The Nightshirt Sightings, Portents, Forebodings, Suspicions

Self-control, willpower, and the “brain fog” effect

Even when we acknowledge the social and economic factors that lead to obesity (cheap, fattening food; huge portion sizes; marketing soda to kids; etc.), don’t we all still, ultimately, blame a person’s weight on their lack of self-control? A fat person just lacks willpower. The most compelling and novel part of Good Calories, Bad Calories (see previous post) is Gary Taubes’ radical reconsideration of the relationship between diet, exercise, and willpower. Basically, he takes the latter out of the picture: Appetite and exercise are governed by our metabolism, not our mind, he argues. A person with a dysregulated insulin system craves food and lacks energy, because essentially they are “famished”; more and more fuel is being stored away in fat cells, but it can’t be accessed and burned.

Taubes doesn’t mention it, but there’s an emerging body of very interesting psychological data on metabolic aspects of self-control and executive mental functions, which could complete the causal feedback loop when it comes to diet and exercise.

It has long been known that the forebrain — the seat of forethought, self-control, willpower, all the “human” aspects of our behavior — is one of the most energy-hungry parts of the body, consuming 25% of the body’s energy. That’s an astonishing amount. Research by psychologists Roy Baumeister and Matt Gailliot has refined this picture: It is now known that executive faculties like concentration and self-control depend specifically on blood glucose, the same fuel used by muscles, and that exerting concentration or control in one task depletes the ability to exert concentration or control in a subsequent task. Experimental subjects who exercised self-control in a task and who temporarily replenished their blood sugar with a sweetened drink were better able to master a temptation in a subsequent task than a control group of subjects who received a beverage with an artificial sweetener. A number of elegant recent studies have replicated this kind of finding, both for glucose and for glycogen, the form in which glucose is stored for future use. (Click here and here to read about this research.)

Superficially, it sounds like drinking sugar aids your self-control. In fact, though, any spike in blood sugar results in a sugar crash (and craving for more sugar) later. The larger takeaway point of this research is that a steady supply of glucose is necessary to power the muscles of self-control, concentration, all the higher mental functions that mark us as human beings. A Paleolithic diet ensures a constant, steady supply of blood glucose, whereas a Western, high-refined-carb diet causes wild swings in blood sugar throughout the day, and over time, a desensitizing of the hormonal homeostat that governs our intake and use of glucose fuel.

There is ample anecdotal evidence from those who have attempted a Paleolithic diet that mental clarity and energy increase when you eschew refined carbs. I originally tried giving up sugar and carbs to lose the fat around my midsection, but the effect I didn’t anticipate, and that became the main selling point for me, was increased mental focus and physical energy. I no longer needed strong coffee to get me through the day or long naps every afternoon.

Not enough large-scale research has been done on this “brain fog” effect of easily digested carbohydrates, but what if the Western diet is not only making us physically sick but also robbing us of the honed mental faculties that are our species birthright? Proponents of a Paleolithic diet liken the hunter-gatherer lifestyle to Paradise before the Fall. Myths of a primordial Eden and subsequent expulsion to a life of sickness and toil may reflect, in the idiom of mythology, a memory of the Neolithic revolution and the lifestyle and health sacrifices it entailed. But what if it’s more than a metaphor? What if all our error and folly, the tendency of our plans to fizzle or go awry, the tendency of our relationships and projects to fail or fall short, and the inability to master our temptations are rooted, at least partly, in the dysregulation of blood sugar?

There is no way to test such a hypothesis — that our lives are fucked up basically because our diet is sapping our cognitive potential — but the possibility that the way we eat has something to do with our inability to follow through with plans, our inability to control our emotions, our inability to be as smart and compassionate as we somehow think we should be is intriguing. At the very least, it will be important in coming decades to find out the size of the brain-fog effect.


I am a science writer and armchair Fortean based in Washington, DC. Write to me at eric.wargo [at]

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