When you create your profile, we ask you for your age, height, weight, gender, and normal daily activity level. We use these factors to determine the calories required to maintain your current weight. We also ask how much weight you would like to lose or gain per week, and with this goal in mind, we subtract calories (for weight loss) or add calories (for weight gain) to determine your daily calorie and nutrient goals.
Though we do recommend trying to stay within all of these guidelines, it should still be possible to lose weight as long as you stay within your daily calorie goal.
For more information on the process we use to determine your goals, please see this article.