Garlic is a vegetable in the allium family and is therefore related to onions, leeks, scallions, and chives. It’s revered for its pungent and spicy taste, and it has been used since ancient times for medicinal purposes in Egypt, Greece, Rome, India, and China, as seen in medical texts. In ancient Greece, garlic was considered a “windy” food that could remove blockages in the body, and Olympic athletes used it to enhance performance. Romans also used garlic to aid strength and endurance in sailors. Other ancient uses of garlic included as a digestive aid in China, as well as heart disease and arthritis treatment in India. Native Americans treated flu-like symptoms with garlic tea.
These traditional uses of garlic were within reason as it has many biological activities including antibacterial, antifungal, antiviral, antiprotozoal, anti-inflammatory, antioxidant, anticancer, immunomodulatory, and antidiabetic activities. The main phytochemical in garlic is the sulfur-containing compound, allicin, which gives garlic its distinctive smell and taste. Allicin is produced when the garlic clove is crushed or injured, and the enzyme alliinase, which is separated by thin membranes, is able to come into contact with alliin. Garlic also contains the phytochemicals quercetin, rutin, and gallic acid.
Health Benefits of Garlic
Garlic benefits the cardiovascular system. According to a 2022 systemic review, garlic use can reduce blood pressure, total cholesterol, LDL cholesterol, triglycerides, and inflammatory markers, and it can increase HDL cholesterol. Additionally, a randomized controlled trial showed that crushed raw garlic (100 mg/kg body weight of study participants) twice per day for four weeks reduced aspects of metabolic syndrome, including blood pressure, triglycerides, fasting blood glucose, and waist circumference.
Another study involving obese patients found that supplementation with 400 mg garlic extract for three months reduced LDL cholesterol and weight, improved markers of endothelial function, and increased total antioxidant status compared to placebo.
Garlic is also shown to improve hepatic steatosis in non-alcoholic fatty liver disease (NAFLD), which can lead to liver disease and is considered a risk factor for cardiovascular disease. In a clinical trial involving 98 adults with NAFLD, participants were given a 400 mg garlic supplement twice daily or placebo for 15 weeks. Results showed that garlic powder consumption improved hepatic steatosis and reduced serum ALT and AST concentrations independent of weight loss, which was also observed. Garlic powder consumption also significantly reduced total cholesterol, LDL cholesterol, triglycerides, fasting blood sugar, and HbA1C compared to placebo.
Another health benefit of garlic is its anti-cancer activity, especially for cancers of the digestive system. A 2022 systemic review and meta-analysis concluded that garlic intake reduces risk of gastric cancer and colorectal cancer. Potential mechanisms involve sulfur compounds in garlic and their role in the regulation of the cell cycle, apoptosis, and migration inhibition in tumor cells. Garlic also has antibacterial effects, and fresh garlic inhibits H. pylori activity in the stomach. H. pylori causes gastritis and contributes to the development of gastric cancer and peptic ulcer disease.
Garlic Intolerance
FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) are non-absorbable, osmotic short-chain carbohydrates that are fermented by bacteria in the small intestine, contributing to digestive symptoms. Garlic falls under the oligosaccharide group, and it contains fructooligosaccharides (fructans) in particular. Some individuals are sensitive to garlic and experience symptoms like gas, abdominal pain, and diarrhea after consuming it. However, because fructans are water-soluble, whole garlic gloves can be sauteed in oil and removed before consuming to add flavor to dishes.
The low FODMAP diet is often used for irritable bowel syndrome (IBS) treatment. However, rather than avoiding all foods containing FODMAPs, a more long-term approach is to repair gut damage and restore gut health. It should be noted that the low FODMAP diet should only be followed for several weeks as it is not suitable for long-term use due to nutrient deficiencies when foods are avoided over the longer term.
How to Use Garlic
Garlic comes in three main forms – fresh, dried, and aged. Aged or black garlic is fermented at medium heat and high humidity for 30-40 days, and the result is a sweeter tasting garlic due to the reaction between sugar and amino acids during the Maillard reaction. Despite being lower in allicin compared to fresh garlic, black garlic has strong antioxidant effects, though it is lower in anti-inflammatory and immunomodulatory activities compared to fresh garlic. Black garlic retains antioxidant activity because more stable compounds are formed, such as S-allyl cysteine (SAC). Notably, prolonged high temperatures could decrease the bioactive compounds in black garlic.
Alliinase activity is influenced by temperature, time, processing, pH, and the food matrix. Because heat destroys alliinase, allicin metabolites are decreased in garlic during cooking. However, allicin formed before cooking remains stable, and it may be best to allow fresh garlic to sit for up to 10 minutes after crushing to maximize antioxidant activity before cooking. Because garlic powder is dehydrated, pulverized garlic, it has similar alliinase activity to fresh garlic, though alliin content can vary by product, and much of the research on garlic powder uses capsules or tablets.
Garlic that is chopped before jarring in oil or acid – as seen in commercial garlic products – is shown to have relatively high amounts of allyl polysulfides, which form due to the breakdown of allicin and are suggested to be responsible for many of the health benefits of whole garlic. Similarly to allicin, allyl polysulfides are metabolized to allyl methyl sulfide, which is used as a quantifiable metabolite to measure allicin bioequivalence.
For therapeutic effects of garlic, it’s recommended to consume 2-4 g of crushed raw garlic daily. If using other garlic products, it’s estimated that to obtain the same equivalence of allicin as 2 g of raw garlic, one would need to consume 11 g of boiled garlic, 5.9 g of roasted garlic, 8.5 g of acid-minced garlic, or 5.3 g of oil-chopped garlic. A personalized approach is recommended based on individual circumstances.
Here is a list of different ways to incorporate garlic into the diet:
- Use fresh, raw garlic in salad dressings and sauces, like chimichurri and pesto
- Add crushed garlic to dishes like soups, stews, and stir fries
- Combine garlic with fish high in omega-3 fatty acids, as these two together have been shown to favorably improve blood lipids
- Sprinkle garlic powder on roasted vegetables or kale chips
- Add fresh or dried garlic to tomato-based dishes to increase lycopene bioavailability
- Cook with the power-packed duo of onion and garlic, which both have active sulfur compounds that may help with blood sugar balance
- Experiment with black garlic in sauces, marinades, and even cookies
- Make garlic tea with lemon or lime and honey
- Include garlic and honey to be synergistic in antibacterial activity
- Save garlic skin, which contains phenolic compounds, to use in homemade broths
Store fresh garlic in a cool, dark place with air circulation. Though many people discard sprouted garlic, it may have higher antioxidant activity after sprouting. Garlic powder should also be stored in a cool, dark place. As with other spices, portion garlic powder to a separate container before using it over a steaming dish, and discard the product if there is clumping or caking to minimize exposure to mycotoxins from mould.
If you have questions about which herbs, spices, or foods can best support your health, talk to your naturopath, doctor, nutritionist, or another qualified healthcare team member for personal options based on your circumstances. Garlic may interact with some medications including anticoagulants, so consult your pharmacist if taking any prescription drugs.
The above information is courtesy of Deanna Minich