McDonald's Filet-o-Fish sandwich is a fried fish patty served on a steamed white-flour bun. The fast food establishment first offered the sandwich in 1962. With 380 calories, the fish sandwich contains fewer calories than many of the burger offerings.Filet-o-Fish is made from pollock or a New Zealand fish called hoki. The fish is combined with wheat flour, water, food starch, corn flour, salt, whey, dextrose, spices, cellulose gum, preservatives and stabilizers to form a patty containing 120 calories. The breaded fish patty arrives at the restaurants frozen and is cooked in a combination of sunflower and canola oil. It is topped with 25 calories worth of American cheese and 90 calories worth of tartar sauce made from soya bean oil, gherkins, onions, egg yolks, corn starch, sugar, vinegar, salt, xanthan gum, capers, calcium chloride, natural flavorings, mustard flour, potassium sorbate and parsley. The white bun contributes 150 calories.Of the 380 calories, 45 percent, or 170 calories, come from fat. The sandwich's 15 grams of protein contribute 60 calories, or 16 percent of the calories. Approximately 40 percent of the sandwich's calories come from the 38 g of carbohydrates.Filet-o-Fish has fewer calories than most of the burgers. An Angus Deluxe provides 750 calories, a double Quarter-Pounder provides 740 calories and a Big Mac provides 540 calories. The plain hamburger, with 250 calories, and the cheeseburger, with 300 calories, are lower in calories than the fish sandwich. Filet-o-Fish also has fewer calories than the grilled chicken sandwich, which offers 420 calories.Although not extremely high in calories, the Filet-o-Fish sandwich contains 640 milligrams of sodium and 40 mg of cholesterol. It also has 3.5 g of saturated fat. The Institute of Medicine, or IOM, recommends limiting sodium intake to 1,500 mg daily. The IOM does not set recommendations for cholesterol or saturated fat, because the organization suggests you eat as little of these as possible. Adding fries to your Filet-o-Fish sandwich order significantly increases your calorie intake. A small fries increases your intake by 230 calories, a medium by 380 calories and a large by 500 calories.