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Breads with a lower gylcemic index tend to be made with coarser pieces of whole grains such as wheat kernels, sprouted grains and rye kernels.Thinkstock

THE QUESTION

White bread and white pasta are enriched with vitamins and minerals but their whole-grain counterparts are not. Which is a better source of nutrients then, white or whole grain? I am concerned, too, about folic acid.

THE ANSWER

In Canada, manufacturers are required by law to add three B vitamins – thiamine (B1), riboflavin (B2), niacin (B3) – as well as iron to white flour to replace what is lost during milling. But that doesn't mean that "enriched" white bread and "enriched" white pasta are better sources of these nutrients than whole-wheat versions. It's a different story, however, for folic acid.

When whole grains are milled, scraped and refined to remove the outer bran layer and the germ layer that's rich in vitamins and minerals, all that's left is the nutrient-poor starchy endosperm. The purpose of enrichment is to bring white flour back to the nutritional level of whole-wheat flour – at least when it comes to thiamine, riboflavin, niacin and iron. Refining removes more than these four nutrients. It also strips out fibre, vitamin B6, bone-building vitamin K and free-radical-fighting vitamin E. A long list of minerals gets discarded, too. Whole grains have significantly more magnesium, potassium, zinc, copper, selenium and manganese than their refined counterparts. They also retain more antioxidants and protective phytochemicals.

These nutrient casualties aren't replaced. So, despite the fact that 100-per-cent whole-grain breads and pastas are not enriched, they outrank (by a long shot) white bread and white pasta when it comes to most nutrients. One exception, though, is folic acid.

Mandatory food fortification of all white flours, enriched pasta and enriched corn meal with folic acid was implemented in 1998 as a means of preventing neural-tube defects, birth defects of the brain and spinal cord. The B vitamin, however, is not added to whole-wheat flour or whole-wheat pastas, making refined bread and pasta a far superior choice – when it comes to folic acid.

One cup of white spaghetti, for example, has 108 micrograms of folic acid (also called folate) whereas whole-wheat spaghetti has only a tiny amount that occurs naturally (7 micrograms).

That said, I don't advise women of childbearing age to rely on eating white bread and pasta to get their folic acid. Women who could become pregnant, even if they are not planning to, should take a daily multivitamin containing 0.4 to 1 milligram of folic acid and eat foods rich in the nutrient. Good (unprocessed) food sources include lentils, cooked spinach, broccoli, asparagus, black beans, avocado, artichokes and oranges.

The enrichment of rice is voluntary in Canada; the only way to know if white rice is enriched with B vitamins and iron is to read the nutrition label and ingredient list. Better yet, choose brown rice to get all of the nutrients that are stripped to make white rice.

There's something else to consider when choosing grains: glycemic index (GI), a measure of how much carbohydrate-containing foods raise blood glucose after eating. The more grains are altered and stripped of their natural parts, the more quickly our bodies are able to digest them.

Refined grains typically score high on the GI scale, meaning they cause blood glucose and insulin to rise sharply. A steady intake of high glycemic grains can lead to hunger and overeating and, worse, insulin resistance, a precursor for type 2 diabetes.

White bread, not surprisingly, has a high GI value ranging from 70 to 89. But so does whole-wheat bread.

(Foods that are ranked high on the GI scale have values 70 or higher; foods considered low have a GI of 55 or less.) Breads with a lower GI tend to be made with coarser pieces of whole grains such as wheat kernels, sprouted grains and rye kernels; 100-per-cent stone-ground, cracked-wheat and whole-grain rye breads have low glycemic numbers.

White rice comes in around 72, whereas brown rice has a GI of 48.

Pasta is a special case. Both whole-wheat and white pasta have a low glycemic index, scoring 32 and 42 respectively. Unlike the starches in bread flour, the starches in pasta are physically trapped in protein molecules, causing them to be digested more slowly. Even so, whole-wheat pasta is nutritionally a better choice.

Read before you buy

Read labels carefully when buying whole-wheat products. Under current regulations, whole-wheat flour can have up to 5 per cent of the wheat kernel (about 70 per cent of the nutrient-rich germ) removed during milling and still be called "whole wheat." Look for the words "whole-grain whole-wheat flour including the germ" on the ingredient list. This flour is 100-per-cent whole grain, containing the bran, germ and endosperm.

Leslie Beck, a registered dietitian, is based at the Medisys clinic in Toronto. She is a regular contributor to CTV News Channel.