The OmniCarb Trial: Reductionism, Revelations and Resolutions

The recently published OmniCarb trial seems, superficially, like another great opportunity to propagate the kind of confusion about dietary details that has precluded us, for decades, from using what we do reliably know about nutrition to get to better health. But look just a bit deeper and it becomes something far more propitious: an invitation to resolve beyond reductionism, just in time for the New Year.

The timing is good because resolutions about diet, weight and health are surely in the offing. The resolution to lose weight is the perennial No. 1 in the United States, and there are no indications this year is any different.

Of course, the fact that "lose weight" is a perennially popular choice tells us something rather plainly: Resolutions don't work very well. If the millions of people who pledged to lose weight this time last year had met with success, there would be millions of fewer candidates to make that resolution this year. It wouldn't take many years of such experience before losing weight dropped off the list of popular choices. Yet there it sits, inevitably, at the top.

So we know that resolutions generally don't work, and there are some rather obvious reasons why. Fortunately, those problems are fixable. We'll get to that before we're done here, but first, back to OmniCarb.

The study purportedly compared the effects of high- and low-carbohydrate diets and high- and low-glycemic diets on measures of insulin sensitivity, blood lipids and some other biomarkers of cardiometabolic health in 163 overweight adults. The diets were assigned for five weeks each, and each of the study participants crossed over to at least two of the four possibilities (i.e., high-carbohydrate and either low- or high-glycemic; low-carbohydrate and either low- or high-glycemic) with a washout period in between.

There is of course a lot nuance in the data, and I commend those of you with that level of interest in the study itself. For everyone else, the punch line populating headlines will suffice: The diets differed almost not at all in their effects on the main outcome measures. A low-glycemic diet, in other words, did not improve insulin sensitivity compared to a high-glycemic diet.

But as noted, that apparent surprise only arises if the trial is viewed very superficially. Let's look deeper. The first obvious question is: What, exactly, did the study participants eat? The answer is variations on the theme of the same, healthful diet called DASH (dietary approaches to stop hypertension). Carbohydrate content was indeed varied from about 40 percent to about 60 percent of calories, and glycemic measures varied from low to high on the standard scale. But the investigators made a point of doing this using similar, and generally nutritious, foods in each case.

In other words, the diets were alike in all ways they could be, varying only -- and not really all that much -- with regard to the two main interventions, carbohydrate content and glycemic effect. They were all certainly more nutritious than the typical American diet. They were all considerably higher in fiber than the typical American diet.

So the first implication beyond the superficial is that whatever the utility of glycemic measures, they cannot stand alone. No one nutrient property tells the whole story about overall nutritional quality. This, however, is not a new discovery. At the height of enthusiasm for cutting out high-glycemic foods some years back, popular diets actually advised against eating all fruit and some vegetables like carrots because their glycemic index is high. I noted back then, as I do again now, that if anyone can find me the person who can blame his or her obesity or diabetes on eating carrots, I will give up my day job and become a hula dancer. Thus far, my grass skirt remains undisturbed in the closet.

Yes, glycemic measures are useful. Yes, they can be constructively incorporated into measures of overall nutritional quality. But no, they do not measure overall nutritional quality alone. And they are prone to both productive use and abuse. In this way, glycemic measures are rather like any other tool -- good for some jobs, but not for others. A table saw is great for ripping a board, but a rather poor choice for opening a bottle of wine.

A second implication is that carbohydrate is not the be-all, end-all when it comes to insulin sensitivity. With all the ranting these days about the insidious evils of carbohydrate, this may seem surprising; but it, too, is a long-established fact. Consumption of protein triggers insulin release, generally more so than does carbohydrate. The lower-carbohydrate assignments in OmniCarb were higher in protein, and effects of the latter on insulin requirements may have more than offset the former.

OmniCarb showed that when all other nutrient properties are mostly equalized, glycemic measures don't explain all that much. But that first requirement is huge. For one thing, when overall nutritional quality is high or low, that will overwhelm the isolated impact of glycemic index or load. For another, the overall nutritional quality of foods will generally determine the glycemic effects into the bargain. Foods that are more nutritious generally -- think, for instance, fiber-rich, whole grains as opposed to fiber-poor refined grains -- tend to elicit a much lesser glycemic response into the bargain.

Glycemic measures are useful, but especially so in the holistic context of overall nutritional quality. They can be used just that way to good effect. They can also be misused.

The generalizable message here is one that extends well beyond OmniCarb or glycemic measures, and pertains well to the seasonal inclination to resolve dietary changes. Those changes, and that resolve, should be about the forest, not just some particular tree.

That observation leads us back to resolutions. When it comes to diet and health, it is time to resolve past reductionism. Excessive dietary reductionism -- "I will just cut this, or add that, or eat only these combined with those by the light of the moon every other Tuesday" --- tends to be absurd. More importantly, it fails to do the job. There is a better way. Here's how:

1. Know that overall nutritional quality trumps any isolated nutrient manipulation.

That's the revelation of the OmniCarb diet, not that glycemic measures, or even carbohydrate content, are irrelevant. Wholesome foods in sensible combinations -- and there are variations on that theme allowing for each of us to choose and love the foods that love us back -- will support both losing weight and finding health. Isolated nutrient manipulations that neglect the big picture will tend to do neither. So resolve not to go on any "diet," but to eat well.

2. Resolve to get ready and set before resolving to go.

Most New Year's resolutions are of the "ready or not!" variety, but that is among the reasons so few survive to see the crocuses come up. If you are going to change your diet, you have to know how to find, choose, afford, order, prepare and share more nutritious foods. This involves a skill set you probably don't have, or you would have been there already. So resolve to get that skill set, before resolving to apply it. A huge, common resolution mistake is to commit to the final step of what should be a logical sequence -- like resolving to be a pilot, but skipping over the flying lessons. Resolve, first, to get the skillpower you need -- and then resolve to apply it.

3. Trade up your choices, rather than giving up what you love.

Giving up foods we love tends to make us miserable, and misery is hard to tolerate. There is a better way. Learn to make better choices in every food category, and by so doing, dial down your intake of sugar, salt, refined starch, food chemicals and calories; dial up your intake of fiber, vitamins, minerals and antioxidants. Trading up incrementally involves no heavy lifting, but does offer, in the aggregate, huge benefits. It also offers the benefit of taste bud rehab.

4. Rehabilitate your taste buds .

By trading up your food choices systematically, you habituate your taste buds to ever more wholesome foods. Taste buds rather readily learn to love the foods they're with, so this process, over weeks, results in you preferring ever better foods. When you actually prefer eating better, there is no risk of "falling" off the wagon. You love the wagon!

5. Take your family with you.

Generally, we "diet" alone, but we live it together. In unity, there is strength. Family is the foundation of culture, so if your family starts eating better together, you have shifted the culture of your household. That is both powerful and sustainable. Going it alone is frail, and fleeting. If you are eating better generally -- as opposed to fixating on some nutrient, food or ingredient -- there is no reason to leave your family behind, and every reason to share. You and those you love can come to love food that loves you back, together.

There you have it. The real revelation about OmniCarb is that it served up no real revelations at all. It reaffirmed fundamental truths about diet and health we have known for a long time. A reminder of those truths is timely as resolutions loom.

This year, go big -- but get there in small steps. Resolve right past the absurdities of prevailing dietary reductionism, but take your time. Don't skip steps. Rely on preparation, not just inspiration. Take your family along.

And then a leaner, healthier you may thoroughly enjoy the arrival of those crocuses.

Happy New Year, from my family to yours.

David L. Katz, MD, MPH, FACPM, FACP, is the founding director of Yale University's Prevention Research Center; president of the American College of Lifestyle Medicine; editor-in-chief of the journal Childhood Obesity; chief science officer for NuVal LLC; and director of the Integrative Medicine Center at Griffin Hospital. A clinician, researcher, author, inventor, journalist and media personality, Dr. Katz is the recipient of numerous awards and recognitions, including an honorary doctoral degree and widely supported nominations for the position of U.S. Surgeon General. He has authored nearly 200 scientific papers and chapters, 15 books, and hundreds of on-line columns and blogs -- with a resulting following of well over a quarter million people. A two-time diplomat of the American Board of Internal Medicine, and a board-certified specialist in preventive medicine/public health, he is recognized globally for expertise in nutrition, weight management and the prevention of chronic disease. He has been acclaimed by colleagues as the "poet laureate" of health promotion.