Obese? A 'poisoned' food supply may be to blame, UCSF expert says / Doctor has yet to test theory that sugar triggers a starvation reaction in the brain
Feeling fat? It might not be your fault.
The obesity epidemic is caused by a "poisoned" food supply that is altering people's biochemistry and driving them to eat more and move less, according to a hypothesis proposed by a UCSF doctor who culled results from thousands of studies on obesity.
It is unfair and unhelpful to blame personal behaviors, especially a lack of self-control, for the country's rising obesity rates, says Dr. Robert Lustig, a pediatrician and nationally renowned obesity expert.
The processed food that is most readily available to Americans -- from potato chips and cookies to yogurt and white bread -- is loaded with sugars that cause the body to believe that 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.
Breaking the pattern of sugar consumption -- a pattern that Lustig compares to nicotine addiction -- is more than just a matter of willpower. It will take a grassroots effort of doctors, community leaders and consumers to force the government and the food industry to get those sugary foods out of mainstream American diets, he said.
"Everyone's assuming you have a choice, but when your brain is starving, you don't have a choice," Lustig said. "When you look at it that way, all of a sudden Big Food looks like the perpetrator, and the patient becomes the victim. Congress says you can't sue McDonald's for obesity because it's your fault. Except the thing is, when you don't have a choice, it's not your fault."
Lustig's hypothesis, published Friday in Nature Clinical Practice: Endocrinology and Metabolism, was met with some skepticism from obesity experts who are reluctant 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. Clearly, there is a link between obesity and people's diets and level of activity, but Lustig says that he has not yet attempted to prove his hypothesis with lab trials. His research 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."
About two-thirds of American adults are overweight, and about one-third are obese, according to the federal Centers for Disease Control and Prevention. Obesity is defined as being 20 percent to 25 percent over the ideal weight for one's height.
Doctors have long assumed that there is a connection between increasing sugar consumption and the country's out-of-control obesity epidemic. A study published in the American Journal of Clinical Nutrition earlier this week suggested that a single can of soda a day can add 15 pounds a year.
And increasingly, physicians are becoming frustrated with patients who are obese or in danger of becoming obese and seem incapable of making the lifestyle changes that are necessary to lose weight.
If Lustig's hypothesis is correct, then it's no wonder physicians are frustrated: Their patients are driven to eat more and exercise less, in much the same way they're driven to drink when they're thirsty.
"Your body is telling you to eat more. Our bodies don't do well fighting biochemical drive," Lustig said. "Try to not drink something after you've eaten a pizza, when you're thirsty."
The idea is that because consumers live in a "toxic environment" where sugar is a staple of so many food items, people are increasingly dependent on the sweetener, he said.
According to Lustig's hypothesis, sugar in large quantities drives up insulin secretion. This insulin floods the brain, and in particular the hypothalamus, which regulates energy use in the body. As a result, leptin, a hormone that tells the brain when the body needs more or less energy, can't get its signal to the hypothalamus because the insulin is blocking the way.
The result is that the body is thrown into starvation mode -- the brain thinks it isn't getting enough energy, so it needs more calories and it needs to save energy, he said. People end up feeling the symptoms of starvation, including malaise, depression, a lack of motivation and, of course, hunger.
"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, Lustig said. It's just a lot more difficult than physicians believe, and the only way to help the population at large lose weight is to make drastic changes in the food that's available.
That means, he said, targeting major food companies that add sugar to everything from hot dog buns and barbecue sauce to potato chips and energy drinks. Even juice, he noted, isn't a healthy option -- the natural sugars in fruit juice cause the same reaction in the body as the high-fructose corn syrup in soda.
Lustig said it also means forcing the government to take stronger measures in educating the public and providing healthy food options. For instance, Lustig observed, in California, families on welfare can buy juice and fresh fruit with food stamps.
A researcher with the American Beverage Association said he has a hard time buying Lustig's hypothesis, if only because sugar was a key component of people's diets long before so many people started getting obese.
"They say people didn't use 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."
Everyone agrees that losing weight can be hugely challenging. The National Weight Control Registry, which monitors 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. "I'm the first one to say let's address the environment. But the registry is an example of how you can live in a toxic environment and live in a healthy weight."
At a Weight Watchers meeting in downtown San Francisco this week, dieters exchanged tips on how to drop pounds when they're surrounded by unhealthy foods and dealing with busy lives that don't leave a lot of time for exercise.
Vittoria Baltazzi, who was leading the discussion, said she doesn't appreciate being considered a victim of her environment, despite the fact that it took her 16 years to lose 30 pounds. She's kept the weight off for six years.
"You can complain that society does this to you, or that you don't have options, but I don't see it that way," Baltazzi said. "If you are conscious of what you're doing, you can overcome your environment."
Finding a balance to fight fat
Eating large amounts of sugar, says UCSF researcher Robert Lustig, tips the balance between insulin and the hormone leptin in the brain. Excess sugar makes the brain switch into starvation response mode. This prompts more eating and increases lethargy in order to conserve energy. The calories from more eating go unused and are stored as fat.
STARVING FOR A DRINK...
A hungry person drinks a soda (typically containing 10« teaspoons of sugar), and the body metabolizes that sugar. As a result, the pancreas increases insulin production. The brain, flooded with reports of increased insulin, decides to either turn the sugar into instant energy or store it as fat.
... AND NEVER FEELING FULL
After digesting the drink, the body should receive a signal of leptin from its fat cells. This signal tells the brain that the body has enough energy. However, large amounts of insulin may drown out the leptin signal, causing the hungry person to remain hungry.
Controls energy balance
Regulates the transfer of sugar into fat
Store energy as fat and produce leptin
Signals long-term energy storage
Produces insulin and digestive enzymes
Editor's note: A correction has been made in the above story.