Treadmill in a tube, a solution to the nation's obesity crisis?

Author:  Simard Jillian
Date:  October 2006

You're jogging at the gym,exhausted, panting, and sweaty, burning off that dry salad you ate for lunch and wondering how far away the nearest McDonald's is. It seems no matter how hard you work or how little you eat, those extra pounds just won't budge. "Isn't there just a shot they can give me to make me thin?" you wonder.

Until recently, this fantasy would have seemed just that,a fantasy. But scientists at the Scripps Research Institute have in fact developed a vaccine that has been shown to reduce body fat in animal models. Commonly referred to as the "fat vaccine," the treatment targets a hormone secreted by the stomach called ghrelin. Ghrelin decreases fat metabolism and increases the amount of stored body fat in the body. Typically, dieters have high levels of ghrelin, making it difficult for them to lose weight. The vaccine, however, uses the immune system to decrease the amount of ghrelin in the brain and thereby curbs both fat storage and weight gain.

Above: The first ten amino acids of ghrelin.

Above: The first ten amino acids of ghrelin.

What people will probably find most attractive about this vaccine, says Dr. Eric Zorrilla, a lead author of this study, is that "the rats who received the most effective vaccines didn't eat differently than the others, including the control models. That makes our findings exciting therapeutically,the vaccine slows the rate of weight gain, while still allowing for normal eating habits."

But what are normal eating habits? Many would argue that the low-fat, low-calorie diets that the rats were fed throughout the study are anything but normal for Americans, whose diets are notoriously rich in fat and calories. It is unknown whether the vaccine would have worked as well had the rats been fed more "Western" diets,over-portioned meals high in fat and calories. This is one of the many doubts that have been raised by other scientists in the field.

More serious concerns involve the potential health risks that the vaccine could pose. How might the vaccine affect human health in the long run? Dr. Susan Roberts, senior scientist and director at Tufts University's Energy Metabolism Laboratory, is among several researchers who remain skeptical of the vaccine's potential. "I'd like to see lifespan data," she says. "Do [the rats] live as long? I'd be worried about anything like this without really good long term safety data. My benchmark is whether I would test something myself,for this, absolutely not anytime in the near future!"

Aware of their colleagues' concerns, the Scripps scientists are currently conducting more in-depth research to hopefully address these concerns. To determine the efficacy of the vaccine on Western diets, the researchers have expanded their study to include diet-induced obese rats during a simulated weight loss in addition to rats with healthy eating patterns. Addressing the issue of long-term safety is more challenging. A promising avenue that the researchers are currently exploring is changing the treatment from an active vaccine to a passive vaccine. Unlike active immunization, in which the vaccine induces the body to produce antibodies itself, passive immunization administers the antibodies directly. Whereas the body's response can be difficult to control or reverse with active immunization, passive immunization is less risky. Using passive immunization, explains Zorrilla, "potential negative, unforeseen consequences could be reversed by stopping treatment, unlike with active vaccination."

Don't bite into that hamburger yet, though. "We don't anticipate anything being tested in humans until we are comfortable with the preclinical work that has been completed," says Zorilla. "We would hope to have something with which we were comfortable to move to human testing in about 2 years, but this is pure conjecture."

Zorilla and his co-author, Dr. Kim Janda, also of Scripps Research Institute, are also careful to caution that "vaccine" is not synonymous with "cure". "We're not claiming that our study answers the question of obesity treatment once and for all," says Janda. "What we are saying,and what our study confirms,is that this looks like a serious workable solution to the problem."

And what a big problem it is,the National Institutes of Health estimate that about two-thirds of American adults are either overweight or obese. Such prevalence has led not only to increased cases of heart disease, diabetes, and other illnesses, but also to an enormous nation-wide economic cost estimated to total over $117 billion. Suddenly that burger doesn't sound too appetizing. Maybe the treadmill isn't so bad after all.