vidence suggests that consumption of berries may confer protection against cardiovascular disease. Berries such as blackberries (Rubus subgenus Rubus), raspberries (Rubus ideaus) and black currents (Ribes nigrumare) good sources of flavonoids, and some evidence suggest that these compounds may modulate oxidative production in humans. Because oxidative stress is associated with cardiovascular disease, this may be the mechanism by which they confer protection. However, berries are also able to modulate plasma levels of lipoproteins. This suggests that berries can correct the abnormalities seen in the metabolic syndrome which are the likely cause of dyslipidaemia. However, it is unclear how flavonoids could affect the plasma levels of cholesterol. Therefore other constituents of berries might be responsible for their lipid modulating effects. For example, berries are also rich sources of fibre which is known to favourable lower cholesterol levels in mammals, including humans.
One of the mechanisms by which fibre might alter plasma levels of cholesterol is through production of short chain fatty acids. Short chain fatty acids are produced in the colon of mammals from fermentation of dietary fibre, and include butyrate, propionate and acetate. These short chain fatty acids are then absorbed, where they are thought to favourably modulate hepatic cholesterol production, thus altering the cholesterol content of lipoproteins. Research has investigated the fermentation of berries in rats in order to determine their effects on short chain fatty acid production. In one study1, rats fed a variety of berries had changes to their colonic microflora indicative of short chain fatty acid production. Blackcurrants increased short chain fatty acid production including propionic and butyric acid, increased faecal wet and dry weight and also increase caecal tissue mass, when compared to blackberries or raspberries.
The researchers concluded that the effects of blackcurrants were likely due to the higher concentrations of mannose containing polymers and higher fibre content compared to blackberries or raspberries. In contrast, raspberries and blackberries contain higher concentrations of glucose, uronic acid and xylose polymers. The dietary fibre would likely increase colonic bacteria fermentation rates and subsequently increase production of short chain fatty acids. The presence of short chain fatty acids in the colon can decrease colonic pH and this increases growth rates of certain species of colonic bacteria and alters colonic diversity and numbers. No anthocyanins were detected in the colon supporting previous work that shows that absorption occurs in the stomach or small intestine. It is therefore unlikely that anthocyanins could account for the changes seen in the colon of the rats, although they may benefit health in other ways.