Obesity: The Facts About Fat

A report released May 28 by the Institute for Health Metrics and Evaluation at the University of Washington in Seattle reveals that in the past three decades, the number of overweight and obese people worldwide has jumped from 857 million to 2.1 billion. Not only that, the United States is home to the world’s highest proportion of obese people, at 13 percent.

Obesity rates in the U.S. have quadrupled for children ages 6-11, tripled in adolescents ages 12-19 and doubled in adults since 1970. Children who are obese by age 5 are four times more likely to be obese in ten years. Calorie intake with a diet rich in refined carbohydrates and fats are the main contributors to the high obesity numbers. In fact, the average caloric intake in the U.S. has increased by 500 calories daily since 2000.

Before we continue, lets get some terms and definitions “straight” before we “talk: Body Mass Index — Also known as BMI, body mass index is a formula that assesses your body weight in relation to your height. This formula provides a measure of your body compositon and has been shown to be an effective predictor of body fat. Thus, BMI correlates with the amount of body fat, but BMI does not directly measure body fat.

Overweight — “Excess of body weight,” defined as having a body mass index, or BMI, over 25

Obese  — “Excess of fat,” defined as having a BMI over 30

Fat Cells — also known as “adipocytes,” are only present in vertebrates (organisms with a backbone). Fat cells are the primary component of adipose tissue and their specialized function is storing energy as fat.

Adipose Tissues — Adipose tissue, or “fat”, is an anatomical term for loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body. There are three types of fat: white, which stores excess energy, and brown and beige, which generates heat. Most adipose tissue is white adipose tissue and serves three functions: heat insulation, mechanical cushion, and most importantly, a source of energy.

Stromal-vascular cells — In addition to fat cells, adipose tissue contains stromal-vascular cells –cells that contribute to structural integrity and are not yet filled with lipids. Every gram of adipose tissue contains 1-2 million fat cells and 4-6 million stromal vascular cells, which under obese conditions will contribute to insulin resistance (developing diabetes) and chronic inflammation.

Am I Overweight Or Am I Obese?

Overweight and obesity are both labels for ranges of weight that are greater than what is generally considered healthy for a given height. People can become overweight at any age. The timing of weight gain tends to vary between men and women. Most overweight women gain their excess weight after puberty. This may be precipitated by pregnancy, oral contraceptive therapy, and menopause. In many men, the transition from an active lifestyle during the teens and twenties to a more sedentary lifestyle thereafter is associated with weight gain. After age 55 to 64 years, men’s weight typically remains stable, and then begins to decline.

How Do We Measure Body Fat?

Methods used to directly measure body fat are not available in daily practice — that is why obesity is calculated by indirect estimation of body fat. The standard measure to calculate overweight and obesity is the body mass index (BMI).
Overweight refers to a weight above the “normal” range, with normal defined as a BMI between 18.5 to 24.9.

The circumference of the waist is another easy measurement of obesity. Waist circumference greater than 35 inches (88 cm) in women, and greater than 40 inches (102 cm) in men increases the risk of obesity-related complications, such as heart disease and diabetes. People who are obese (with a BMI greater than 30) and who have larger waist sizes may need more aggressive weight-loss treatment than others. Calculate your BMI here:

Body Mass Index

Body mass index (BMI) is a formula to assess your body weight in relation to your height. This formula gives a measure of your body composition and has been shown to be an effective predictor of body fat. To calculate your BMI, enter your height and weight below.

Calculate your BMI by entering your height & weight.

in inches:
in pounds:
in centimeters:
in kilograms:
Your result:


Body Composition Body Mass Index (BMI)
Underweight Less than 18.5
Normal 18.5 – 24.9
Overweight 25.0 – 29.9
Obese Greater than 30.0

Do We Need Fat?

Fat is a nutrient and actually crucial for normal body function. Without it we could not live. Not only does fat supply us with energy, it also makes it possible for other nutrients to do their jobs. Our body is constantly creating and destroying fat cells, but the body maintains a fixed number of fat cells, which is generally set during adolescence. However, growth in number can also occur in adulthood.

How Do We Become Obese?

In adults, the major bulk of adipose tissue (“fat”) is a loose association of lipid-filled cells called adipocytes. Fat cells grow larger than their original size when they fill with lipids, which are a group of fat and fat-like substances, including cholesterol. When our adipocytes fill with lipids and reach a critical size, young, unspecialized cells in our bodies are stimulated to turn into more fat cells, increasing the number of fat cells as a result. So we really have two mechanisms that increase our weight. We can enlarge our existing fat cells, and we can add more fat cells, but we cannot get rid of them.

We can shrink fat cells. We can also enlarge fat cells. Once we reach adulthood, the number of fat cells we have more or less stays the same. When we put on a large amount of weight, these fat cells enlarge in size. The opposite holds true when we lose a lot of weight – they shrink. Weight loss reduces the volume of the fat cell but never reduces the number of fat cells. Preventing the accumulation of fat cells is most important.

Prevalence of Obesity

According to the Centers for Disease Control, obesity rates vary by state, from a low of 20.5 percent in Colorado, to a high of 34.7 percent in Louisiana in 2012, the most recent figures available. In 13 states, obesity rates are equal to or greater than 30 percent.  Severe or morbid obesity, marked by a body mass index equal to or greater than 40, was found in 6.3 percent of the U.S. adult population in 2010.

Life Expectancy

Obesity in adulthood decreases life expectancy for both men and women, as evidenced by the Framingham Heart Study, a long-term, ongoing cardiovascular study on residents of the town of Framingham, Massachusetts. The study began in 1948 with 5,209 adult subjects from Framingham, and is now on its third generation. In the Framingham study, participants age 40 years who were obese lived six to seven years less than those of normal weight. Those who were overweight but not obese at age 40 years lived three years fewer than the normal-weight subjects. Another study called the Prospective Studies Collaboration, which actually was a group of studies that shared information about the link between BMI and health, found that each 5 unit increase in BMI was associated with a significant increase in mortality from each of the following disorders: ischemic heart disease, stroke, diabetes, chronic kidney disease and cancer.

Take a look at the adult (20 years +) BMI table below. It shows us that a woman who is 5 foot 4 inches tall is considered overweight (BMI is 25 to 29) if she weighs between 145 and 169 pounds. She is considered obese (BMI is 30 or more) if she weighs 175 pounds or more. A man who is 5 foot 10 inches tall is considered overweight (BMI is 25 to 29) if he weighs between 174 and 202 pounds, and is obese (BMI is 30 or more) if he weighs 209 pounds or more.

Download BMI Chart

Your Lifestyle AND Surroundings Matter

Physical activity — A sedentary lifestyle lowers energy expenditure and promotes weight gain. Of all sedentary behaviors, prolonged television watching appears to be the most predictive of obesity and diabetes risk. Obesity is more prevalent in adults with physical, sensory, or mental health disabilities.
Sleep deprivation — The proportion of adults in the United States sleeping less than seven hours per night has increased from 16 to 37 percent over the past 40 years, a lifestyle change that may have negative metabolic consequences.
Cessation of smoking — Weight gain is very common when people stop smoking. This is thought to be a result of nicotine withdrawal, at least in part. Because of the predictable weight gain after cessation of smoking, it is important to add to your exercise program a decreased caloric intake as part of your lifestyle change.
Social networks — Social influences may affect one’s risk of obesity. A report of a social network constructed from the Framingham Offspring Study shows the likelihood of becoming obese increases by 57, 40, or 37 percent in those who had a friend, sibling, or spouse who became obese.

Treatment Is Important

More than two-thirds of adults in the United States are either trying to lose weight or maintain their existing weight. However, only 20 percent are eating fewer calories and exercising at least 150 minutes a week (the bare minimum required for weight maintenance).

For initial weight loss, establish a realistic weight loss goal with emphasis on decreasing total daily caloric intake and increasing energy expenditure with regular daily exercise. Low-fat and low-carbohydrate diets are recommended, as well as the Mediterranean Diet.

Liposuction, the most common cosmetic surgery in the world, removes a percentage of your total body fat but it doesn’t improve insulin sensitivity or cardiovascular risk. After liposuction, your fat mass will regrow in about a year if you exceed the number of calories recommended for your body type and if you fail to maintain an appropriate amount of physical activity.

Weight loss surgery, also called bariatric surgery, is reserved for people with severe obesity who have not responded to other weight loss treatments.

If you have been overweight or obese for a long time, you may very well have metabolic issues that warrant professional intervention. This is a matter of life and death and should not be taken lightly. Next month we will discuss weight loss in more detail.

Until next time!

Stephanie Coulter, MD


Special thanks to Dr. Karla Campos for her assistance in writing Straight Talk.

Learn more from the Centers for Disease Control on common questions related to BMI and Obesity
BMI Percentile Calculator for Children and Teens
How reliable is BMI as an indicator of body fatness?
If an athlete or other person with a lot of muscle has a high BMI, is that person still considered to be overweight?

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