the recommended daily allowance.

Because Guinness contains a lot of unmalted barley, which contains more fiber than malted grain, it is also one of the beers with the highest levels of fiber, according to Bamforth. (Note: Though the USDA lists beer as containing zero grams of fiber, Bamforth said his research shows otherwise.)

Bamforth researched and co-authored studies recently published in the Journal of the Institute of Brewing and the Journal of the American Society of Brewing Chemists, The Science of Beer.

Here's more potentially good news about Guinness: Despite its rich flavor and creamy consistency, it's not the highest in calories compared with other beers. A 12-ounce serving of Guinness Draught has 125 calories. By comparison, the same size serving of Budweiser has 145 calories, a Heineken has 142 calories, and a Samuel Adams Cream Stout has 189 calories. In the United States, Guinness Extra Stout, by the way, has 149 calories.

This makes sense when you consider that alcohol is the main source of calories in beers. Guinness Draught has a lower alcohol content, at 4.2% alcohol by volume (ABV), compared with 5% for Budweiser and Heineken, and 4.9% for the Samuel Adams Cream Stout.

In general, moderate alcohol consumption -- defined by the USDA's dietary guidelines for Americans as no more than two drinks per day for men or one drink per day for women -- may protect against heart disease. So you can check off another box.

The not-so-great

Guinness is still alcohol, and consuming too much can impair judgment and contribute to weight gain. Heavy drinking (considered more than 15 drinks a week for men or more than eight drinks a week for women) and binge drinking (five or more drinks for men, and four or more for women, in about a two-hour period) are also associated with many health problems, including liver disease, pancreatitis and high blood pressure.

According to the National Council on Alcoholism and Drug Dependence, "alcohol is the most commonly used addictive substance in the United States: 17.6 million people, or one in every 12 adults, suffer from alcohol abuse or dependence along with several million more who engage in risky, binge drinking patterns that could lead to alcohol problems."

And while moderate consumption of alcohol may have heart benefits for some, consumption of alcohol can also increase a woman's risk of breast cancer for each drink consumed daily.

Many decades ago, in Ireland, it would not have been uncommon for a doctor to advise pregnant and nursing women to drink Guinness. But today, experts (particularly in the United States) caution of the dangers associated with consuming any alcohol while pregnant.

"Alcohol is a teratogen, which is something that causes birth defects. It can cause damage to the fetal brain and other organ systems," said Dr. Erin Tracy, an OB/GYN at Massachusetts General Hospital and Harvard Medical School assistant professor of obstetrics, gynecology and reproductive gynecology. "We don't know of any safe dose of alcohol in pregnancy; hence we recommend abstaining entirely during this brief period of time in a woman's life."

What about beer for breastfeeding? "In Britain, they have it in the culture that drinking Guinness is good for nursing mothers," said Karl Siebert, professor emeritus of the food science department and previous director of the brewing program at Cornell University.

Beer in general has been regarded as a galactagogue, or stimulant of lactation, for much of history. In fact, according to irishtimes.com , breastfeeding women in Ireland were once given a bottle of Guinness a day in maternity hospitals.

According to Domhnall Marnell, the Guinness ambassador, Guinness Original (also known as Guinness Extra Stout, depending on where it was sold) debuted in 1821, and for a time, it contained live yeast, which had a high iron content, so it was given to anemic individuals or nursing mothers then, before the effects of alcohol were fully understood.

Some studies have showed evidence that ingredients in beer can increase prolactin, a hormone necessary for milk production; others have showed the opposite. Regardless of the conclusions, the alcohol in beer also appears to counter the benefits associated with increased prolactin secretion.

"The problem is that alcohol temporarily inhibits the milk ejection reflex and overall milk supply, especially when ingested in large amounts, and chronic alcohol use lowers milk supply permanently," said Diana West, co-author of "The Breastfeeding Mother's Guide to Making More Milk."

"Barley can be eaten directly, or even made from commercial barley drinks, which would be less problematic than drinking beer," West said.

If you're still not convinced that beer is detrimental to breastfeeding, consider this fact: A nursing mother drinking any type of alcohol puts her baby in potential danger. "The fetal brain is still developing after birth -- and since alcohol passes into breast milk, the baby is still at risk," Tracy said.

"This is something we would not advocate today," Marnell agreed. "We would not recommend to anyone who is pregnant or breastfeeding to be enjoying our products during this time in their life."

Regarding the old wives' tale about beer's effects on breastfeeding, Marnell added, "It's not something that Guinness has perpetuated ... and if (people are still saying it), I'd like to say once and for all, it's not something we support or recommend."

The ingenuity

Assuming you are healthy and have the green light to drink beer, you might wonder why Guinness feels like you've consumed a meal, despite its lower calorie and alcohol content.

It has to do with the sophistication that goes into producing and pouring Guinness. According to Bamforth, for more than half a century, Guinness has put nitrogen gas into its beer at the packaging stage, which gives smaller, more stable bubbles and delivers a more luscious mouthfeel. It also tempers the harsh burnt character coming from the roasted barley. Guinness cans, containing a widget to control the pour, also have some nitrogen.

Guinness is also dispensed through a special tap that uses a mixture of carbon dioxide and nitrogen. "In Ireland, Guinness had a long history of hiring the best and brightest university graduates regardless of what they were trained in," Siebert said. "And they put them to work on things they needed. One was a special tap for dispensing Guinness, which has 11 different nozzles in it, that helps to form the fine-bubbled foam."

The foam is remarkably long-lasting. "After you get a freshly poured Guinness, you can make a face in the foam, and by the time you finish drinking it, the face is still there," Siebert said.

'It's a good day for a Guinness,' unless you're pregnant

The famous advertising Guinness slogans -- including "It's a good day for a Guinness" -- started through word of mouth, said Marnell. "In 1929, when we were about to do our first ad, we asked (ourselves), 'What stance should we take?' So we sent around a group of marketers (in Ireland and the UK) to ask Guinness drinkers why they chose Guinness, and nine out of 10 said their belief was that the beer was healthy for them. We already had this reputation in the bars before we uttered a word about the beer.

"That led to the Gilroy ads that were posted," Marnell explained, referring to the artist John Gilroy, responsible for the Guinness ads from 1928 to the 1960s. "You'll see the characters representing the Guinness brand -- the toucan, the pelican -- and slogans like 'Guinness is good for you' or 'Guinness for Strength.' But those were from the 1920s, '30s and '40s."

Today, he said, the company would not claim any health benefits for its beer. "If anyone is under the impression that there are health benefits to drinking Guinness, then unfortunately, I'm the bearer of bad news. Guinness is not going to build muscle or cure you of influenza."

In fact, Guinness' parent company, Diageo, spends a lot of effort supporting responsible drinking initiatives and educating consumers about alcohol's effects. Its DrinkIQ page offers information such as calories in alcohol, how your body processes it and when alcohol can be dangerous, including during pregnancy.

"One of the main things we focus on ... is that while we would love people to enjoy our beer, we want to make sure they do so as responsibly as possible," Marnell said. "We would never recommend that anyone drink to excess, and (we want to make people) aware of how alcohol effects the body."

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And again: Most health providers in the US would advise forgoing all alcohol if you are pregnant, nursing or have other health or medical issues where alcohol consumption is not advised.

So responsibly celebrate St. Patrick this year a little wiser about the health benefits and risks with one of its signature potables.