Everyone loves a bargain. They're hard to resist. From Groupon to your local grocery store, couponing is a great way to get a deal — unless that coupon is for food. Then it can have a seriously unhealthy downside.

Think about the sorts of groceries you can buy with coupons. Coupons for fresh, unprocessed, healthy foods are a rarity, while coupons for processed snack foods, candies, beverages, and cereals are common.

Many grocery stores offer online coupons shoppers can print at home and use in the store or redeem with store loyalty cards. Because coupons are designed to influence what consumers buy at the grocery store, they encourage the purchase of unhealthy foods.

Over a four-week period researchers in California found over 1,000 coupons available online from six national grocery stores. They analyzed them according to food categories.

Twenty-five percent of the coupons were for chips and other snack foods, candies, and desserts. Coupons for prepared meals made up another 14 percent, with coupons for beverages, half of which were for sodas, juices, and sports/energy drinks, were another 12 percent. Eleven percent of the coupons were for breakfast cereals.

The numbers for fresh, unprocessed foods were dismal — less than one percent for fruits and only three percent for vegetables. Unprocessed meats accounted for another one percent of coupons.

Food prices influence the choices shoppers make at the grocery store, according to Andrea Lopez and Hilary K. Seligman of the University of California, San Francisco Center for Vulnerable Populations. Government data demonstrates that as the cost of snacks decreases, consumption increases.

And on a more healthful note, other studies show that lower prices and economic incentives tend to lead to an increase in consumption of fruits and vegetables.

There are two big reasons why it's rare to see coupons for produce: First, the price of fresh fruits and vegetables is difficult to forecast due to changing market conditions; and second, unsold fruits and vegetables cost supermarkets $15 billion a year. The losses associated with spoiled produce are an accepted cost of the grocery business.

“Coupons influence consumer purchases both by discounting price and by acting as an ‘informational stimulant,’ reminding consumers of the product,” Lopez and Seligman write. “Grocery retailers may be uniquely positioned to positively influence Americans’ dietary patterns.”

Offering coupons for perishable food items may have benefits for both consumers and retailers — healthier food for consumers and less waste for retailers. Grocery stores could become promoters of healthy eating by simply tweaking the types of coupons they offer customers, particularly now that they can put up online specials in an instant.