US natural foods grocer Whole Foods Market has said that second-quarter profits dropped 13% on costs associated with its US$565m acquisition of Wild Oats last August.

Net income slid to $40m in the three months to 13 April, down from $46m posted for the comparable period a year ago. During the quarter, the group said charges related to the Wild Oats acquisition totalled $8.6m, or 6 cents a share.

Sales increased by 28% to $1.9bn, up from $1.4bn, while sales at stores open a year or more rose 6.7%. However, the Austin-based retailer left its full-year sales guidance unchanged.

Whole Foods said it has so far rebranded 27 Wild Oats stores. At these stores, sales have increased 12%, the company added.

"We are continuing to produce higher sales, comps and sales per square foot than our public competitors, and the results in our core stores are strong," said John Mackey, chairman, CEO, and co-founder of Whole Foods Market.