Yet another false nutritional dilemma

The headline of a recent Boulder Daily Camera article, "Carbs not the enemy: CU Boulder physiologist shares key to weight loss, metabolic health" is misleading. Despite the Camera being my local paper, I became aware of this article only after one of my East Coast friends, an instigator extraordinaire, told me that it had appeared on the Facebook timeline of one of the running world's more energetic, self-important, and prickly cranks, who had parroted the "carbs are not the enemy" line, and gone on to yammer indulgently about how people who can't lose weight should simply be exercising more. Because I maintain a longstanding policy of not associating with this person both practical and historical reasons, I decided to refrain from commenting on his Facebook page and review the article here instead.

Nowhere in this piece does the University of Colorado researcher, Inigo San Millan, claim that carbohydrates, specifically, are not to blame for people gaining weight, although that's part of the story. He's pointing out that homing in on any one macronutrient is futile, despite America's cyclic obsession with demonizing fats (circa 1988-1990), carbs (mid-1990s and beyond), gluten (who the hell cares), and whatever else comes along (soon). (The gluten-free craze has nothing to do with weight-loss-through-supermarket-choices specifically, but is emblematic of the same futility.)

San Millan says, "Metabolic flexibility is the ability for your body to quickly switch back and forth between fat and carbs, efficiently using whatever fuel sources you throw at it."

This makes perfect sense from the standpoint of evolutionary biology. Animals in nature cannot count on any particular food or food type being plentiful at any given time; for example, while you're likely to access have plenty of fruit or grain in the summer, you might have to rely almost exclusively on fatty sources of protein in the winter ("you" being an earlier version of Homo sapiens, circa 50,000 BCE or so and living at European latitudes). This implies that your body needs to be able to convert all sorts of foodstuffs into energy capable of sustaining a very active lifestyle (Cro-Magnon people who sat on their asses and played Nintendo all day probably didn't live long, and were probably rejects anyway just like today's gamers).

This article, like practically everything in the mainstream press about the topic of diet, weight and exercise, makes two category errors:

1. It posits that people who are heavier than they wish to be get that way because of either dietary mistakes or a lack of activity;
2. Worse than that, it implicitly assumes that tremendous variability in human metabolism doesn't exist across the population.

We all know runners who can get fit a lot quicker than others, or people who can develop great muscle mass with comparatively little effort. But people seem unwilling to acknowledge that some people really do gain or lose weight a lot more easily than others do, and that the whole "calories in-calories out" model is a failed dinosaur. (That's plainly not to say that food intake is divorced from weight, but the "calories in, calories out" model as most of us learned it is largely bogus.)

There is simply no magic sports or weight-loss diet, and this would be true even if people's metabolisms were all identical. America as a whole will keep trying new ones and recycling old ones, because there is money to be made in promoting magical fixes. But in reality, over the course of over 30 years of running, the basic composition of my own diet hasn't made a damned bit of difference in my weight or race performance. Experience suggests that I could go as high as 85 to 90 percent carbs or as low as 50 to 55 percent carbs and wind up with the same basic results (marathon day and the couple of days beforehand excluded). And running well over 100 miles a week into my thirties didn't result in me being any leaner than running 40 or so miles a week does now, owing to a combination of my genetic tendency to not gain weight and the fact that I unconsciously balanced intake and expenditure when I was exercising more.

Some people really do retain a surprising amount of adipose despite seemingly spartan diets. It's unfortunate but true. So while "Get off the couch, and if that's not good enough, throw the whole couch away" is facile enough, it really isn't the whole story.