Forget old low-carb diet plans that focused on processed protein bars and shakes. This year, the keto diet got high marks for low carb. Keto, short for "ketogenic," is all about training the body to burn fat for fuel. How? By eating fat—and lots of it. Most keto diets recommend getting at least 70 percent of your daily calories from fat and the rest from protein. The goal is to eat as few carbohydrates as possible. Proponents say it helps them drop weight fast with little or no hunger in addition to perks like more energy and mental clarity. (Interested? Here's everything you need to know about the keto diet.)

If you’ve been eating fast food for years, get real about your approach: You’re probably not going to stick to an organic, gluten-free, paleo overhaul for very long. "You want to change as little as possible to create calorie deficit," says Dr. Seltzer, who insists the best way to support sustainable weight loss is to incorporate small changes into existing habits. So instead of giving up your daily BLT bagels in favor of an egg-white wrap, try ordering your sandwich on a lighter English muffin. Or say you eat a snack bar every afternoon: Swap your 300-calorie bar for a 150-calorie alternative. "Your brain will feel the same way about it, so you won’t feel deprived," he says.

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