Recent attention to the provocative new research about trimethylamine-N-oxide (TMAO) and the foods that cause us, or really our resident bacteria, to produce this compound preliminarily linked to heart disease risk, raises a fundamental question we often fail to ask: How does a food affect our overall diet, and thereby, our health? I think it's in much the way a tossed pebble affects a pond.
The TMAO story is intriguing and provocative in its own right, but I've opined on that already and won't belabor it here. Let's just consider what it means when dietary research is translated into recommendations to eat, or avoid, particular foods. The new studies, theoretically, provide a new potential argument against eating meat and eggs.
Turning first to eggs, we may note that historical cautions against egg consumption by those with or at particular risk of heart disease were never explicit about what to eat instead. The advice began, and ended with: Watch your cholesterol, avoid eggs.
I think that advice was wrong, and we have studies from my own lab – including one conducted among adults with established coronary disease and now under review for publication – to back me up. But right or wrong, the advice was limited, in the way that our dietary advice has been for far too long. We have repeatedly focused on just one food, just one nutrient, just one ingredient – and engendered an endless litany of unintended consequences as a result.
Stated simply, there are many ways not to eat eggs! You can not eat eggs, because you are eating oatmeal, berries and walnuts instead. Honestly, as a breakfast for the average American, that would be trading up. I endorse eating fewer eggs if it means more breakfasts like this.
But you can also not eat eggs by eating more donuts. You can not eat eggs by eating more bagels, Danish and toaster pastries. At the level of our culture, Madison Avenue tells us we have done something very much like this. After all, America once warmly embraced the incredible, edible egg – and now America Runs on Dunkin'. Was it the removal of eggs that made room for more donuts and such? To date, no one has bothered to find out.
When foods are added to the diet, they either increase total eating – or displace something else. With regard to eggs, the question then becomes: If the average American, or for that matter the American concerned with heart disease, ate more eggs – what would they eat less of as a result?
Our own research offers some tantalizing early hints. In our most recent study among adults with coronary disease, assigning two eggs daily did, predictably, increase cholesterol intake. But it also resulted in a significant reduction in consumption of starch and sugar. Sugar intake went down some 16 grams per day on average.
This leads to a vitally important question, begging an answer: Other things being equal, does the inclusion or exclusion of eggs improve overall diet quality and general health? This is a question research can answer – and we have a proposal under review to help get that very party started.
This of course is not just about eggs. Foods with an entirely wholesome reputation also figure in this mix. I mentioned walnuts above as part of that oatmeal breakfast. A large volume of research, again including studies from my own lab, suggest health benefits when walnuts are added to the diet. We have shown this in adults with, and at risk for, diabetes.
Partly, of course, this is just due to the diverse concentration of nutrients in walnuts – although not obviously just to any one of them. As I've noted on prior occasions, the active ingredient in walnuts is, quite probably, walnuts.
But there is again the consideration that people deriving more calories from walnuts may derive less from other foods apt to be less nutritious. If more walnuts also means fewer cheese puffs, or pork rinds, or chips or gummy bears – then the benefits are compounded, coming both from what is added to the diet and what is removed or reduced.
The same pertains to meat. If eating less meat means less fatty and processed meats and more beans and lentils, it is undeniably trading up. If it means swapping out lean meats for more starches and sugar, then not so much.
The long-smoldering debate about the net health effects of soy owes something to this construct as well. If soy in the form of, say, tofu replaces meat, there may again be health benefits not just from what is added to the diet but also what is subtracted.
Ultimately, no one food exerts much influence on our health out of context. It is the context of overall diet that qualifies as one of the primary influences on health. Any food thrown into, or plucked out of, a diet induces much the same effects as a pebble tossed into a pond or a fish jumping out, with ripples issuing to the banks in all directions.
This is a simple and obvious reality, but one to which our research has long been inattentive. It's time to rectify that, and conduct studies that address how overly simplistic dietary recommendations translate into real-world effects on diet and health. While waiting for research and formal dietary recommendations to catch up, you might consider the ripples through your own diet and decide whether or not you like where they are going.
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David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.