A new study has found that polyphenols, dietary substances from vegetables, fruits and green tea, bring about a change in the energy metabolism by increasing the fatty acid breakdown and influence the glucose use in fat cells as they can stimulate energy-sensing regulatory protein SIRT1.
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.
The study was conducted by Vincent de Boer at RIKILT - Institute of Food Safety in Wageningen, Netherlands.
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.
As part of the study, Boer examined rats to study the mechanisms and effects of a polyphenol-rich diet. Relevant polyphenol metabolites that are found in humans called Quercetin were also examined.
Quercetin is a polyphenol that is highly abundant in the human diet, such as onions, apples and tea.
Boer found that lung cells had a greater fatty acid catabolism if the rats 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.
Boer found that the SIRT1 activity can be stimulated by various polyphenols, particularly those 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.
Boer concluded that 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.