Unhealthy snacking can undo the benefits of eating healthy meals, British researchers say.

A team from King’s College in London examined the snacking habits of 854 people in the ZOE PREDICT study. The participants, 95% of whom identified as snackers, were mostly female (73%) and ate an average of 2.3 snacks a day.

More than a quarter of the participants said they ate healthy meals but also snacked on low-quality foods such as highly processed foods and sugary treats. Along with leaving this group feeling hungry, these low-quality snacks were linked to a higher body mass index, visceral fat mass and triglycerides concentrations immediately after a meal – all of which are associated with metabolic syndrome, a group of health conditions that can lead to heart disease and stroke.

Meanwhile, the participants who frequently ate high-quality snacks were more likely to have a healthy weight compared with those who consumed unhealthy snacks and the non-snackers. Healthier snacks also resulted in decreased hunger and better metabolic health.

“Considering 95% of us snack, and nearly a quarter of our calories come from snacks, swapping unhealthy snacks such as cookies, [chips] and cakes to healthy snacks like fruit and nuts is a really simple way to improve your health,” said study author Sarah Berry, a researcher in nutritional sciences at King’s College.

Berry and her fellow researchers add that snackers should pay attention to when they eat, because snacking after 9 p.m. often is associated with poorer blood markers. That’s because late-night snacks tend to be energy-dense and high in fat and sugar.

The study was published online in the European Journal of Nutrition.