BeFit works like most food tracking applications in that it lets you count exactly how many calories you're taking in. If you take in fewer calories than you expend, then you'll lose weight over time. BeFit includes over 7,000 foods from the FDA/USDA food database. Spotlight search is built into the application to make it easy to search for foods, and when you find them they're displayed with a full Nutrition Facts panel like those on food packages.
You can create a huge number of individual tracking lists, rename them, and sort them. If you're just looking for certain nutrients to track (e.g., carbs or saturated fats), you can hide other nutrients, then get a running total for those items you're interested in.
BeFit 1.0 is US$15.95 and existing customers of Jon Brown Designs get a 50% discount. All purchasers of BeFit 1.0 receive free upgrades through version 3.0. There's a demo available from the BeFit website.