Certain periods of a person’s life can cause weight gain to result in a larger number of fat cells.  Obesity occurring during these periods is difficult to treat.  The first period is between 12 and 18 months of age.  Parents should carefully monitor the amount and type of food consumed by their child during this time.  Adolescence, or between 12 and 16 years of age, is also a difficult time for weight gain.  Because their bodies are changing so rapidly, adolescents often gain more weight than they should.  Advanced adulthood, when a person’s metabolic rate begins to slow down, is a dangerous time for weight gain.  Pregnant women often find losing “baby weight” to be difficult.  Until recently, scientists believed that the increased number of fat cells gained during these times were impossible to lose.  However, studies have now shown that these fat cells can be destroyed if a person maintains a lower body weight for a period of time.