A quarter of vegetarian meat substitute products contain insufficient protein.
New SafeFood research found many of the plant-based products on sale here were highly processed, and full of sugar and salt.
Many of the products are placed in food categories that provide protein, such as meat, poultry, eggs, fish, and nuts.
The study found that 34% of consumers who buy meat substitutes do so because they think they're healthy and better for them, while 15% said they were buying them for environmental reasons.
The top three meat substitute products were burgers (41%), mince (31%) and sausages (29%).
Safefood’s director of human health and nutrition, Dr Catherine Conlon, told Breakfast Briefing shoppers should always check the label.
She explained: “In terms of the products themselves, we found they have a wide variation in nutritional content.
"Around half of them are a good source of protein - but around a quarter of them are not a source of protein. These are in foods which are in a category where you’d expect to get protein from.
“There are some good points: they are a source of fibre, and overall they’re lower in fat.
"But the reality is they’re highly processed - whether it’s a meat-based sausage roll or vegetarian sausage roll, it’s still processed."
Dr Conlon said people should check for products that are a good source of protein, and low in fat & salt - and also only eat them occasionally.
She said it’s generally a good idea to get protein from lots of sources, with the likes of beans and peas a good and healthy source of protein for those who don’t want to eat meat or animal products.
Last year, MEPs rejected a bid to ban the use of phrases such as 'burgers' and 'sausages' for plant-based foods.
Campaigners said the move was "rightly rejected as disproportionate nonsense", but criticised a continued ban on terms such as 'almond milk' for plant-based dairy alternatives.