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Getting To Know Fat

How Apples, Pears Play An Endocrine Role


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Battle of the Fat Hormones

There is more at play than getting off the couch and cutting calories when a person with obesity tries to lose weight. Other factors that impact the struggle to drop both pounds and comorbidities include –

Leptin - No more, I’m stuffed!

A hormone released by adipose tissue
Signals a feeling of satiety to the hypothalamus in the brain

Excessive stores of adipose tissue equal overly high concentrations of leptin and resistance to its appetite suppressive effects

Has inflammatory actions

Resistin - The insulin resister

A hormone released by adipose tissue

Has been linked to insulin resistance and the inflammatory process

Adiponectin - The Yang to the Yin

A hormone released by adipose tissue

Improves satiety and has anti-inflammatory effects

Counteracts negative effects of other adipose-derived hormones, such as difficulty controlling appetite and comorbidities

In state of obesity, can become overwhelmed by actions of competing hormones

Increases as the body loses fat
There is more to the body's stores of fat than the excessive padding that meets the eye.

Body fat, or adipose tissue, actually functions as an endocrine gland. It secretes a wide range of protein signals and factors called adipokines, which can impact attempts at weight loss and raise the risk of cormorbidities associated with obesity.

Adipokines such as leptin, resistin, and adiponectin, are the "language" of fat. They send messages and network with other organs and metabolic systems about changes in the amount of adipose tissue to help the body regulate its fuel usage. Excessive stores of adipose tissue secrete large concentrations of adipokines, which work to increase the risk for comorbidities.

Pathology of fat

As a person packs on the pounds, there is a rise in an adipose-derived adipokine called resistin. Although research on resistin still is in its infancy, this hormone is believed to cause tissues to be less sensitive to the action of insulin, the calling card of type 2 diabetes.

"Obesity tends to make people insulin resistant, so there is a greater risk of becoming diabetic," says Christine Kessler, RN, MN, CS, ANP, BC-ADM, a nurse practitioner with the Diabetes Institute in the department of endocrinology and metabolic medicine at Walter Reed Army Medical Center in Washington.

Both resistin and leptin, along with other adipokines, are known to have inflammatory and prothrombotic actions. For people with obesity, this results in a chronic state of mild inflammation, which increases the risk of comorbidities in addition to diabetes, such as metabolic syndrome and hyperlipidemia.

"We also know people with obesity have a three- to four-fold increase in cardiovascular disease," says Kessler. "Obesity also carries an increased risk of cancers and early dementia."

Brown fat versus white fat

Different types and locations of fat have different effects on the risks of comorbidities associated with obesity.

"Apple-shaped" people tend to gain weight in their abdomens and visceral organs, including the heart, liver, and omentum, in the form of brown fat. This type of fat is strongly associated with the more serious comorbidities of obesity.

"We now believe that the brown fat infiltrating visceral organs is more pathogenic than the subcutaneous brown fat that you see on the outside," says Kessler.

In contrast, "pear-shaped" people tend to gain weight in their thighs and buttocks in the form of white fat. Although excessive amounts of white fat may not appear attractive, it is believed white fat could offer some protection against the adipokines secreted by brown fat. The good news is both white and brown fats are lost when an overweight person loses weight, according to Kessler.

New research is delving deeper into the pathophysiology of fat that accumulates in the abdomen. A 2008 study presented at the June 9 American Diabetes Association's 68th Scientific Sessions found lipid release from abdominal fat was substantially elevated during the night. These lipids drain directly to the liver, where they may accumulate as triglycerides and cause dysregulation of glucose and insulin metabolism, increasing the risk of type 2 diabetes, according to University of Southern California researchers.

Fat begets fat

If dieting seems like an eternal yo-yo struggle, there's good reason for it. In the battle of the bulge, the body's stores of adipose tissue fight back in an attempt to maintain a consistent weight.

Adipose tissue secretes the hormone leptin, which has many functions, one of which is signaling a feeling of satiety to the hypothalamus. Leptin basically helps the brain know when it's time to stop eating.

Unfortunately, people with excessive stores of adipose tissue have such large amounts of circulating leptin that they can become resistant to its effects.

"A lot of people with obesity have leptin resistance so it takes longer to feel satiated, and they quickly get hungry again," says Kessler. "Fat makes people feel very hungry."

The Yang to the Yin

Achieving weight loss dramatically increases circulating levels of adiponectin, another hormone released by adipose tissue. In contrast to leptin and resistin, adiponectin's action is to counteract the negative effects of other adipose-derived hormones.

In a state of obesity, adiponectin can become overwhelmed by the actions of competing hormones. But as the body loses fat, adiponectin levels rise. "Adiponectin is the yang to all the yin," Kessler says. "It tends to improve satiety and to be anti-inflammatory and antithrombotic."

Catherine Spader, RN, is a contributing writer for Nursing Spectrum/NurseWeek. To comment, e-mail editorDC@nursingspectrum.com. To read more on this story, log on to www.Nurse.com/ClinicalNews.