A standard cheese sandwich can contain almost 15g of saturated fat - the equivalent of five pieces of deep fried chicken, according to new research.
Many high street cheese sandwiches contain more than half the amount of saturated fat adult women are supposed to eat across a whole day, the study for Unilever found.
Britons buy 11 billion sandwiches a year, or 200 a year for the average individual, with cheese the most popular filling, according to a report this year by the British Sandwich Association.
The average cheese sandwich contains 11g of saturated fat, more than half the 20g guideline daily amount for women and over a third of the 30g limit for men, the Unilever report said.
Other sandwiches with high levels of saturated fat include the All Day Breakfast (8.6g), club sandwiches with bacon and chicken (11.7g) and egg and cress (9g).
Dietician Sian Porter said: "The sandwich is a daily food for most of us but we don't realise how much saturated fat it can contain.
"As the government has acknowledged that 80% of the nation is eating too much saturated fat and needs to reduce its consumption, the results further reinforce the need to educate consumers on the health risks of over-consumption and the importance of eating a diet lower in saturated fat."
Ms Porter's own research last month found an EAT cheddar and Branston mayonnaise sandwich contained 14.6g of saturated fat, a Pret a Manger cheddar ploughman's had 14.3g, a Tesco deep fill ploughman's had 13.7g and a Sainsbury's cheese and pickle sandwich contained 13g.
High levels of saturated fat in sandwiches was of particular concern when added to other daily foods such as two pats of butter on toast (10.8g), a cappuccino (2.6g), meat, ready meals, cakes and biscuits, the report said.
A study by analysts TNS Worldpanel in May found that an average 20-year-old male eats 40g of saturated fat on a typical weekday - 30% more than guidelines recommend. High levels of saturated fat can raise blood cholesterol, particularly low density lipoprotein cholesterol, which is a risk factor for coronary heart disease.