Robert Lustig is the UCSF pediatric endocrinologist famed among other things for his widely viewed Youtube video, "Sugar, the Bitter Truth." He delivered a brief lecture as part of a Stanford's "Cafe Scientifique" series the other day and I attended, keen to hear his latest take on the role of sugar and hormones in the obesity and diabetes epidemics. Here's a quick overview of the points that most struck me.
• 20 million American kids are overweight. There are 366 million diabetics worldwide in 2011, which amounts to 5% of the world's population. Type 2 diabetes is "chewing through the world's healthcare dollars; we have to solve this," he says. We already pay a 50% premium for health care costs for obesity-related health problems.
• In the past 30 years there has been a six-fold increase in the prevalence of obesity. The root cause is a mismatch between our current food environment and our innate biochemistry (personal note: I was glad to hear this, since that was the main message of my book Farewell, Club Perma-Chub).
• For the most part, the obesity we see today is caused by the phenomenon of leptin resistance. Leptin, a hormone which normally signals the brain that the body has sufficient energy stores, stops working in the obese person.
• If you have low leptin, the brain thinks you are starving, no matter how much fat is on your body. "If we can fix leptin resistance there wouldn't be obesity," says Lustig. Low leptin feels like starvation--obesity is a manifestation of brain starvation. The starvation response causes "recidivism" in dieting, or the tendency to regain all the weight lost.
• It's the action of another hormone, insulin, that blocks what leptin is supposed to do. Elevated insulin blocks leptin signaling. Again, the brain thinks the body is starving and doesn't know it's actually fat.
• If we lower insulin, the body is no longer being told to store fat -- we have more energy to burn. When insulin is high, the blood glucose goes to fat. When insulin is low, blood glucose is at your service to burn as fuel (resulting in the urge to exert and exercise).
• To improve leptin sensitivity, drop your insulin. To drop insulin, reduce carb consumption.
• High sugar is a pain reliever and activates the opioid system.
• The more sugar in your system, the faster your tissues brown (just as with cooking), and the faster you die.
• Metabolic problems are found when consumption exceeds 200 calories of day of sugar. (American average is 22 teaspoons/day of added sugar, which is 350 cal)
• Sucrose is half glucose, half fructose. Fructose induces insulin resistance, which induces leptin resistance.
• All aspects of metabolic syndrome derive from fatty liver, which results from excessive alcohol or fructose consumption.
• Sugar is, by a humongous margin, the most potent variable explaining diabetes rates worldwide. (I'm omitting the actual number because Dr. Lustig says the data are still unpublished.)
• You can have a normal biomass but have a fatty liver driving metabolic syndrome. Body size is not the whole story.
• Leptin resistance is not a mere aberration, it had an evolutionary role, conferring selective advantage on the humans who could store the fat from gorging on summer/fall fruit to enable survival through a long food-free winter.