The Nutrition Advice See-Saw
This is Stephen Devries, a preventive cardiologist and director of the nonprofit Gaples Institute for Integrative Cardiology. I would like to speak about controversies in nutrition. With some recent studies of low-fat vs low-carbohydrate diets that have attracted a great deal of attention, I would like to address the hazards of dietary recommendations that focus on a single macronutrient such as fats or carbohydrates. I would also like to offer some nutrition tips that can help guide our discussions with patients.
As if there weren't already enough confusion about diet, a recent study fanned the nutritional fire with the comparison of low-fat vs low-carbohydrate diets for weight loss and reduction of cardiovascular risk. In this study, a reduction of 500 calories per day achieved with a low-carbohydrate diet led to greater weight loss and more significant reduction in cardiovascular risk factors than caloric restriction achieved with a low-fat diet. How are we to apply these results to make nutritional recommendations for our patients? Unfortunately, in this study, the specific foods that were eliminated in the low-fat and the low-carbohydrate groups were not specified, and that is a problem.
I would like to take a step back and address the issue of why it's best not to make dietary recommendations that emphasize any individual nutrient, whether it is carbohydrate, fat, or protein. The first problem is that dietary advice to eat more or less of a specific nutrient is difficult to follow because we don't eat nutrients; we eat foods. It's far better to give patients advice about specific types of whole foods, especially those in a Mediterranean-style diet that emphasizes vegetables and fruits, whole grains (in place of refined grains), more fish and less red meat, and the predominant use of olive oil for cooking. Another problem that arises from dietary advice that focuses on reducing a particular nutrient like fat or carbohydrates is that when a diet is defined by what is missing (as in low-fat), it doesn't necessarily specify what it should be replaced with. Consider that there are only three macronutrients: carbohydrates, fats, and protein. If calories are held constant, a reduction in fat intake, for example, would be accompanied by an increase in carbohydrates or proteins. In that case, were the results achieved accounted for by the reduction in fat or by the increase in carbohydrates or protein?
No Fat Egalitarianism
Another issue is the problem of grouping all macronutrients together as if they were of identical health value. As it turns out, the quality of each specific type of carbohydrate or fat matters much more than the amount. For example, black beans and chocolate chip cookies are both high-carbohydrate foods but with obviously very different health attributes. Simply designating a food as high- or low-carbohydrate tells you very little about its health value. When it comes to carbs, one of the ways that the quality can be measured is in terms of the glycemic load or the degree to which that food will increase the blood glucose level. The values for glycemic load are not always intuitive. For instance, although the glycemic load of a donut certainly is not low, it might surprise many of your patients to learn that a bagel will send glucose level soaring much more than a donut. The take-away message is that a food doesn't have to be sweet to raise your sugar level, and the bagel has even more sugar-raising carbohydrate than the donut.
Turning our attention to fat, the same issues apply with respect to going beyond the low-fat or high-fat designation and focusing instead on the quality and the health attributes of individual fats. Here the discussion gets a bit trickier. All fats are not created equally. Certainly, trans fats have no place in our diet. That much we know. What about the others? Dietary patterns shown to reduce cardiovascular risk (such as the Mediterranean-style diet) are relatively high in monounsaturated fat that predominates in olive oil, as well as in omega-3 polyunsaturated fats like those in fish. Neither monounsaturated or polyunsaturated fats are prone to raising the level of low-density lipoprotein (LDL) cholesterol.
The Type of Fat Matters
Saturated fats are a different story because they are well known to raise LDL cholesterol, and therefore recommendations call for limiting their intake. A controversial meta-analysis published in 2010 called into question the link between saturated fat and cardiovascular disease. How can this finding make sense? Was our advice to limit saturated fat misplaced? As it turns out, it appears that the advice to reduce saturated fat intake was in fact on target, although it was incomplete. Newer evidence shows that the net health benefit of reducing saturated fat depends on the type of calories that the saturated fat is replaced with. Replacing saturated fat with refined carbohydrates offers no health benefits. However, replacing saturated fats with polyunsaturated fats, especially the healthy omega-3's, is a very desirable move with significant benefits for cardiovascular health. This is yet another example of the principle that a healthy diet is a function of not only what is taken away but also what replaces it.
Although we tend to group all saturated fats together, the fact is that there are many different kinds of saturated fats that each have unique properties. For example, a saturated fat called myristic acid predominates in butter. Palmitic acid is found in meat. Both of these saturated fats tend to raise LDL levels substantially. On the other hand, stearic acid found in chocolate doesn't raise LDL-C. Lauric acid, the saturated fat that predominates in coconut oil, raises LDL-C less than palmitic acid, but it also raises high-density lipoprotein (HDL) cholesterol more than the other saturated fats. We are on the verge of developing a more complete understanding of the biologic properties of saturated fats and the realization that they are not all alike.
I hope that you are convinced that the most useful dietary discussion goes far beyond a simple recommendation to cut macronutrients, like carbohydrates or fats. Instead, we need a more nuanced concept that appreciates that there are both healthy and less healthy carbohydrates and fats so that we can move to a more comprehensive and evidence-based approach that shies away from individual nutrients but instead focuses on whole foods, mostly from plants, that contain the best health benefits for prevention and as an adjunct to treatment of cardiovascular disease. I'm Stephen Devries. I look forward to your questions and comments.
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Cite this: Nutrition Advice: Can We Stop the 'Low-Fat, Low-Carb' Lingo? - Medscape - Feb 04, 2015.