How's that diet going? Did you have great results at first — pounds falling off and squeezing back into a favorite pair of jeans — but now the scale is stuck? You're puzzled, because you've been carefully following the same diet and exercise regime day after day, but suddenly, you're not getting the same results.

You've hit a plateau and it's a common phenomenon during dieting. Below are nine reasons your scale is stuck, and how to get it heading south once again:

1. You're eating too much. Sad to say that as your weight drops, the number of calories you eat needs to drop as well if you wish to continue to lose weight. You can't still consume the same number of calories you were eating at 150 pounds and lose the same amount of weight now that you weigh 135. You may be eating more than you think by unwittingly increasing portion sizes. Re-evaluate your portion sizes by carefully measuring your food for a few days.

2. You're eating too little. If you've drastically cut calories, you may not be getting the calories your body requires to meet the minimum for basic metabolic needs. In other words, your body thinks it's starving and will slow to conserve energy, and you'll lose less weight. Add some calories for a couple of weeks — perhaps 100 a day — and see if that jogs the scale's needle.

3. You need more protein. A double-blind, randomized study reduced calories by 500 a day in a group of dieters. The study, which was published in Nutrition & Metabolism, found that volunteers who took a protein supplement daily lost more weight from fat than muscle when compared to dieters who weren't given the protein supplement. Protein keeps metabolism from falling, and it contains the amino acid leucine that helps burn body fat. Protein also helps dieters feel fuller.

4. Your body is bored with your workout routine. If you religiously stick to the same exercise routine, your body adjusts and burns fewer calories. To combat, switch to different exercises. For example, move from a treadmill to a bike, or add either some extra time to each workout, or sneak in an extra workout during the week. Tweak your exercise routine at least every six weeks, and consider changing it completely once every three months.

5. You may be gaining muscle. If the scale's not budging but your clothes are fitting better, you may be replacing fat with muscle, and your body mass index (BMI), may be dropping. Go here to calculate your BMI.

6. Your meds are slowing weight loss. Some medications, including antidepressants, insulin, steroids, and drugs to control high blood pressure may be interfering with weight loss. Check with your doctor to see if this is a possibility and if an alternative is available.

7. You're not getting enough sleep. Many studies have shown that not getting enough high-quality sleep can slow your metabolism. A study from Weill Cornell Medical College in Qatar found that missing just 30 minutes of sleep can disrupt your metabolism and lead to weight gain. Those who didn't get enough sleep were 72 percent more likely to be obese.

8. You may have a hormone imbalance. Medical disorders such as a thyroid disorder or polycystic ovary syndrome, could cause your body to retain weight, says fitness expert and wellness coach Jillian Michaels. If you've tried all of the above steps and still can't lose weight, consult your doctor.

9. You could be relying too much on takeout or restaurant food. Even though some restaurant and takeout foods list calorie counts, many fitness experts contend they are unreliable. Cook your own food to make sure you know what's going into it, and use scales and measuring cups to measure portions.