Long-term consumption, early in life, of foods that quickly digest into simple sugars may program the body to make excess insulin–and abdominal fat. These findings, from an Australian study in rats, suggest how diet might foster an individual’s susceptibility to obesity and diabetes.
Dorota B. Pawlak and her group at the University of Sydney fed 2-month-old rats diets that nutritionally resembled what most people now eat–about 20 percent protein, 35 percent fat, and 45 percent carbohydrates, which are sugars and starches. However, half of the animals received carbohydrates with a low glycemic index (GI), which signifies foods that digest slowly. The rest got high-GI carbs (SN: 4/8/00, p. 236). These break down rapidly, releasing the simple sugar glucose into the blood.
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By the trial’s end, after 7 weeks, the animals all weighed about the same. However, those that had dined on the high-GI foods had more fat–for example, 15 percent more fat at a site that’s a model for abdominal fat in people–the scientists report in the January Journal of Nutrition.
Animals from the two groups also had begun responding differently to carbohydrates. Rats that had been getting a high-GI diet showed blood concentrations of insulin–a hormone the body makes to move glucose into cells–that peaked more quickly after a meal and that stayed high longer than those in the rodents raised on the low-GI fare.
Jenny Brand-Miller, a coauthor of the study, suspects that oversecretion of insulin produced the extra fat in the high-GI animals. She also notes that these rats ended up making excessive insulin in response to every sugar and starch they consumed–not just high-GI ones. “It’s as if they’d become hypersensitized, making overkill amounts of insulin every time,” she says.
Such oversecretion is a hallmark of insulin resistance, a metabolic change that precedes adult-onset diabetes. Brand-Miller says her findings suggest that childhood diets might make the body vulnerable to this disease.