The Physiology of Willpower

This paper (PDF)1 looks more than a little interesting:

Past research indicates that self-control relies on some sort of limited energy source. This review suggests that blood glucose is one important part of the energy source of selfcontrol. Acts of self-control deplete relatively large amounts of glucose. Self-control failures are more likely when glucose is low or cannot be mobilized effectively to the brain (i.e., when insulin is low or insensitive). Restoring glucose to a sufficient level typically improves self-control. Numerous self-control behaviors fit this pattern, including controlling attention, regulating emotions, quitting smoking, coping with stress, resisting impulsivity, and refraining from criminal and aggressive behavior. Alcohol reduces glucose throughout the brain and body and likewise impairs many forms of self-control. Furthermore, self-control failure is most likely during times of the day when glucose is used least effectively. Self-control thus appears highly susceptible to glucose. Self-control benefits numerous social and interpersonal processes. Glucose might therefore be related to a broad range of social behavior.

I find this interesting, in that the days I get less work done (due to e.g. spending more time on Less Wrong) are often days when I don't eat breakfast right away, and am generally undereating (like today).


1. Matthew T. Gailliot, Roy F. Baumeister. (2007) The Physiology of Willpower: Linking Blood Glucose to Self-Control. Personality and Social Psychology Review, Vol. 11, No. 4, 303-327

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The amount of will-power or self-regulatory strength that is used up when making choices depends on the type of choice being made. Autonomous choices don't result in ego-depletion. If you're doing things you want to do, things you like doing, your brain doesn't have to expend 'will-power'.

Choice and Ego-Depletion: The Moderating Role of Autonomy

The self-regulatory strength model maintains that all acts of self-regulation, self-control, and choice result in a state of fatigue called ego-depletion. Self-determination theory differentiates between autonomous regulation and controlled regulation. Because making decisions represents one instance of self-regulation, the authors also differentiate between autonomous choice and controlled choice. Three experiments support the hypothesis that whereas conditions representing controlled choice would be egodepleting, conditions that represented autonomous choice would not. In Experiment 3, the authors found significant mediation by perceived self-determination of the relation between the choice condition (autonomous vs. controlled) and ego-depletion as measured by performance.

Claims that the extent to which will power is exhaustible depends on one's belief about it's exhaustibility:

This needs to be checked for the direction of causality-- maybe people have accurate beliefs about how depletable their willpower is.

That was my first thought, but it appears they accounted for that — "The researchers designed a series of four experiments to test and manipulate Stanford students' beliefs about willpower. After a tiring task, those who believed or were led to believe that willpower is a limited resource performed worse on standard concentration tests than those who thought of willpower as something they had more control over."

This is a great insight, but it's slightly off in that the term "willpower" groups together several unlike things, some of which are affected by glucose depletion and some of which are not. Willpower includes both the ability to resist things which are tempting but unwise (ie, impulse control), and to do things which are necessary but unattractive (ie, motivation). The paper deals exclusively with impulse control, which is linked to glucose levels; motivation, on the other hand, is not. In my experience, elevated blood glucose levels provide an excess of the former kind of willpower, but sap the latter.

Apparently, the brain also burns lactate.

Lactate fuels the human brain during exercise Bjørn Quistorff, Niels H. Secher, and Johannes J. Van Lieshout Abstract

OP's paper gives at least some (but not many) examples where manipulations in glucose levels modified cognitive performance. However they mostly just observed that attention leads to lower glucose levels, which would also be observed if glucose would be one among many energy sources.

Also, before eating all that candy, note (from OP's paper)

One study administered glucose drinks to participants and found that poor glucose tolerance (indicated by glucose levels remaining high after the person consumed the drink) was associated with poorer performance on a dichotic listening task, which is another classic attention- control task and requires participants to ignore infor- mation presented in one earphone in order to track and process the information coming in the other ear (Allen, Gross, Aloia, & Billingsley, 1996).

I.e. high glucose levels lead to lower cognitive performance.

Perhaps your conclusion misinterprets the results. The glucose tolerance test was given at a different time than the cognitive test, and so no connections between glucose levels and performance should be made. The idea is that ineffective glucose metabolization is an individual difference associated with lower cognitive performance.

For future reference, if the link goes dead (pjeby, add this to the article): the paper is
Matthew T. Gailliot, Roy F. Baumeister. (2007) The Physiology of Willpower: Linking Blood Glucose to Self-Control. Personality and Social Psychology Review, Vol. 11, No. 4, 303-327

A lot of the willpower exercise I attempt involves resisting my desire to consume sugary things. It seems counterintuitive to say the least that my inability to resist the products of Reese's has to do with my not having consumed enough Reese's recently.

Interesting point. If glucose really is instrumental to self-control, it would naturally follow that impulses to consume sugar would stand out as unusually difficult to resist.

Out of curiosity, have you tried to drink large amounts of water when you feel like it? It seems to reduce most sweets cravings for me, but mine aren't particularly strong in the first place. I have no idea if it would work for other people, but it's very easy to test.

I would try this, but I don't like water. I drink milk with food, and juice if I'm thirsty outside of mealtimes. I'll only drink water if I'm at a restaurant, where they tend not to have milk, or in some other situation where it's my only sensible option.

This is quite curious, water is very neutral in taste, especially when it's cold. Wouldn't drinking too much milk or juice cause any side effects? They're both very high in sugar.

Water has got a taste, at least to me. It's not that it tastes bad, it's just not something I'll drink voluntarily when there are satisfactory alternatives.

Have you tried Aquafina? I used to hate water, but I've gotten to like reverse-osmosis purified water in general, and Aquafina in particular.

It's probably crossed my palate at some point. I half-suspect that I'm tasting something that leaches out of the plastic bottles into the water, rather than something that's supposed to be there, when I react badly to bottled water; I'd probably need to do tests with empty bottles and tap water and a blindfold to be sure.

Yeah Alicorn, I noticed something similar with a few of the plastic bottles I've come across. Sometimes they taste weird, or smell funny or change the taste of what's put in them. Hopefully whatever is leeching out of the bottles isn't carcinogenic.

Hopefully whatever is leeching out of the bottles isn't carcinogenic.

The material the bottle is made out of should be printed on it somewhere (probably the bottom, by the recycling triangle). PET or PETE is considered safe by the FDA, as well as a few others, but there are some that are known to leach. Also, reusing bottles and heating bottles are generally poor ideas, unless you know the material it's made from is designed for that.

I would try this, but I don't like water.

If it gives you stomach problems, note that adding something to it can break the surface tension that causes the problems. My wife prefers tea to water for this reason, but in a pinch can just throw a bit of stevia or almost any other powdered substance into the water to make it drinkable.

It's not a matter of it wreaking havoc on my digestion. I just don't like it.

Do you live in Europe and/or by water do you mean the mineral water they tend to serve there? Because that would put you in agreement with nearly everyone from the US...

No, I live in the United States, and I don't drink bottled water of any kind if I can possibly avoid it, I just drink tap water when I have to drink water.

Huh. I have been to places where I found tap water to have a very bad taste, unnoticed or at least uncommented upon by those who lived there. The particular place I'm thinking of had well water with high iron (I think it was) content.

I can detect differences in tap water flavor in different locations, but I don't like any of them enough to drink them when there's something else I do like.

Out of curiosity, have you tried to drink large amounts of water when you feel like it?

I've noticed that drinking 3 large glasses (about 1.5 quarts) of water when foggy often helps me concentrate again.

Supposedly even a moderate level of dehydration has quite a large impairment on basic metabolic processes. It's entirely possible that, in some cases, drinking extra water would improve cognition generally.

Have you tried measuring your glucose levels?

Also if you do it wrong, frequent glucose spiking means insulin resistance means metabolic syndrome, and you really don't want that.

Personally, I'll take energy/mood swings over repeatedly stabbing myself. But if they manage to find a way to measure glucose without doing that, I'm all over it.

Have they solved the problem of glucose meters costing 10 cents and each test strip costing your firstborn yet?

Also if you do it wrong, frequent glucose spiking means insulin resistance means metabolic syndrome, and you really don't want that.

Interesting link; I appear to have at least 5 of those 9 insulin resistance symptoms, and have had them pretty much since I got a car and stopped bicycling and walking everywhere. I think I just got a lot more motivation to exercise. ;-)

BTW, if I trick myself into thinking I've taken more sugar than I actually have (e.g. chug a bottle of Coke Zero), I feel a willpower boost but if I actually use it and (say) exercise more than I otherwise would, then I end up feeling very dizzy. (Has anyone else found the same?)