The use of garlic (Allium sativum) and other members of the genus Allium span thousands of years (Rivlin, 2001). Today garlic, a well-known culinary herb, is cultivated across the globe. Humans have had an interest in the potential medicinal benefits of garlic since recorded time, as garlic is "one of the earliest documented examples of plants employed for treatment of disease and maintenance of health" (Rivlin, 2001). The traditional uses of garlic, taken in numerous forms (and by various means) for its medicinal properties are vast. According to the Natural Medicines Comprehensive Database, garlic has been used in the treatment of such disparate conditions as respiratory disorders, alopecia, tooth pain and warts (n.d.). Indeed, "modern science is tending to confirm many of the beliefs of ancient cultures regarding garlic, defining mechanisms of action and exploring garlic's potential for disease prevention and treatment" (Rivlin, 2001).
The antimicrobial and bacteriostatic properties of garlic are widely recognized (Guzeldag, Mercimek & Matyar, 2014) prompting garlic's use in food preservation by ancient Chinese and Japanese cultures (Rivlin, 2001). The antibacterial activity of allicin, "one of the active principles of freshly crushed garlic homogenates," has been reported to inhibit a broad range of both gram-negative and gram-positive bacteria, “including multidrug-resistant enterotoxicogenic strains of Escherichia coli” (Ankri & Mirelman, 1999). Additionally, garlic and other Alliums help promote populations of healthy intestinal flora (Short, 2016a).
Gastrointestinal lesions, "such as gastric ulcers, duodenal ulcers and gastric cancers" have been strongly associated with infection by Helicobacter pylori (H. pylori) (Iimuro, et al., 2002). In fact, H. pylori, a gram-negative bacterium, is "the first formally recognized bacterial carcinogen" as well as "one of the most successful human pathogens" (Kusters, van Vliet & Kuipers, 2006). The standard H. pylori treatment regimen involves two antibiotics, most commonly amoxicillin, clarithromycin, and metronidazole, and a proton pump inhibitor (PPI) (Moghadam, Navidifar, & Amin, 2014). Unfortunately, "these therapies have several inherent problems, including the appearance of resistance to the antibiotics used and associated adverse effects, the risk of re-infection and the high cost of antibiotic therapy" (Ayala, Escobedo- Hinojosa, de la Cruz-Herrera & Romero, 2014).
According to a review by Ayala, et al. (2014), because the development of a vaccine to prevent or eradicate H. pylori has been slow to emerge, efforts to research new therapeutic approaches has prompted the investigation of various alternative and complementary therapies to treat infection by the pathogen, including the use of garlic. Indeed, the "in vitro anti-H. pylori activity of garlic, in the form of extracts and compounds, have been well documented," with only a few studies reporting a negative result (Ayala, et al., 2014).
Efforts by Guzeldag, Mercimek, & Matyar (2014) demonstrated the efficacy of extracts of fresh, organically grown garlic on the inhibition of H. pylori, in vitro. The positive results of the study led the authors to contend that garlic extracts are capable of producing levels of inhibition of the pathogen on par with commercially available materials and, that fresh garlic extracts may provide an economical and viable means of developing novel ways of preventing or eradicating the infection in vivo. Guzeldag, et al. (2014) conclude "further investigations are necessary because the effectiveness of these inhibitions may be related to the type of garlic or may be affected by the solubility and rate of diffusion in medium.”
The objective of research by Moghadam, et al. (2014) was to determine the antimicrobial effects of fresh garlic juice on multi-drug resistant strains of H. pylori, in vitro. The study results demonstrate that fresh garlic juice was able to inhibit the growth of drug-resistant H. pylori strains, in the laboratory setting. These results suggest a potential use of fresh garlic as a complement to pharmaceutical antibiotic therapy for in vivo treatment of drug-resistant strains of the bacteria. The authors conclude "the combination of garlic and commercial antibiotics might increase the chance of treatment of peptic ulcer disease" (Moghadam et al., 2014).
An investigation by Jonkers, et al. (1999) involved the testing of a hypothesized synergistic effect in the inhibition of H. pylori with garlic and pharmaceutical antibiotics, and garlic and a PPI drug (omeprazole). The study used both pulverized raw garlic and commercially available garlic powder tablets. Garlic was found to have a growth inhibitory effect on H. pylori, and, a synergic effect observed for the combination of garlic and omeprazole. These results suggest a potential role for garlic in a reduction of the use of pharmaceutical antibiotic treatment for H. pylori infection. Although the research by Jonkers, et al. was published in 1999, it appears to be the most recent of several investigations which demonstrate the potential complementary role of garlic, in one form or another, in the treatment of H. pylori infections in humans. Unfortunately, the results of the limited in vivo studies undertaken have been disappointing and indicate that the viability of the bacterium remains unaffected with garlic (Ayala, 2014).
Animal studies have shown limited success using garlic in the treatment of H. pylori. A frequently cited 2002 study by Chinese researchers, Iimuro et al., involved an investigation of the effect of a garlic extract on Mongolian gerbils inoculated with H. pylori. Four hours after inoculation with a broth containing the bacteria, designed to induce gastritis, the gerbils were fed garlic extract in doses of 1, 2 and 4% for six weeks. At the end of the experiment the animals were euthanized, and their stomachs examined for evidence of gastric disease. The results indicated that a dose-dependent relationship between administration of the garlic extract and a reduction in H. pylori-induced gastritis, prompting the researchers to conclude that "garlic extract may suppress the early stage of H. pylori-induced gastritis" (Iimuro et al., 2002) in the animals.
As articulated by Sivam (2001), though over 2,000 studies on the chemical and biological effects of garlic have been published, this fact may erroneously provide an impression that the medicinal uses of the plant have been well examined and that there are challenges to research in this area due to the inclusion in research of garlic products of undefined composition. “Few studies have used a chemically characterized product” and, because “the composition of garlic depends on the source, age, storage conditions, type of processing and method of consumption” (Sivam, 2001) various forms of the plant are referred to as ‘garlic’ in published literature. Additionally, Sivam reminds readers that “the amount and composition of organosulfur compounds vary within different strains of garlic, and the problem is compounded by the volatile and reactive nature of these compounds” (Sivam, 2001). As noted by Ulbricht (2013), “Overall, studies in humans show no effect of garlic on gastric or duodenal ulcers” however, “preliminary human studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of developing several types of cancer, including gastric and colorectal malignancies”.
Due to the aforementioned issue regarding variations in garlic research methodologies, and the because of the inconsistent results between the effects of garlic on H. pylori in the laboratory and the clinical settings, a more efficacious use of garlic in regard to gastric health may be the plant’s role in the prevention of disease. As infection with H. pylori is indicated in the pathogenesis of several gastric diseases, including gastric cancer and mucosa associated lymphoid tissue lymphoma (MALT) and “these ailments can be avoided if the infection by the bacteria can be prevented” (Ayala et al., 2014), several studies on the preventative effects of garlic on gastric cancer has been undertaken. A 2011 meta-analysis of cohort and case-control studies by Zhou et al. determined that the intake of allium vegetables in the diet exhibited chemopreventive effects and “that high levels of Allium consumption reduced risk for gastric cancer” (Zhou et al., 2011). However, the study’s authors caution that potential for the existence of confounding factors and exposure misclassification exists and “further studies are required to establish this association” (Zhou et al., 2011).
As noted by the World Health Organization, fruits and vegetables are “important components of a healthy diet, and their sufficient daily consumption could help prevent major diseases” ("Diet and Physical Activity," n.d.); indeed, all populations can benefit from consuming adequate amounts of these foods. In addition to consuming sufficient daily amounts of fruits and vegetables, patients concerned about, or at increased risk for, developing gastric cancer should be encouraged to include more dietary sources of Alliums to take advantage of the chemoprotective properties of the members of the genus. Crushed garlic cloves are rich in beneficial organosulfur compounds (OSCs), thought to be the active principles constituents responsible for the many of its beneficial health effects (Schäfer & Kaschula, 2014). Due to the volatile nature of OSCs, alterations occur during cooking, making fresh, unprocessed garlic the preferred form for dietary consumption (Schäfer & Kaschula, 2014). Patients wishing to take garlic in dietary supplement form should be advised that the acid environment of the stomach destroys some of the health promoting constituents of garlic therefore, an enteric coating on garlic powder tablets or capsules can help retain the bioactivity of the product (Bone & Mills, 2013).
The ultimate determinate of effective nutrition education is behavioral change, however, behavior change is “an ongoing process rather than a single event” (Short, 2016b). Various models of behavioral change theory exist. "Stage theories specify an ordered set of 'stages of readiness to change' into which people can be classified and identify the factors that can facilitate movement from one stage to the next” (Horwath,1999). The Transtheoretical Model (TTM) involves "stage-matched interventions and proactive recruitment procedures” (Prochaska & Velicer, 1997). TTM “posits that health behavior change involves progress through six stages of change: precontemplation, contemplation, preparation, action, maintenance, and termination” (Prochaska & Velicer, 1997).
Through asking a patient questions relevant to a health behavior change a healthcare provider can assess a patient’s current stage related to the behavior change in question; subsequent questioning, appropriate to the patient’s current stage, can help the provider individualize counseling on the desired health behavior change (Short, 2016b). With TTM healthcare providers can help patients to recognize the value of including garlic and other Alliums in their diet, aid them in setting goals to achieve the behavior and assist them in attaining those goals and maintaining the behavior. Ultimately, patients will realize the health related benefits of doing so.
References Cited
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Short, J. (2016b). Behavior Change Theories. Course presentation, Natural Therapies: Herbology and Detoxification at Logan University.
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