Losing weight is no walk in the park, and staying committed to your new healthy lifestyle can be even more challenging. We asked nutritionists and a celebrity trainer (she works with Sofia Vergara and Kelly Ripa!) for their advice on how to make sure your new figure doesn’t disappear into a Girl Scout Cookie box.

1) Your metabolism is slower now—and you don’t realise it.
Basically, that smaller number on your scale actually means your body metabolizes a smaller number of calories, too. “The amount of calories you burn is closely tied to your body weight,” says Karen Ansel, R.D. “An overweight person generally burns more calories during a workout because they weigh more and it requires more energy to move and maintain all that extra weight. But after you’ve lost those pounds, your body requires less calories, so you burn a smaller amount each day.” Ansel warns that if you don’t adjust the amount you eat to correspond to your new size, the weight you lost will inevitably creep back on.

2) You’re not sleeping enough.
Not only does sleep help you feel more energized, but it also keeps your waistline in check.Why? “When you don’t catch enough Z’s, you’ll look to snacks for that much-needed burst of quick energy,” says Amy Shapiro, R.D. “Your body [also] produces more gherlin, [a hormone that] makes you want to eat more, and less leptin, [which is] the hormone that tells you when to stop eating.” Not to mention that when you’re exhausted, your metabolism slows down, according to research from the University of Chicago. So if you’re short on shut-eye, start counting sheep as soon as you finish this article.

3) You don’t have a Plan B.
Celebrating a dieting victory with a cheeseburger isn’t how it works, unfortunately (OK,except for every once in a while). “Anybody will regain lost weight if they go back to their old eating habits,” says Ansel. “One of the best strategies for lasting weight loss is to focus on healthy foods in smaller portions.” So instead of looking for a quick fix throughout your weight loss plan, try to make tiny changes that’ll stick for the long run, like always having a vegetable on your plate or opting for whole grains over processed foods, says Ansel.

4) You’re wasting your willpower.
Despite the myth of having an iron will, studies show that we’re only given a finite amount of self-discipline each day. So if you’re draining your willpower reserves on resisting a piece of dark chocolate when research shows one piece here and there is actually good for you, you’ll be more tempted to eat unhealthily later. Melissa Hartwig, author of the upcoming book The Whole 30, suggests planning to complete your hardest or least-fun tasks—like prepping all of your healthy meals or squeezing in a hardcore workout—first thing in the morning, when your willpower (and motivation) is at its highest. And there’s no need to overly restrict calories at breakfast, since your brain needs the energy. “You need to preserve some willpower for later in the day—especially between dinner and bedtime—so you don’t feel tempted by sweets after a long day.”

5) Mentally, your old habits linger.
Just because you’re changing what you eat doesn’t mean you automatically took care of how or why you eat. “But it’s important to address your underlying feelings towards food so that you don’t go back to giving [it] too much power as a form of comfort or guilty pleasure,” says Melissa Halas-Liang, R.D. She recommends looking to your environment for answers: “Do you feel pressure to eat when you’re socializing with friends out at a restaurant, or is your leisure time spent surfing the Internet or watching movies? Do you fall into the trap of the ‘good value’ appeal– getting more food for less money and then feeling compelled to finish it?” Keeping a journal can help illustrate why some of your poor food choices are back, and how to remedy them. “You can white-knuckle your way through any cleanse or detox through sheer willpower,” Hartwig adds, “but if you haven’t chosen a program designed to actually change your bad habits, then your brain and metabolism will be ready to betray you once your diet is over.”

6) You’re working out the same way.
When you lose weight, you lose fat and muscle – simply put, you use calories tomake both fat and muscle, so when cut back, you end up losing both. (Side note: if you up your protein intake, it can help your body maintain the muscles it needs to keep your metabolism burning.) “It’s important to always change up your workouts so that your muscles are challenged in a variety of ways, which will avoid both a mind and a body plateau,” explains celebrity trainer Anna Kaiser. A boring routine not only means that you won’t physically push yourself as hard as you would when you’re excited about the workout, but also that your muscles will already know what to expect. Work out smarter with high-intensity interval training, also known as HIIT (think running as fast as you can on the treadmill for one minute, followed by one to two minutes of slowly jogging), so that your body continues to repair muscle and burn extra calories without the risk of becoming complacent in your workout.