What Does Total Body Fat Consist of?

The Significance of Body Fat

We may not always appreciate body fat, especially when it gathers in certain areas like our bellies or thighs. However, fat plays a crucial role as a source of stored energy when we are unable to access food for extended periods. Body fat, also known as adipose tissue, contains not only fat cells but also nerve and immune cells, as well as connective tissue. Within this matrix, fat tissue releases hormones that regulate metabolism and appetite, such as leptin and adiponectin. It also affects insulin sensitivity through hormones like tumor necrosis factor-alpha and interleukin-6. In addition, various immune cells found in fat tissue, such as macrophages, neutrophils, and eosinophils, contribute to both anti-inflammatory and proinflammatory processes. Fat cells also secrete proteins and produce enzymes that support immune function and the production of steroid hormones.

Fat cells can increase in size and number. The number of fat cells in our bodies is established soon after birth and during adolescence. It tends to remain stable in adulthood, as long as our weight remains relatively constant. However, consistently consuming excessive calories can lead to an increase in the size of fat cells and their storage in different areas throughout the body. This can result in a higher risk of chronic inflammation, disruptions in healthy metabolism, and the potential development of new fat cells. These larger fat cells also become resistant to insulin, which further raises the risk of type 2 diabetes and cardiovascular disease. While weight loss can shrink fat cells in size, it does not reduce their number.

Obesity, characterized by an excessive amount of body fat, is a prevalent and costly medical condition in the United States. It is strongly associated with an increased risk of heart disease, stroke, type 2 diabetes, certain types of cancer, and premature death from these diseases. Gaining a better understanding of body fat’s functions and various types can enhance our comprehension of this condition.

Different Types of Body Fat

Fat tissue comes in various forms, including white, brown, beige, and even pink. Some types of fat are essential for maintaining good health.

Types

1. Brown fat: Infants have the highest amount of brown fat, which helps keep them warm. It is activated by cold temperatures to generate heat. The quantity of brown fat does not change with increased calorie intake. Individuals with overweight or obesity typically have less brown fat compared to lean individuals.
2. White fat: This type of fat consists of large round cells and is the most abundant. It is primarily responsible for storing fat and tends to accumulate in areas such as the belly, thighs, and hips. White fat cells secrete over 50 hormones, enzymes, and growth factors, including leptin and adiponectin, which improve the liver and muscles’ response to insulin. However, excessive white fat cells can disrupt these hormones, leading to insulin resistance and chronic inflammation.
3. Beige fat: Beige fat is a subtype of white fat that can convert to perform similar functions as brown fat. It has the ability to generate heat in response to cold temperatures or during exercise.
4. Pink fat: Pink fat refers to white fat that turns pink during pregnancy and lactation. It plays a crucial role in the production and secretion of breast milk.
5. Essential fat: Essential fat can consist of brown, white, or beige fat and is vital for normal bodily functions. It is found in most organs, muscles, and the central nervous system, including the brain. Essential fat helps regulate hormones like estrogen, insulin, cortisol, and leptin. It also contributes to body temperature regulation and aids in the absorption of vitamins and minerals. When body fat falls below a certain level (less than 5% in men and less than 10% in women), there may not be enough essential fat to support these essential functions.

Location

1. Subcutaneous fat: This layer of fat is located directly beneath the skin’s surface and provides cushioning for the bones and joints. It is the most abundant type of fat in the body and tends to accumulate around the waist, hips, upper back, buttocks, and thighs. While high amounts of subcutaneous fat can increase the risk of disease, it is not as significant as visceral fat.
2. Visceral fat: This type of fat is commonly referred to as “belly fat” or “central obesity” as it accumulates deep in the abdominal cavity, surrounding organs such as the pancreas, intestines, liver, and heart. Having a large amount of visceral fat is associated with a higher risk of cardiovascular disease, diabetes, and certain cancers. Visceral fat may also release inflammatory chemicals called cytokines, which contribute to insulin resistance.

Measuring Body Fat

Determining body fatness, or obesity, involves various methods that differ in accuracy and limitations. Combining multiple methods, when possible, can provide a better prediction of an individual’s health risks related to weight.

Body Mass Index (BMI)

One of the most commonly used tools for estimating excess fat is the body mass index (BMI). BMI measures excess weight by calculating the ratio of an individual’s weight to their height. Although BMI has limitations, research has shown that it often correlates with more accurate measures of fat mass and fat-free mass, such as underwater weighing and dual X-ray absorptiometry. Unlike these expensive and invasive methods, BMI is noninvasive, easy to calculate, and applicable anywhere.

However, BMI cannot determine the distribution of fat (e.g., belly fat), muscle mass, or bone mass, which all contribute to overall weight. Age, sex, race, and ethnicity can also influence BMI. For example:

• Women tend to have more body fat and less muscle mass genetically compared to men.
• Highly trained athletes may have a higher BMI due to increased muscle mass and lower body fat.
• Older adults generally carry more body fat than younger adults.
• While BMI and weight typically decline in the elderly, visceral abdominal fat may continue to increase.
• Individuals with larger body frames may have a higher weight due to greater bone mass rather than fat mass.
• Some studies have found that Black individuals have less body fat and more lean muscle compared to other ethnicities with the same BMI. However, Blacks and Hispanics have higher obesity rates in the U.S., resulting in a greater overall burden of obesity-related diseases in these groups.

Considering these factors, BMI is often used as a screening tool for potential weight-related problems rather than a diagnostic tool for specific conditions. Its accuracy in predicting health risks can vary across individuals and racial and ethnic groups. Certain populations may have higher rates of obesity without corresponding rates of metabolic diseases, and vice versa. Southeast Asians, for instance, may have a normal BMI but still be metabolically unhealthy.

For a quick calculation of BMI, follow these steps:

1. Divide your weight in pounds by your height in inches.
2. Divide the result by your height in inches.
3. Multiply the answer by 703.

Interpreting the BMI number:

• The World Health Organization defines a “normal” weight as a BMI between 18.5 and 24.9. A BMI of 25.0 to 29.9 is categorized as “overweight” or “pre-obesity,” while a BMI of 30 or higher is classified as “obesity.” Obesity is further divided into Class I (BMI 30.0 to 34.9), Class II (BMI 35.0 to 39.9), and Class III (BMI 40 or higher).

At the population level, a high BMI is generally associated with an increased risk of disease and premature death. Numerous studies have demonstrated a clear relationship between BMI and mortality. Both individuals categorized as underweight (BMI < 18.5) and those with overweight or obesity (BMI > 25) have higher mortality rates. The lowest mortality rate from any cause is generally associated with a BMI range between 22.5 and 24.9. However, it’s important to consider certain methodological flaws when studying this relationship. Some previous studies failed to account for variables such as smoking, cancer, heart disease, or age-related weight loss, which can lead to misleading results suggesting a survival advantage for overweight individuals.

Waist Circumference

Some researchers argue that waist circumference is a better indicator of unhealthy body fat compared to BMI. It specifically addresses visceral abdominal fat, which is associated with metabolic problems, inflammation, and insulin resistance. Waist circumference is a reliable predictor of disease risk and premature death. It provides a clearer picture of health because abdominal fat can increase even when total weight remains the same. Increasing waist size over time may be an even stronger warning sign of health risks, especially in individuals who are not overweight.

The Nurses’ Health Study, for example, analyzed the relationship between waist size and death from heart disease, cancer, or any cause among middle-aged women. The study found that women with the highest waist sizes (35 inches or larger) had nearly double the risk of dying from heart disease compared to women with the smallest waist sizes (<28 inches). The risk of death from cancer or any cause increased steadily with each additional inch around the waist. Even women with a “normal weight” (BMI < 25) had a higher risk if they had a waist size of 35 inches or higher. Their risk of death from heart disease was three times higher than that of normal-weight women with smaller waists.

To measure waist circumference:

• Wear thin clothing or no clothing.
• Stand up straight and wrap a flexible measuring tape around your midsection, crossing it at the level of your navel (belly button).
• The tape should be snug but not too tight.
• Inhale and exhale regularly while measuring.
• Repeat the measurement 2-3 times for consistency.
• A waist size larger than 40 inches for men and 35 inches for women increases the chances of developing heart disease, cancer, or other chronic diseases.

Waist-to-Hip Ratio

Similar to waist circumference, waist-to-hip ratio (WHR) is used to measure abdominal obesity. It is calculated by dividing the waist measurement by the hip measurement. WHR is a simple and inexpensive tool that predicts disease risk and premature death. Some argue that WHR may be a more reliable indicator than waist circumference alone, as waist size can vary based on body frame size. However, a large-scale study found that both waist circumference and WHR were equally effective at predicting the risk of death from heart disease, cancer, or any cause.

Interpreting WHR values can be more complex since a higher reading can be caused by excess abdominal fat or decreased lean muscle mass around the hips. Additionally, cut-off points defining health risks can vary by ethnicity. For example, Asians may show higher metabolic risk with higher body fat at a lower BMI. As a result, the cut-off value for a healthy WHR is 0.80 or less for Asian women, compared to 0.85 or less for Caucasian women.

To measure and interpret WHR:

• Stand up straight and measure your waist circumference as described above.
• Then, measure the widest part of your buttocks.
• Divide the waist size by the hip size.
• A WHR of more than 0.90 for men and 0.85 for women indicates abdominal obesity.

Waist-to-Height Ratio

Waist-to-height ratio (WHtR) is a simple and inexpensive screening tool for measuring visceral abdominal fat. Research has shown that WHtR predicts cardiometabolic risk factors, such as hypertension and premature death, even when BMI falls within a healthy range. When the waist circumference is less than half of one’s height, it signifies lower risk.

To calculate WHtR:

• Divide waist circumference in inches by height in inches.
• A measurement of 0.5 or higher indicates health risks related to visceral obesity.

Additional Measures of Body Fat

Although less commonly used, here are some other methods for measuring body fat:

• Dual-energy X-ray absorptiometry (DEXA): This method measures bone density, lean mass, and fat mass using X-rays.
• Bioelectrical impedance analysis (BIA): BIA measures body fat by sending a small electrical current through the body. It estimates body composition based on the current’s resistance.
• Skinfold thickness: This method involves using calipers to measure the thickness of skinfolds at various locations on the body. These measurements are then used to estimate body fat percentage.

It’s essential to remember that each method has its strengths and limitations. Consulting with a healthcare professional can provide personalized recommendations based on your specific circumstances.

Conclusion

Understanding the different characteristics of body fat is crucial in recognizing its impact on health. By considering various measures such as BMI, waist circumference, and waist-to-hip ratio, we can gain valuable insights into the distribution and health risks associated with body fat. However, it’s important to interpret these measures alongside other factors such as age, sex, race, and ethnicity. Taking a comprehensive approach to assessing body fatness can help individuals make informed decisions about their overall health and wellbeing.

Source: 5 WS