Health effects of polyphenols

May 15 2007

Polyphenols, dietary substances from vegetables, fruits and green tea, bring about a change in the energy metabolism.

Dutch researcher Vincent de Boer has discovered that polyphenols increase the fatty acid breakdown in rats and influence the glucose use in fat cells.

De Boer carried out his doctoral research at RIKILT - Institute of Food Safety in Wageningen. Much research into the health effects of polyphenols is carried out in vitro. However in the body, polyphenols are quickly and easily converted into polyphenol metabolites. This research was carried out with rats to study the mechanisms and effects of a polyphenol-rich diet. Relevant polyphenol metabolites that are found in humans were also examined.

Quercetin is a polyphenol that is highly abundant in the human diet, such as onions, apples and tea. The study revealed that quercetin metabolites mainly end up in the lungs of rats. Subsequently De Boer discovered that lung cells had a greater fatty acid catabolism if the animals constantly received quercetin in their feed.

The energy-sensing protein SIRT1 is an important regulatory protein that can prolong the life span of model organisms such as yeast and fruit flies. In humans, SIRT1 is possibly involved in the regulation of energy use. The SIRT1 activity can be simulated by various polyphenols. De Boer discovered that polyphenols from green tea stimulated the activity of isolated SIRT1. The quercetin molecule also did this, but an important human quercetin metabolite had the opposite effect. Therefore in intestinal cells, quercetin had no effect on the activity of SIRT1. In experiments with fat cells, both quercetin and a quercetin metabolite were found to change the glucose use in the fat cell.

A change in the energy regulation might be an important process for the realisation of possible health effects of polyphenols in the food. This provides new starting points for further research into the molecular mechanisms of polyphenols. This will allow the health effects of polyphenols to be accurately described.

Polyphenols are substances of plant origin that occur in numerous fruits and vegetables. Due to their possible health effect, polyphenols are currently sold as nutritional supplements. Yet the scientific basis for the health claims for polyphenols is mostly weak. Results from in vitro studies are often directly translated into possible beneficial health effects in humans. De Boer’s research shows that in vivo research with polyphenol metabolites is necessary to study the effects of polyphenols.

Vincent de Boer recently received a Rubicon fellowship from NWO for his new research into the role of mitochondrial SIRT1 analogues in aging and energy metabolism. He will carry out his research at the Department of Pathology at the Harvard Medical School in Boston.