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"Genes for building or burning fat tissue are, for the most part, simply suggestions Ė tendencies Ė and turning them on or off depends on the choices you make." Neal Barnard, M.D., president of the Physicians Committee for Responsible Medicine
Shutdown Your Fat Genes Ė Turn on Your Thin Genes
A 53-year-old lawyer whose weight has been yo-yoing up and down for years asked me recently what effect genes have on body fat. Relying on an article I researched and wrote some years ago for The Lean Advantage 2, I told him that genes play a part in weight control, but for the vast majority of people lifestyle is far more important. Some people have an inherited tendency to be fat, but that only means they have to work harder at weight control than people with thin genes. Very few people are doomed by genetics to be fat. A tendency to be overweight can usually be overcome with exercise and correct eating.
Shortly after that conversation I came upon a wonderful new book by Neal Barnard, M.D., called Turn Off the Fat Genes (Harmony books, 2001). Dr. Barnard has studied the many recent findings on the role of genes in body weight control and come up with a revolutionary new program for activating thin genes and suppressing fat genes. Happily, we know a lot more about the subject than we did a decade ago. Dr. Barnard has take our newfound knowledge and written a very engaging and readable book telling us how to take charge of the genes that control our weight. He confirms what I told my lawyer friend, but adds sophistication and eminently usable detail.
Dr. Barnard explains that many genes are involved in weight control, but that understanding their actions is not so difficult, if we focus on the basic functions they control. He says: "[Genes] can influence your taste and appetite. They can affect your tendency to store fat. They can adjust your calorie burning ability and how well exercise works for you. Thatís about it." In his book, he makes complex information easy to understand and apply by focusing on five key gene effects.
According to Dr. Barnard, former President Bush probably canít help it that he doesnít like broccoli. "Taste is genetic," writes Dr. Barnard. "Some genes favor a sweet tooth, and some genes really do make you dislike broccoli." George H. W. Bush probably inherited sensitive taste buds which can detect even a hint of bitterness in foods. So broccoli and other cruciferous vegetables leave him cold. More importantly, he may also find sweet and fatty foods too strong for his sensitive palette. Thatís a mixed blessing, of course. While he may find it easy to pass up fattening desserts, heís also at risk for turning away healthy vegetables.
Iím just the opposite. My wife will tell you that Iíve never turned my nose up at anything sheís served during our many years of marriage. I like just about everything. Iím what Dr. Barnard calls a nontaster. Strong tastes donít turn me off. I like broccoli and grapefruit. Unfortunately, I also have a fondness for cake and ice cream. On holidays when Iím exposed to gooey desserts, I find myself wanting more long after the sensitive tasters at the table have had their fill.
"Fear not," says Dr. Barnard. "Overall, the difference in weight between tasters and nontasters is not major." Taste genes influence, but do not necessarily control, what we choose to eat. The key is to know your poison, so to speak, be aware of your vulnerabilities. "Tasters [like Bush] have to choose healthy foods that do not set off their taste alarms," Dr. Barnard advises, "and nontasters [like me] need to be sure not to overdue in their quest to enjoy food."
Injected leptin, a hormone made by our genes, causes fat mice to slim down almost overnight. But it doesnít help overweight humans, according to Dr. Barnard. That doesnít mean it isnít important, however. Dr. Barnard says itís very important to the operation of our appetite control system.
Leptin is made by fat cells. As we gain weight, the added fat makes more and more leptin, which sends a stronger and stronger signal to our brain. "As leptin goes up, appetite goes down," Dr. Barnard explains. "It provides a feedback system designed to tell the body when it has enough fat."
Giving leptin to overweight people doesnít help, because they already have plenty. A problem arises when they lose weight, however. Their shrinking fat stores produce less and less leptin, which signals the brain to up appetite in order to replenish the lost fat. Itís our natural survival system at work.
"You definitely do not want to court a decrease in leptin. It could make your appetite soar," warns Dr. Barnard. "If you let your leptin level fall, you are playing with fire, and that is exactly what happens anytime you go on a calorie-restricted diet." You donít even need to lose weight for this to happen, according to Dr. Barnard. "Just cutting down on food slows down your leptin production," he says.
Diets which call for restrained eating, according to Dr. Barnard, sets you up for a binge. "As far as your body is concerned, you are starving, trudging through a desert with no food to eat, and if this keeps up, the result could be life-threatening." Rather than counting calories, reducing portion size and skipping meals, Dr. Barnard suggests changing the type of food you eat.
The trick, heís says, is to select meals from plant sources. Avoid animal products and keep vegetable oils to a bare minimum. He suggests eating high-fiber foods, which satisfy hunger with less calories; they are filling, but not fattening. You eat more volume of food, but it contains less calories. The best high-fiber choices are vegetables, beans, whole grains and fruits. Follow those guidelines, he says, and you wonít have to count calories or feel deprived. Youíll automatically eat fewer calories Ė without increasing hunger and reducing leptin.
Thatís nothing new, of course. Iíve recommended the same thing in my books for more than 20 years. Whatís new is Dr. Barnardís explanation of the role played by leptin. Itís helpful to understand how our appetite control system works. Itís important to not only know what to eat, but why as well. It gives you confidence in your diet and provides motivation.
Dr. Barnard and I part company on the need for a strict plant-food diet, however. He even goes so far as to recommend soy milk instead of cowís milk -- because of the fiber in soy milk. Thatís a bit much. After all, thereís only one gram of fiber in a cup of nonfat soy milk, and regular skimmed milk is more nutritious. He discourages all animal products, because they "present your digestive tract with a large calorie load that has no fiber at all." Thatís too extreme for me.
I agree with the emphasis on high-fiber foods. My own diet contains more fiber than Dr. Barnard recommends. On my last visit to the Cooper Clinic, computer analysis showed my fiber intake to be 66 grams per day. Barnardís rule of thumb is around 40 grams of fiber per day.
As I explain in Lean for Life, you donít have to be a total vegetarian to derive the major benefits of a vegetarian diet. It does no harm to add a little meat, fish or chicken -- and an occasional egg -- to a vegetable-based meal. It adds flavor and eating pleasure, which is critical to sticking with a diet long-term; nobody will eat foods they donít enjoy for very long. The key is to keep in mind that the plant-based food, not the meat, is the main course. I believe my "near vegetarian" approach is a better way to consume fewer calories without causing hunger and cravings Ė and keep leptin levels up.
The Fat-Building Gene
The gene that makes lipoprotein lipase (LPL) is responsible for whether food is stored or burned. Dr. Barnard calls it the "gate keeper to your fat cells." LPL is an enzyme that hangs out on the walls of the tiny blood vessels in your fat tissue and in your muscles. It decides whether to extract the fat particles that pass by and store them in your fat cells or, alternatively, pass them into your muscles cells to be burned as energy. "In essence, LPL acts like a shovel that moves fat into your cells," says Dr. Barnard. "In fat cells, you store it. In muscles cells, you burn it."
Barnard says you can change a tendency to store fat into a tendency to burn it by reducing the fat in your diet. Thatís because LPL is looking for food fat. "The fat on your thighs, abdomen, or anywhere else is made largely of fish fat, chicken fat, beef fat, dairy fat, vegetable oil, or fryer grease," writes Dr. Barnard. Surprisingly, lab tests can examine your fat deposits and determined what youíve been eating, according to Dr. Barnard.
He agrees that the body can make fat from excess carbohydrate and protein, but he says, "Your body strongly prefers to build body fat from food fat." That makes sense, of course, if the fat you eat is deposited practically unchanged in your fat cells.
It is well-known that fat calories are more easily converted to body fat than other calories. As I explained in The Lean Advantage 3: "Dietary fat can be turned into body fat with just 3% of its energy used in the conversion process, while it takes 23 % of the calories from carbohydrate to turn it into fat stores. In other words, if you consumed 100 excess carbohydrate calories, only 77 of them will turn up as body fat; but if you consume the same number of excess calories as fat, 97 will turn up on your body as fat stores."
Dr. Barnard suggests that we counteract the fat-building gene by denying the LPL enzyme the food fat it prefers. And heís not talking about cutting back. "I donít mean taking the skin off your chicken and switching to 2% milk," says Barnard. "I mean really getting away from fat."
Barnard says some fat in our diet is essential, but he insists that the amount is only about three to four percent of calories. Getting enough fat is no problem, according to Dr. Barnard. "If you were to build your diet from vegetables, fruits, beans, and grains, without any added fat at all and without any animal products, your fat intake would be roughly 10 percent of calories."
Thatís what he recommends. The recipes in his book include no animal products; theyíre made up entirely of plant foods.
Again, I believe thatís too extreme and unnecessary. I agree that fat is the enemy. But that doesnít mean we should try to eliminate all fatty foods. Yes, the saturated fat found in animal products should be severely restricted. But Iíve found that a little fat makes meals more satisfying. And as I explained in Challenge Yourself, it may actually help you burn more of the calories you eat, rather than store them in your fat cells.
I make it a point to include a small amount of high-quality animal protein (chicken, fish, lean beef, skim milk or nonfat yogurt, and an occasional egg) in every meal, along with a little "good fat," usually in the form of fatty fish, nuts or nut butter, or ground flax seeds. I believe this satisfies my nutritional needs better than a strictly vegetarian diet, and Iím sure it makes for a more enjoyable and sustainable diet. (For more details, see Challenge Yourself.)
Youíll have to decide which approach suits you best. I believe both will keep your fat-building gene in check.
The Insulin Gene
Contrary to many popular diet books, Dr. Barnard says: "Insulin is your best friend when it is working properly." Whatís more, "Carbohydrates are not the enemy," says Dr. Barnard. "They are, in fact, our natural energy source." Insulin, made by a gene on chromosome 11, can stimulate calorie burn. The problem is it can also shut down fat burn. The trick of is finding a proper balance between the two functions. Again, according to Dr. Barnard, the key is the type of food you eat.
The job of insulin is to push the proteins and sugars we eat into our cells to build body parts and provide fuel (glycogen) for our movements. "Insulin travels to your muscles, liver, and fat tissues, where it pushes proteins and sugars into your cells," says Dr. Barnard. "As it does so, it temporarily shuts down your fat burning machinery," he adds. That makes sense, of course, because thereís no need to burn fat when food is being pushed into the cells.
Happily, the building process inside the cells speeds up the metabolism and burns calories. "[Itís] is a big job, causing your cells to actually release calories in the form of heat, " says Dr. Barnard. This after-meal metabolism boost is called the thermic effect of food (TEF). "Itís a nice way to burn calories," says Barnard. "All you do is eat, and your body does the rest. These calories are gone forever Ė they never even get a chance to turn into fat."
The foods with the biggest TEF are those containing plenty of complex carbohydrates or a mixture of carbs and protein. "For example, broccoli and other vegetables are about 50 percent complex carbs and 40 percent protein, a mix for a good burn," says Dr. Barnard. "On the other hand, butter, chicken grease, and [egg yoke] are just fat, and deliver a much poorer burn." Again, plant foods win out over animal foods.
Under normal circumstances, the interruption in fat burning is brief. A problem arises if you become flabby and out of shape, however, because your insulin doesnít work as well. The extra fat on your body requires more insulin and your calorie-burning system becomes sluggish. "The body produces more and more insulin, and it shuts off fat burning more effectively than it should," says Dr. Barnard.
Youíre insulin also works overtime if you snack constantly. An endless stream of junk food never gives your insulin a chance to rest. "If you have a constant supply of snacks, your body has no need to use its fat, and insulin keeps your fat-burning processes slower than they would normally be," Dr. Barnard writes.
A lack of fiber is also a problem. "Normally, fiber Ė plant roughage Ė helps keep insulin levels in check by slowing the release of sugars from the food you eat," Dr. Barnard counsels.
To keep your after-meal calorie burn up and minimize fat-burn stoppage Dr. Barnard suggests a diet high in healthy carbohydrates and fiber, and low in fat.
In addition, Dr. Barnard warns against the ultra-high protein diets some writers recommend on the theory that protein foods have a little or no carbohydrate and, therefore, should have no effect on insulin. "Research has shown otherwise," says Dr. Barnard. "Protein is a powerful stimulus for insulin release, just as sugar is.... Beef and cheese cause a bigger insulin release than pasta." Says Dr. Barnard: "A better answer is to choose high-fiber, natural plant foods."
In short, Dr. Barnard suggests that we "give our overworked insulin a bit of time off while boosting our metabolism."
The Exercise Effect
As I told my lawyer friend, genes do have an effect on weight control. Some of us are predisposed to be fatter Ė or leaner Ė than others. For example, Dr. Barnard points out that studies of identical twins showed that if one twin burned calories slowly during exercise, his twin usually did as well. Likewise, if one burned calories quickly, his twin was again similar. No matter what our family background, however, everyone benefits from exercise.
Whether your muscle fibers are predominantly fast or slow, exercise will make them better fat/calorie burners. It increases the blood supply to the muscles, bringing more oxygen and calories to be burned for energy. "If you start an exercise program and stick with it," says Dr. Barnard, "it will increase the number of capillaries reaching each muscle cell by as much as 40 percent within a few months." Simply walking briskly for a half hour per day will substantially increase your fat-burning capacity, according to Dr. Barnard. Exercising more intensely at regular intervals adds to the benefit, of course.
Exercise increases the fat-burning activity of the LPL enzymes we talked about earlier. "It slows down the LPL enzymes in fat tissues, making it harder to store fat, and increases LPLís activity in muscles, pushing fat into muscle cells to be burned," Dr. Barnard explains. The effect is almost instantaneous. "A single bout of exercise causes LPL activity in muscle cells to spike up to10 times its previous level," says Dr. Barnard. "The effect is temporary," he adds, "but regular physical activity keeps it going strong."
Exercise continues burning extra calories long after the exercise is over. "After a workout, your body strengthens your tired muscles and repairs their stresses and strains, " Barnard writes. This can take 24 hours or more and have a substantial effect. Says Dr. Barnard: "Building new proteins burns a lot of calories and can account for 10 to 15 percent of your RMR [resting metabolic rate]."
Exercise prevents or delays the decline in metabolism that many people experience with age. "[It] preserves your muscles," says Dr. Barnard. "Muscle tissue is better than fat tissue at burning off calories, so if you keep your muscles from wasting away, your body will be able to burn calories faster."
Still, in a major omission, Barnard makes no mention of strength training. He talks a lot about the benefits of aerobic exercise, but offers not one word on weight training. He apparently does not recognize the value of weight training for building and preserving muscles. A few decades ago, when aerobics was almost synonymous with health and the benefits of weight training were not widely recognized, this might have been acceptable. Now, however, when the superiority of strength training as a builder and preserver of muscle is almost universally recognized, I find it practically unforgivable. (For a discussion of the role of weight training in body fat control, see my book Lean for Life.)
Nevertheless, everybody with a serious interest in weight control should read Turn Off the Fat Genes; itís available in your local bookstore. Iíve barely skimmed the surface of the valuable information offered by Dr. Barnard on taking charge of the genes that control your weight. The plant-based menus and recipes by Jennifer Raymond alone are worth the price of the book.
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