It can be hard enough to make the right decisions when it comes to doing the weekly shop but it seems that your choice of shopping bag could be making a difference. A new study has shown that using a recyclable canvas shopping bag could increase the number of treats that make their way into your trolley. The research was carried out by Harvard and Duke University, who examined loyalty cardholder data from more than 142,000 shopping trips in one branch of a major supermarket chain in California. According to the Huffington Post, they also recruited volunteers that were divided into two groups - one that brought their own bag and one that didn't. It was found that people who took their own reusable bag into supermarkets were 33 per cent more likely to pick up unhealthy snacks than those who used shop-bought plastic bags. "Grocery store shoppers who bring their own bags are more likely to purchase organic produce and other healthy food. But those same shoppers often feel virtuous, because they are acting in an environmentally responsible way. "That feeling easily persuades them that, because they are being good to the environment, they should treat themselves to cookies or potato chips or some other product with lots of fat, salt, or sugar."