Lingonberries 'could prevent weight gain' They were then divided into groups, where all except a control group were fed a type of berry - lingonberry, bilberry, raspberry, crowberry, blackberry, prune, blackcurrant or açai berry. When the mice were compared after three months, the lingonberry group had "by far the best results," the researchers said. The mice that had eaten lingonberries had not put on more weight than the mice that had eaten a low-fat diet - and their blood sugar and insulin readings were similar to those of the "low-fat" mice. Their cholesterol levels and levels of fat in the liver were also lower than those of the animals who received a high-fat diet without any berries. Blackcurrants and bilberries also produced good effects, although not as pronounced as the lingonberries. The good results from lingonberries may be due to their polyphenol content, according to the researchers, who are continuing work to understand the molecular mechanisms involved in their effect, while studying whether the effect can be observed in humans. Karin Berger, a diabetes researcher at Lund University, said: "Up to 20 per cent of our mice's diet was lingonberries. It isn't realistic for humans to eat such a high proportion. "However, the goal is not to produce such dramatic effects as in the "high-fat" mice, but rather to prevent obesity and diabetes by supplementing a more normal diet with berries." She added: "In our study, the açai berries led to weight gain and higher levels of fat in the liver." The researchers warned against eating large quantities of lingonberry jam, because boiling the berries can affect their nutrient content and jam contains a lot of sugar. They recommended eating frozen lingonberries on cereal or in a smoothie.