How do doctors define obesity? (body fat, bmi,etc)

Written by Tena Moore


Obesity is defined as having excessive body fat that puts one’s health at risk. Although there are other ways to determine obesity, such as measuring body fat, most doctors usually determine obesity by using a ‘body mass index’ (BMI) number. A BMI number is generated by using the person’s height and weight to determine a number that will show whether a person is obese, overweight, a healthy weight, or underweight. For adults, a BMI number of 30 and over is considered obese.

Body Mass Index is found by using a specific formula:

Weight, divided by Height in Inches (squared), multiplied by 703 = BMI

Did that make sense? Here’s an example.

Let’s say I am 5’4” tall and weigh 147 lbs.

I would take my height and turn it into inches. There are twelve inches in a foot, so that is 64 inches. First, multiply 64 by 64 = 4,096, to get the height squared. Take the weight (147 lbs.) and divide it by the height squared, 4,096. Lastly, take that number and multiply it by 703. The answer is 25.2297 – in other words, my BMI would be 25 and slightly overweight. I could enter the ‘normal weight’ category, and increase my health, by losing a couple of pounds.

BMI Weight Categories:

Underweight: Less than 18.5

Normal Weight: 18.5 – 24.9

Overweight: 25.0 – 29.9

Obese – 30.0 +

If this seems like too much calculating, it is very easy to search online for a ‘BMI Calculator’ that will do the work for you. Just input your weight and height and the rest will be calculated automatically.



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Restricting Carbs Changes Liver Processes

Most Americans will agree: restricting carbohydrates is a good way to lose weight. Take out the bread, pastries and other high carbohydrate foods and the weight drops off. Regardless Americans have been increasing their consumption of carbohydrates and restricting fat intake. Most people look at fats to determine what they will eat and choose low fat options, even if this means high carbohydrates.

Subsequently, obesity is higher than it has ever been and non-alcoholic fatty liver disease (NAFLD) is becoming a major health issue. Even small children are being hit with this disease. If not treated right away, it can lead to cirrhosis, fibrosis and inflammation of the liver, which oftentimes leads to a liver transplant. Usually the disease can be reversed by eating healthy, exercising and losing weight.

Jeffery Brown of the University of Texas Southwestern Medical Center put together a study to find out the difference in metabolism when people eat low-carbohydrate diets, low-calorie diets, and balanced diets. Previous studies had suggested that a high-carb diet could lead to fatty deposits in the liver.

For the study, fourteen people with a body-mass-index (BMI) between 25 and 35 were chosen, along with 7 healthy subjects with a BMI less than 25. They split the fourteen subjects with a 25 to 35 BMI into two groups and had them follow either a low-calorie diet or a low-carbohydrate diet for two weeks. The other seven subjects with a healthy BMI followed their regular, healthy diet. All subjects had to undergo an overnight metabolic study assessing the metabolic pathways of the tricarboxylic acid cycle (TCA cycle) and the hepatic glucose production cycle.

What they found was that the weight healthy group with a BMI of under 25 who ate carbs as a normal part of their diet had enough energy to create glucose formation through the TCA cycle. Those who restricted their carbs did not.

The researchers found that a low-carbohydrate diet modifies hepatic energy metabolism and creates a dependence on lactate and amino acids for glucose production by the liver, instead of the liver using glycerol. A low carbohydrate diet also caused the liver to create more glucose with lactate or amino acids – increasing the rate of glucose formation. Unfortunately, they did not measure the amount of fatty acid that was delivered to the liver.

They also found that all groups had similar hepatic glucose production. While the healthy group and the low calorie groups maintained glucose production levels normally, the low carb group maintained the same by increasing glucose using amino acids and lactose.

The study was reported in the November 2008 issue of Hepatology.

The researchers suggest that this shift in glucose metabolism could be helpful to those who have NAFLD and need to dispose of hepatic fat. More studies are planned to measure fatty acid deposits and more.