According to the Centers for Disease Control and Prevention, in general, obesity results when a person’s body fat accumulates over time, mainly as a result of what is called a chronic energy imbalance.
In other words, the calories consumed exceed the calories expended in such activities as exercise.
Obesity is a major health hazard worldwide.
It is also extremely costly, as it is associated with workplace absenteeism, mainly because of obesity’s association with other diseases, such as diabetes, hypertension, heart disease, and some cancers.
Of course, eating is only part of the story when it comes to obesity.
Other conditions may exist, such as thyroid disease, genetic predisposition, and/or taking certain medications.
What is the health care definition of obesity?
According to the National Heart, Lung, and Blood Institute (in cooperation with the National Institute of Diabetes and Digestive and Kidney Disease), obesity is most often defined in terms of body mass index, or BMI.
These numbers are based on a person’s weight and height, with most health care professionals agreeing that there is a strong correlation between BMI and total body fat content.
A person who is overweight is usually considered to have a BMI of 25 to 29, while a person who is obese has a BMI of 30 or higher. (For more about BMI, see this chapter.)
What are some reasons for so many people being overweight or obese in the United States?
Although the subject is highly debated, a great deal of research has indicated that there are several major reasons for the overweight and obesity problems in the United States.
And the list of reasons is very long and often convoluted as not everyone has the same chemistry, eats the same, or lives under the same conditions.
But there are some suggestions for why people have gained so much weight over the past several decades.
For example, serving sizes have changed over that time both in homes and in restaurants (in other words, people often eat more now, mainly because food is often plentiful and available).
In addition, the average American diet tends to include many foods that are high in fats and sugars.
The standard portion size for many foods has increased over the past several years, including “supersized” portions at fast-food restaurants that offer more calories, sugars, and fats.
This type of diet, coupled with a lack of physical activity, often leads to people’s becoming overweight and obese.
In addition, life has become more stressful for many people.
Stress often leads to a change in eating habits (mainly eating more) in response to negative emotions such as sadness, anger, and boredom.
Poor diet and sedentary lifestyle are the two biggest reasons for being obese. America is facing an obesity epidemic, with nearly 36% of Americans falling into this category.
What is fat in the human body?
Fat in the human body is medically called adipose tissue and is found in several places in the body.
Fat is made up of unique cells, simply referred to as fat cells.
In general, fat cells are found beneath the skin and on top of both kidneys, along with some that is stored in the liver and a small amount in the muscles.
In most people, the number of fat cells remains the same after they reach puberty (exceptions are if an adult has liposuction or if the person gains a significant amount of weight).
And while the number of fat cells remains the same, each cell can get larger, which is why people “gain weight” without increasing the number of fat cells. (For more about how fats are metabolized, after ingestion, by the digestive tract, see the chapter “How Diabetes Affects the Digestive System.”)
What are white and brown fats?
In general, fat cells are divided into white and brown fats.
Overall, a person carries white fat, or fat that cushions the body near the surface and makes up around 90 percent of body fat.
These fat cells are large and have little cytoplasm and a small nucleus, with a fat droplet making up around 85 percent of the cell’s volume.
They are most important to energy metabolism and heat insulation in the body.
Brown fat is mostly found in newborn babies between the shoulders and is important to making heat (called thermogenesis) as newborns do not have much white fat to insulate their bodies and retain heat.
The cells have a small amount of fat droplets and many mitochondria, or cell organelles (structures within the cell) that can generate heat.
Adults usually have little or no brown fat, but if they do, it is most often found around the upper back, the nape of the neck, the armpits, between the shoulder blades, and deep in the chest cavity.
Is there a connection between white and brown fat, obesity, and diabetes?
According to some studies, and even though most adults carry few or no brown fat cells, some researchers believe that the proportions of white and brown fat cells may be connected to being overweight or obese. They suggest that because brown fat primarily burns calories and white fat stores calories, some overweight and obese people may have less brown fat than adults who are not obese, or the brown fat in a person who is overweight or obese is not as efficient in burning calories. Either way, the fat is more readily stored in these people than burned off.
Exercise may also change a person’s white fat.
In a 2016 study, researchers found that exercise may help to control weight and to fend off diabetes by changing white fat into brown.
This may be due to a boost in a hormone, irisin, that is produced during exercise.
This previously unknown hormone apparently migrates mostly to fat and, through several biochemical processes, causes some of the normally white fat cells to turn to brown fat cells, fat that is known to burn calories and improve control of insulin and blood glucose.
Where does fat collect in the abdomen, especially fat that can lead to obesity?
Two types of fat associated with obesity collect in the upper body (abdomen).
The intraabdominal fat, also called visceral or organ fat, collects around organs and represents about 10 percent of the upper-body fat.
Around 90 percent is called regular, organ, or abdominal subcutaneous fat and is found under the surface of the skin.
It is the type of fat that can be grasped with a hand and is located between the skin and the outer abdominal wall.
While fat found under the surface of the skin may be in some ways connected to abdominal obesity and metabolic risk factors, the intra-abdominal fat is thought to be a much stronger indicator, even predictor, of metabolic abnormalities, diseases, and a person’s mortality.
Who discovered the connection between upper-body obesity and the risk of such diseases as diabetes?
I n 1947, French physician Jean Vague (1911, 2003) was the first person to mention that upper-body obesity was somehow linked to such diseases as gout, atherosclerosis, and diabetes. Later, this finding was further attached to the metabolic syndrome, the clustering of at least three of five conditions, with upper-body obesity being one of the five conditions.
Why is intra-abdominal (visceral or organ) fat thought to affect a person’s health?
Research indicates that fat cells (in particular, intra-abdominal [visceral] fat cells) are considered to be biologically active, with some scientists thinking of the fats as similar to an endocrine organ or gland. This is because the fats can produce hormones and other substances in a person’s body, along with affecting other hormones in the body, that can affect the person’s overall health. The following are some of the connections researchers have made between visceral fat and health:
Cardiovascular disease , Visceral fat pumps out immune-system chemicals called cytokines that can contribute to the increased risk of cardiovascular disease. The cytokines, along with other chemicals in the body, are believed to have a bad effect on cells’ sensitivities to insulin, blood pressure, and blood clotting.
Diabetes , Visceral fat is connected to many of the conditions included in diabetes. For example, it is associated with glucose intolerance and insulin resistance (see next on the list), which are in turn connected to type 2 diabetes.
Insulin resistance , Research indicates that visceral fat secretes more of retinol-binding protein 4 (referred to as RBP4), a molecule that increases insulin resistance (when the body’s muscle and liver cells don’t respond to the normal levels of insulin and blood glucose levels rise). Thus, if the visceral fat increases, the RBP4 level also increases.
Portal vein connection , Intra-abdominal fats can also be harmful depending on their location in the body.
For example, if the excess visceral fat is located near the vein that carries the blood from the intestinal area to the liver, it can cause a problem. (The vein is called the portal vein and has other functions, too.) In particular, intra-abdominal fat can release substances such as free fatty acids that can travel to the liver, where they influence the production of blood lipids.
This condition is often associated with higher LDL (the “bad” cholesterol), lower HDL (the “good” cholesterol), and insulin resistance. (For more about cholesterol, see the chapter “How Diabetes Affects the Circulatory System.”)
Women’s health , Other research suggests that for some women, intra-abdominal fat may also be associated with breast cancer and the need for gallbladder surgery.
Dyslipidemia , Dyslipidemia is a condition in which the body has an abnormally high amount of lipids, mainly triglycerides, cholesterol, or both. It is thus connected to intra-abdominal fat.
Inflammation , Research indicates visceral fat is often associated with inflammation in various parts of the body. Thus, because this fat can trigger low-level inflammation, it is usually considered a risk factor for certain chronic conditions associated with inflammation, such as asthma.
Other disease connections , Some research has recently tied several other diseases with visceral fat.
One is dementia, one study found people in their early 40s with high levels of visceral fat (compared with those without such fat at that age) were nearly three times more likely to develop dementia, including Alzheimer’s, by their mid-70s to early 80s.
Another is colorectal cancer.
Some studies indicate that a person with a great deal of visceral fat may have three times the risk of developing colorectal adenomas (or what are usually referred to as polyps) than people with much less intra-abdominal fat; it was also found that these types of polyps in a person’s colon are connected to insulin resistance.
Can intra-abdominal fat be measured?
Yes, there are several ways to measure intra-abdominal (visceral) fat, although some are more accurate than others.
The most accurate ways to date are CT scans and full-body MRIs, but not everyone can afford to pay for these methods.
Another procedure uses a bioelectrical impedance machine that uses an electric current to differentiate between fat tissues in the abdomen.
Still another approach can be done at home, although it is not as accurate as a CT scan or bioelectrical impedance machine.
It entails measuring the person’s waist and hip circumference with a tape measure, then dividing the waist by the hip measurement.
In most cases, a number greater than 1.0 for men and 0.85 for women is considered excessive amount of visceral fat, whereas a lower number (for example, for a man a result of 36/40, or 0.9) means there is not as much in terms of intraabdominal fat.
But this is only an estimate because some of the fat will be subcutaneous fat.
To make the number more accurate, measure the waist when you are lying down, then divide by the hip measurement.
Since the subcutaneous fat usually will fall to the side of the body when it is lying down, the visceral fat will remain.