Carbs: Beyond The Basics

The pros and cons of using the glycemic index for carb counting and meal planning

By Tracey Neithercott
February 2014

Carbs count. Eat too many and your blood glucose can spike. It’s the first lesson people with diabetes learn at diagnosis: Watch the number of carbohydrate grams you eat at each meal or snack. That’s all well and good, but what about the type of carbohydrate you choose to eat? Increasingly, researchers are asking that question. Their answer may surprise you.

The GI Revolution

Back in 1980, most people with diabetes were using carbohydrate exchange lists, and “glycemic index” was a term foreign to researchers, doctors, and patients alike. Scientists at the University of Toronto, led by David Jenkins, MD, PhD, DSc, began digging around in the body’s glucose response to different foods, and the term came into use. In a 1981 study published in The American Journal of Clinical Nutrition, the researchers listed what they called the glycemic index for 62 common foods.

The glycemic index (GI) measures the glucose response to a given number of grams of carbohydrate. Imagine a chart with a line representing glucose levels during the first two hours after you eat 50 grams of carbohydrate. The area under that line, when compared with results from a test using 50 grams of pure glucose, indicates a food’s glycemic index (graph, opposite). Foods with a high glycemic index have higher peaks and more area under the line than those with a low GI. The glycemic index, then, is a ranking of foods from zero to 100 based on blood glucose levels after eating. So 50 grams of a plain white baguette has a GI of 95 (and a taller graphed line) while 50 grams of an apple has a GI of 39 (and a shorter line).

“If you’re carb counting and if you have 20 grams of carbohydrate from an apple or a banana or rice, it’s [as if it’s] all the same,” says Thomas Wolever, BM, BCh, DM, PhD, coauthor of The New Glucose Revolution: The Authoritative Guide to the Glycemic Index—the Dietary Solution for Lifelong Health, professor in the Department of Nutritional Sciences at the University of Toronto, and coauthor of the 1981 glycemic index study. “But it’s not.”

You might imagine that the glycemic index would be useful for people with diabetes. Yet more than three decades after its discovery, the glycemic index still isn’t among the most-recommended meal-planning tools.

The Glycemic Load

Graphing Blood Glucose Response
To determine the glycemic index of foods, researchers plot glucose levels for two hours after subjects eat portions containing 50 grams of carbohydrate and compare the area under each line with that of pure glucose.

SOURCE: Adapted from The American Journal of Clinical Nutrition, January 2009

In its 2013 nutrition position statement, the American D
iabetes Association says picking low-GI foods over high-GI ones “may modestly improve glycemic control.” Yet despite the ADA’s slight encouragement, the recommendations note that while some studies showed drops in A1C (a measure of average glucose for the past two to three months) from following a low-GI diet, others found no blood glucose improvement at all.
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Autism and Toxic Chemicals: Are Pollutants Fueling Rising Prevalence?

Date: February 18, 2014
Researchers link more pollutants to disorders of brain development; call for global prevention strategy to control their use

A new report implicates a growing number of industrial chemicals as contributing to autism and other disorders of brain development. The authors call for a global strategy to reduce exposure.

The report appears online in Lancet Neurology. The authors are Harvard environmental epidemiologist Philippe Grandjean and Mount Sinai Medical School pediatrician and epidemiologist Philip Landrigan.

The new report summarizes evidence from published studies on industrial chemicals and brain toxicity and updates the review that the authors conducted in 2006.

Five known threats to brain development
Their 2006 review identified five widely used industrial chemicals as “developmental neurotoxicants.” Such chemicals can contribute to developmental brain disorders such as autism. The five were lead, methylmercury, polychlorinated biphenyls, arsenic and toluene.

In addition, the 2006 report identified more than 200 industrial chemicals that cause brain damage in adults. The authors warned that many of these might likewise cause developmental brain disorders.

Six more chemicals on the danger list
The new report adds six chemicals to the list of developmental neurotoxicants. They are high-doses of manganese or fluoride, the pesticides chlorpyrifos and DDT, the solvent tetrachloroethylene and polybrominated diphenyl ethers. Polybrominated diphenyl ethers are flame retardants applied to furniture.

Manganese and fluoride become toxic only at unnaturally high levels. The doses in vitamins and dental-hygiene products are safe.

While exposure to some of these chemicals is common in North America, the highest exposures tend to occur in developing nations, notes Alycia Halladay, Autism Speaks senior director for environmental and clinical sciences.

“Most exposures are hard for individuals to control themselves,” Dr. Halladay adds. “One way to prevent exposure is through regulation. Examples include the elimination of lead from gasoline and paint and the Clean Air Act.”

Meanwhile, Dr. Halladay agrees with the authors’ call for more research on the hundreds of toxic industrial chemicals now polluting the environment.

Many other neurotoxicants are likely contributing to a “silent pandemic” of developmental brain disorders, Drs. Grandjean and Landrigan write. As evidence, they cite studies linking autism risk to prenatal exposure to high levels of air pollution. (Click here for the full text of one of these studies, funded in part by Autism Speaks.)

Autism Speaks funds further research
Autism Speaks has funded a number of studies on autism risk and air pollution. In addition, it is currently supporting several studies collecting information on autism risk and exposures to other types of toxic chemicals.

To further speed discoveries, Autism Speaks is also funding the development of the Early Life Exposure Assessment Tool (ELEAT). Designed for autism research, this instrument allows investigators to combine the results of multiple studies on early environmental exposures. By increasing sample sizes, this will boost scientists’ ability to uncover toxic effects.

Learn more about Autism Speaks Environmental Factors in Autism Initiative here. For a full list of Autism Speaks studies on environmental risk factors for autism, click here.

Explore all the research Autism Speaks is funding using this website’s grant search.