Dr. Robert H. Lustig, pediatric endocrinologist and nationally renowned obesity expert at the University of California, San Francisco, says that the obesity epidemic is caused by a "poisoned" food supply that is changing people's biochemistry and driving them to eat more and move less. He proposed this hypothesis that was published on Aug. 11 in Nature Clinical Practice: Endocrinology and Metabolism, after gathering results from thousands of studies on obesity. He says that it is unjust and of no use to blame personal behaviors, especially a lack of self-control, for the country's rising obesity rates.
Processed foods like potato chips, cookies, yogurt and white bread are readily available to Americans. These foods are rich in sugars that cause the body to believe it is hungry, which makes people feel compelled to consume more calories and conserve energy, he said.
"Sugar makes the body produce more insulin, which blocks hormones that would normally tell the brain to stop eating", he said.
However, Lustig's hypothesis is doubted by obesity experts who are hesitating to label overweight people as victims of their food supply with not a lot of hope to lose weight without major changes in America's food culture.
Definitely, there is a link between obesity, people's diet and activity level but Lustig has not tried to prove his hypothesis with laboratory trials. It was based on the results of obesity studies published between 1994 and 2005.
"I disagree with some of the details, particularly regarding the effects of insulin, and I think some of it is fairly speculative," said Dr. Peter Havel, a nutrition researcher at UC Davis. "It is really more of a hypothetical proposal rather than a review of established science. But I think there are some interesting ideas proposed in the article, many of which could and should be tested in animal models."
According to the federal Centers for Disease Control and Prevention, around two-thirds of American adults are overweight, and one-third is obese. Obesity is described as being 20-25% more than the ideal weight for one's height. Physicians are getting worried with patients who are obese or in danger of becoming obese and do not seem capable of making the lifestyle changes that are necessary to lose weight.
If Lustig's hypothesis proves to be right, then it is no wonder physicians are frustrated: Their patients are driven to eat more and exercise less, just the same way as they are driven to drink when they're thirsty.
According to Lustig's hypothesis, large amount of sugars increase insulin secretion, which in turn floods the hypothalamus, which regulates energy use in the body. In this way, insulin blocks the path of another hormone, leptin, which tells the brain about the energy requirement. This ends up in the body going into starvation mode -- the brain thinks it isn't getting enough energy, so it needs more calories and it needs to save energy.
"It's because of the toxic environment that the insulin rises and the problem behavior ensues," Lustig said. "That's why all of these diet programs don't work. That's why telling people to diet and exercise alone won't work, unless you improve the toxic environment as well."
"That's not to say losing weight is a hopeless cause. It's just a lot more difficult than physicians think, and the only way to help the population at large lose weight is to make drastic changes in the food that's available." he said.
"In the late 1960s, food processors discovered a technique for converting corn - which is grown abundantly and cheaply - into a processed sugar. That new product, high-fructose corn syrup, is a sweetener that affects metabolism in a very negative way," says Lustig.
Fructose is present in several beverages and processed foods, including juices and fruit drinks, barbecue sauce and ketchup, hamburger buns and pretzels. "While fructose tastes like sugar and is used as a sugar, its biochemical structure is different from sugar, which prevents it from being metabolized or broken down as a sugar," he explains.
Lustig sums up on how these biochemical disorders are the root causes of obesity: "The higher your insulin, the more your brain thinks you're starving. The more your brain thinks you're starving, the less you want to exercise and the more you want to eat. This only drives more food intake, which drives your insulin even higher, which interferes with your leptin even more, which makes you think you're starving even more. It's a vicious cycle."
"This is a very different way of looking at obesity," Lustig emphasizes. "While most people blame obesity on a lack of self-discipline, research shows today's foods and drinks actually trigger the behaviors that promote gluttony. Obesity is biochemical, not behavioral."
It means that the government has to be compelled to take stronger measures in educating the public and providing healthy food options.
A researcher with the American Beverage Association said he has his own doubts about Lustig's hypothesis, if only because sugar was a key component of people's diets long time back so many people would have started becoming obese.
"They say people didn't used to drink a lot of soft drinks, but when I was a kid I used to drink Kool-Aid and lemonade. That's basically sugar and water and the flavoring," said Richard Adamson, senior scientific consultant with the American Beverage Association. "The problem is not the sugar. The problem is we have less physical activity."
Losing weight is a big challenge. The National Weight Control Registry, which checks about 6,000 people who say they have lost 30 pounds or more and kept it off for at least a year, shows that most of the registrants have maintained their weight loss by exercising about an hour every day.
"That's a major lifestyle change, and not one that a lot of people can easily make. But it's possible", said Dr. James Hill, a pediatrics professor at the University of Colorado Health Sciences Center, who helps run the registry.
"One of the messages I don't want to send to people is you're destined to be overweight or not overweight, because I do believe there is some personal responsibility," Hill said.