Fat Cells & Obesity

In order to grasp the etiology of the rapidly growing obesity epidemic, it is necessary to understand the relationship between obesity and fat cells. There are some misconceptions and stereotypes regarding the obese, and many of them overlook the fact that the number of fat cells, not only weight, plays a role in the development and formation of an obese individual. According to John Karam’s article, “Fat Cells--Not Fat People,” there is new evidence refuting the common definition of obesity as an excessive amount of total body fat and supporting a more accurate definition of obesity as an excessive amount of fat per adipose cell.

Body Fat

Body fat is categorized as either essential fat or storage fat. As defined in Krause’s Food and Nutrition Therapy, essential fat, which is necessary for normal physiologic functioning, is stored in small amounts in the bone marrow, heart, lung, liver, spleen, kidneys, muscles, and lipid-rich tissues in the nervous system. Storage fat, on the other hand, accumulates under the skin and around internal organs to protect them from trauma. It is the primary energy reserve of the body and is stored as triglycerides in depots made up of adipose tissue. Storage fat is expendable and is found in greater amounts in obese individuals.

Types of Adipose Tissue

While composed primarily of fat, adipose tissue also contains water and protein. There are two major forms of the tissue: white adipose tissue, or WAT, and brown adipose tissue, BAT. WAT is the conventional form of fat found in most obese individuals. According to Mahan, WAT serves three major functions, including: heat insulation, energy storage, and cushioning to protect abdominal organs. BAT is found mostly in infants and small amounts in adults around the scapular and subscapular areas. Its primary function is to burn energy and produce heat in response to a cold environment. Because brown cells burn calories, recent studies such as Sven Enerback’s article, “Human Adipose Tissue,” support BAT as a possible regulator of human energy expenditure, which may play a therapeutic role in obesity and obesity-related diseases.

Adipocytes

An adipocyte is made up of a large triglyceride surrounded by cytoplasm containing mitochondria and a nucleus. It follows a normal pattern of growth and development. Karam’s article states that the number of adipocytes in an adult stays the same whether weight increases or decreases. The fat tissue increases either by increasing the size of the cells already present when lipid is added, known as hypertrophy, or by hyperplasia, which increases the number of fat cells. Hypertrophy can occur at any time in the lifespan while hyperplasia usually occurs as part of the growth process in infancy and adolescence. Weight gain occurs by either hypertrophy, hyperplasia, or a combination of the two.

Fat Cell Development

Hyperplastic-hypertrophic obesity occurs when an infant or child develops excess adipose cells and each cell greatly expands. While cell numbers increase in both lean and obese children into adolescence, the numbers increase faster in obese children than lean children. While most adults have the normal amount of fat cells, body fat increases primarily as an in increase in adipose cell size in adult-onset obesity. According to Mahan, fat cell numbers do not increase until maximum cell size is reached. Prevention is the key to obesity prevention because once fat is gained, it is difficult to lose.

Therapeutic Goals in Obesity

The more common hypertrophic adult onset obesity is usually the type most easily treatable for reduction and maintenance. In contrast, reduction of hyperplastic-hypertrophic obesity is rarely achieved. According to Karam’s article, until there are improved techniques in fat cell measurement, therapeutic goals in managing obesity should primarily aim to reduce levels of circulating insulin, glucose, and triglycerides.