Does a Good Diet Guarantee Good Health?

To be sure, dietary factors contribute to bad health at least some of the time for some people.  But, how large a role does diet play?  Stated differently: even if you eat well all the time, are you guaranteed to be free of cancer, heart disease, and diabetes?  Far from it according to two recent studies.  

The first was published Friday in Science by Tomasetti, Li, and Vogelstein, who investigated cancer causes.  When discussing the things that can cause cancer, causes normally fall into one of two broad categories: nature (environmental factors) or nurture (inherited genetic factors).  These authors, however, point to a third factor: as we grow, our cells naturally replicate themselves, and in the process, unavoidable DNA replication errors occur which ultimately lead to cancer.  The authors calculate that these replication errors or  

mutations are responsible for two-thirds of the mutations in human cancers.

Secondly, I ran across this interesting paper published a couple weeks ago in the Journal of the American Medical Association.  The authors attempted to ferret out how many deaths from heart disease, stroke, and type 2 diabetes (what the authors call "cardiometabolic deaths") that result each year annually come about from over- or under-consumption of certain types of foods.  As this critic pointed out, it is important to note that the authors estimates are associations/correlations NOT causation.  As such, I'd suggest caution in placing too much interpretation on the impacts from different types of food.  Nonetheless, there were a couple of other less-well-publicized results which I found interesting.

First, the authors found:

In 2012, suboptimal intake of dietary factors was associated with an estimated 318 656 cardiometabolic deaths, representing 45.4% of cardiometabolic deaths.

Stated differently, 54.6% of deaths from heart disease, stroke, and type 2 diabetes seems to be caused by something other than diet.   

The other result that I found interesting from this study is that there has been a big decline in so-called cardiometabolic deaths.  The authors write:

Between 2002 and 2012, population-adjusted US cardiometabolic deaths per year decreased by 26.5%.

Some of this decline, they argue, is due to reduced sugar consumption and increased nut/seed consumption from 2002 to 2012.

Why does all this matter?  Because these statistics help us understand the impacts of dietary and lifestyle changes.  To illustrate, let's take the above cancer statistic: 66.7% of cancers are caused by unavoidable replication errors. That leaves 33.3% of cancers, some of which are diet and lifestyle related and some of which are caused by inherited genetic factors.  For sake of simplicity, lets say you have zero risk from inherited genetic factors. Also note that the National Cancer Institute suggests that the chances of getting a new cancer in a given year are 454.8 per 100,000 people (or a 0.45% chance).  

Putting it all together, your chance of getting cancer from random errors in DNA replication is 0.667*0.45%=0.30%, and your chance of getting cancer from diet and lifestyle factors (assuming no inherited risks) is 0.333*0.45%=0.15%.  So, even if you could completely eliminate the cancer risk from diet and lifestyle factors, you'd go from a 0.45% chance of getting a new cancer to a 0.30% chance, a reduction of 0.15 percentage points.