Liver and onions, fried together in a pan, is a traditional health food so popular it was once lambasted in the comic strip, "The Far Side." Although liver and onions were thought healthy long enough ago that almost everything science believed about nutrition has changed, this meal still pulls its weight.
Serving Size and Calories
The USDA identifies a serving of liver and onions as one slice of liver with one slice of onion. This amounts to about 100 g of food per serving. Such a serving contains 156 calories. Of those calories, 28 come from carbohydrates, 93 from protein and 35 from fat.
A 100-g serving of liver and onions contains 3.9 g of total fat. Unhealthy saturated fats make up 1.2 g of this, with heart-healthy unsaturated fats comprising the rest. According to Dr. Walter Willett in "Eat, Drink and Be Healthy," the ratio of good fats to bad fats is the most important aspect when considering the fat content of a food.
One serving of liver and onions carries 7.4 g of carbohydrates. These are evenly split between sugar carbohydrates and complex carbohydrates. Willett reports that complex carbs break down slowly, feeding your bloodstream a steady stream of energy for several hours. Sugar carbohydrates cause spikes and valleys in your blood sugar, which can stress your pancreas and lead to food cravings and weight gain.
One serving of liver and onions delivers 25 g of protein, about 44 percent of your USDA recommended daily allowance. Since this protein comes from the liver, it's a complete protein. Like most animal proteins, it contains all the amino acids your body needs, but can't make for itself.
Liver is incredibly rich in A and B vitamins. One serving of liver and onions contains well over your daily requirement for vitamins A, B2 and B12. It contains more than half your daily vitamins B3 and B6, along with smaller but substantial doses of vitamins B1, pantothenic acid and folate.
A single serving of liver and onions contains nearly six times your daily required copper. It supplies between one-quarter and one-third of your daily iron, phosphorus, zinc and selenium. It also delivers smaller but significant amounts of magnesium and manganese. This comes at the cost of just 62 mg of sodium per serving, or about 3 percent of your daily limit.
The human liver processes toxins. Because of increased pollution, baby advice book "Eat, Drink and Be Healthy" includes liver on its list of foods to be avoided by expectant mothers.