Robert Lustig, MD
Insulin and LeptinLustig’s own groundbreaking studies more than a decade ago stimulated the development of his controversial ideas about metabolism and biological feedback in weight control. One not-yet-popular idea is that, calorie for calorie, sugar causes more insulin resistance in the liver than other edibles. The pancreas then has to release more insulin to satisfy the liver’s needs. High insulin levels, in turn, interfere with the brain’s receipt of signals from a hormone called leptin, secreted by fat cells, Lustig believes. In the 1990s, Lustig worked with children diagnosed with hypothalamic obesity, a disorder that can occur after brain tumor surgery. The children were making more insulin than was necessary for normal energy storage in fat cells. Lustig thought the kids were not receiving signals from leptin, which helps send a message that the appetite has been sated. Lustig concluded that the children’s brains were fooled into thinking that they were starving. Lustig administered a drug called octreotide, known to block insulin release. Insulin levels fell; the children ate less, lost weight, spontaneously became more active and improved their quality of life. Lustig tried the same treatment with obese adults, and found that a subset responded in the same way as the children with hypothalamic obesity. Eating stimulates secretion of insulin and leptin. The conventional view holds that insulin, like leptin, feeds back in the brain to limit food intake, Lustig explains. But Lustig does not think that chronically elevated insulin levels feed back negatively to curb eating. Instead, chronically elevated insulin blocks leptin’s negative feedback signal, Lustig believes. “Most people think insulin does the same thing as leptin,” he says. “I think it does just the opposite.” Lustig believes that fructose generates greater insulin resistance than other foodstuffs, and that fructose calories, therefore, fail to blunt appetite in the same way as other foods.
A Calorie Is Not Just a CalorieLustig also is at odds with mainstream scientific viewpoints when it comes to explaining how fructose is shunted through biochemical pathways and converted into fat and other molecules. Unlike conventional calorie counters, Lustig does not believe all food calories have the same impact on fat storage and energy expenditure, regardless of whether they come from fat, protein or carbohydrate. Fructose, a type of carbohydrate, is not metabolized like other foodstuffs, and not even like glucose, the other major carbohydrate, Lustig says. In addition, Lustig claims that fructose is just as bad as alcohol in causing fat storage in the liver and in causing fatty liver disease. Lustig advances these controversial ideas primarily by citing already published studies, most of them by other researchers. But he also tries to enlist bench scientists in research collaborations in the hopes that additional studies will prove to others that these ideas are correct.
Sugar No Better Than FatEach sucrose molecule consists of one molecule of fructose joined to one molecule of glucose. In the gut, these two components are quickly split apart. High-fructose corn syrup is a less expensive mixture of glucose and fructose. There is no point in belaboring the difference, Lustig says. “High-fructose corn syrup and sucrose are exactly the same,” Lustig says. “They’re equally bad. They’re both poison in high doses.” Over the past century, Americans have increased their fructose consumption from 15 grams per day to 75 grams per day or more, Lustig explains. The trend accelerated beginning about three decades ago, when cheap, easy-to-transport high-fructose corn syrup became widely available. Much of processed food labeled “reduced fat” instead has sugar added to make it more palatable, Lustig says. But when it comes to harmful health effects, sugar is worse than fat, he claims. Consumption of either results in elevated levels of artery-clogging fats being made by the liver and deposited in the bloodstream. But fructose causes even further damage to the liver and to structural proteins of the body while fomenting excessive caloric consumption, Lustig says.
Four Simple GuidelinesLustig prescribes four simple guidelines for parents coping with kids who are too heavy:
- Get rid of every sugared liquid in the house. Kids should drink only water and milk.
- Provide carbohydrates associated with fiber.
- Wait 20 minutes before serving second portions.
- Have kids buy their “screen time” minute-for-minute with physical activity.
Childhood Obesity: Adrift in the “Limbic Triangle”
Michelle L. Mietus-Snyder and Robert H. Lustig
Annual Review of Medicine 59:147-162 (February 2008)
Childhood Obesity: Behavioral Aberration or Biochemical Drive? Reinterpreting the First Law of Thermodynamics
Robert H. Lustig
Nature Clinical Practice Endocrinology & Metabolism 2(8):447-458 (2006)
Adolescent Overweight and Future Adult Coronary Heart Disease
Kirsten Bibbins-Domingo, Pamela Coxson, Mark T. Pletcher, James Lightwood and Lee Goldman
New England Journal of Medicine, 357(23):2371-2379 (Dec. 6, 2007)
Overweight Adolescents Projected to Have More Heart Disease in Young Adulthood
UCSF News Release, Dec. 5, 2007
Prevalence of Overweight and Obesity in the United States, 1999-2004
Cynthia L. Ogden, Margaret D. Carroll, Lester R. Curtin, Margaret A. McDowell, Carolyn J. Tabak and Katherine M. Flegal
JAMA, 295(13):1549-1555 (April 5, 2006)