It is breakfast time. Are you going to have oats or bacon and eggs? Will it be a power shake or a bitter cup of espresso to get you started? If you’re agonising over basic decisions like what foods to eat for breakfast, you are likely depleting the energy you need to make bigger, more important decisions late in the afternoon. These could be crucial decisions like what budgets to cut, whether or not you should let a board member go, and could even influence your ability to resist the temp’s alluring “come hither” looks before the day is through.
Social scientist Roy Baumeister has made a breakthrough in understanding willpower by proving that self-control is a limited cognitive resource, is affected by what he calls “decision fatigue” and is directly linked to how much glucose is available in a person’s body. The Eppes Eminent Professor of Psychology says that using up or straining willpower reserves leaves people without enough cognitive function to make decisions that could be crucial to well-being.
Speaking to iMaverick from New Haven, Connecticut, Baumeister says understanding the relationship between willpower and the energy that drives this cognitive function is vital: “Physiologically, and this is a rather simple explanation, some of the body’s energy is converted into making possible the advance psychological operations of self-control which is the process of over-riding one response to make another one possible. It is an advanced form of action control.”
Whether you’re deciding on bacon versus kippers, whether to tell a lie or which share portfolio to invest in, the resources used are all the same. “It is important to understand that you have one stock of energy that we use for everything so every act of self-control uses the same resource and the same willpower,” says Baumeister. “If you exert control over your behaviour in any respect, it uses the same energy source regardless of whether you’re deciding to have a second slice of cake or making a complex moral decision.”
Baumeister says when people realise willpower is limited, it can be better controlled. “You never really want to get down to zero willpower. You always want to have some will power in reserve. Being at zero would render you vulnerable to any desire that came along and leave you open to persuasion if someone wanted to sell you something or to coerce you into doing something.” Willpower, he adds, isn’t just used for decisions but is central to social behaviour like making ourselves be nice to people and trying to get along with difficult folks.
Scientists have for a long time understood that glucose is central to brain function, but Baumeister’s research shows that self-control is a complex and “expensive” brain activity which is especially dependent on glucose. In his research “The Physiology of Willpower: Linking Blood Glucose to Self-Control”, Baumeister shows that fluctuations in glucose have a profound impact on self-control and that willpower failures are linked to the quantity of glucose available and a person’s ability to use this efficiently.
In the study, subjects where shown a video but were told to suppress their facial reactions. Participants who were forced to limit their reactions experienced a drop in blood glucose levels, but other subjects free to react the way they wanted, didn’t show any drop.
The subjects were given a cognitive challenge when the video had ended, and it was found that during the task, those with the lower glucose levels (and who were forced to suppress their facial reactions) fared much worse. But when these subjects were given sugary lemonade, their glucose levels were restored and their self-control was replenished.
Watch John Tierney talk about “Willpower” on ReasonTV:
type="application/x-shockwave-flash">

