The
Skinny on Fat
Researchers have some ideas about how fat goes from being a few vanity pounds to representing an actual health risk.
Television commercials tell us. Magazine ads deliver the message. Newscasters warn us.
Americans are too fat.
And fat is dangerous. And the only way to lose that fat is to go on a low-carbohydrate regimen, guzzle an all-liquid diet, or swallow an herbal pill.
The national psyche is looking at itself in the mirror and coming to terms with a sprawling gut and bulging saddlebags. After years of super-size fast-food meals, people are paying increased attention to the problems of poor diet and obesity and their effects on health.
“Every day, I see something about fat in the news or on TV,” says obesity expert Michael I. Goran, Ph.D., professor of preventive medicine and physiology and biophysics at the Keck School of Medicine of USC. “The truth is this: No one really knows why too much fat is bad.”
Fat and disease
Yes, Americans are packing on the pounds.
From 1976 to 1980, about 13 percent of Americans had a body mass index that branded them as obese (see Mass Appeal, page 14). That figure climbed to nearly 23 percent from 1988 to 1994 and 30 percent from 1999 to 2000, according to the National Center for Health Statistics. Today, about 59 million American adults—the equivalent of the entire population of France—are thought to be obese.
It is not just adults, either. Children, particularly Latino and African-American youth, are heftier than ever.
Research has shown that several health risks and conditions go hand in hand with obesity. Type 2 diabetes, heart disease, stroke, high blood pressure, some types of cancer, abnormal sleep (known as sleep apnea), osteoarthritis and gallbladder disease are all more common among those considered obese, according to the North American Association for the Study of Obesity.
Type 2 diabetes, in particular, has made news because of the growing number of Americans who are being diagnosed with it, and the mounting proportion of children and adolescents who are showing signs of the disease.
Among healthy people, the body’s cells use the hormone insulin to absorb glucose (a sugar) from the blood to use for energy. In diabetes, though, cells grow resistant to the effects of insulin. The body creates more insulin to make up for the resistance. But after a while, the body’s natural pumps are overworked and lose the ability to make insulin. Also, the body cannot use insulin properly.
As a result, glucose builds up in the blood. That, in turn, causes health problems spanning from kidney failure to blindness.
Nearly 90 percent of people with type 2 diabetes are overweight. Researchers believe that being overweight overtaxes the body’s ability to use insulin to control blood sugar, but the precise links are elusive.
Fatty acids
“Fat has been our friend for a million years,” says Goran. “It is an important tissue of the body. It is only now we’re seeing its negative effects.”
Fat serves some basic human functions. It serves as a back-up storehouse of energy, as well as insulation from cold and protection for organs.
From an evolutionary perspective, this ability to store emergency energy is critical. Those whose bodies stored away more fuel during times of plenty were the ones who survived times of scarcity. And their genes survived to be passed down the line.
Scientists believe that a predisposition to high levels of insulin in the blood in response to food is, in part, responsible for the ability to store away a larger amount of fat to be used during prolonged hunger. But in much of today’s modern world, when a stuffed-crust pizza is a phone call away and ice cream beckons from the freezer shelf, famine is a rarity—and the pounds creep on without coming off.
But how does fat go from merely being a few vanity pounds to representing an actual health risk? Researchers have some ideas.
First among them is the portal theory.
Richard N. Bergman, Ph.D., the Keck Chair in Medicine and professor and chair of physiology and biophysics at the Keck School, has contributed significantly to this line of research. In a nutshell, the portal theory suggests that visceral fat—fat within the trunk and middle of the body—secretes free fatty acids that flow into the liver through the portal vein, the vein that carries blood from the abdominal organs to the liver. Too much fat may mean too many free fatty acids. Too many free fatty acids coming through the portal vein seem to make the liver produce too much glucose.
With so much glucose, the body pumps out more insulin to try to control the sugar’s high levels. Over time, this might contribute to insulin resistance.
“Normally, insulin should suppress the release of glucose, but when so much glucose is being released that insulin can’t properly suppress it, that’s tantamount to insulin resistance,” Bergman says. The portal theory also fits with the finding that visceral fat seems linked to more health complications than fat in the hips and thighs.
Fat cells
But other theories have come on the scene.
The ectopic fat theory, for example, proposes that fat poses a problem when it gets into places it is not supposed to be. Such sites include muscle, liver and pancreatic tissue. Recent research has shown that fat accumulation where it is out of place is linked to severe insulin resistance. Scientists believe that this type of fat storage might damage nearby cells.
The endocrine organ theory suggests that fat cells themselves produce substances that may be harmful in excess.
In the last five years, scientists have come to know that fats act through hormones. Rather than being inactive blobs, fat cells actually emit hormones such as leptin, resistin, adiponectin, interleukin-6 and tumor necrosis factor alpha, which have important roles in the body. Leptin, for one, is thought to help keep fat stores in check by sending messages to the hypothalamus in the brain to indicate a sense of fullness and satisfaction during meals, signaling individuals to stop eating.
Researchers such as USC’s Bergman are studying such hormones in great detail, seeking to understand how their levels change due to obesity, how they influence metabolism and disease and whether these hormones come from different types of fat cells.
Just for starters, it could be that fat cells in the upper body—those more abundant in people with an apple-shaped physique—may produce more of certain hormones than fat cells concentrated in the lower body—those more abundant in people with a pear-shaped physique. And cells that comprise visceral fat may release different types and amounts of hormones than cells that make up subcutaneous fat, the fat found just under the skin.
Fat cells seem to respond to hormones, too. Scientists recently showed that some lean women may accumulate abdominal fat during times of stress in response to the stress hormone cortisol, for example. Researchers have long known that people who have diseases characterized by a larger-than-normal release of cortisol tend to have a lot of abdominal fat. Fat cells in the central region of the body tend to grow in response to the hormone.
Fat factors
Despite the diet fads that already are drawing on this area of research, scientists say there is still much to discover about how fat is laid down in the body and how it works. Genes undoubtedly play a role in how susceptible the body is to fat’s multitude of challenges, they say. In some cases, it may also be that too much fat merely accompanies the behavioral and genetic factors that lead to disease.
Some health professionals are advocating that patients shift their thinking away from an unhealthy obsession with fat and yo-yo dieting, and instead aim for changes that will help them become metabolically fit. Research has shown that exercising regularly, even if it is just going on walks, contributes significantly to reducing risk for type 2 diabetes and cardiovascular disease. Exercise combined with consistent, wise food choices made with help from a health professional can go a long way toward improving the body’s efficiency and quality of life.
And, if embraced as a new lifestyle, it might even cut the fat, too.
What is Fat?
Fat tissue is made up of fat cells. Each fat cell is a tiny pouch containing lipids. After puberty, the body stops making additional fat cells. The body accumulates fat by adding to the fat in each fat cell.
During digestion, fats from food are broken down into their parts and then reassembled in intestinal cells. They then pass into the lymphatic system and eventually flow into the bloodstream.
After another round of breakdown and reassembly (with the help of insulin), the fat molecules make it into fat cells.
The body can also turn carbohydrates or protein from food into fat, but it is less efficient and much more difficult than simply drawing on dietary fat as a source. Given the choice, the body will break down carbohydrates for immediate energy needs and reserve the fat in fat cells for energy use when other energy sources are depleted. n
Mass Appeal
Health professionals often use body mass index, or BMI, as a measure of body composition in adults.
BMI is based on a ratio of weight to height. Physicians combine BMI with information about additional risk factors, such as cigarette smoking, triglyceride and cholesterol levels, and family history of heart disease, to understand a patient’s risk for obesity-associated diseases.
To calculate your BMI, measure your height in inches and weight in pounds. Multiply weight by 703. Then divide the result by height, and finally divide that result again by height. Or go online to a BMI calculator at www.nhlbisupport.com/bmi. Experts group BMI into these categories:
• Underweight: BMI below 18.5
• Normal: BMI between 18.5 and 24.9
• Overweight: BMI between 25.0 and 29.9
• Obesity: BMI of 30.0 and above
Many professionals also consider waist size along with BMI in their assessment. Wrapping a measuring tape snugly around the waist gives a measure of the circumference, which hints at the amount of abdominal fat. Too much abdominal fat, when out of proportion to total body fat, can raise alarm. Disease risk increases when the waist measures more than 40 inches in men and more than 35 inches in women.
Physicians today usually suggest weight loss to those who are obese and to those who are overweight and have two or more associated risk factors. n
-
Back Next Index