The BRC/KPMG retail sales monitor for July says even seasonal products performed disappointingly, although sales went up during sunny spells.
KPMG head of retail Amanda Aldridge said: "Grocery sales growth has slowed, with the summer holidays and patchy performance of seasonal produce being key factors. But reports of a major slowdown are grossly exaggerated."
BRC director general Bill Moyes said: "The figures show sales slowing but remaining positive. However, consumer confidence remains an issue."
The July report shows like-for-like sales volume growth slipped to 3.8% from 4% in June and total sales growth fell to 6.5% from 6.9% the previous month.