Calories

There are around 135 calories in a 3 oz. serving of beef kidneys. Approximately 25 percent of those calories, or 36 calories total, come from fat. Protein makes up around 99 calories in a 3 oz. serving of kidneys.
Vitamins

Vitamins
Beef kidneys are also a good source of several important vitamins. A single 3 oz. serving contains 21 mcg of vitamin B12 at over 800 percent and 2.5 mg of riboflavin at nearly 200 percent of the required daily amount for the average adult. Other vitamins in lower quantities include 1.3 mg of pantothenic acid at 26 percent, 3.3 mg of niacin for 22 percent, 0.3 mg of vitamin B6 at around 20 percent and 70 mcg of folate at almost 18 percent.
Minerals

Minerals
You can also obtain several essential minerals from eating beef kidneys. These include 143 mcg of selenium for over 250 percent, about 5 mg of iron for 50 percent, 500 mcg of copper at over 50 percent, 258 mg of phosphorus for over 36 percent and 2.4 mg of zinc delivering around 25 percent of what an average adult needs each day. Smaller quantities of other minerals, such as calcium, magnesium, potassium, sodium and manganese, are also available in beef kidneys.
Other Information

Other Information
A 3 oz. serving of cooked beef kidneys is particularly high in cholesterol, delivering around 600 mg or around 200 percent of the daily recommended amount. There is no significant fiber in beef kidneys.