When we re-published a Listener archive article in November about the health benefits of onions, it became one of the most read nutrition stories of the month, so here’s one we also “prepared earlier” about the humble onion’s close cousin, garlic, its health benefits and whether fresh is best.
Question:
Garlic appears a lot in the recipes that come with my food-delivery service. I gather garlic is good for our health. Is fresh better than the pre-crushed product in jars?
Answer:
Garlic (Allium sativum) is a vegetable with an intense aroma and powerful reputation. It’s also a potent antimicrobial that acts against bacteria, fungi and parasites, making it a favourite for marinating or preserving fresh meat. In the past, it was used as a traditional cure for various skin conditions. But of more interest in recent decades has been its antioxidant, anti-inflammatory and lipid-lowering properties.
For instance, clinical trials have shown garlic lowers cholesterol in people with high cholesterol levels. And in diabetic patients, adding olive oil to garlic reduced cholesterol and triglyceride levels, noted a review of garlic published last year. Research suggests garlic may reduce cardiovascular-disease risk and associated risk factors such as hypertension and diabetes.
Although garlic contains hundreds of different chemical compounds, it is the sulphur-containing ones that provide its potent aroma and are most likely responsible for many of its health-promoting properties. Allicin is the main organosulfur compound, and it has powerful blood-thinning properties. Allicin and the metabolites formed from it by our bodies are the subject of much research.
When garlic is crushed, allicin forms through a chemical reaction. An enzyme called alliinase is released from the cell walls when the garlic is crushed, and this then interacts with alliin inside the plant cells to form allicin. The more allicin in the garlic, the better it is for our health.
The choice is clear from a health perspective when comparing freshly crushed garlic with that found in commercially prepared products. A study published in the Journal of Agricultural and Food Chemistry found raw crushed garlic stored in water at room temperature loses half its allicin content within six days. When crushed garlic is stored in oil, it loses half its allicin within an hour. On the plus side, the allicin may have broken down into compounds that retain some blood-thinning properties. However, the degradation of allicin during storage results in reduced antimicrobial activity.
Light cooking has minimal effect – if the garlic is crushed before cooking. But the longer it is cooked and the higher the heat, the fewer beneficial compounds that will be left in the final dish. Microwaving probably destroys most of garlic’s blood-thinning effects, too.
So, to maximise health benefits, use fresh garlic, crush it before cooking and cook it only lightly.
Making good garlic great
Fresh garlic will keep for a long time in a cool, dark place, but don’t refrigerate it or place it near fresh ginger, which will dehydrate it.
Peel garlic cloves by pressing them under the flat side of a knife. Then either put the clove through a crusher or slice it finely, then crush with a knife blade before adding to a meal.
Add crushed garlic to recipes towards the end of cooking to limit the exposure to heat. Avoid microwaving garlic if possible.
This article was originally published in the Listener on March 6, 2021.
