DR.DENNIS BIER & USDA DIET GUIDELINES

Director of the Children's Nutrition Research Center, Baylor University, Houston Texas

Every five years the USDA releases new dietary guidelines. Every time they do this the guidelines are different from the ones before. This is because a panel of experts from across the country considers thousands of new studies and forms a consensus based on that data. I spoke with one of the panel members, Dennis Bier, M.D. about the new guidelines. Check the resource guide at the end of the interview for more information.

Q: Would you tell us something about the process by which the new guidelines were determined?

A: The dietary guidelines are regulated by public laws that require the USDA and Department of Health and Human Services to revaluate the previous guidelines and determine whether changes are needed based on new scientific information. These agencies, with advice from government, scientific, industry and consumer groups, appoint a committee of leading experts from around the country representing a variety of viewpoints.

The 11 member committee met several times to discuss whether the scientific information concerning human nutrition had changed since the last guidelines. The committee considered large stacks of scientific literature that had appeared since the last guidelines. The committee also received written testimony from more than 200 scientific groups, consumer groups, industry sources and other interested parties. Public testimony was also heard.

The committee, which is made up of people with a broad range of opinions, then argued the issues to a point where a consensus was formed. I think it is an extraordinarily open and fair process.

Q: The guidelines appear to put a strong emphasis on the benefits of antioxidant vitamins. While recommending nutritional sources of antioxidants, the guidelines stop short of recommending that most Americans take vitamin supplements. Why is this?

A:In the last five years there has been a vast amount of new data about the potential value of antioxidants in terms of aging, cancer and prevention of chronic disease. Antioxidants are required by all cells, performing a metabolic function of disposing of oxygen free radicals. It is clearly essential that we get enough of them. What we don't know with any degree of certainty is how much added health benefit there is from taking more than the essential amount. Further, it is not even entirely clear what the minimally essential amounts of some antioxidant compounds are. There are many new antioxidants recently identified in foods that we are only beginning to learn about. So it is very difficult to recommend that any one eat lots of the few antioxidants available as supplements, since the preponderance of available scientific information does not point convincingly to an added benefit over consuming apparently adequate amounts in a balanced diet .

The reason for recommending food rather than supplements is that there are numbers of antioxidant compounds in food that you won't get by taking specific antioxidant supplements. So the committee believes that we don't know enough to be able to recommend one antioxidant over another or the proper proportions of a mixture of antioxidant supplements. The prudent course is to eat food that contains antioxidants in the amounts and proportions occurring in nature, optimizing your diet that way.

Q: The guidelines provide very little endorsement for taking supplements of any kind. Is this the same situation?

A:The committee's position is that if you eat an adequate diet there is limited information except in selected groups that supplementing nutrient intake, over and above that, confers any particular benefit. Taking pills alone leaves out many of the known and unknown nutrients and non-nutrient components in foods that are known or believed to be helpful. For example, an athlete may excessively load up on a diet composed of virtually all carbohydrates, while reducing his or her intake of essential fatty acids that occur in some fats and the essential amino acids that occur in proteins. The athlete may take vitamin supplements thinking this will optimize the diet, but in fact it will not since the essential fatty and amino acids will still be missing.

We also said that taking supplements within the range of the RDA (recommended daily allowance) is not considered to be harmful. It is in the area of mega-supplements where there may be problems.

One area that should be strongly emphasized is folic acid in women of child-bearing age. This message has not reached the general population. There are very clear data that adequate folate intake prior to and at the time conception as well as during the first month of pregnancy (when many women do not yet know they are pregnant) will reduce the incidence of neural tube defects in the infant's developing brain. Therefore it is essential for young women to make sure they are receiving enough folic acid in their diets. If they are not, or if there is any question about their intake level, they should be sure to take a folic acid supplement of 400 micrograms daily.

Another example of where supplements may be required would be elderly shut-ins who are not getting much sunlight. They may need supplemental vitamin D to help maintain bone strength. similarly, pregnant women with poor iron intake may require iron supplements.

Q: The guidelines are designed for people over two year of age. Are there any guidelines for those under two years?

A:There are no federal standard dietary guidelines for children under the age of two. Indeed, one of the recommendations of the dietary guideline advisory committee was that this issue should be considered within the next five year period before the next issue of the guidelines is due.

Q: The guidelines emphasize that any ethnic diet can be healthy. Why the new emphasis on ethic diets?

A:The guidelines recognize that America is becoming more ethnically diverse. Most ethnic diets contain a large variety of healthy food choices, and we wanted to acknowledge that.

Q: The guidelines also for the first time say that a vegetarian diet is OK, but with certain caveats.

A:The primary concern about vegetarian diets for kids or adults are B12, which can only be obtained from animal sources, and calcium and vitamin D, which most Americans obtain from dairy products. One must also make sure to get enough of the essential minerals, particularly iron and zinc. While these minerals are present in plants, there is some question about the bioavailability, e.g. iron in meat is absorbed into the body considerably better than iron in plants. But there is no question that children can grow and develop normally on a vegetarian diet as long as the nutrients content is adequate.

Q: The new guidelines talk a lot about fat, cholesterol and body weight. How do these fit together?

A:The guidelines have much to say about fat in the diet, controlling fat intake, maintaining weight, and increasing physical activity. A large amount of the calories in our diet come from foods containing fat. One of single most important messages in the new guidelines concerns the importance of maintaining body weight and increasing physical activity. It is extremely important that young people leaving high school should realize that they should not continue getting fatter, but should maintain physical activity and watch their weight.

The other concept we tried to emphasize, is that there are good reasons to limit fat intake. Often the foods that contain saturated fats also contain cholesterol. Saturated fat has an independent effect on what happens to blood cholesterol. By watching the foods that contain both, you tend to reduce the intake of both. But you also have to be aware that even after reducing fat intake, you still have to watch your total caloric intake.

Q: What is the consensus on the relationship between eating sugar and hyperactivity?

A:We haven't heard the last of this topic. Some people think high sugar intake promotes attention deficit hyperactive disorder while others are not convinced. The committee looked at a lot of blinded studies considering this question and the majority have failed to show any effect of sugar on hyperactive behavior. Thus, it is hard to confirm this presumed effect of sugar in carefully controlled clinical studies. However, I assume we have not heard the last of this issue yet since many parents remain convinced that there is an effect. It is hard to confirm this effect in a clinical study.

Q: What other nutrition issues do you see being considered prior to the next guidelines five years from now?

A:The guidelines are the basis for many government educational and implementation tools like the food guide pyramid. The USDA has not yet decided whether the new guidelines have changed enough to require changes in the pyramid. For example, a representative of the National Bean Council came and testified before the committee. They reaffirmed that beans are vegetables and should be placed in the broader part of the pyramid containing vegetables, rather than near the narrow tip of the pyramid in the meat group, where beans are now included since beans, like meat, are a good alternate source of protein. this is a logical position and the new dietary guidelines emphasizes the dual role of beans.

Some of the continually developing issues of antioxidants will also become more important as data from new studies become available. another area where discussion is likely concerns specific population groups. for example, guidelines for elderly adults and children may be developed. the various roles of salt, sugar and alcohol in the diet are also likely to continue to receive attention. these issues will surface again as new scientific information becomes available to the committee charged with formulating the next guidelines in the year 2000.