Eating garlic - either raw or as a supplement - does not lower cholesterol levels, a US study has found.
There has been a belief that garlic could help, supported by positive lab and animal studies.
But a comparison of raw garlic and two garlic supplements in Archives of Internal Medicine found none of the three had any effect.
British experts said a healthy diet combined with plenty of exercise was the best way to prevent heart disease.
"There were no statistically significant effects"
Garlic has been used for thousands of years in the treatment of cardiovascular diseases - the first recorded use was in ancient Egypt 3,500 years ago.
Recently allicin, a compound in garlic has been shown to prevent the formation of cholesterol in over 90 animal studies and, in the early 1990s, studies in humans also suggested there could be benefits.
But the studies were poorly designed, and did not provide conclusive proof.
Even so, garlic supplements are often promoted as cholesterol-lowering agents, the researchers carrying out this latest study say.
Bad breath
They monitored 170 people aged 30 to 65 who had moderately high LDL (bad) cholesterol levels for six months.
They were divided into four groups.
One was asked to eat a four-gram clove of garlic each day, the second were given a powdered garlic supplement, the third had aged garlic extract - which has been treated in alcohol for up to two years - while the fourth group had a dummy supplement.
All were advised to avoid foods known to contain garlic and to cut their intake of onions and chives, which are known to contain some of the same chemical compounds found in garlic.
Blood cholesterol levels were assessed each month.
Writing in Archives of Internal Medicine, the researchers led by Dr Christopher Gardner, said the findings had contradicted their expectations that garlic, particularly in its raw form, would be effective in lowering cholesterol.
They said: "There were no statistically significant effects of the three forms of garlic on LDL cholesterol concentrations."
No serious side effects were seen - although half of those in the raw garlic group (28 people) reported body odour and bad breath.
Balanced diet
However, the researchers say the results of this study should not be applied to everyone.
"Garlic might lower LDL in specific subpopulations, such as those with higher LDL concentrations, or may have other beneficial health effects."
Judy O'Sullivan, of the British Heart Foundation, said: "This small study shows that eating raw cloves of garlic or taking garlic supplements has no benefit for the heart.
"However, eating garlic as part of a balanced diet will help to add variety and flavour, and it is a healthier alternative to salt, for example."
She added: "In order to reduce your risk of developing coronary heart disease, it's best to eat a diet rich in fruit and vegetables and low in fat, especially saturated fat, and keep physically active."
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