Dietician Sian Porter found cheddar and pickle sarnie from sandwich chain Eat contained 14.6g of saturated fat.
Pret, a Manger's buttie had 14.3g, Tesco's had 13.7g and one from Sainsbury's contained 13g.
The recommended daily limit for women is 20g, and 30g for men.
"We don't realize how much saturated fat a cheese sandwich can contain," The Sun quoted Porter, as saying.
Saturated fat affects cholesterol, which can cause heart disease.
Jim Winship of the British Sandwich Association said: "It's ludicrous. Other foods have much higher fat levels."