Insight: Roy Baumeister, psychologist

'Willpower is not like intelligence – you can learn it'

Baumesiter: If people want to improve their willpower in their daily lives they should eat healthy food

Dr Roy F Baumeister is the co-author of Willpower: Rediscovering Our Greatest Strength (£20, Allen Lane). Baumeister was described by Freakonomics' Stephen J Dubner an "extraordinarily creative scientist". Willpower, written with The New York Times' John Tierney, is a fascinating introduction to Baumeister (and others') work in analysing how willpower is controlled, both behaviourally and physically, and gives readers an idea how to adjust their behaviour to increase their own self-control. Baumeister is a currently professor of social psychology and the Francis Eppes eminent scholar at Florida State University.

To best control your willpower, you need to understand all the things that drain it and understand what makes it fluctuate. It goes up and down with both physical and metal tasks. Acts of self-control deplete your willpower; decision-making depletes it; physical things such as getting a cold or premenstrual syndrome deplete it.

The connection to glucose is important to know [ie, glucose in your blood can influence the parts of your brain that control willpower] as it is to know that glucose doesn't come straight back once you've eaten something. It takes a while for the food to be translated into glucose. But you can build self-control through regular exercise – by trying to improve yourself a little bit and making positive changes.

It's over-simplified to think that a sugary snack will improve your glucose levels [and therefore increase your willpower]. Glucose is made from any kind of nutritional food. We do actually use sugar in the laboratory – but I don't recommend it for ordinary use. Glucose in sugar sends you up fast and down fast again. In the lab, we only have people for a little while and we want to get something that works very fast. If people want to improve their willpower in their daily lives they should eat healthy food, something that can burn off over a longer period.

In psychology there's usually a little bit of genetic influence on almost everything – I suspect there's some in willpower too. We don't know how much [willpower] people are born with. The important thing is that you can learn and acquire and improve at any point. Willpower is not like intelligence where you're born with a certain amount and that's pretty much the level you're going to be at for the rest of your life. Willpower you really can improve, even in adulthood. So some people may get a little bit of a head-start over others, but it's a long race.

People in general do like to have multiple choices [when buying things]. But in terms of depleting their resources, it is a little bit exploitative to try to get them artificially into a state of decision fatigue, so I would not advocate that. But I'm not surprised that some will do it, or let it happen. It's not surprising that companies design things so you have to make the exhausting decisions first and the expensive decisions later, such as when choosing the options for a car. That does exploit human weakness.

I think we're adapting rather slowly [to modern inventions that can distract us]. The bad news is that there are more temptations and they're more readily available than ever before. But the good news is that things on the internet can help – you get these things that track how many steps you take or how well you're sleeping or how you're spending your money – give you the chance to get more useful feedback than before.

Occasionally I see things in my life that we've worked on in the laboratory but this is not a personal quest for me. I'm aware when my willpower may be depleted and know not to make a decision. It makes it easier to control these things – that's our hope with this book, that people will understand how willpower works and can then use the knowledge to improve.

Violence starts when self-control stops. People have aggressive impulses – learning to control and restrain them is important. Criminals – almost as a class – one of their defining attributes is relatively poor self-control. If you're rehabilitating prisoners or educating juvenile offenders or potential offenders, learning how to use self-control and building up their capacity for self-control both seem like really promising and valuable ideas.

My impression of people who spend 10 years or so in the military is that they're often extremely disciplined [after they leave the army] and even look down on civilians for how they lacking they are. I think military discipline does do some good but it has a negative effect on people.

It depends on who's going in for the army too – it's not necessarily a sample of average citizens but often people who may have had fewer prospects and may have had lower self-control to start with. There's a lot to look at before you can draw firm conclusions – but my impression is that people who spend time in the military often have excellent discipline. Of course over those years, they've probably embraced those discipline ideas and internalised them. It might be different if someone feels like [the discipline] is something being forced on them.

Making small positive changes and trying to cultivate good habits [is key to building willpower]. Self-control works, much more than we realise, through habits and routines. Breaking bad habits and establishing good ones is a much better path to success than using your willpower to bail you out of a crisis.