A single letter differentiates the word “coach” from the word “couch.” But when it comes to achieving weight loss goals, that difference is a big one. Solicit the advice of a diet coach and you could drop up to 9 percent of your body weight in 24 weeks; forgo the support, and there’s a 50 percent chance you’ll give up and find yourself on the c-o-u-c-h. That’s why we reached out to leading dieticians for their number one weight-loss tip—the single piece ofadvice you need to stay off the couch, out of the cookie jar and focused on your weight loss goal.