When you want something sweet, all those fat-free, sugar-free options seem like a smart choice for weight loss. But researchers at Cornell University found that overweight people who choose low-fat versions of snack foods rather than the regular kinds consume, on average, twice as many calories. "The terms 'fat-free' or 'sugar-free' can create a green light effect, triggering people to eat more," says dietitian Cynthia Sass, RD. But many fat-free foods have about the same number of calories (or more) as their full-fat counterparts. 
●Put tempting foods out of sight, out of mind. We naturally gravitate toward foods that are easiest to reach. So put candy on a high shelf or inside another bag behind something else so you’ll be less likely to go get it, says Cynthia Sass, co-author of “The Flat Belly Diet!” Put smarter choices, such as fresh fruit or popcorn, in bowls where they’re visible and within arm’s reach. Keep a water bottle with you so you won’t have to rummage through the fridge or walk to a vending area to get a drink.
Everyone is different. How quickly you burn calories when you are not physically active can be very different from other people based on your specific genes, biology, and past. While scientists know that there are 3,500 calories in one pound, simply eating 500 fewer calories every day for a week (or 3,500 fewer calories in a week) does not always end in losing exactly one pound.