The sulfates found in garlic are thought to be responsible for its health benefits and flavour.
Study leader Dr Peter Rose explained the mix of results was likely due to the vast array of compounds in garlic, mainly sulphuric ones.
Different levels of the compounds are released through chopping garlic, pressing it for oil or fermenting it in alcohol – known as the ‘Ancient Tibetan Garlic Cure’.
This could explain the strikingly different results into the health effects of garlic, the researchers said.
But Dr Rose and colleagues admitted it was still a mystery as to which method of eating garlic is the most beneficial.
This means they can’t yet provide solid evidence on whether chewing a raw clove will provide greater benefits than enjoying a slice of garlic bread.
Dr Rose said: ‘Each of these preparative forms could have a different effect within mammalian systems.
‘And that’s what makes this research so complex, because we don’t really understand how these compounds are metabolised in humans.’
Garlic is a member of the allium family of plants, along with onions, leeks and and chives, which absorb sulfate from the soil.
These same sulfur compounds are what give garlic its distinct taste, and lingering smell.
Scientists have previously found while sometimes the consumption of garlic has a biological effect, other times it does nothing.
WHAT IS THE HISTORY BEHIND GARLIC AND ITS MEDICAL BENEFITS?
Garlic originated in middle Asia, and the first recorded use of garlic was in the Sumerian civilisation, 8,000 years ago.
The Egyptians were also fond of the plant, and it is reported that a papyrus from 1,500 B.C. recommends garlic for treating ailments such as heart disease, stimulating digestion and improving libido.
The ancient Greeks and Romans used garlic for a range of health issues, from treating animal bites to bladder infections.
Hippocrates, the founder of modern medicine, prescribed garlic for conditions such as treating sores and aiding in pulmonary conditions.
The plant has even been used topically when ground up with animal fat by many cultures.
Louis Pasteur wrote in 1858 that garlic killed bacteria.
In the 20th century, missionary doctor Albert Schweitzer was said to have used the seasoning to treat dysentry in Africa.
More recently it has been found treat animals infested with ticks, and one Russian 1955 study claims garlic bound to heavy metals in the body, aiding in their elimination.
Dr Rose said: ‘When it comes to human intervention studies, there’s been quite a lot of disparity.
‘I think it needs re-investigating, just because of the sheer complexity of the diversity of these sorts of compounds and the different distribution of them between different garlic products.’
Garlic has been found to have a significant effect on lowering blood pressure in both experimental and clinical studies, and has been found to contain many potent compounds with anti-cancer properties – particularly allylsulfide derivatives.
Although there are claims that garlic may reduce blood sugar levels in diabetic animals, the effect of garlic on human blood sugar levels is unknown.
One theory Dr Rose and his colleagues have is that the sulfur compounds in garlic may affect gaseous signally in the body.
This is a process which plays an important role in cell signalling – and recent studies performed in laboratories has linked the two.
Altered levels of gaseous signally molecules are present in many diseases, implying garlic has the ability to protect against them.
For now, however, Dr Rose says people must remember garlic is no ‘magic bullet’, although there are potential health benefits in consuming it.
Writing in the journal Trends in Pharmacological Sciences, he added: ‘I don’t think there is one individual plant species that is a cure-all.
‘But there are certainly plant species that are strongly associated with reducing disease risk within humans.
‘Variety is the spice of life, but understanding the chemistry of some of your spices is probably a very advantageous thing to do.’
Culled from www.dailymail.co.uk