Risks Associated with Weight and BMI
Obesity rates have been on a steady rise over the past few decades. The U.S. Centers for Disease Control (CDC) estimates that over 66 percent of U.S. adults are overweight or obese. In addition, a growing number of children and adolescents are living with weight issues — over 17 percent of adolescents over age 12, almost 19 percent of six to 11 year olds, and nearly 14 percent of children between the ages of two and five are considered overweight, according to the 2003–2004 National Health and Nutrition Examination Survey (NHANES).
Being overweight or obese is a primary risk factor for developing prediabetes and type 2 diabetes. The U.S. Department of Health and Human Services (HHS) reports that over 80 percent of people with type 2 diabetes are clinically overweight.
Why Is Weight a Risk Factor?
Too much fat makes it difficult for the body to use its own insulin to process blood glucose and bring it down to normal circulating levels. Here are the specifics:
Overweight people have fewer available insulin receptors. When compared to muscle cells, fat cells have fewer insulin receptors where the insulin binds with the cell and “unlocks” it to process glucose into energy.
More fat requires more insulin. The pancreas starts producing larger and larger quantities of insulin in order to “feed” body mass, and consequently insulin resistance turns into a catch-22. Excess blood sugar must be stored as fat, and excess fat promotes further insulin resistance.
Fat cells release free fatty acids (FFAs). During lipolysis (the breakdown of fat within cells), free fatty acids are released into the bloodstream, interfering with glucose metabolism. Abdominal fat appears to release higher levels of FFA.
Women of reproductive age who have developed polycystic ovarian syndrome (PCOS) are at an increased risk for type 2 diabetes. PCOS is a hormonal disorder characterized by enlarged ovaries containing fluid-filled cysts. Insulin resistance and impaired glucose tolerance are features of PCOS.
Leptin, a hormone in fat cells that helps to metabolize fatty acids, has provided an important clue to the relationship between obesity and type 2 diabetes. Discovered by Rockefeller University researchers in 1995, leptin (after the Greek leptos, meaning “thin”) also plays a part in sending a satiety — or “all full” — signal to the brain to stop eating when body fat increases, and an “empty” signal when body fat is insufficient.
It appears that a type of leptin resistance may lead to a situation where fatty acids are deposited instead of metabolized, leading to eventual insulin resistance. Leptin may also play a role in signaling the liver to release stored glucose.
Obesity and body fat are measured by body mass index (BMI) — a number that expresses weight in relationship to height and is a reliable indicator of overall body fat. People with a BMI of 25 to 29.9 are considered overweight; those with a BMI of 30 or over are obese.
The NIDDK reports that 67 percent of people with type 2 diabetes have a BMI 27 or higher and 46 percent have a BMI 30 or higher. You should aim for a BMI of 18.5 to 24.9, which is considered normal.
BMI is calculated differently for children and for young adults ages two to 20. A charting system called BMI-for-age compares each child's weight in relation to other children of the same age and gender on a growth chart in terms of percentiles. For example, a girl in the 13th percentile would weigh the same or more than 13 percent of girls the same age.
A healthy BMI for children is considered to be between the fifth and 84th percentiles. Growth charts used for assessing pediatric BMI-for-age are based on National Health and Nutrition Examination Survey (NHANES) data and generated by the U.S. Centers for Disease Control (CDC).
A BMI-for-age that is at the 95th percentile or higher is considered overweight, while the 85th to 94th percentile is “at risk” for being overweight. The term at risk for overweight is confusing and somewhat misleading. The CDC has not created an “obese” BMI-for-age category for children and teens, primarily because of the social stigma associated with the term obesity.
Therefore this category corresponds roughly to the adult overweight BMI category, meaning that children who fall into the “at risk” category are considered overweight by health care providers, not just in danger of becoming overweight as the label implies. And the pediatric “overweight” category corresponds to the adult obesity category.
Body mass index (BMI) table
Having an apple-shaped body, with excess pounds packed in the midsection rather than the hips, is another hallmark of insulin resistance. In fact, the National Institutes of Health recommends that waist circumference be used as a screening tool for evaluating the risk of heart disease and type 2 diabetes.
Classification of Overweight and Obesity by BMI, Waist Circumference, and Associated Risk of Type 2 Diabetes, Hypertension, and Cardiovascular Disease
Disease Risk Relative to Normal Weight and Waist Circumference
From the National Institutes of Health; National Heart, Lung, and Blood Institute
Another type 2 risk sometimes related to weight is an inactive lifestyle. Exercise, even at a moderate level, reduces blood glucose levels. People who lead sedentary lifestyles, exercising fewer than three times a week, are more likely to develop type 2 diabetes than those who get up and move on a regular basis.