This review provides an insight into the evidence suggesting that plant polyphenolic compounds (natural, synthetic or semi-synthetic organic chemicals that have multiple phenol units in their structure) play a significant role in the treatment of metabolic syndrome. Many studies have proven that a relationship exists between diet and metabolic syndrome. The effects of plant polyphenols, which are usually obtained from fruits, on various metabolic disorders are thus being investigated. This review examines the role of the following plant polyphenols: resveratrol, quercetin, epigallocathechin -3-gallate, and curcumin.
Metabolic syndrome is a leading disorder worldwide. It is a predisposing factor in the development of cardiovascular diseases. An obese person with excess fat stored in the abdomen suffering from any two of the following health complications: diabetes, high blood pressure, high cholesterol and high triglycerides, is said to be suffering from metabolic syndrome. Diabetes, high blood pressure, high cholesterol, high triglycerides and obesity are all interlinked. The energy obtained from food is used in maintaining and supporting the basic functions of the body and excess energy is stored as fat in the adipocytes or fat cells. These adipocytes release cytokines (proteins that are mediators and regulators of inflammatory processes) and other hormones that affect the blood circulation system. When released in excess, these cytokines (like interleukins, tumor necrosis factor-a) and hormones (like resistin, leptin, and adiponectin) act as modulators of cardiovascular diseases. Sirtuin molecules prevent the proliferation of adipocytes and increase the release of insulin, thus regulating the energy levels.
This review is based on publications reporting studies on polyphenols and the metabolic syndrome from the MEDLINE database. Publications with information on individual polyphenols were sought. The referenced articles found in the original articles were also reviewed. Information on ongoing trials with polyphenols was obtained from the clinical trials database at the website www.clinicaltrials.gov. Data on resveratrol, quercetin, epigallocathechin-3-gallate and curcumin was collected. Information on polyphenol combinations found in teas, grape products, chokeberries, coffee and chicory, cocoa, cinnamon, bitter melon, and other plant products was also reviewed.
* Resveratrol is found in grapes and other berries. These activate sirtuins and decrease the accumulation of fat. They also inhibit the conversion of glucose to lipids. A study was conducted on obese rats, in which they were fed a resveratrol-rich diet. These rats were found to have lower blood pressure, and lower glucose and insulin resistance. Results are being awaited from a human trial, which was completed in Washington recently.
* Quercetin, found in many fruits and vegetables, has been found to reduce glucose and lipid levels in obese rats. A human trial was performed on 93 individuals with metabolic syndrome. Those who consumed quercetin were found to have a lower blood pressure with little change in lipid levels.
* Epigallocathechin-3-gallate, found in tea, was shown to affect insulin secretion and maintain blood pressure in rats. A human trial with 100 obese individuals was conducted. It was found that those who consumed epigallocathechin-3-gallate had a small decrease in their blood pressure.
* Curcumin is found in turmeric and has been shown to reduce weight, and reduce cholesterol in some animal studies.
* Green tea and black tea were found to reduce glucose levels, body weight, and triglyceride levels in diabetic rats. In human beings, green tea has been found to improve blood flow in brachial artery, reduce triglyceride levels, and lower the glycosylated hemoglobin level.
* Grape seed extract was found to significantly decrease the blood pressure in 27 individuals with metabolic syndrome. It was also associated with lowered triglyceride levels in 44 women.
* Chokeberries were also associated with significant reduction of triglycerides, cholesterol and glucose in rats fed with high-cholesterol and hyperglycemic food.
* Indefinite results were obtained from the use of coffee, chicory, cocoa, cinnamon and bitter melon extract in trials.
Metabolic syndrome is a chronic disorder. The studies reviewed were of a very short duration. They do not sufficiently provide any conclusive evidence. Questions on when to administer the polyphenols and the age group of patients to be treated have not been answered. The human pharmacokinetics (how these phenols are metabolized in the body) have not been studied in all the compounds.
Studies on the etiology and course of metabolic syndrome have shown that plant polyphenols can be used as a treatment option. This review concludes that polyphenols exert a positive influence on the glucose and cholesterol levels in metabolic disorders. This research provides hope for future studies on polyphenols. Carob pulp, kudzu root, and amla have also been found to play a beneficial role in the treatment of metabolic syndrome. New formulations of polyphenols may also be found and investigated. The combination of individual polyphenols like resveratrol and quercetin was found to show a better effect. Future studies testing the effects of a wider variety and combinations of polyphenols are suggested.
For More Information:
Polyphenols: Planting the Seeds of Treatment for the Metabolic Syndrome
Publication Journal: Nutrition, 2011
By E. Paul Cherniack; Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida and Bruce W. Carter Veterans Affairs Medical Center, Miami, Florida
*FYI Living Lab Reports Are Summaries of the Original Research.