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Guarana antioxidant capability trumps that of green tea, study finds

By Will Chu , 23-Aug-2016
Last updated on 23-Aug-2016 at 14:03 GMT2016-08-23T14:03:19Z

The guarana (Paullinia cupana) plant's flavanol content far exceeds that of traditional green tea. ©iStock/artpritsadee
The guarana (Paullinia cupana) plant's flavanol content far exceeds that of traditional green tea. ©iStock/artpritsadee

Seeds of the native Brazilian shrub guarana have been found to contain antioxidant levels more than ten times that of green tea.

Details of the guarana (Paullinia cupana) plant, which appear in the Royal Society of Chemistry’s journal Food and Function, reveal that its flavanol content far exceeds that of traditional green tea.

Further results have demonstrated favourable antioxidant enzyme activity (superoxide dismutase, catalase and glutathione peroxidase) and lower biomarker levels of oxidative stress in healthy overweight subjects.

Guarana is a shrub native to the Amazon and its seeds have long been used as a stimulant. Today guarana consumption is widespread in the form of supplements and shakes.

Nutrient studies have essentially focused on the stimulant properties of guarana seeds due to its high caffeine content and it is now widely used in energy drinks.

However, the seed’s polyphenol content is often overlooked especially as they contain a rich source of phytochemicals with catechins, epicatechins and proanthocyanidins as its most abundant compounds.

In this study, the effects of guarana on antioxidant markers and antioxidant enzyme activities in individuals were assessed over a month-long period.

The team also looked at the bioavailability of catechins and their metabolites, as the accepted phytochemicals responsible for the biological effects.

Superior guarana

Subjects were given guaraná powder and asked to consume one bottle every morning before breakfast at home.©iStock

Researchers from the University of São Paulo's Public Health School (FSP-USP), selected 12 subjects aged 20–65 with a BMI of between 25 and 30 kg m2.

The month-long study was conducted in two stages. First, subjects were instructed to continue with their normal diet and lifestyle. They were asked not to drink alcohol or consume anything containing guarana for that month.

Blood samples were taken from the subjects on day one and 15 after an overnight fast. Once done, subjects consumed a 300 ml guarana drink.

A second blood sample was taken an hour later and subjects received a breakfast meal and were asked to fill out a questionnaire.

Between day one and 15, subjects were given guarana powder and asked to consume one bottle every morning before breakfast at home.

Researchers then measured the subjects' absorption of catechins and their metabolites and looked for signs of stress markers including oxidation of ‘bad cholesterol' low-density lipoprotein (LDL).

Oxidation of LDL can cause atherosclerosis and increase the risk of cardiovascular disease.

They also performed tests to inspect DNA damage due to oxidative stress.

In the subjects, blood cell DNA in blood samples taken one hour after guarana consumption was in better shape than expected suggesting the existence of an effective antioxidant compound or a boost in performance of the blood cell’s enzyme antioxidising capabilities.

Coffee commonalities

The researchers thought that guarana compounds followed a similar mechanism to that of phenolic compounds found in coffee. ©iStock

"All these markers depend on the presence of catechins in the bloodstream," said Lina Yonekura, the study’s lead author and assistant professor at Kagawa University's School of Agriculture in Japan.

"The improvement in the parameters we assessed was associated with a rise in the concentration of plasma catechins after guarana intake, showing that guarana was indeed responsible for this effect."

The team thought it plausible that the increase of catalase and glutathione peroxidase activities observed in the study followed a similar mechanism to that of phenolic compounds from coffee, which also increased the activity of these antioxidant enzymes.

The team’s view is supported by previous studies that identify epicatechin as a preventer of stroke damage via a pathway known as Nrf2.

This pathway has been shown to regulate the expression of antioxidant proteins that protect against oxidative damage triggered by injury and inflammation. Flavonoids too have been shown to be moderate Nrf2 activators.

“The activation of Nrf2 and subsequent processes leading to an increase in detoxifying and antioxidant enzymes may partially explain the health effects of phytochemicals with fast clearance rates and low plasma concentration such as catechins,” the study noted.

Source: Food and Function

Published online ahead of print, DOI: 10.1039/c6fo00513f

“Bioavailability of catechins from guaraná (Paullinia cupana) and its effect on antioxidant enzymes and other oxidative stress markers in healthy human subjects.”

Authors: Lina Yonekura et al.

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