There are definitely some weight-loss rules you can bend a little and still drop pounds . On the other hand, if you're serious about slimming down, here are five strict rules that shouldn't be broken if you want to see the number on your scale go down.
Always Eat Breakfast
Skipping meals is a big mistake  in nutritionist Cynthia Sass's eyes, especially breakfast. Enjoying a hearty and nutritious meal in the morning can actually jump-start your metabolism and encourage pounds to drop. Choose a breakfast that's high in protein to give you energy as well as full of fiber to keep you satisfied for hours.
Related: 22 Breakfast Recipes That Can Help You Lose Weight 
You Have to Make a Change to See a Change
Unfortunately, you can't continue eating huge bowls of ice cream after dinner and expect to see the scale numbers drop. In order to encourage a change in your weight, you need to make healthier lifestyle changes that include eating nutritious, balanced meals most of the time, with the occasional splurge. Remember, you're not just dieting — you're changing your eating habits. That's the principle behind the 80/20 rule . Jessica Alba 's trainer, Yumi Lee, says, "You can't be 100 percent all of the time, but you can be 80 percent all of the time."
Related: The 80/20 Formula Is the Key to Weight-Loss Success 
Healthy Foods Don't Mean All You Can Eat
Nuts, nut butter, avocados, sweet potatoes, orange juice, brown rice — these foods are all highly nutritious, but that doesn't mean they're void of calories. You still need to be aware of serving sizes, even for foods that are super good for you.
Related: Know the Right Portions of Your Favorite Healthy Foods 
Calories in Can't Exceed Calories Out
Losing weight is about simple math: you have to burn or cut out 500 calories a day  to lose one pound in a week. If you burn 250 calories on a morning run, you'll need to cut out 250 calories from your diet that day. Don't get in the mind-set that a workout gives you a free pass to splurge, because you'll end up taking in more calories than you burned, which will result in weight gain instead of weight loss.
Related: The Workouts That Help You See Weight-Loss Results Faster 
Once the Weight Is Gone, You Can't Go Back to Your Old Ways
You used to guzzle a can of Coke with your lunch, but when you decided to lose weight, you replaced it with a seltzer. Now that the weight is off, don't go back to your soda habit. Losing weight is a forever lifestyle change, not something you do until you reach your weight-loss goal. Once you go back to old eating habits, the weight will quickly creep back on.
Related: Research Shows This Is How to Lose Weight and Keep It Off