Connie Leas (Boulder Creek, CA), a freelance writer, has worked as a technical writer for many corporations in the military-support, payroll services, insurance, and biotechnology industries.

fat

It’s Not What You ThinkBy Connie Leas

Prometheus Books

Copyright © 2008 Connie Leas
All right reserved.
ISBN: 978-1-59102-612-9

Contents

Foreword…………………………………………………………………….15Acknowledgments………………………………………………………………17Introduction…………………………………………………………………19CHAPTER 1. GOOD THINGS ABOUT FAT……………………………………………….23CHAPTER 2. WHAT IS FAT, ANYWAY?………………………………………………..31CHAPTER 3. HOW YOUR BODY DIGESTS AND USES FAT……………………………………37CHAPTER 4. WHAT YOUR FAT CELLS DO………………………………………………45CHAPTER 5. WHO SAYS YOU’RE TOO FAT?…………………………………………….55CHAPTER 6. WHY YOUR BODY WANTS TO KEEP ITS SHAPE…………………………………67CHAPTER 7. CHOLESTEROL CONTROVERSIES……………………………………………81CHAPTER 8. SATURATED FATS: HEALTHFUL FOOD……………………………………….95CHAPTER 9. OILS: ESSENTIAL AND OTHERWISE………………………………………..105CHAPTER 10. WHAT’S WRONG WITH TRANS FATS………………………………………..119CHAPTER 11. THE PROBLEM WITH LOW-FAT DIETS………………………………………129CHAPTER 12. DIVERSITY AND BALANCE………………………………………………141CHAPTER 13. FAT, THE FARM, AND FAMILY…………………………………………..151APPENDIX A. CHEMICAL SUBSTANCES PRODUCED OR ACTIVATED BY FAT CELLS…………………165APPENDIX B. DETERMINING YOUR BODY FAT USING GIRTH MEASUREMENTS…………………….167APPENDIX C. FAT CONTENT OF FOODS……………………………………………….171References…………………………………………………………………..179Bibliography…………………………………………………………………213Index……………………………………………………………………….215

Chapter One

GOOD THINGS ABOUT FAT

the fat you carry around has useful functions. It stores energy for future use, produces important chemicals, builds cell membranes and neural structures, provides padding, insulates against cold, supplies fuel, and supports your immune system. Fat can be your friend!

STORED ENERGY

The most obvious purpose of fat is for storing energy-something it does very well. Each gram of fat stores about nine calories’ worth of energy, about twice more than a gram of carbohydrate. (Calories are the number of heat units you get by “burning” fuel.) One reason fat can store more energy than carbohydrates-gram for gram-is that it contains no water. Stored carbohydrates, on the other hand, are about two-thirds water. If, like plants, you stored carbohydrates for energy instead of fat, you’d be too huge to get around. Think of potatoes.

A single pound of fat contains about 3,200 calories of energy-enough to get you through many days without food. If you’re a typical woman, your body is about 25 percent fat; if you’re a man, it’s more like 15 percent. Because you’re probably lugging around many pounds of fat, you can go for weeks without food. If you’re an average-sized man, for example, you might be storing 141,000 calories’ worth of energy in your fat tissue, enough calories, at 2,000 a day, to last seventy days. The more stored fat, the longer you last without food. (Because women are fatter than men, in times of famine they outlast men.) One man who weighed 456 pounds went for 382 days without food, under medical scrutiny, and lost 276 pounds. (He’s listed in the 1971 Guinness Book of World Records.) Don’t try this at home, but if you find yourself a contestant on the Survivor show, you won’t have to worry about starving to death.

HORMONE PRODUCTION

Energy storage is only one way your body uses fat. Your fat tissue also functions as a tremendously dynamic endocrine organ-he biggest endocrine organ in your body. (An endocrine organ is one that secretes hormones into the blood; hormones are substances, such as estrogen, that regulate various bodily functions.) Scientists have only recently discovered that fat tissue is not just a passive storage depot. Instead, fat cells are busily releasing hormones into the bloodstream just as the pituitary and thyroid do. So far, scientists have discovered roughly twenty-five different hormones and other compounds produced by fat cells. The hormones released by fat cells affect metabolism, weight, and overall health. Besides producing hormones, fat cells also release other compounds, including immune-system cells. Unlike other endocrine organs, which stay about the same size, fat can make more of itself. The more fat tissue, the more hormones get made-a situation that can be problematic, as I’ll discuss in chapter 4.

CELL MEMBRANE MATERIAL

Fat is the primary building material both for cell walls and for the sheaths that surround and protect nerves. Because fat doesn’t dissolve in water, it’s the only material that’s just right for this job (you wouldn’t want your cell walls dissolving into mush). Acting as both a border and a wall, it defends and defines the cell’s borders, keeping in those things that belong and excluding those that don’t. But what belongs in and what belongs out constantly changes, depending on the cell’s requirements. It’s up to fat to regulate the traffic.

Fat can cope with the changes because it comes in hundreds of variations. In fact, the membrane of a single living cell can contain many types of fat, a quality that’s critical for proper cell functioning. Cell walls are studded with proteins that function both as channels for letting chemicals in and out and also as sensors that trigger changes inside the cell. A wide diversity of fats make it possible for particular fats to interact with particular proteins, controlling their assembly and helping them interact with their environment. Some fats are also involved in a hugely complex web of signaling responses involving hundreds of different proteins. The signaling controls just about every cellular activity, including cell growth and movement, programmed cell death, and the transport of chemicals into and out of cells. Thus, cell membrane fats are key mediators of the cell’s interactions with its environment.

Clearly, the cell membrane is not just a passive wall to stop cell innards from leaking away. Rather, it’s a complex and dynamic cellular organ in its own right. The successful reception and processing of chemical messages depend on the health and integrity of cell membranes, of which fat is a key element.

PADDING

The spongy quality of fat makes it a good shock absorber. It protects our joints, internal organs, and eyeballs. The fat your body uses for padding is called structural fat and serves as a kind of bubble wrap to protect brittle tissues and vital organs from the bumps and bangs of everyday life. Structural fat doesn’t expand or shrink after you reach maturity and doesn’t store fat for energy-that is, it’s not retrievable.

Structural fat is arranged in various configurations throughout your body to perform specific functions. The most familiar locations of structural fats are the soft pads under the tips of your fingers and toes as well as the pads of your feet. In the case of feet, the fat is encased between bands of collagen that are tightly bound to both the skin and the heel of the bone. The fat absorbs the impact between the heel and the ground. As Caroline Pond explains it in The Fats of Life, “[W]ithin milliseconds after impact, the bands recoil to their original shape.” In this way the fat protects your bone and its joints from the shock of impact at every stride, and the recoil may help place your bones in correct position as you transfer your body weight from the heel to the ball of your foot. What’s more, the mechanical properties of the structural fat in your foot provide feedback in the form of neural sensations that inform your nervous system about the position of your joints and how much your tissues are stretched. In this way, your body can automatically control stride, movement, and balance.

Structural fat situated behind and around your eyeball determines how your eyeball is positioned in your skull. Fat also encloses the large optic nerve. In the lungs, specialized fats function as a sort of anti-glue, enabling the tiny pockets in the lung to fill easily with air and preventing them from sticking together. The pockets pack into a small space when the lungs are deflated, but respread readily on inflation.

INSULATION

Fat located below the surface of your skin provides some insulation from the cold, although fur or feathers would do a better job of it. Fat limits the transfer of heat from your body’s core. Because blood flows through muscle at a higher rate than it does through fat, especially during vigorous exercise, your body loses heat more quickly from superficial muscles than from superficial fat. But the main evolutionary purpose of fat is for survival during periods of food scarcity, not as an insulating mechanism.

THE IMMUNE SYSTEM

The energy you store as fat can bolster immunity and combat infection. When you’ve got an infection or a severe wound or burn, the concentration of fatty acids in your bloodstream rises just as it does if you’ve gone for a long period without eating. This is because your immune system requires fat to “feed” your infection-fighting lymphatic system. Specifically, it needs polyunsaturated fatty acids to build the cell walls of lymphocytes (white blood cells) that are your first line of defense against disease. In fact, nearly all major lymph nodes and parts of their connecting ducts are embedded in fat tissue.

Skinny people are more likely to succumb to infectious disease than fatter people. In fact, people rarely die just from starvation. Instead, their loss of body fat lowers their resistance to disease so effectively that the immediate cause of disease is usually an infectious disease or pneumonia-like inflammation of the lungs. Apparently, the immunity conferred by fat cells is a result of the anti-inflammatory substances produced by the fat cells.

Using rodents as test subjects, a team of researchers at Indiana University, Ohio State University, and Johns Hopkins University discovered that sudden removal of fat (from the groin area) decreased the animals’ immune systems. They found that even a small decrease in body fat decreases immunity, which in turn increases susceptibility to disease. The researchers also found that immune system function improved after the fat tissue grew back.

PROTECTION FROM TOXIC SUBSTANCES

Body fat can also mediate the effects of environmental toxins on your nervous system. Many pesticides and other toxic substances are fat soluble. If you are exposed to such chemicals and have little body fat to dilute them, they are likely to concentrate in nervous tissue where they can lead to neurogenerative disease. Dr. Andrew Weil, in his book Healthy Aging, even postulates that “this is the reason that ALS (amyotrophic lateral sclerosis-Lou Gehrig’s disease) appears more frequently in athletes. At the Integrative Medicine Clinic at the University of Arizona, I have seen a number of men in their thirties with this devastating diagnosis, an unusually young age group for the onset of ALS. All had a history of participating in extreme sports and competitive, ultra-athletic events, and all were extraordinarily lean.”

Dr. Roy Walford, a pathologist at the University of California, Los Angeles, was a leading authority on the concept of using a restricted-calorie diet to combat the effects of aging and disease. Apparently, being on a near-starvation diet tells your body that food is scarce. This is a stressful situation that triggers a gene that in turn triggers physiological changes that slow down the aging process in the interests of survival. Because a calorie-restricted diet has been shown to prolong the lives of laboratory animals, Dr. Walford followed such a regimen for the last thirty years of his life. He died of Lou Gehrig’s disease at age seventy-nine. He was five foot nine and weighed 130 pounds. While Dr. Weil’s theory about low body fat and Lou Gehrig’s disease may not stand up to scientific scrutiny, it seems like a plausible notion. It also illustrates how little we understand about ideal body composition.

SEXUAL ATTRACTION

A man with a paunch used to be considered good marriage material. His paunch showed that he was well fed, and thus well off. Perhaps more than that, his paunch may have also been a sign of his virility: It’s the male sex hormone, testosterone, that’s responsible for this selective buildup of fat in his abdominal region. Among primates, such as apes, it’s the dominant males that sport the prominent paunches.

For women, plump hips and thighs were probably the best man bait. Because a wide pelvis is best adapted for childbirth, accentuating the pelvis with fat hips and thighs advertised a potentially successful breeder. It’s less clear whether large breasts had much attraction for the prehistoric man, since there’s no special relationship between breast size and capacity for milk (but maybe the guys didn’t know that).

Noting that, on average, an adult woman has about twice as much body fat as the average man, Desmond Morris, in his book The Naked Woman, A Study of the Female, theorizes that female fatness is one of the traits-along with a higher voice and finely boned face-that evolved via natural selection. Fatter-and therefore more childlike-women were more successful at mating, he believes, because those infantile traits elicited protective responses in males.

FAT-FREE PEOPLE

A rare disorder, called lipodystrophy, strips the body of fat, in either just a few areas or everywhere. The condition comes in various forms. Sometimes it’s caused by defects in the genes responsible for creating the enzymes needed to manufacture fat or maintain fat cells. Infants born with this genetic defect show muscle definition instead of the normal baby fat. They usually have voracious appetites and grow tall but never deposit an ounce of fat on their frames. Other forms of the disease, which appear to be unrelated to gene mutations, show up in childhood or adolescence. In some cases, fat disappears from the entire body; in other cases it disappears only from the upper half, with the lower half sometimes overly fat. In these cases, the cause is thought to be an immune system malfunction, in which the body attacks and destroys its own fat cells.

Studying people with lipodystrophy points out the importance of fat for normal body functioning. People with lipodystrophy are plagued by metabolic problems. In particular, their bodies are highly resistant to insulin. As a result, they develop diabetes. Without fat cells to store the fat, the fat in the bloodstream-whether extracted from digested food or synthesized by the body-has nowhere to go, so it either stays in the blood or is deposited in tissues like the liver, where it is converted to glycogen, then released later into the blood as glucose. With all the excess fat and sugar in their bloodstreams, people with lipodystrophy are at just as high a risk for heart disease as those with diabetes. Lipodystrophy is common among people with AIDS. In this case, fat disappears from the face, arms, and legs, but accumulates in the neck, trunk, and abdomen. Scientists don’t know what causes lipodystrophy in people with HIV.

The functions of fat mentioned here don’t begin to cover all its uses, partly because so little is known. Scientists have only recently begun to delve seriously into its biological complexities, spurred partly by the discovery of leptin in the mid-1990s (see chapter 6) and partly by the drive to find pharmaceutical solutions to the “obesity epidemic.” For sure, our bodies are unimaginably complex and intricate systems, and fat is a key, though little-understood, player.

(Continues…)

Excerpted from fatby Connie Leas Copyright © 2008 by Connie Leas. Excerpted by permission.
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