1. Do your math. Find out what your Basal Metabolic Rate is. This is the the minimum caloric requirement needed to sustain life in a resting individual and a simple formula gives you a good idea of how many calories you burn in a typical day.
Women:
655 + (4.3 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)
Men:
66 + (6.3 x weight in pounds) + (12.9 x height in inches) - (6.8 x age in years)
2. Track it. Now that you know your BMR, track everything you eat everyday. Create a simple spreadsheet that tracks how many calories you are consuming at every meal. The math is simple, any calories consumed above your BMI will lead to weight gain, anything below your BMI will lead to weight loss. This will give you a good understanding of what you need to cut in order to maintain your weight during the Holidays. There are thousands of websites and smartphone apps, that can help you track calories in food and when you are eating out.
3. Factor in exercise. Subtract the amount of calories you are burning from exercise to your total calorie consumption of the day. For example, if your BMR is 1500 and you burn 400 calories during an hour work out and you consumed 1500 calories during the day, your total caloric intake for the day is -400. You burned more than you consumed = weight loss.
4. Plan ahead. Do your shopping and plan what you will be eating for the week. Find a low calorie recipe book and buy healthy snacks and try to eat 4 or 5 meals a day. This will boost your metabolism and help you burn fat. You can also use a dietary supplement to help ease hunger and flush your system.
5. Stay on Track. If you have a bad diet day, that's okay. It happens to the best of us. It's okay to start over tomorrow and get back on track. even if you have two or three bad days in a row, you can still get back on track. Look at your daily spreadsheet and see that the damange is repairable. What isn't repairable is having a bad day and giving up on your diet. It's a constant battle that's won one day at a time.