The cost of a basket of groceries increased by 1% in July, the second consecutive increase after seven months of falling prices, figures show.
A basket of 35 popular items cost £83.44 in July, up from £82.83 in June, according to the mySupermarket Groceries Tracker.
The cost is still 2.5%, or £2.15, cheaper than it was at the same time last year, although the figure has dwindled from the previous month's 4%.
MySupermarket suggested shoppers were starting "to feel the Brexit bite as grocery prices go up".
The groceries comparison website said the increase was driven by a sharp rise in the cost of popular products such as pasta, up 10%, onions, up 9%, and fresh peppers and pasta sauce, both up 6%.
However some products fell in price, such as bananas, down 7%, and carrots and frozen pizza, both down 3%.
It is the first consecutive month of price rises since November 2015.
MySupermarket chief executive Gilad Simhony said: "It looks like we are entering a period of intense uncertainty in the grocery sector and this is likely to result in the extreme fluctuation of pricing for popular everyday products.
"Supermarkets are working in uncharted territory and are trying everything to lure shoppers whilst navigating themselves through what could be a time of prolonged instability.
"Shoppers should keep a close eye on whether their favourite grocery products are creeping up in price as the difference across supermarkets can have a big impact on their wallets over a longer period of time."