I believe in the next ten years we'll increasingly learn that many of the corrosive effects of eating poorly aren't due to an overabundance of sugar, fat, or carbohydrates; they're due to the chemicals in processed foods and our environment interacting with the body's epigenetic machinery in unpredictable and unhealthy ways.
Now, it should be noted that our cells are, as a rule, marvels of self-regulation: it's downright hard to get them 'out of whack'. We see this in the amount of biological redundancy in many cellular processes, in the relative infrequency of obvious dysregulation (e.g., the chance of a cell turning cancerous), and in the layered conditionals for cell suicide should something go seriously wrong.
But in eating Western food, and living in a Western environment, we're continuously flooded with a menagerie of biologically active chemicals that evolution hasn't had a chance to foolproof our cell machinery against. Biology is filled with examples of how evolution often does not protect against that which it hasn't been exposed to-- for a slightly crass illustrative analogy, consider that smallpox blankets may be to native americans what twinkies are to us. It takes time and, yes, often selection to get used to new things. Certainly, following conventional wisdom, some health problems may be caused by an imbalance in our intake of macronutrients-- too much fat or sugar, for instance-- but our ancestors didn't eat perfect diets and evolution has had some time to work on protecting us against these. The chemicals in processed foods, pesticides, and such, however, are an entirely new enemy, and known to affect epigenetics, a regulatory context in which hidden maladaptive changes can accumulate and affect one's phenotype.
This epigenetic dysregulation via processed foods, pesticides, and pollution I'm hypothesizing might happen directly, with these synthetic chemicals interacting with chromosomes, methyl groups, and such to push and prod gene regulation in unnatural ways, or indirectly via metagenetics (changing the constitution of our gut flora, which in turn influences our gene expression and epigenetics. Alternatively, following Michael Pollan, perhaps the absence of natural enzymes in highly processed foods could lead to these epigenetic outcomes.
How much damage did smallpox do to the Native Americans? Quite a lot. How much damage has eating Twinkies done to us? I fear the answer here will also turn out to be, Quite a lot.
At any rate, eating organic and staying away from processed foods is currently considered more of a philosophical lifestyle choice than one with definite health consequences. This very well may change over the next few years as we start to learn more about the intersection of food and epigenetics.
. Most synthetic pesticides are, in fact, used because of their demonstrable ability to circumvent their targets' cellular safeguards and cause malfunctions.
. 2005 The Flavoring Agent Dihydrocoumarin Reverses Epigenetic Silencing and Inhibits Sirtuin Deacetylases. PLoS Genet 1(6): e77. doi:10.1371/journal.pgen.0010077
- Unfortunately, this is a difficult hypothesis to test. The gold standard would be to compare the epigenetic configurations of identical twins raised apart, in similar demographics but eating different diets and surrounded by different pollution levels. But there are only so many identical twins available for study.
- This hypothesized connection can be taken in either direction: one, that the sea of chemicals which surrounds us in modern life has detrimental epigenetic effects; and two, that a significant amount of the physiological (and perhaps social) malaise of Western societies can be traced back to epigenetic changes induced by our chemical environment.
Edit, 5-12-09: Nicholas Wade of the NYT has a great piece on epigenetics up-- From One Genome, Many Types of Cells. But How?