Obesity is the second leading preventable cause of death in the United States, it results in some 300,000 deaths annually and contributes to major diseases such as hypertension, diabetes, cancer and stroke. Why is there so much obesity in America today, perhaps the story of Jenny and Susie will clear up some misconceptions.

Jenny eats plenty, about 3,000 Calories a day for her 135 pound body, but only 60 grams of fat, which are 18% of her total calories. Susie tries to stick to 2,000 calories, but she eats the typical Standard American Diet (SAD) with about 40% of calories from fat. This is 90 grams of fat, more than she burns most days, so she stores surplus fat.

Many individuals, like Susie think they have a genetic tendency to become overweight. This belief was reinforced by a report in 1994 by Rockefeller University researchers that a gene in mice could malfunction and cause obesity, and that there may be a parallel process in humans.

That report has given overweight people an excuse to be obese. They now believe they are victims of their genetics.

The study found a gene in mice that causes fat cells to produce a protein, leptin that signals when the body has enough fat. This protein tells the body when to stop eating and influences metabolism as well when to quit storing fat. If the gene malfunctions the signal protein is not made, and fat continues to be eaten and stored. Researchers found that rodents lacking the leptin gene or leptin receptors become obese. Although humans also produce leptin, the hormone doesn't seem to play a major role in human obesity. In fact, obese humans actually have elevated levels of leptin, suggesting that the body can't use its available supply.

Researchers at UC Davis Medical Center, Duke University Medical Center and the French Centre National de la Recherche Scientifique (CNRS) March 3rd, 1997 announced identification of a gene that may help explain why some people can eat a rich diet and stay slim while others eat the same diet and get fat. The discovery is reported in the March issue of Nature Genetics.

The newly identified gene, dubbed uncoupling protein 2 or UCP2, contains the blueprint for a previously unknown heat-generating protein that may play an important role in the cause and treatment of obesity. The protein appears to be responsible for burning excess calories in the diet as surplus body heat, before the calories can be stored as fat. As a result, people who have more of the protein burn more fat, while people who have less of the protein store more calories as fat. The protein also may govern the development of fevers during illnesses, and may make specific tissues heat up in response to inflammation. In people with rheumatoid arthritis, for example, inflamed joints are sometimes hot to the touch.

UCP2 in contrast to leptin, is produced throughout the body and appears to respond to fat intake. According to Craig H. Warden, assistant professor of Pediatrics and Rowe Program in Genetics at the UC Davis School of Medicine and Medical Center, and lead author of the study, energy expenditure&emdash;how many calories we burn, may prove to be a more important variable in obesity than energy consumption than how many calories we eat. He said there is surprisingly little evidence to support the general assumption that fat children or adults overeat. Instead, it appears that they burn too little energy. Energy expenditure takes three forms: physical activity, resting metabolic rate, and thermogenesis or heat production. UCP2 affects the last of these by burning calories as heat rather storing them as fat.

"Even small changes in thermogenesis could potentially have a big impact on a person's weight over the long-term," Warden said. "For a typical adult, just a 1 percent reduction in body heat could translate into a five-pound weight gain over the course of a year, all other things being equal. By the same token, raising body temperature by just 1 percent would result in a five-pound weight loss. Obesity could be a problem of a one-tenth of one degree alteration in body temperature."

The average healthy human body temperature is 98 degrees Fahrenheit, but an individual's normal temperature may be one or two degrees higher or lower than that.

I personally discussed the research with Warden and the bottom line seems to be some people are not burning fat as well as other people. What I understand from this is that some people can eat more fat than others can and burn it. While those with the less expressed gene need to keep their fat consumption down.

Co-author Richard S. Surwit, professor and vice chair for research in the department of psychiatry and behavioral sciences at Duke University Medical Center said, "We found that some mice gained a little bit of weight when we switched them from a low-fat to a high-fat diet, while others blew up like balloons. And the difference wasn't due to how much they ate or how active they were."

The most important thing to note is that the mice did not get fat unless fed a relatively high fat diet.

"It turned out that the mice that did not become fat showed an increase in expression of this gene when they ate a high-fat diet, and their body temperature went up. The mice that got fat, on the other hand, did not show as much expression of the gene, and their body temperature did not go up as much."

This genetic model is easy to understand given plenty of fat. Suppose the fat supply is limited&emdash;in other words, consider a low-fat diet. If extra fat is not there it can't be stored, so this genetic extrapolation from mice to men shouldn't cause a problem. Right?

Some might argue that if the defective gene doesn't tell the body to quit storing fat and there is no more available in the diet, then the body will say "I've gotta have more fat so I'll make the darned stuff." We're back to the old conversion of carbohydrate to fat story. The question of what is more important Calorie counting (total calorie balance) or restricting fat intake to just what you need (fat balance).

If you're like Susie and believe the amount of food you eat is the main factor in controlling your weight, and your genes will decide if you'll turn it into fat, look at the research.

There is a large record of studies on the dietary fate of carbohydrate that go back more than 30 years. This includes biochemical studies, clinical studies on animals and people, and epidemiological studies. The largest proportion of these data can be explained if the principal source of stored body fat is eating excess fat. Under normal dietary and metabolic conditions, the conversion of carbohydrate to fat is negligible (less than 2%, according to the numbers). When dietary fat is restricted to less than is needed to meet the needs for essential body fats, then your body can manufacture fat from carbohydrate, but only if you over-eat massive amounts of carbohydrate.

A study that found significant conversion of carbohydrate to fat and weight gain, fed people 3,500 to 5,000 calories, restricted their fat intake to 3%, and did not let the group exercise. Note, that not only did it take massive over-feeding to stimulate fat production from carbohydrate, it took severe fat restriction.

If you starve your body of fat and pig out on too many calories (large meals), then the surplus is converted to fat and stored.

Overall, the evidence that eating too much fat is the main cause of excess stored body fat is large and convincing. Those who disagree ignore the majority of the data and rely on a few studies that are ambiguous. They are also big on anecdotal stories of weight gain on low-fat diets. The unanswered question is whether these stories are not really about low-fat diets, but fat starvation diets, in which case they are consistent with the clinical nutrition data.

The message is eat low-fat, not no fat. Eric Jequier, Ph.D., at the University of Lausanne, Switzerland, wrote in a recent review of published studies "Fat synthesis from carbohydrate in adipose tissue is of little importance." This means that when you eat a balanced low-fat diet, you won't manufacture fat. So far there have been five studies of low-fat (20% to 25% of total calories), unrestricted-calorie diets for overweight people: in each case, they lost weight.

You are more likely to gain weight easily if your parents are overweight. Doesn't this emphasize that there is a strong genetic component? Yes, in some cases, but perhaps not as often as we tend to believe. The difficulty with family studies on overweight people is that it's hard to separate genetic effects from learned habits.

Overweight parents who eat too much fat tend to provide the same food choices for their children as for themselves, so their kids eat too much fat, too. This is not genetics; this is eating what is available.

Fortunately, at an early age children have an instinct for high levels of physical activity&emdash;they play a lot. Unfortunately, this doesn't last too long, and surely the emergence of overweight children grows out of a continued consumption of fat coupled with a gradual slide in the level of physical activity.

There are studies on identical twins that suggest when they are brought up in different environments, if one is obese it is probable that the other will be too.

The estimates of experts in the field, such as Claude Bouchard, Ph.D., at Laval University in Quebec, are that the heritability of obesity in twins may be as high as 70%. In the general population it is closer to 20% to 25%, although it can be as high as 40%. These estimates say that although a significant amount of obesity is connected with genetics, a larger amount is not.

There is another troubling aspect of the genetic link. Data shows that Americans have the highest incidence of obesity in developed countries; for example, obesity is twice as prevalent in the U.S. as in France (small wonder our heart disease rate is so much higher; you don't need the Mediterranean diet to explain this).

The U.S. is a nation of immigrants. Do we really believe our current rate of obesity has become so much higher than people in the countries of Europe, Asia, and Africa from whom we descend, by genetic changes in so few generations? This does not seem reasonable. Besides, Asians who emigrate to the U.S. and change to American eating habits tend to become more overweight than those who stay home. Weight gain does not wait for genetics, it crops up in a single generation and therefore is due mainly to the SAD diet, aided by less physical activity. The average American weighs ten pounds more today than they did less than twenty years ago. Nearly one third of Americans have become obese. Our genetics haven't changed in this short time, fat consumption and activity level has. There is a genetic influence that can be explained by the body types we inherit.

Body types
There are three body types 1.) ectomorph (small body frame), 2.) mesomorph (medium body frame) and 3.) endomorph (large body frame). Through helping people to get in shape I have observed that ectomorphs tend to be slender they need to eat more healthy fat and protein to gain lean body mass. Mesomorphs only need to exercise and eat right. Endomorphs are genetically programmed to be big, the choice is to be muscular or fat. Endomorphs want to eat more calories, they feel deprived when they don't get them. Endomorphs have the most difficulty with fat. They absolutely need to put on muscle and restrict their fat intake. If you are this type, you need to follow the recommendations for increasing your metabolism and definitely increase your muscle mass.

If your parents are overweight it is important not to be complacent, shrug, and say "I can't fight family history."

Many diet studies use self-report data, which are notoriously unreliable; sometimes people under-reported their food intake by as much as 100%. Many obese people tend to over eat, snacking on such high fat foods as chips, doughnuts, and candy. We have not seen published reports of obese people who compulsively over-eat on fruits and vegetables: FAT IS THE PROBLEM.

What is more, in many overweight people there is a large psychological factor, and it is immeasurably hard for them to change their eating habits. There is plenty of evidence that suggests this could help because there are obese people who achieve weight control through diet and exercise when they persevere.

In summary, to put the study on obese mice into perspective, genetics may be one of the important factors in overweight problems. This should not get in the way of recognizing the main cause of being overweight is eating too much fat coupled with too little physical activity. Rather than waiting expectantly for the next magic potion, genetic engineering, which may help some people with weight control problems, we need to hammer at the same old message: limit your fat intake:

Convert your desired body weight to kilograms by multiplying pounds by 0.454 (or dividing by 2.2). This is the average number of grams of fat per day you may eat.
To lose body fat, this number should be reduced by up to one half keeping in mind that healthy fat is essential to good health.

There has been some recent evidence from the Calorie lab that some people burn fat more slowly than others do, however, the bottom line of their research showed that fat restriction coupled with exercise always resulted in fat loss as long as this lifestyle change was maintained. In my years of practice as a physician and a fitness trainer, I learned how to get different types of people in shape and keep them in shape. Metabolism of fat seems to be different in every individual. Most highly active people can eat 30% of their calories from healthy fat while most sedentary individuals need to decrease their fat intake to below 20% and get more active. Unfortunately, fat tends to anesthetize the brain and produce lethargy. This makes it difficult to get started. Another road block is the difficulty in radically changing from the SAD diet that is high in fat, sugar and salt, because the body will desperately crave these substances when they are denied. In my past dietary foibles, I noticed that if I ate salty foods in a few hours I would crave sugary foods and vice-versa. It takes about three weeks to break the habit and learn to enjoy healthy foods. The positive aspect of this is, if you persist and go three weeks with just healthy foods you will actually enjoy them. Your taste buds will be rejuvenated and you will experience subtle tastes like never before.

My challenge to you is to make a commitment for just three weeks. The reason for three weeks is that 21 days is the period of time it takes to break a bad habit and establish a new one. It won't be easy, but I guarantee it will be worth it.

Dr. Bailey appears regularly on TV and radio talk shows, he as written numerous magazine articles and he travels around the world speaking about optimal wellness of the body, mind and spirit. He also develops personalized wellness programs for individuals, families and corporations.


Dr. Bailey also does consultation worldwide over the phone, mail or by e-mail.


Dr. Bailey's Office

Dr. Bailey's Adorable Ragdoll cats

For more information on losing fat see Dr. Baileys latest book.

Topics of the Week