Index sorts bad carbs from the good

Scripps Howard

With three young children, his spouse working full-time, and shift work to juggle, Mark Stewart has a busy life. So there is little hesitation when it’s his turn to prepare dinner: He gets the water boiling, cuts the vegetables for the sauce, and has a big batch of spaghetti on the table in no time.

“Pasta is definitely a staple in our family’s diet,” he says. “It’s an easy meal to make; it’s healthy, and we enjoy it a lot.”

In this anti-carbohydrate era, when it has become gospel that carbs are the express lane to obesity, these are the words of a heretic: doubly so because he shuns red meat and more than half his diet consists of carbs including pasta, whole-wheat breads and fresh fruits and vegetables.

But Stewart, a Toronto firefighter, has many things that the Atkinsites, the South Beachers, the Zonies and followers of other trendy diets can only long for: a trim, buff body, boundless energy, good blood pressure and rock-bottom cholesterol.

What he has realized is that carbohydrates are not the monolithic evil they are made out to be: There are good carbs and bad carbs.

The good ones are those that break down slowly in the body and provide a steady source of energy. The bad ones give you a quick rush and leave you feeling hungry again not long after.

What he is doing, almost unwittingly, is choosing food based on its glycemic index, a measure of the speed at which food is digested and converted into glucose, the body’s source of energy.

The glycemic index has spawned some of the hottest new entries in the diet book wars, with titles including “The New Glucose Revolution,” by University of Toronto professor Tom Wolever, and “The GI Diet,” by Rick Gallop, past president of the Heart and Stroke Foundation. What distinguishes GI from its competitors, however, is that it is more a scientific theory than a weight-loss fad.

“It’s not a diet; it’s a way of thinking of food,” said David Jenkins, a nutritional scientist and director of the Risk Factor Modification Center at St. Michael’s Hospital in Toronto.

He published the first research on the glycemic index in 1981, but, in his words, “it sank like a stone.” Over the years, however, the evidence slowly accumulated as Jenkins and others published groundbreaking work on how dietary choices influenced rising rates of obesity, diabetes, heart disease and some forms of cancer.

Today, the GI approach is being hailed as the missing piece of the nutritional puzzle, the underlying explanation for why the high-carb, low-fat and carb-free approaches have all failed.

“This is emerging as one of the most promising, if not the most promising nutritional development ever,” said Simin Liu, an assistant professor in the department of epidemiology at the Harvard School of Public Health.

The body converts all carbohydrates _ bread and sugar alike _ into sugar molecules that are burned or stored. The faster carbs are broken down by the digestive system, the quicker blood sugar goes up and the higher the GI of a given food. The GI value of pure glucose is set at 100, and every other food is ranked on a scale of 0 to 100 based on the actual effect on blood glucose levels.

Almonds rate a 0, apple juice 30, spaghetti 38, cheese pizza 60, Coca-Cola 63, a white bagel 72, a baked potato 85, and a fruit roll-up 99.

The blast of sugar that comes from high GI foods makes insulin levels go up and stresses the pancreas, our body’s insulin factory. Insulin is a hormone that activates cells to absorb sugar in the form of glucose. This, in turn, leads to insulin resistance, a precursor of diabetes and heart disease.

In modern times, we have adopted a diet of soft, chewy, processed foods that go down smoothly. We tend to think of these easily digestible foods as good, but in scientific terms, they are not. The body processes them quickly, demanding massive insulin production and leaving us hungry again only hours later.

Over time, this leads not only to unhealthy weight gain but to pancreatic burnout, a key contributor to many chronic diseases.

The glycemic index is the underlying rationale for limiting carbs in popular diets like Atkins, South Beach, the Zone and Sugar Busters, but Jenkins believes the idea has been perverted.

“To cut out carbs from the diet, that was sad,” he said. “But they are revising their statements so that now they are not carbohydrate-exclusion diets but more selective carbohydrate diets.”

In fact, most foods on the banned lists are high-GI foods. Low-GI carbs such as peas, beans and lentils are encouraged.