The Public Health Implications of the 2010 Dietary Guidelines

An Expert Interview With David L. Katz, MD, MPH

Janet Kim, MPH

Disclosures

February 15, 2011

In This Article

Dietary Cholesterol

Medscape: You published a blog posting recently about the new guidelines, offering your perspective, which would be interesting to address further. For one, you expressed concern about the report's ongoing pairing of dietary cholesterol with saturated fat. Could you elaborate on your objection?

Dr. Katz: Actually, the timing of this proves to be particularly interesting. The USDA just made an announcement: On the basis of its most current analysis of a representative sample of eggs, they are, on average, 14% lower in cholesterol than previously thought and actually quite a bit higher in vitamin D content as well, probably related to changes in the feeding practices of hens. Although we don't have a clear explanation in regard to the why, we have a definitive statement of the what.

It's good news if you're concerned about the cholesterol content of eggs -- that they actually have less cholesterol than we thought -- but I'm not sure that we needed to be concerned about the cholesterol content of eggs in the first place. What I'm referring to is literature – intervention and observational studies -- that has mostly proliferated over the past decade to a decade and a half. My own laboratory has contributed 2 papers[1,2] to date on the basis of intervention trials that evaluated daily egg feeding in healthy adults and in adults with hyperlipidemia. In both instances, we looked at endothelial function and a number of other cardiac risk measures and found no harmful effects whatsoever from ingesting 2 eggs a day. Many other studies have found exactly the same result. Indeed, some studies that have involved egg feeding have found benefits related to insulin resistance and type 2 diabetes, presumably because the diet is being shifted to higher protein and lower refined carbohydrates.

Large epidemiologic studies, probably the most famous of which is the Nurses' Health Study at Harvard University, Boston, Massachusetts,[3] also have shown no association between egg intake and cardiovascular disease or all-cause mortality. We actually have an expanse of both intervention trials in small populations and epidemiologic studies in large populations, both in the United States and in Europe, suggesting that: (1) dietary cholesterol does not meaningfully or consistently raise blood cholesterol levels; and (2) no specific association exists between eating eggs and the risk for heart disease.

The reason that I wanted to get involved in this part of the discussion has to do with my professional mission, which is to try to optimize health outcomes through lifestyle means with a particular emphasis on diet and nutrition. You have to ask the question: If eggs are not harmful, and if indeed eggs may be beneficial, what is the net effect on the quality of diet and the quality of health when you give people advice to avoid eggs? My years as a clinician in the trenches has made it very clear that patients in cardiac care units won't get eggs, but they will get waffles and bagels. In the general public, people with or concerned about heart disease will eat donuts and muffins, even as they're avoiding eggs. We have abundant evidence now to suggest that an excess of refined starches and simple sugars are contributors to the risk for heart disease.

My fundamental concern is that advice to avoid cholesterol and to avoid eggs is actually doing net harm to the quality of the diet. I think it's an important issue, and I don't understand why the dietary guidelines lump dietary cholesterol together with saturated fats. They are clearly distinct in the research literature. The evidence about saturated fat is now being debated, and I think the reason for that is because not all saturated fatty acids are created equal. In particular, palmitic and myristic acids are atherogenic, whereas stearic and lauric acids probably are not, but saturated fat as a class is meaningfully associated with the risk for heart disease. Certainly, industrially produced trans fat, as a class, is associated with the risk for heart disease. Dietary cholesterol is not. So they tarred with a broad brush that I think is inappropriate, and it seems we'll have to wait for the 2015 dietary guidelines for cholesterol to be treated fully in accord with the available science.

Medscape: The revised guidelines now encourage increasing seafood intake and specify the recommended quantities to consume. You noted that this new guidance might pose some uncertainty for consumers who need to monitor their intake of dietary cholesterol. How would you interpret this particular recommendation for clinicians and the American public?

Dr. Katz: The problem here resides with the cholesterol recommendation, not the seafood recommendation. I have real-world experience with this because I have patients who have read the cholesterol guidance asking me, "Doc, is it okay to eat shrimp? I know they have heart-healthy fats, but they also have cholesterol and I know I'm supposed to avoid cholesterol." If we continue to advise people to restrict their intake of cholesterol, they will be concerned about cholesterol-containing foods. This is the only internal conflict that I noted in which the guidelines themselves will produce confusion. I think that other things about the dietary guidelines are substantially less than perfect, but these are probably the best guidelines that we've ever had.

The specific recommendation for cholesterol is < 300 mg/day for the average adult and < 200 mg/day for the adult with or at high risk for heart disease. Of course, people are not counting the number of shrimp or scallops that they eat and tallying the total exposure to cholesterol, and nobody wants to go out for a seafood dinner and look at it through that particular lens. What people will tend to do is to simplify: If they're supposed to avoid cholesterol, they will avoid foods that contain cholesterol. If cholesterol is not a worry, and foods happen to contain cholesterol that are otherwise good for them, then they will unconcernedly eat those foods. I think that, in fact, is the right formula. People concerned about their heart health absolutely can eat eggs and not necessarily count the milligrams of cholesterol, and they certainly can eat shrimp, scallops, and other seafood and not count the milligrams of cholesterol.

I really don't know how you can make sense out of the guidance in this area. People will think they should eat seafood because the guidelines say that it's good for them, and think that they should avoid it because the guidelines say to restrict dietary cholesterol. My recommendation is that seafood is fine. I would point out, though, that not all seafood is created equal. The guidelines are a little bit blunt here. For example, lobster is not a source of omega-3 fatty acids and is extremely high in sodium, so the seafood that's recommended would be scallops, mussels, crab, and shrimp, among others, which are rich sources of omega-3. They do contain cholesterol, but as noted, I don't consider this a concern.

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