Operating expenses at Killingly-based United Natural Foods grew by nearly $12 million to $108 million in the fourth quarter of this year, a 12 percent increase from the same period in 2006. The company cited increased fuel and insurance costs and start-up expenses at new distribution facilities in Florida and Washington for the expense increase. In the same period, net income grew by 3.5 percent to $13.1 million from $12.7 million last year. The company’s net sales increased by 14 percent to $706.8 million from $620 million in Q4 2006.