Chapter 2, Problem 1.1CS

Summary Introduction

To explain: Whether Person T was underweight or normal weight based on her body mass index when she weighed 107 pounds.

Introduction: Body mass index (BMI) is obtained by dividing weight (in kg) by square of height (in m). If the BMI is greater than 18.5, then it is considered underweight. The BMI of 18.5-24.9 comes under normal weight, and people with 25-29.9 are overweight, and people with BMI of 30 and higher have obesity.

Explanation of Solution

Person T is 5 ft 5 in. (1.65 m); her current weight is 107 pounds (48.53 kg) and her previous weight was 121 pounds (54.88 kg). Both her FSH and LH levels are low, and she cannot ovulate. After sometime, she regains 7 pounds and her LH level becomes normal, but her FSH level is still low and the luteal phase of her cycles is abnormally short. When her weight reaches 119 pounds (53.97 kg), her LH and FSH levels, ovulation, and menstrual cycles becomes normal.

The critical level of body fat (usually indicated by a body mass index over 20 kg/m²) is needed to trigger and sustain normal reproductive functions in women. Low levels of body fat during adolescence is related to delays in the onset of menstruation and reduced fertility later in life. Impaired fertility in underweight women often takes the form of delayed time to conception and amenorrhea. Lowered libido and reduced sperm production have been identified in underweight men with low levels of body fat.

The formula for the body mass index is as follows:

$\text{Body mass index }\left(\text{BMI}\right)=\frac{\text{Weight in }\left(\text{kg}\right)}{{\left[\text{height in (m)}\right]}^2}$

Substitute $48.53\text{ kg}$ for weight and $1.65\text{ m}$ for height in the above formula.

$\begin{array}{c}\text{Body mass index }\left(\text{BMI}\right)=\frac{48.53\text{ kg}}{{\left(1.65\text{ m}\right)}^2}\\ =17.83{\text{ kg/m}}^2\end{array}$

Person T was underweight when she weighed 107 pounds as her BMI was 17.83.