Nutrition Hotline
by Reed Mangels, PhD, RD
This issue’s Nutrition Hotline examines popular claims that garlic can improve many vital aspects of your health.
QUESTION: “Are all the health claims I hear about garlic true? Some of my family and friends swear by it.”
ANSWER: You’re likely not the only person who knows someone on a garlic binge. A lot of claims are made for health-enhancing effects of garlic, promising, for instance, that garlic can kill germs, protect your heart, and prevent colds.
Or that garlic cures acne, improves your sex life, and repels mosquitoes (apparently in addition to vampires).
Garlic—a plant in the allium family, related to onions and leeks—has been used since ancient times both as a medicine and as a condiment or seasoning in foods. Even if you don’t use it for medicinal purposes, you probably eat garlic fairly regularly. It’s a common ingredient in soups, dips, casseroles, and other cooked dishes. The edible bulbs or cloves have a distinctive flavor and odor that tends to linger on the breath.
The truly devoted pop a whole fresh clove a day in hopes of health benefits. It’s not hard to identify them. I’ll never forget the evening I spoke at a community-wide heart health intervention program and was caught up afterwards in a throng of hundreds of participants, several of whom nearly bowled me over with the overpowering odor of garlic as they approached to talk diet.
Are the benefits of garlic worth the social cost? What’s the truth about the health claims?
Here’s what we know. In addition to vitamins and minerals, plant foods such as fruits and vegetables contain other health-supporting components called phytochemicals. There are likely thousands of these substances in foods, but we don’t know a lot about many of those that have been identified at this point.
One class of phytochemicals that there is a substantial body of research on, however, is plant sulfur compounds. Garlic is a rich source of sulfur compounds.
In fact, the Agency for Healthcare Research and Quality (AHRQ) in 2000 published an evidence-based report on garlic and its health benefits. A summary of the report can be found online at www.ahrq.gov/clinic/epcsums/garlicsum.htm.
The report assessed whether garlic (fresh, cooked, or in supplement forms) lowers blood lipid levels, blood pressure, and blood sugar or reduces the risk of death or disability from heart disease or cancer.
According to AHRQ:
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There wasn’t enough evidence to draw conclusions about the potential for garlic to prevent heart attacks. Garlic may lower blood cholesterol levels slightly in the short term (up to three months).
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The evidence did not support the claim that garlic lowers blood pressure or blood sugar levels.
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A limited amount of research from case-control studies suggested that eating garlic lowers the risk of laryngeal, stomach, colorectal, and endometrial cancer as well as colorectal polyps. However, single case-control studies suggested that garlic did not protect against breast or prostate cancer.
No word on acne, sex, or mosquitoes—an evidence base built on sound science doesn’t exist yet.
The AHRQ report did document some adverse effects of garlic, though. Smelly breath and body odor topped the list. Other potential side effects included gas, abdominal pain, and dermatitis (inflammation of the skin).
Another limitation noted in the AHRQ report was the wide variability in the types of garlic preparations used by study subjects. Studies reviewed did not always distinguish whether subjects used raw or cooked garlic or did not give the name or specifications of garlic supplements.
The bottom line? Garlic may confer health benefits, but many questions remain, complicated by a lack of information about the various forms in which garlic was used in studies. If you can eat it without suffering side effects, though, there doesn’t appear to be any reason not to enjoy it.
Unless you eat enough to clear a room.
