The American Heart Association lists sardines as an important source of omega-3 fatty acids, but the 505 mg of sodium per 3 1/2-oz. serving in Atlantic sardines and the 414 mg of sodium per serving in Pacific sardines offsets this healthy attribute. Sardines provide more sodium, calcium, phosphorus, potassium, B-12 and vitamin E than milk, mackerel, salmon or tuna. Sardines also provide more choline than milk or tuna, but less than mackerel or salmon.

Sardines make a good substitute for mackerel, salmon or tuna. Atlantic sardines in oil provide 1 1/2 times the calcium in an 8-oz. glass of whole milk, more than twice as much phosphorus and choline, slightly more potassium, eight times the B-12 and 12 times as much vitamin E per 3 1/2-oz. serving, according to the USDA Nutrient Database for Standard Reference. Only mackerel comes close to providing as much calcium as sardines and none of the others provide as much phosphorus, choline, potassium, B-12 or vitamin E.

Rinsing the oil, tomato sauce or mustard from the sardines helps lower the sodium content, but soaking them in water afterward does an even better job due to diffusion -- the tendency for elements to distribute themselves evenly throughout a fluid. Place the sardines in a colander and run water over them for five minutes, then space them 1/4-inch apart in a shallow baking dish and cover them with water. Soak the sardines for 2 to 4 hours in the refrigerator before discarding the water and patting them dry with paper towels.

Soaking the sardines in milk is another way to lower the sodium content. Cut the crusts from slices of white bread and use them to cover the bottom of a shallow baking dish. Place the sardines on the bread slices and cover everything with milk. Allow the sardines to soak for 2 to 24 hours before rinsing them and patting them dry.

You can also lower the sodium by spreading a layer of cooked white rice, pasta or mashed potatoes made without any salt or spices in the bottom of a shallow baking dish. Place the sardines a 1/2-inch apart on the cooked rice, pasta or mashed potatoes. Cover them with more rice, pasta or mashed potatoes at least 1-inch deep. Refrigerate overnight. Rinse the sardines and use the rice, pasta or mashed potatoes to thicken chowder. Potatoes and other high-starch foods will draw salt from the sardines as long as they are not already salted.