Except for some brief maligning during the 1980s low-fat craze, protein has always been a dietary star. Well-known fad diets —Zone, Atkins, and South Beach—all emphasize limiting simple carbohydrates like white flour and sugar in favor of a higher-than-average dose of protein. Even among non-dieters, protein is a dietary given, and yet many don't know exactly why it's so essential to their health.
Here's an easy way to understand it: When you eat protein in any form—whether it's from tofu, chicken, lentils, or dairy—your body breaks it down into its component amino acids, which function as our bodies' building blocks. Our cells combine amino acids to make everything from bones to muscles to skin, enzymes, hormones, and blood.
It's important to eat protein everyday because our bodies can't store it like they can store fat and carbohydrates. We use it or lose it. To keep from upping your overall fat intake (saturated fat in particular), you want to make sure that protein comes from lean sources.
Plant proteins are some of the leanest around. (To learn about sources for plant-based protein read Understanding Complete Plant Proteins.) The majority of Americans, however, get most of their protein from animal sources: meat, fish, poultry, eggs, and dairy, and that's what we'll focus on here.
Animal protein can be part of a healthy diet. The trick is to realize that animal proteins come packaged with other nutrients, including, in many cases, saturated fats. For example, a nicely marbled 6-ounce rib-eye steak boasts 38 grams of protein, but it's chock full of fat, too—44 grams worth.
In contrast, consider the ubiquitous skinless chicken breast. It has practically no saturated fat, but a 6-ounce portion has over 40 grams of protein.
Between those two extremes you have a whole range of healthy choices, including: