If the results can be translated to humans, anthocyanins extracted from blueberries and strawberries could find a role in the burgeoning weight loss and management market, estimated to already be worth $7bn (€5.2bn) globally.
"The recent findings that anthocyanins could possibly affect the development of obesity, at least in animal models, have generated considerable interest," explained the researchers, from USDA Arkansas Children's Nutrition Center and the University of Arkansas.
Lead author Ronald Prior reports in the Journal of Agricultural and Food Chemistry that the male C57BL/6J mice consuming a high-fat diet (45 or 60 per cent of calories from fat) and supplemented with the purified anthocyanin extracts from both berries gained significantly less body weight and body fat than the control animals.
Mice were fed a range of diets - low-fat (containing 10 per cent fat), or high-fat (45 or 60 per cent fat).
The diets were given with or without freeze-dried powders from whole blueberries (BB) or strawberries (SB) for 92 days or purified anthocyanin extracts from either berry for 70 days.
Prior and co-workers report that supplemental berries or extracts had no effect on weight gain, body weight, body fat, or body protein when consumed with a low-fat diet.
On the other hand, consumption of the purified anthocyanin extracts from strawberries and blueberries gained 13 and 34 per cent less body weight than the control animals, respectively.
Supplementing the high-fat diets of the animals with whole fruit extracts of blueberries was found to increase body weight gain and body fat, compared to control animals fed the same high-fat diet.
Supplementing the same diet with strawberry whole fruit extracts did not result in any significant differences in these measures, compared to controls.
"We chose to study the whole berry because that is what is most available and consumed," explained Prior.
"Our results with the whole berries in this study with strawberries and blueberries did not produce a significant protection against dietary fat induced obesity in the mouse model."
"What is not known is whether there are other factors in the berries besides anthocyanins that may either positively or negatively affect the development of obesity.
"Another major question is whether a single anthocyanin, and if so which one, is responsible for the effects observed previously or whether several anthocyanins have similar effects," he added.
With 50 per cent of Europeans and 62 per cent of Americans classed as overweight, the food industry is waking up to the potential of products for weight loss and management.
The slimming ingredients market can be divided into five groups based on the mechanisms of action - boosting fat burning/ thermogenesis, inhibiting protein breakdown, suppressing appetite/ boosting satiety (feeling of fullness), blocking fat absorption, and regulating mood (linked to food consumption).
Source: Journal of Agricultural and Food Chemistry Published online ahead of print, ASAP Article , doi: 10.1021/jf071993o "Whole Berries versus Berry Anthocyanins: Interactions with Dietary Fat Levels in the C57BL/6J Mouse Model of Obesity" Authors:
R.L. Prior, X. Wu, L. Gu, T.J. Hager, A. Hager,L.R. Howard