No matter how slim you are, we all have body fat distributed throughout the body. Adipose tissue is an organ of our body and plays a vital role in determining our health. Like the fat in our food, some types of body fat are better than others, and too much adipose tissue can have a detrimental effect on our health.
The function of fat cells
As an organ, fat in the body has various roles which affect our overall physiology. Fat helps insulate us against temperature extremes and when your body utilises it, fat is a reliable energy source. Fat forms cell membranes and creates compounds such as vitamin D, hormones and bile.
Fat is vital for the absorption and storage of some key nutrients. Without an adequate intake of fat, fat soluble vitamins A, D, E and K won’t be able to function.
While the ideal amount of body fat varies from person to person, what we do know is having too much or too little body fat can cause significant health issues.
The types of fat in your body
Adipose tissue is made up of fat cells or adipocytes that are distributed around the body depending on the individual. There are several types of fat:
- Subcutaneous fat
This form of fat is what you feel when you pinch your love handles or squeeze your belly fat. It’s located just under the skin, makes up nearly 80 percent of all body fat and is generally considered less harmful than other types of deeper fat.
Subcutaneous fat cells secrete leptin, often referred to as the “obesity hormone” or “fat hormone”. Leptin helps inhibit hunger as well as regulate energy balance. If the person has excess subcutaneous fat, leptin levels increase and overtime, causes resistance to the hormone. The more the person eats, the more the fat cells produce leptin.
- Visceral fat
Visceral fat surrounds your internal organs inside the abdominal cavity. Increased visceral fat can be detrimental to your health. Unlike subcutaneous fat, visceral fat secretes large quantities of the pro-inflammatory cytokine interleukin 6 (IL-6).
IL-6 is implicated in a whole list of chronic diseases including diabetes mellitus, with researchers believing the pro-inflammatory cytokine main be the leading cause of insulin resistance. The presence of visceral fat also drives your risk of heart disease, stroke and dementia.
- Intrahepatic fat
The fat inside the liver is known as intrahepatic fat. Obesity and aging increases intrahepatic fat accumulation, which can lead to non-alcoholic fatty liver disease and metabolic complications including insulin resistance, diabetes and coronary heart disease.
- Epicardial fat
The visceral fat deposits surrounding your heart is known as epicardial fat. It can potentially cause inflammation and has a direct effect on heart function and coronary atherosclerosis. Epicardial fat is associated with serious health problems including obesity, diabetes and hypertension. These visceral fat deposits are also implicated in the presence of coronary artery disease.
- Gluteofemoral fat
Gluteofemoral fat is body fat distributed around your hips, thighs and bottom, and is typical of a pear-shaped body type. Unlike fat around the abdomen, fat in the lower part of the body may be protective against heart disease and diabetes. This type of fat accumulates over time and is much harder to break down than the fat deposits in your upper body. When broken down there are much fewer pro-inflammatory cytokines released compared with visceral fat which is why carrying gluteofermoral fat is less detrimental to your health.
- Intermuscular fat
These fat deposits are those between and within the muscles, found beneath the muscle fascia. It’s a good predictor of decreased muscle function and mobility, particularly in older adults. It’s also implicated in a variety of conditions including stroke, insulin resistance and diabetes. Injury to the muscles, obesity, age, inactivity and disease are all factors that increase the levels of intermuscular fat.
- Intramuscular fat
Intramuscular fat is found within the muscle and occurs during ageing and in some pathological circumstances. It serves as an energy storage for the body that can be used during exercise. Higher levels of intramuscular fat have been associated with abnormal blood pressure, lipids and glucose levels mainly due to the levels of body fatness overall. However, higher levels of intramuscular fat alone are associated with the presence of metabolic syndrome.
- Brown fat
Brown fat is considered more like muscle than fat, because when activated it burns fat. Recent studies have found that lean people have higher levels of brown fat than those who are overweight or obese. Children also have more brown fat to help protect them from the cold. In adults, the brown fat is more active in the colder months to assist with temperature regulation.
Fat is disturbed differently between genders and populations
Where your fat is distributed around the body could actually be more critical than the total amount of fat you’re carrying. For example, central obesity is associated with a greater risk of heart disease, stroke, hypertension, diabetes, gall stones and even some types of cancers. In fact, overweight people with no abdominal fat are suspected to have less health complications than those who do carry fat around their mid-section.
Your gender can greatly depict where you’re more likely to carry excess body fat and your disease risk. Upper-body fat is more common in men, which increases their risk of heart disease, stroke, diabetes, hypertension and some cancers.
Women on the other hand, are more likely to carry their fat in the lower body which is generally not associated with chronic diseases. To a lesser extent than men, women post-menopause often begin to store the fat around their waist and abdomen due to a reduction in oestrogen.
Fat is also distributed around the body in different populations. Japanese men for example, carry more body fat for a given BMI than white Australians. Australian Aboriginal women have a greater waist circumference when compared to Australian of European descent.
South Asian people have smaller subcutaneous fat reserves with greater risk of visceral fat gain than white people. And black Americans carry more subcutaneous fat and less visceral fat than white Americans.
The harmful effects of inflammation and fat tissue
Chronic inflammation contributes to a whole host of chronic diseases. Inflammation of fat tissue is implicated in the development of metabolic syndrome problems including type 2 diabetes.
Adipose tissue secretes proteins, known as adipokines, that help regulate your energy balance as well as other body functions. In the event adipose tissue is allowed to accumulate, especially around the abdomen, genes are activated creating adipokines involved in inflammation and insulin resistance. Elevated blood lipids due to a high-fat diet or obesity also promotes inflammation.
Inflammation is also driven by an increase in the number of immune cells located in the adipose tissue. Scientists have found that high calorie diets cause fat cells to make a group of proteins called major histocompatibility complex II (MHCII). These proteins are usually activated to support the immune system fight off pathogenic viruses and bacteria. In overweight people, adipocytes generate false distress signals which activates the immune cells causing inflammation.
The occurrences of this inflammation starts with an excess of nutrients entering the bloodstream. These are converted and stored as fat and stimulates the secretion of leptin. As the person continues to consume a high calorie diet, leptin levels increase and cause nearby CD4 T cells to become excited. This eventually leads to the proteins producing MHCII, resulting in inflammation.
Essentially this is an uncontrolled immune response to the modern day, high calorie diet and is likely to have severe long-term consequences for people who are overweight or obese.
All these factors explain why chronic inflammation is associated with obesity and an excess of adipose tissue contributes to metabolic syndrome and leads to chronic diseases. As you would expect, weight loss will see a reduction in the number of immune cells located in the adipose tissue, will lead to hormone regulation, and will alter the gene expression which will result in an improved inflammatory status long term.