A fall in pub sales resulted in an overall decline of 0.8% in the casual eating out market during April, according to the Coffer Peach Business Tracker.
While restaurant groups saw like-for-like trading increase by 2.5%, the overall results were brought down by a 2.7% fall in pub business, compared with April 2015.
Regionally, London outperformed the rest of Britain, with like-for-likes up 1% against a 1.3% fall outside the M25.
April's performance was explained partly by the cold weather, the early Easter in March, and a general slowdown in the economy prior to the EU referendum.
However, the underlying trend in business has been flat since the beginning of the year, with like-for-like figures showing zero growth in February and an increase of only 0.6% in March.
Peter Martin, vice-president of CGA Peach, which compiles the tracker together with Coffer Group, RSM and UBS, said: "The cold weather in the month also helps to explain why restaurants did better than pubs, as poor weather always tends to favour restaurants and good weather pubs.
"But taken together we are seeing a slowdown in market growth. Industry sentiment at the start of the year was that 2016 was going to be a tougher year than last, and that seems to be panning out."
Total sales for the month among the 31 companies in the Tracker cohort were up 3.1% on 2015, reflecting the fact that groups are still opening new sites, if at a slower rate than previously.
The underlying annual trend shows like-for-like performance across the sector up 1.5% for the 12 months to the end of April.
Paul Newman, head of leisure and hospitality at RSM, said that the slowdown in growth was partly driven by an increasing number of "exciting new concepts" taking market share from the established, mainstream operators whose results dominate the Tracker.
"This disruption is provoking these operators to review their brand portfolios and is driving increasing trade merger and acquisition activity in the sector, as witnessed by Whitbread acquiring a stake in Pure and PizzaExpress acquiring upmarket pizza delivery chain Firezza," he said.
The 31 companies analysed in Coffer Peach Business Tracker include Pizza Hut, Casual Dining Group, TGI Fridays, Living Ventures and Wagamama.