Garlic

Health Benefits
(Source: World's Healthiest Foods, George Mateljan)

While garlic ranks as an excellent source of manganese and vitamin B6, a very good source of vitamin C and copper, and a good source of selenium, phosphorus, vitamin B1, and calcium in our WHFoods rating system, it is the sulfur compounds in garlic that serve as its spotlight nutrients in terms of overall health benefits. The sulfur-containing compounds in this allium vegetable have been shown to provide us with health advantages in a wide variety of body systems, including: our cardiovascular system, immune system, inflammatory system, digestive system, endocrine system, and detoxification system. We'll start with a quick look at these unique sulfur-containing compounds.

Sulfur-Containing Compounds in Garlic

The six categories of sulfur-containing compounds presented below will give you an initial look at the remarkable complexity of this allium vegetable. In terms of potential health benefits, each of these compounds has been studied fairly extensive. However, it is also worth noting here that the majority of studies have not focused on the presence of compounds in fresh garlic consumed as a food, but rather on garlic supplements, whether they be oils, tablets, powders, or other types of extracts.

  • Sulfur-Containing Amino Acids and Peptides

    • cysteine

    • methionine

    • S-allylcysteine

    • S-allylmercaptocysteine

    • glutathione

    • S-ethyl cysteine (SEC)

    • N-acetyl cysteine (NAC)

  • Thiosulfinates

    • allicin

    • allyl sulfinates

    • methyl allyl sulfinates

  • Sulfoxides

    • alliin

    • garlicins

    • methiin

    • isoalliin

  • Sulfides, Diallyl Sulfides and Polysulfides

    • hydrogen sulfide (H2S)

    • diallyl sulfide (DAS)

    • diallyl disulfide (DADS)

    • diallyl trisulfide (DATS)

  • Vinyldithiins

    • 1,2-vinyldithiin

    • dehydrovinyldithiins

  • Ajoenes

    • E-ajoene

    • Z-ajoene

While there are far more details here than can be covered in a summary food profile, we would like to point out two basic types of health benefits associated with these sulfur-compounds. First are the benefits associated with sulfur itself. Even though this mineral does not have public health recommendations associated with it and is not included as a DRI (Dietary Reference Intake) nutrient by the National Academy of Sciences, it is well-known to play a critical role in our health, especially in connection with cellular detoxification system, the health of our joints and connective tissue, and oxygen-related metabolism. It is important not to overlook this sulfur-richness of garlic since it is a property of garlic that is not found in most foods that we eat.

Second are the benefits associated with unique forms of sulfur in this food. At the top of the list here would be allicin and its breakdown products. As indicated above, allicin is a thiosulfinate. The most immediate breakdown products of this thiosulfinate are the diallyl sulfides and polysulfides (DAS, DADS, and DATS). But in the presence of other sulfur-containing groups called thiols, these sulfides can also release free hydrogen sulfide (H2S). This H2S may be involved in the cardiovascular benefits of garlic since it appears able to work synergistically with nitric oxide (NO) in optimizing blood vessel elasticity.

Cardiovascular Benefits of Garlic

Garlic provides us with cardiovascular benefits in a variety of different ways. In fact, so diverse are these different pathways for cardiovascular support that new studies keep discovering new ways in which garlic helps protect this body system. By far the best researched of these pathways are the antioxidant and anti-inflammatory properties found in this allium vegetable. Chronic unwanted inflammation is, of course, a special risk within our blood vessels since it can contribute to damage of our blood vessel walls, formation of plaque, and eventual clogging of our blood vessels. The vinyldithiins, diallyl polysulfoxides, and a sulfur-containing compound called thiacremonone have been most closely associated with the anti-inflammatory activity of garlic in our cardiovascular system.

Right alongside of this anti-inflammatory support is the antioxidant support provided to our heart and blood vessels through consumption of garlic. In this antioxidant category, the many forms of cysteine found in garlic have received special research attention, as have the presence of glutathione and selenium. Of course, it is also important to remember that garlic is an excellent source of the antioxidant mineral, manganese, and a very good source of vitamin C, another key antioxidant nutrient. Finally, it has been interesting to see how the generation of pyruvate from sulfur-based interactions in garlic might be linked with the antioxidant health benefits provided by this vegetable. Researchers have long been aware of the capacity of pyruvate—a highly common organic acid present in many metabolic reactions throughout the body—to provide us with antioxidant support. However, a more recent research focus has involved the generation of pyruvate from garlic whenever the alliin in garlic gets converted into allicin. Each time that this conversion process occurs (with the help of the enzyme called alliinase), there is a potential for two molecules of pyruvate to be formed. Formation of pyruvate during this chemical reaction may be important in the provision of antioxidant benefits from this allium vegetable.

Finally, it would be important to include the anti-platelet activity of garlic's ajoene molecules in this summary of its cardiovascular health benefits. Platelets are one type of blood cell, just like red blood cells or white blood cells. On average, however, platelets are about five times smaller than red blood cells, and one of their key functions is to prevent excessive bleeding by helping seal off cuts and wounds. Under certain circumstances, however, the platelets can begin to clump together in a way that can eventually present us with health problems in the form of an unwanted blood clot. Researchers have demonstrated the ability of garlic's ajoenes to decrease our risk of unwanted clotting due to excessive platelet clumping (called platelet aggregation).

All types of health benefits from garlic described above combine together to make this allium vegetable helpful in reducing our risk of numerous cardiovascular diseases. Including in this list are: heart attack (myocardial infarct), coronary artery disease (CAD), high blood pressure (hypertension), and atherosclerosis. In addition, it is worth noting that the everyday flexibility of our blood vessels has been shown to improve with intake of garlic.

Potential Changes in Cancer Risk Associated with Garlic Intake

Unfortunately, most of the garlic-cancer studies that we have seen fail to analyze intake of garlic in its natural food form. Instead, these garlic studies have focused on use of garlic supplements (like garlic oil softgels or garlic capsules/tablets containing powdered extracts). So we're at a disadvantage in drawing firm conclusions about cancer risk for people who enjoy garlic in their meal plans.

Among these supplement-focused studies, risk of digestive tract-related cancers seems most consistently impacted by garlic intake. In particular, risk of cancers in the upper digestive tract (including the mouth, pharynx, larynx, esophagus, and stomach) seems to be most commonly impacted.

Other Potential Health Benefits of Garlic

As mentioned in the section above, sulfur-containing compounds in garlic have been shown to support our body's detox processes, especially processes involving sulfur or the role of glutathione-S-transferase (GST) enzymes. Also of special interest in this detox area has been the potential role of garlic's allyl sulfides.

The antibacterial, antiviral, and antifungal properties of garlic are fairly well studied, although not necessarily within the context of human diseases and their development. And like the cancer studies on garlic, most of these antimicrobial studies have involved the use of garlic supplements rather than its food form. Due to the strong research interest in garlic and gastric cancer, several studies have examined the potential for garlic compounds to help prevent overgrowth of the bacterium Helicobacter pylori in the stomach or overadherence of this bacterium to the stomach wall. However, results in this area have been mixed. In several studies, the ajoenes present in garlic have been successfully used to help prevent infections with the yeast Candida albicans. We have also see a study showing the ability of crushed fresh garlic to help prevent infection by the bacterium Pseudomonas aeruginosa in burn patients.

One exciting new area of research involves the potential role of garlic to support bone health. As mentioned earlier in this article, the diallyl disulfides (DADS) in garlic have been identified as the garlic compounds that help protect our cardiovascular system from damage by cigarette smoke. With respect to bone health, studies have shown that cigarette smoking increases our risk of osteoporosis, inadequate bone mineral density, and inability to heal from bone fractures. Conversely, intake of garlic may be able to reduce risk of these problems by offsetting some of the potential damage caused by chronic exposure to cigarette smoke. Especially interesting in this context is the potential of garlic to help protect osteoblast cells from damage. Osteoblasts are bone cells that help produce new bone matrix. If garlic intake can help protect these cells from potential damage by cigarette smoke, it may be able to help support formation of new bone matrix and maintenance of existing bone structure.

A final promising area of research on the potential health benefits of garlic involves blood sugar regulation. One focus in this area involves a hormone released by our fat cells called adiponectin. When there is too little adiponectin in our blood, our risk of type 2 diabetes and certain cardiovascular problems gets increased. In what we would describe as preliminary studies, 12 weeks of garlic consumption has been shown to increase blood levels of adiponectin in human participants. Researchers believe that this process may be closely connected with simultaneous production of another key regulatory molecule called nitric oxide. While more follow-up studies are needed, these initial results show a potential for garlic intake to lower our risk of type 2 diabetes through what would be called hormone-related pathways. We have also seen a recent research showing significant decreases in fasting blood sugar levels following garlic intake. The authors of this research actually combined results together from seven previous studies to do a more robust analysis of the garlic-fasting blood sugar relationship. In their conclusions, these researchers suggested further confirmation of blood sugar impacts by examining other markers of blood sugar regulation including PPG (postprandial glucose, i.e., the amount of sugar in our blood following a meal) and hemoglobin A1C (the percent of red blood cells to which sugar becomes attached).

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