Research has long shown a connection between obesity and infertility in women.  And it’s not just women that need to watch the scale. Recent research has shown that obesity can negatively impact male fertility as well, leading to lower sperm counts.

Watching your carbohydrate and junk food intake is also advisable. Research on women dealing with PCOS (polycystic ovarian syndrome) has shown that may improve their symptoms, even without weight loss. The lower-carb diet led to more regular menses and increased fertility potential.

Studies have also shown that being underweight could cause you have difficulty becoming pregnant. The main reason is women who are underweight may not ovulate or have a regular menstrual cycle because they do no have enough fat for proper hormonal balance. For some people who are underweight it can seem difficult to put on weight and keep it on.


The BMI, or Body Mass Index, is a number calculated by taking your weight in kilograms and dividing it by height in meters squared. The Centers of Disease control states that BMI “provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems.”1

A BMI of less than 18.5 classifies a person as underweight; between 18.5 and 24.9 as normal; between 25 and 29.9 as overweight; 30 and 39.9 as obese and over 40 as morbidly obese as depicted in the chart below:

1) Body fat measurement: While BMI is used as proxy for body fat, it is a much better idea to just measure body fat. Health is generally better with lower body fat percentages regardless of the BMI, and this includes populations with documented diseases like diabetes. I recommend striving for maximum muscle mass and a body fat below 15% for men and 23% for women. These numbers are within the “fitness range” of recommended body fat according to the American Council on Exercise.

2) Waist to hip circumference: Since it is becoming very clear that the distribution of body fat is an important indicator is disease risk, it makes sense to examine it. People with fat distributed around the abdomen are at higher risk for heart disease and diabetes, so aiming to reduce the ratio is a better idea than trying to reduce BMI. In other words, if you just focus on “losing weight” you may very well end up losing muscle as well and looking like a shrunk down version of your former self, with the same risk of serious disease as before.

As always, it is important to look at the “big picture” rather than focusing on a particular calculation to evaluate your chances of developing an obesity-related illness.