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.

In general, dietary iron is absorbed poorly. Animal foods (poultry, red meat and fish) seem to be the best for iron absorption. Plant sources include dried fruits, leafy green vegetables, nuts, legumes and whole-grain products.

Q. Which is the best oil?

A. They’re all pretty much equal in terms of weight control - meaning that all oil has about 120 calories per tablespoon. Yes, regular vegetable oil has the same number of calories as olive oil. Just because an oil is heart healthy doesn’t mean it’s calorie free.

The best oils?

“While most of the vegetable oils are pretty low in saturated fat, technically canola and soybean are the best,” Lichtenstein said. “They are both high in omega-3 fatty acids, and soybean oil is high in polyunsaturated fat while canola is high in monounsaturated fat - both of which are heart healthy.”

Q. Is it true that cooking sprays like Pam and Mazola have no fat?

A. No. To qualify as fat-free, a food must have less than 0.5 grams of fat per serving. The key words here are “per serving.” These claims are based on standardized serving sizes, which can be unrealistic or confusing.

Even though Pam has less than 0.5 grams of fat per serving, technically qualifying it for the fat-free claim, the Food and Drug Administration thought such an assertion would be misleading for a product that is essentially 100 percent fat. The compromise was to allow Pam and other similar products to put the words “for fat-free cooking” on the label.

I’m still a fan - as long as you’re careful about how long you’re spraying!

Q. Does “no added sugars” mean that a food is low calorie or reduced calorie?

A. No. The words “no added sugars” and “without added sugars” only mean no sugar or sugar-containing ingredients (such as fruit juice, applesauce or dried fruit) are added during processing or packing. So don’t be fooled - read the Nutrition Facts and check the calories per serving.

Q. Is there any benefit to washing meat and poultry?

A. No. Believe it or not, washing poultry or meat (with water) doesn’t effectively reduce the pathogens that cause food-borne illnesses, said Mark Sobsey, a professor of public health at the University of North Carolina at Chapel Hill.

In fact, washing these foods could actually increase your risk of getting sick because it could easily spread germs on your hands and around the sink, warns Sobsey. The best way to make sure your food is safe is to heat it to the proper temperature, making sure no red or pink is visible.

Charles Stuart Platkin is a syndicated health, nutrition and fitness writer and a certified personal trainer.