Atkins supporters would say that you don't need to worry about the calories you eat — as long as they don't come from carbs. Dietitians and other weight-loss experts know the truth: calories in equal calories out. In other words, if you eat more calories than your body uses, they will be stored as fat.

It's true that different energy sources have varying amounts of calories. Here's the breakdown:

  • 1 gram of carbohydrates equals four calories
  • 1 gram of protein equals four calories
  • 1 gram of fat equals nine calories
  • 1 gram of alcohol equals seven calories

Though carbs and protein are only half as caloric as fat, you can't eat them with wild abandon. The best plan is to eat a healthy mix of all three energy sources. Approximately 45-60 percent of calories should come from carbohydrates, 15-20 percent should be protein and the remaining 25 to 35 percent can come from fat (mostly from monounsaturated sources).

One way to keep track of the calories you eat is by keeping a food diary. Most dietitians recommend a food and activity diary as the first step toward getting a handle on how many calories you consume. Try keeping track of what you eat, drink and how you exercise for at least three days, including a weekend day. Be completely honest and write down the cookie you shared with a friend or the leftover PB&J sandwich you finished from your son's plate. You'll be surprised when you start to see the "hidden" sources of calories that you're eating.