Those birthday cupcakes your co-worker brought in may be a kind gesture, but not when it comes to your health. While you’re sitting with healthy snacks in your desk drawer, your workplace is being bombarded with enticing, unhealthy foods brought in by co-workers, sales reps and perhaps even your boss. If you indulge, you could be eating over 1,000 calories a week, a new study suggests.

Researchers at the CDC, the Centers for Disease Control and Prevention, looked at what over 5,000 people ate and drank at work, using information from a U.S. Department of Agriculture Food Acquisition and Purchasing Survey.

That 1,000 or so extra calories a week from “just eating a little bit” of the free food brought into your workplace could amount to a 15-pound weight gain in a year.

The food people reported eating at work at least once a week was brought into the workplace for meetings and social events, left in common areas or purchased from vending machines or cafeterias. This workplace eating contributed nearly 1,300 calories, typically empty calories — calories from added sugars and solid fats — to their diets. Much of the food was high in sodium and refined grains. Whole grains and fruit were far less common.

Over 70 percent of the calories came from food that was free. In other words, the roughly 25 percent of the people eating at work didn’t buy food in a vending machine. It was there for the taking.

“To our knowledge, this is the first national study to look at the food people get at work,” said Stephen Onufrak, a CDC epidemiologist. “Our results suggest that the foods people get from work do not [reflect] the recommendations in the Dietary Guidelines for Americans.”

Employers can change this. Worksite wellness programs could promote healthy foods that are also appealing to employees. Company policies could ensure that food provided in cafeterias or vending machines follow the Dietary Guidelines for Americans. Healthy foods could be served at meetings and social events. Companies that need help implementing such policies would benefit from the services of a registered dietitian/nutritionist.

According to Onufrak, worksite wellness programs could potentially reach millions of people, and they have been shown to be effective at changing health behaviors, which, in turn, reduces employee absences and health care costs.

In the meantime, if you notice your weight is creeping up, keep in mind that 1,000 extra calories a week from “just eating a little bit” of that free food brought into your workplace could amount to a 15-pound weight gain in a year.

The research was presented at the American Society for Nutrition’s annual meeting.