Both males and females experience hormonal changes before the 1st physical signs of puberty are manifested. As sex hormones increase, changes in the body's proportion of lean, fat, and skeletal mass occur. For females an increase in body fat begins at 7 years and continues through ages 16-18 years.
Increase in Height and Weight
Most girls grow fastest about six months before they start their first period (menarche). You'll probably gain weight in puberty -- most girls do. You may notice more body fat along the upper arms, thighs, and upper back.
They also gain more fat than boys in preparation for their menstrual cycle. They go from gaining about 5 pounds a year before puberty, to 12-23 pounds during puberty as shown below. Girls' growth happens in stages as they tend to fill out before they grow up.
Growth Spurt Ages and Normal Growth
Generally, girls get more curvy and boys get more muscular. The timing of weight gain is something to note as well. The growth spurt ages differ for boys and girls. During the start of puberty, around age 10 to 12, girls begin to see a lot of body changes.
Lean body mass in girls diminishes from approximately 80 percent to 75 percent by the end of puberty, while the amount of body fat increases. In comparison, the percentage of lean muscle mass in boys increases from about 80 percent to 90 percent by the time they reach adulthood.
More significant weight gain is normal during the preadolescent ages of roughly 9 to 12 and adolescence – as a child matures into a young adult. It's not unusual for the body to store fat during this time as it prepares for the rapid growth and changes associated with puberty.
Puberty – Increased hormones in a child's body during puberty (between the ages of 10 and 14 for girls and between the ages of 12 and 16 for boys) leads to growth and possible expansion of “baby fat” areas. This typically takes place in girls' belly, breast area and hips. Boys' shoulders will get broader.
It's considered a normal transformation for girls to gain weight, particularly in the stomach area. What is this? Don't fret too much if you notice your daughter is gaining belly fat before puberty. It's all part of the growth plan.
As you go through puberty, you'll get taller, your hips will get wider, and your waist will get smaller. Your body also begins to build up fat in your belly, bottom, and legs. This is normal and gives your body the curvier shape of a woman.
Researchers have found that the number of fat cells in your body is set during adolescence and remains constant through adulthood, regardless of whether you gain or lose weight. The findings may help to explain why it can be so hard for some people to drop pounds and keep them off.
During puberty, the body begins making hormones that spark physical changes like breast development in girls, testicular enlargement in boys, and spurts in height and weight gain in both boys and girls. These changes continue for several years.
Puberty in women normally occurs between 11 and 14 years of age. If a girl reaches a particular weight (around 100 lb (45 kg)), the onset of puberty is triggered. The heavier the child, the earlier puberty occurs, possibly affecting risk of later disease.
Both males and females experience hormonal changes before the 1st physical signs of puberty are manifested. As sex hormones increase, changes in the body's proportion of lean, fat, and skeletal mass occur. For females an increase in body fat begins at 7 years and continues through ages 16-18 years.
The typical fat-gain areas for many women are the hips, arms and thighs, giving them what is termed a 'pear-shape'. The other areas where many women accumulate fat are the chest and the abdomen. Such women have slim arms and legs, and are seen as 'apple-shaped'.
Noticeable weight gain may occur prior to a growth spurt as excess fat helps promote growth. As a child goes through puberty, their stores of body fat may change. For example, girls tend to gain more fatty tissue in the hips, thighs and buttocks, while boys may have an increase in fat on their stomachs.
As a child's entire body size increases, the amount of body fat stays relatively stable, giving her a thinner look. Also during this stage of life, a child's legs are longer in proportion to the body than they were before.
Lifestyle issues — too little activity and too many calories from food and drinks — are the main contributors to childhood obesity. But genetic and hormonal factors might play a role as well.
According to the Centers for Disease Control and Prevention (CDC), most 13-year-old girls weigh around 76–148 pounds (lb) and most 13-year-old boys weigh between 75 and 145 lb, but this can vary widely. The average weight of a 13-year-old will depend on a number of factors.
It is usually easier to lose weight as a teenager than as an adult due in part to metabolic differences. It is beneficial to achieve and maintain a healthy weight as a teen and carry it forward into adulthood.
In some children, weight spurts happen before height spurts. Other children just gain more weight than they need for their height. This is how children become overweight. Parents, family members, and friends can all help a child who is at risk of or has become overweight.
So according to a bmi chart your suggested weight range is 112 - 151Lbs. But many factors such as bone mass, muscle mass and fat percentage are important too. If you are a lot over or under this weight range, consider changing your diet and/or exercise. You are still young so don't push it.