A recent study on weight gain found that the potato chip is the biggest cause of the pound-a-year creep that plagues many of us. The study found that chips added more weight than soda, candy, or ice cream.The New England Journal of Medicine analyzed changes in lifestyle and diet of more than 120,000 people, covering two decades.On average, participants gained almost 17 pounds over the 20 year stretch. Another relative of the potato chip, the french fry, was also a factor in significant weight gain.