Question: In your book Healthy Aging, you recommend eating whole grains but not whole-wheat flour products. Why?

Answer: Whole grains are a great source of important nutrients, including protein, fiber, vitamins, minerals and especially carbohydrates that are low on the glycemic index (GI), a ranking of carbohydrate foods on the basis of how they affect blood sugar (glucose). This is important for many people because eating a lot of foods that are high on the glycemic index will produce spikes in blood sugar that can lead to insulin resistance over time. Insulin resistance is associated with obesity, high blood pressure, elevated blood fats and an increased risk of type 2 diabetes and other chronic diseases.

Grains in their natural form have a low glycemic index, while processed carbohydrates, including those made with flour or puffed grains, have a high GI. The reason is that it takes longer for digestive enzymes to reach the starch inside whole grains or grains cracked into large pieces, slowing the conversion of starch to sugar.

True whole grains include wild rice, barley, quinoa, millet and wheat berries. You can be pretty sure you're eating a natural grain with a low GI ranking if you have to chew it or can see grains or pieces of grains in food products. The more your jaw has to work, the better. But when grains are pulverized into flour, whether whole or not, their surface area expands dramatically, providing a huge, starchy surface area on which the enzymes can work.

Consequently, the conversion to sugar happens very quickly.

Whole-wheat bread and products labeled "whole grain" are usually made with flour. Finely textured whole-wheat bread has the same GI as white bread - about 70, making both high-GI foods. I recommend cutting down on all products made with flour and increasing consumptions of grains in their more natural state.

Q: What do you think of acai, a berry said to be one of the most nutritious foods in the world? Acai juice is showing up in natural-foods stores, and all I know about it is that it's very expensive.

A: Acai (pronounced ah-SAH'ee) is a Brazilian berry (Euterpe oleracea) that's being touted on the Internet and elsewhere for its high antioxidant content. Reportedly, acai provides 10 times the antioxidants found in red grapes and 10 to 30 times the anthocyanins found in red wine. It's now being promoted as an aid to weight loss, lowering cholesterol and boosting energy.

Brazilian natives have traditionally used acai berries to treat digestive disorders and skin conditions, according to University of Florida researcher Stephen Talcott, who has been investigating the antioxidant effects of the berry. He and colleagues have published findings from laboratory studies showing that extracts from acai berries caused leukemia cells to self-destruct. While Talcott cautioned that the study doesn't show that acai could prevent leukemia in humans, he noted that compounds that show good activity against cancer cells in cell cultures are likely to have beneficial effects in the body.

Past research on other compounds hasn't shown this to be true, and in my mind this is a big inferential leap that needs to be validated by further research.

Talcott is now looking into the effects of the antioxidants in acai on healthy humans. This study is aimed at determining how well the compounds are absorbed into the blood and how they affect blood pressure, cholesterol levels and related health indicators.

Acai berries are highly perishable and traditionally used immediately after picking. For that reason, acai is available outside Brazil only as juice or products that incorporate juice such as smoothies, powders and capsules. There are no studies on products containing acai, which tend to be pricey and which many people find unpalatable.

Acai may be rich in antioxidants, but that doesn't mean high concentrations of those phytochemicals are making it from the berries into the juices, smoothies and the like.

Until we know more about these products, I recommend sticking closer to home for your antioxidants. Opt for organically grown blueberries, which are easily obtainable in fruit form, are much less expensive and give you fiber as well as plenty of antioxidants. And don't forget black raspberries and pomegranates, both of which have good scientific evidence for their health benefits behind them.

drweil.com