The Diet Detective: Fat content only one piece of puzzle

Here are a few of the latest truths, myths and facts that I've uncovered in my effort to decipher what's what in the world of nutrition. See if you're a nutrition expert:

Q. Do fats, carbohydrates, protein and alcohol all have the same number of calories per gram?

A. No. Fat is the most expensive calorically at nine calories per gram. Next is alcohol at seven calories per gram. Carbohydrates and protein both have four calories per gram.

Total calories are nothing more than a combination of the fats, carbohydrates and protein in a particular food. So if a food has 1 gram of fat (nine calories), 2 grams of carbohydrate (eight calories), and 1 gram of protein (four calories), it should have about 21 total calories.

Q. Is it true that whole milk has only about 3 percent fat?

A. Yes. The fat percentage refer to how much of the milk's total weight comes from fat.

Whole milk is about 88 percent water, 3.25 percent protein and 5.25 percent lactose (milk sugar), says Christine Bruhn, a professor of food science at the University of California at Davis. It's about 3.25 percent fat on average, and therefore about 96.75 percent fat free.

However, that doesn't mean there aren't tremendous calorie differences among types of milk.

• Whole milk (1 cup): 150 calories, 70 calories from fat.

• Two percent milk (1 cup): 120 to 130 calories, 45 calories from fat.

• One percent milk (1 cup): 90 to 100 calories, 20 calories from fat.

• Skim milk (1 cup): 80 calories, 0 calories from fat.

Q. Which has more calories: unhealthy saturated fat or "heart-healthy" monounsaturated and polyunsaturated fats?

A. All fats have virtually the same number of calories. All kinds of fat have nine calories per gram, says Alice H. Lichtenstein, a nutrition professor at Tufts University.

Nevertheless, saturated fat - from animal sources - has been linked to high cholesterol and should be limited in your diet. Unsaturated fats have heart-healthy properties - but still nine calories per gram.

Q. What is the most common nutrient deficiency in America?

A. Iron deficiency is the most common, says Mary Cushman, associate professor of medicine and pathology at the University of Vermont.

Those at highest risk include infants, teenage girls, pregnant women and the elderly. Iron is an essential mineral necessary for the formation of hemoglobin, which carries oxygen in the blood, and myoglobin, which carries oxygen in muscle tissue.