Obesity

The Venus of Willendorf

Todd T. Eckdahl

• Publisher: Momentum Press
• Year: 2018
• ISBN:
  9781944749729
• Topic: Biological Sciences
• Subtopic: Genetics & Genomics
• Index: Biological Sciences

This book describes how obesity results from an imbalance between the intake of food energy and the expenditure of energy from physical activity and increases the risk of serious health problems including heart disease, stroke, osteoarthritis, and several types of cancer.

Obesity is a global health problem that has reached epidemic levels. The worldwide prevalence of adult obesity is 13 percent of adults and 7 percent of children. The author explains how body mass index (BMI) can be used to screen for obesity, but that its diagnosis depends on clinical measurement of total body fat content and distribution. The book describes rare forms of obesity caused by a single gene or a genetic syndrome, and common obesity, a complex disease caused by multiple genetic and environmental risk factors.

The book presents examples of obesity susceptibility genes and describes obesity genetic testing. It details how obesity can usually be treated with dietary changes, increased physical activity, and behavioral modification, but that people with extreme obesity or those who have serious health complications, require pharmaceutical or surgical interventions. Dr. Eckdahl discusses promising prospects for the treatment of obesity involving new pharmaceuticals, stem cell therapy, gene therapy, and fecal microbiota transplants.

CHAPTER 1

Symptoms and Diagnosis

Obesity occurs when an imbalance in energy intake and expenditure causes the body to accumulate and store unhealthy amounts of fat tissue. Obesity is accompanied by changes in physical appearance that can be quantified for use in obesity screening as well as physiological changes that can be clinically measured for the diagnosis of obesity. The accumulation of excess body fat has adverse health consequences for people who are overweight or obese. Some consequences impact daily life, such as breathlessness, increased sweating, joint pain, and fatigue, whereas others increase the risk of long-term health complications, including heart disease, stroke, liver disease, hypothyroidism, breathing problems, osteoarthritis, gallbladder disease, sexual and reproductive problems, and several types of cancer.

Screening for Obesity

In extreme cases, increases in body weight and body size are readily apparent signs of obesity, but usually it is hard to discern the borderlines between obesity and overweight, and between overweight and healthy weight. The most commonly used screening tool for obesity, body mass index (BMI), is also known as Quetelet’s Index because it is based on a formula first used by Adolphe Quetelet to conduct population studies of obesity in the nineteenth century. BMI is easily calculated as the ratio of weight, in kilograms, to height squared, in meters: BMI = weight (kg)/height (m)². With the English units of pounds and inches, the formula is: BMI = [weight (lb)/height (in.)²] × 703.1. There are many examples of online BMI calculators for both kinds of units (see three URLs in Bibliography). Because BMI is based on easily obtained measurements that are less expensive than more intrusive clinical data, BMI has gained widespread popularity as an indicator of obesity among both clinicians and members of the public. Organizations such as the WHO and the CDC have seized the opportunity to establish BMI as an easy-to-use screening tool for obesity because it shows a moderate correlation with direct clinical measurements of obesity, and a strong correlation with the occurrence of health complications associated with it. Table 1.1 lists the weight categories for children and adults based on BMI that are used by the WHO and the CDC. Adults with a BMI of 25 or higher are classified as overweight, and those classified as obese have a BMI of 30 or more. For example, a person who is 6 ft tall is considered overweight if they weigh 185 lb or more, and obese if they weigh 222 lb or more. For someone who is 5 ft 4 inches tall, the overweight range begins at 146 lb, and the obesity range begins at 175 lb.

For children, health organizations use population-level statistical sampling to account for the impact of age and sex on BMI when determining weight status. The WHO conducted the Multicenter Growth Reference Study (MGRS) from 1997 to 2003 to collect weights and heights for about 8,500 children of various ages from diverse worldwide ethnic and cultural backgrounds. For each age, and separately for boys and girls, the data were used to establish a median as the midpoint of the BMI distribution, and a standard deviation, which measures variation. The WHO determined that children aged 5 to 19 years have a healthy weight if their BMI is within 1 standard deviation of the MGRS median. Children with a BMI more than 1 standard deviation above the median are classified as overweight, and those with a BMI more than 2 standard deviations above the median are classified as obese. Children are considered to be underweight if they have a BMI that is more than 2 standard deviations below the median. Based on the assumption of a normal distribution, 68 percent of children in the MGRS had a healthy weight, and about 5 percent were obese. The WHO provides age- and sex-specific BMI charts that are used to determine the weight category for children aged 5 to 19 years. For children younger than 5 years of age, the WHO uses stricter standards for weight classification based on BMI. Children less than 5 years old with a BMI more than 2 standard deviations from the median for their age are considered to be overweight, whereas those with a BMI that is 3 standard deviations or more from the median are classified as obese. The CDC used a similar population-level statistical sampling approach when it conducted a national survey of age- and sex-specific childhood BMI from 1963 to 1994 that resulted in the information in Table 1.1. The BMI cutoffs used by the CDC for obesity and underweight are 2 standard deviations from the median, which are the same as those used by the WHO. A child with a BMI in the highest 5 percent is obese, and a child with a BMI in the lowest 5 percent is underweight. According to the CDC, a child with a BMI in the 85th to 95th percentile is classified as overweight, and a child with a BMI in the 5th to 85th percentile is considered to have a healthy weight. The CDC provides a useful online tool that calculates a BMI for a given male or female child to determine a percentile, and reports weight status (see URL in Bibliography).

Table 1.1 WHO and CDC weight categories for children and adults based on BMI

Weight classification	BMI
	Adults	Children 5 to 19 years
Underweight	< 18.5	< 5th percentile
Healthy weight	18.5 to 24.99	5th to 85th percentile
Overweight	25.0 to 29.99	85th to 95th percentile
Obese	> 30.0	> 95th percentile

BMI is used to determine overweight and obesity, but because it depends on weight, it is not a direct measure. BMI is a surrogate measure of body “fatness,” and is at best a screening tool for overweight and obesity. BMI is most appropriately used as a population-level statistic, but when it is applied to individuals, it becomes less reliable because of confounding variables such as bone density, body type, sex, and age. Muscle is about 18 percent denser than fat, so another confounding variable is the ratio of muscle to fat tissue in the body. BMI misclassifies people as overweight or obese who have an unusually high density of muscle, such as athletes. Because BMI is calculated as height divided by the square of weight, shorter people are misclassified as thinner than they really are, and taller people are misclassified as fatter. A suggested solution to this problem is to tweak the BMI formula by dividing height by weight raised to the power 2.5.

Another problem with BMI is that it does not take into account differences in the distribution of body fat that affect the risk of health complications associated with obesity. A commonly used measure of abdominal obesity is waist circumference (WC). WC should be measured at the midpoint between the last rib and the upper margin of the hip with a stretch-resistant measuring tape using a moderate amount of tension. The person should be standing with feet close together, and the measurement should be taken just after a breath has been exhaled. According to the National Heart, Lung, and Blood Institute, for people with a BMI between 25 and 35, a WC greater than 40 in. (102 cm) for men or 35 in. (88 cm) for women is associated with an increased risk of cardiovascular disease, hypertension, and type 2 diabetes. The predictive value of WC varies among different ethnic groups, and its value is reduced for people with a BMI greater than 35. The waist-to-hip ratio (WHR) is defined as the ratio of WC divided by hip circumference, measured at the widest part of the buttocks, making sure to keep the measuring tape parallel to the floor. WHR is correlated with heart disease and diabetes. The WHO defines abdominal obesity as a WHR greater than 0.90 for males and 0.85 for females, whereas the National Institute of Diabetes and Digestive and Kidney Diseases sets WHR obesity cutoffs at 1.00 for men and 0.80 for women. The waist-to-height-ratio (WHtR), also known as the waist-to-stature ratio, is obtained by dividing WC by height. Higher WHtR values have been correlated with an increased risk of heart disease and stroke. For males and females under 50 years old, public health research shows that a healthy WHtR is 0.5 or less, whereas people over the age of 50 years are considered to be obese if they have a WHtR greater than 0.6.

Diagnosis of Obesity

When used to describe molecules associated with obesity, the term fat means lipids, including oils, waxes, fatty acids, cholesterol, phospholipids, and triglycerides that contribute to energy metabolism, cell signaling, and the structure of cells. The tissue with the highest fat content is adipose tissue, and it is about 80 percent fat. Fat also accumulates in nonadipose tissues such as muscle, pancreas, and heart. The healthy fraction of body mass that is adipose tissue is 21 percent, but its distribution in the body varies widely according to sex, age, ethnicity, and environmental factors, especially those associated with diet and physical activity. Subcutaneous adipose tissue is found just beneath the skin, where it serves as a protective physical barrier and as insulation against temperature extremes. Internally, adipose tissue is distributed as visceral adipose tissue that pads the organs of the chest, abdomen, and pelvis, and as nonvisceral adipose tissue in muscles, bone marrow, between muscles, and in the interface between muscle and bones. The cellular composition of adipose tissue is primarily adipocytes (fat cells), which have intracellular compartments that store fat, but adipose tissue also contains blood cells and endothelial cells. Adipose tissue can be categorized according to its primary function. The primary function of white adipose tissue is to store metabolic energy in the form of fat molecules, whereas brown adipose tissue helps to regulate internal body temperature in response to environmental variation. Mammary gland adipose tissue supports the production of milk, and bone marrow adipose tissue supports the development of blood cells and bone cells. Adipose tissue is beneficial when it is not produced in excess.

The clinical diagnosis of obesity depends on reliable tools that directly measure the content and distribution of adipose tissue in the body. The skinfold test, also known as the caliper test, is a measure of subcutaneous adipose tissue. For this test, the patient should be relaxed and standing, and should not have just recently exercised. A specialized caliper is used to pinch the skin in a standardized manner, and the thickness of the skinfold is recorded as the average of two measurements in each location. For men, the skin is pinched on one side of the body at the chest, abdomen, and thigh, and for women, it is pinched at the triceps, thigh, and the top of the hip. There are several methods by which the direct measurement of subcutaneous adipose tissue is used to calculate body fat percentage (BFP), based on assumptions about the distribution of fat in adipose tissue and other tissues. The most common method is to use the Jackson-Pollock formula to calculate body density and the Siri equation to calculate BFP. The American Council on Exercise (ACE) established five BFP categories: essential, athletic, fit, acceptable, and obese. For women, the BFP cutoff between acceptable and obese is 32 percent and for men it is 25 percent. According to the ACE, the skinfold test has an error rate of 3.5 percent when performed by a qualified technician.

Another clinical method for estimating BFP is bioelectrical impedance analysis (BIA). BIA is conducted with a portable and noninvasive instrument that uses the impedance of a small electrical current flowing through body tissue from one wrist to the opposite ankle to estimate total body water, which is in turn used to calculate BFP. BIA accuracy is reduced by dehydration and exercise before measurement, both of which decrease total body water and cause an underestimation of BFP by as much as 4 percent. Measurements of BFP with BIA can also vary by 4 percent depending on how recently the patient had a meal. The accuracy of BIA instruments varies widely, and most consumer-grade instruments underestimate BFP.

BFP can also be measured by exploiting the difference in density between adipose tissue and muscle. Underwater weighing, also known as hydrostatic weighing or hydrodensitometry, is a noninvasive way to estimate the overall body density of a patient by comparing their dry weight to their we...

Table of contents

• Cover
• Title Page
• Copyright Page
• Contents
• Acknowledgments
• Introduction
• Chapter 1 Symptoms and Diagnosis
• Chapter 2 Causes and Contributing Factors
• Chapter 3 Treatment and Therapy
• Chapter 4 Future Prospects
• Conclusion
• Glossary
• Bibliography
• About the Author
• Index