For years, people have been arguing:

(1) Whether you should limit your saturated fat or limit your carbs and not worry about the saturated fat;

(2) How much salt you should consume.

On the first, if we had to pick, we would choose the Gary Taubes/Nina Teicholz side, which is that poor quality carbs (refined flour, white rice, and sugar), not fats or even saturated fats, are the bad guys for most people.  On the second, we quite firmly believe that for most people without high blood pressure, salt is fine in moderation.

However, we have two perspectives, overall, that get very little attention.

Perspective #1: the lack of clear evidence is, by itself, evidence

If indeed the impact were large one way or the other on either fats/carbs or salt/no salt, we would know it by now. There is a rule of thumb in epidemiology that big effects require only small sample sizes to reveal themselves. For example, the Freis study (which, by the way, I found a mistake in–and if anyone doesn’t believe me I’ll send them the thank-you note from NIH) required only 573 veterans to conclude that very high blood pressure caused strokes. And doctors and tobacco companies knew smoking caused lung cancer way back in the 1940s, after observing only a few hundred cases.

By contrast, tens of millions of people have been observed, hundreds of thousands have participated in (usually loosely) controlled trials…and yet there is no consensus, no clear direction of the evidence. There may be a diet that is better than other diets–but for most people the composition of the diet probably doesn’t matter much within reason, beyond avoiding junk food.

Consider three things that DO matter: exercise, smoking, and sugar. (We say “sugar” as opposed to carbs generally. Carbs generally probably do matter for most people, but that statement would take us out of certainty into opinion.)  The evidence is quite overwhelming on all three of those things. If you exercise, don’t smoke, and partake of a generally healthy diet low in sugar, you’ve achieved the “80-20 rule” for good health…and we don’t know what the other 20 is.

And even this 80-20 rule (except for smoking) is likely overwhelmed by factors that are beyond your control, like family history. We all know smokers who lived forever, people who “did everything right” who died young etc.

Perspective #2: Why do we assume that the answer is the same for everybody?

Note that we said “for most people” several times above. That was not an accident. One size probably does NOT fit all. (Coincidentally, another blogger wrote on this exact topic this morning, related to obesity.)

Humans differ in many ways. Why do we assume there is a “right answer” in the case of diet?  Isn’t it possible that people whose ancestors evolved in the tropics react differently to different foods than people who evolved in very cold climates?  It’s certainly true for salt. Ethnic groups and races evolving in climates with cold winters needed to salt their foods to preserve them. They ended up consuming far more salt than we do today. Salt was the world’s most important traded commodity for centuries. Invading armies would take over the salt works. “Salzburg” was even named after salt. Conversely, ethnic groups and races from the tropics had year-round access to food, preservation wasn’t an issue…and now African-Americans in particular have high rates of hypertension.

Likewise, dairy. Lactose intolerance varies widely by global region. For example, people of Northern European descent have evolved to have a much lower likelihood of lactose intolerance than people of Asian descent, which has implications for nutrition status and hydration status. However, even amongst people who suffer from lactase deficiency, many can still drink milk in small amounts and consumption of fermented milk products, such as yogurt and buttermilk, can help them get the benefits of milk without the discomfort.

So why wouldn’t variations like this be true for many other dietary components?  Why wouldn’t some people fare better on a high-fat diet while others do better with more carbs? Why wouldn’t it be true that as long as overall diet quality and calorie content are within generally healthy parameters there are quite possibly millions, even tens of millions, of healthy ways to eat? John P. Ioannidis of Stanford, easily the leading thinker on medical research today, makes this point exactly in his piece published this week in the American Journal Of Clinical Nutrition, in which he criticizes not only the conduct of nutrition research, but the flawed conclusions that all too many people draw from this stilted and often irrelevant body of literature.

Where does this take us?

Naturally, these conclusions invalidate the business model of most of the wellness industry. Vendors tend to demonize one type of food or another. For years they were advocating low-fat diets (and finding huge savings).  Now they are advocating low-saturated fat or low-carb diets. It doesn’t matter which, because the savings are always huge, in wellness.  (The irony, of course, is that in the working-age population, most medical spending is unrelated to diet.)

There is ONE THING that OVERWHELMS the impact of everything else on health, that is NOT OPEN TO CONTROVERSY.  That, of course, is exercise.  A little is better than none, some is better than a little, and within reason a lot is better than some. But many wellness vendors would have us believe there are shortcuts to good health, that coincidentally are profitable for them. Crash-dieting contests, like HealthyWager’s, are one example. Other vendors advise us to micromanage our diets, often with a level of blatantly incorrect certitude, as in this Cerner example:

These distractions have employees and HR people believing there are automatic shortcuts to good health, when there are none. Exercise is a commitment, not a shortcut. but it is a way to good health.  Just not one that is likely to make wellness vendors a lot of money.

Worse, once the wellness apologists admit that all this lowfat/crash-dieting stuff is nonsense, it means their entire history of savings claims based on those initiatives becomes one big lie. So you can bet that crash-dieting contests and bad diet advice will remain staples of the wellness industry, right up there with annual checkups and overscreening.