Maybe your oldest child can take or leave candy. Your middle child is averse to anything sweet. Yet your youngest binges on sugary foods and struggles with his weight. You feed all three kids a balanced diet and parent the same way. What gives?
Robert H. Lustig, MD, an obesity specialist at the University of California, San Francisco, says genetics and what's known as leptin resistance may play a part in how some kids react to the sugars found in processed foods. These sugars include glucose and fructose, as well as sucrose (the chemical name of cane or beet sugar) and high-fructose corn syrup (HFCS, glucose and fructose derived from corn starch).
He says what parents swear are sugar "crashes" -- crankiness a few hours after having too many sugar-laden treats -- don’t come from changing blood glucose levels, as is commonly believed.
Research shows no direct causation between dietary sugar and behavior, says Lustig. "At most, we see fidgeting," he says, as a response to sugar consumption. He says the body's response to sucrose and HFCS is to make insulin, which puts sugar into fat cells for storage. Fat cells then make leptin, a hormone produced by fat cells to regulate appetite and fat storage.
"Leptin goes to the base of the brain and signals a response, telling the body it's eaten enough -- to go and burn off that caloric excess," he says. "This is why you might see fidgeting. You don't see a sugar 'crash.'" True hypoglycemia, he says, is when blood glucose levels dip beneath 60 milligrams per deciliter (mg/dL), which your typical sugar binge comes nowhere close to causing.
Sugar consumption, much like certain drugs and behaviors, triggers the release of dopamine in the brain's reward center. "Obese kids eat sugar to try to stimulate a dopamine response," Lustig says. "They can't get it because they've developed leptin resistance, so they eat more. It's not that they're 'crashing.' They can't get the reward response. It's more like withdrawal, which can trigger irritability."
Lustig, who is the lecturer behind the seminar "Sugar: The Bitter Truth," which viewers have seen more than 8.3 million times on YouTube, says leptin resistance is a chronic condition -- and doesn't develop overnight. Parents should keep a close eye on their kids' sugar intake. When kids cut down on sugar, leptin resistance slowly improves.
Not every child reacts to sugar in the same way, and some may be more susceptible to its sweet pull than others. "There may be genetic reasons for this," he says. Researchers are still trying to determine how genes may play a role.
Lustig refuses to sugarcoat the facts.
Sugar harms health. Most doctors, researchers, and nutritionists agree that too much sugar in the diet can lead to health conditions in children and adults, such as unwanted weight gain, diabetes, and heart disease, plus liver, metabolic, and dental issues.
Read the label. A surprising amount of added sucrose and high-fructose corn syrup is in condiments, beverages, granola bars, yogurt, and sports drinks.
How much is enough? Lustig says kids should not have more than 12 grams, or 3 teaspoons, of added sugar per day. That includes no more than 24 ounces of sugar-sweetened drinks per week.
Sugar research can cause confusion. Lustig says that while research shows no conclusive or direct causative connection between sugar consumption and bad health, dozens of independent studies -- those not sponsored by the food industry -- show correlation, citing a 2016 meta-analysis of 60 sugar studies.
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