This 12-week program should allow you to shed roughly 20 pounds, Nicholls says. (Those of you hoping to lose more might need to give the program 16 weeks to reach your goals; those with less to lose may need only eight weeks.) The plan focuses on natural, whole foods. It employs lots of cardiovascular exercise to burn bodyfat, and strength training to maintain and/or build muscle, which simultaneously boosts your metabolism and shapes your muscles. It requires you to take the time to plan meals and menus, to shop for and prepare your food, to set the alarm clock and have your workout clothes ready and your sneakers packed in your gym bag.

The key to the diet is change. Nicholls, who advises noncompetitors as well as the pros, says consistently changing your meals and eating patterns is the best way to shake off stubborn fat and avoid the plateaus that are part and parcel of most diets. "I try to have my clients constantly change things around. I've found that a body can adapt to a certain set schedule and hit plateaus in as little as 2-3 weeks," he explains. To avoid this, and add variety to the diet as well, his plan involves constantly rotating the types of macronutrients (proteins, carbohydrates and fats) you eat.

In general, Nicholls recommends a base of approximately 40 grams of protein and 25-40 grams of carbohydrates - derived from either "starchy" choices, such as potatoes and oatmeal, or "fibrous" choices, such as broccoli and cauliflower - at each meal. If your protein is lean and your carbohydrates "clean" (not processed), your fat intake will average roughly 4 grams per meal. Yet daily dietary fat totals will differ depending on your varied protein and carbohydrate choices for that day.

"This is just a base," Nicholls emphasizes. "You always want to rotate. For example, at one meal you may take in 60 grams of protein but only 15-20 grams of carbohydrates (two medium-sized chicken breasts and a small dinner salad). Or it may just be the opposite; you may take in a smaller amount of protein and an equal amount of carbs (35 grams of each)." The point, he notes, is to constantly confuse your body so your metabolism doesn't have time to adjust.

Remember, this diet is for a noncompetitor. If you're a highly conditioned athlete or have an interest in competing, the plan may not provide you with enough calories (energy) to sustain your training. Make each snack another primary meal and make further adjustments if necessary. And if you feel like the diet is driving you crazy, either due to out-of-control food cravings or low energy, modify it slightly to incorporate a little bit of the foods you need to keep you sane. Sure, looking lean is a great goal, but even more important is eating for health and avoiding the vicious cycle of deprivation, overeating and guilt that can turn you into a disordered eater.