Don’t go shopping on an empty stomach: no glucose – no willpower!

Blog Post No. 41

4th November 2016

Copyright © Renata Taylor-Byrne 2016

Renata’s Coaching & Counselling blog: Don’t go shopping on an empty stomach!



My last blog was about habits – changing them and starting new ones. But to make any changes in our behaviour, we need willpower. And willpower is fuelled by the glucose in our bodies that we get from our diet. Food is much more important and powerful than we realise.

Our willpower is strong if we have a good supply of glucose in us. But when we face the challenges of our daily lives, and the constant decision-making that we have to do throughout the day, slowly our level of glucose drops, and this can strongly affect our behaviour.

Yes.  Decisions take energy, which is provided by blood-glucose, which is provided by the foods that we eat.

In this blog I’m going to give you some amazing examples of how our mood and behaviour is affected by low blood sugar, because of lack of food. Also in the blog are some brief summaries of the research into how willpower, energy and self-control are dependent on the food we eat and what we drink. I’ll also mention some suggestions that show how you can benefit in your daily life from the valuable insights that researchers have identified in this area.

Let’s look at one experiment:

The ‘Radish’ experiment


This experiment was conducted by Roy Baumeister (1996).

A group of students, who’d been fasting (so they were all about equally hungry), were asked to enter a room which was filled with the smell of warm, freshly-baked cookies (biscuits).

The students then had to sit at a table which had 3 different types of food on it: warm cookies, some pieces of chocolate, and a dish of radishes.

After that they were split up into 3 groups:

# The first group was a control group of students, who were not offered food of any kind.

# In the second group, participants were invited to eat the cookies or the chocolate, which was on the table.

# And in the third group, the participants were only allowed to eat the radishes.

To increase the pressure on the students, the researchers left the room, and, from a private vantage point, watched the students as they ate their food.

A few of the students in the ‘radish’ group picked up the cookies and smelled them, but then put them back again, and didn’t give in to temptation, even though it was clear that they really wanted to eat them.


Then all the students were taken into a room where there was a selection of puzzles laid out. These puzzles were actually unsolvable, and the researchers wanted to see how long the students would work at attempting to solve the puzzles before they gave up.

(Apparently the value of giving them this task, which is used by many stress researchers, is that it’s a very useful indicator of people’s general level of perseverance).

The results were as follows:

1. The students who had been allowed to eat the cookies typically worked on the puzzles for twenty minutes.

2. The control group of students also managed to work on the puzzles for twenty minutes (even though they had no cookies or radishes to eat).

3. What about the radish-eating students? They gave up after only eight minutes! This is a large and significant difference by the result levels of laboratory experiments. The researchers concluded that the temptation of looking at the cookies and having to control their desire to eat them, had affected their energy levels considerably.

The value of the ‘radish’ experiment

This experiment shows that people’s ability to keep going at a task is reduced by being frustrated beforehand. Baumeister called it “ego depletion,” meaning that people have a reduced ability to manage their thoughts, feelings and actions if they have had to use their self-control repeatedly. And the radish-eating students had had to control their feelings about the cookies and chocolate!

When frustrating experiences take place, it causes a slow-down in a specific part of the brain (called the anterior cingulate cortex). And this is the specific part of the brain that is essential for self-control. So too many frustrations results in slower brain activity and people then can’t control their reactions to events as well as they normally could. The result is that they struggle to do things that normally wouldn’t be a problem for them.

How our relationships can be affected by ego-depletion


A marital therapist called Don Baucom, when he heard about this research experiment conducted by Baumeister, stated that this helped him to understand a common pattern that he’d observed in the dual career couples that he had been counselling for many years. But (up to that point) he hadn’t understood the meaning behind the pattern.

What many couples had reported to him was that as soon as they got home from work, they would start having arguments about really insignificant things, and this took place every evening. This naturally was causing the couples a lot of unhappiness.

And what he had done sometimes was recommend that they try to go home early from work. He’d realised that the long hours at work were badly affecting their energy.

When they got home after a tough day at work they’d got nothing left to help them handle their partner’s irritating habits. They had no energy left to be generous or considerate with their partner, and had no energy to stop sarcastic comments being said.


Baucom realised that the couples would really benefit if they left work early while they still had some energy left. He could see that when the stress levels at work were high, it had a serious effect on people’s marriages. People were using up all their willpower on the job and had nothing left when they got home.

One of the most revealing examples of the effects of low blood sugar – (a low level of glucose in the bloodstream) – was the research that was done into the decision-making patterns of Israeli Judges.


The Israeli Judges

A team of psychologists, led by Shai Danziger of the Ben-Gurion University, and Jonathan Levav  of Columbia University, reviewed over a thousand decisions that Parole Board judges made over a period of 10 months, in an Israeli prison, in 2010.

After hearing appeals by the prisoners, each judge had to then listen to advice from criminologists and sociologists on the parole board, in order to decide whether they should allow the prisoner to go out on parole or not. They had to bear in mind that there was a risk that if parole were to be granted, then the prisoner might go on to reoffend.

israeli-judgesEach judge, on average, granted parole to one out of three prisoners. What was apparent was that there was a pattern which emerged in the decisions made by the judges and it was this:

If a prisoner appeared in front of the judge in the early morning session, they were granted parole approximately 65% of the time. And if a prisoner appeared later in the day, they got parole less than 10% of the time.


Another pattern emerged in the judges’ behaviour half-way through the morning.  Before 10.30am, the parole board would stop for a short break, during which the judges would eat a sandwich and a piece of fruit. This would give them a boost of energy, in the form of glucose, into their bloodstreams.

Apparently the prisoners who appeared just prior to the break, had a 15% chance of getting parole, but the prisoners who were seen immediately after the break had a 65% chance of being granted parole.

Then, amazingly, the same pattern emerged after lunch. Around 12.30 pm the likelihood of being granted parole was only 20%, in this period of time, before the lunch was served. And if you were seen by the judge immediately after lunch, the likelihood of being granted parole increased to more than 60%!


Why did their decision-making follow such marked patterns?

Roy Baumeister and John Tierney (2012) are of the opinion that when we make decisions, we use up energy (in the form of glucose). This would have meant that the judges became drained of energy after a morning of decision-making, and that if there were any doubt in their minds about the wisdom of granting parole to a prisoner, if they had very little energy, the judges would opt to maintain the status quo, and play safe and keep the prisoner in jail.

Decision-making reduces our willpower, (by reducing the fuel that it depends upon!), and if we are making decisions all day, then as our energy gets depleted, we then choose easy options, or avoid making decisions, to escape from the hard labour of thinking.

Watching a video with words flashed on the screen

Another experiment measured the glucose levels of participants before and after they did a simple task of watching a video. As they watched the video, at the bottom of the screen were words, which were flashed onto the screen at varied intervals. There were two groups, as follows:

# The first group of people were told to pay no attention to the words on the screen, and they could just relax and watch in any way they wanted to.

# The second group of people had been told that they had to avoid reading the words. When the glucose levels (of this second group) were checked, they had a big drop in their brain’s glucose levels.

students-watching-screenWith regard to the first group, the levels of glucose had remained constant in these people, who had been told to view the screen however they wished.

So it was apparent (from the second group, by contrast with the first) that having to make mental efforts to avoid seeing words flashed on the screen, used up the glucose levels in their brains.

But scientists have to be very careful about the conclusions they form, and go back and check their inferences using additional experiments.

Checking out the accuracy of the research results

A later experiment, using lemonade, was conducted, to make sure that there really was a connection between decision making and a reduction in glucose levels in people.

The ‘lemonade’ experiment

Researchers gave out drinks of lemonade to two groups of people:

# One group were given lemonade drinks with diet sweetener in them.

# The other group were given lemonade with a small amount of sugar, to give them a quick shot of glucose.


When these two groups of participants started playing a computer game, the differences in the drinks they had consumed became very obvious.

To reduce the participants’ willpower, the computer game had been rigged, and after a while it became apparent that it was very difficult to play.  Slowly the participants began to get annoyed. But the participants with the sugar in their drink just moaned a bit and kept going.

The other participants (with the diet drink) started swearing and hitting the computer. And when an insulting (scripted) remark was made by one of the experimenters, then the people who had not got any glucose in their drinks became angry at the experimenter’s provocative remark.

This led to the following insight:

“No glucose – no willpower: the pattern showed up time and time again as researchers tested more people in more situations”, stated Baumeister and Tierney. (Page 49)

The implications of these findings for us

What can we learn from these experiments?

If our willpower is greatly reduced, then this can result in low levels of self-control. And this can cause us major problems.

Here’s an example: When we go shopping, because of all the different types of offers and goods on display in the shops, we use up lots of energy (glucose) paying attention to many different things, which are often potential choices to make, which are also potential decisions to wrestle with.  As a result, we can suffer from decision fatigue, just like the people in the research experiments.

Here’s an example:

Choosing an outfit

 swatchesCompanies selling goods know about the energy-draining effects of decision-making and can use it to their advantage. Here is an account by a Columbia University psychologist called Jonathan Levav. He had to buy a bespoke suit (made-to-measure by a tailor), for a wedding that he would be attending.

At the tailors, he went through all the different choices of fabrics, style of linings, style of buttons and other aspects of his new suit design.

How did this affect him?

By the time I got through my third pile of fabric swatches I wanted to kill myself”, Levav said. “I couldn’t tell the choices apart any more. After a while my only response to the tailor became: ‘What do you recommend?’ I just couldn’t take it.”

As it turned out Levav didn’t go ahead with the suit purchase (partially helped by the $2,000 price tag).

But because he felt overwhelmed and exhausted by all the choices he was given, and the decisions he was asked to make, this gave him an idea for some research experiments. One scenario for his research, conducted with other colleagues, was to observe what happened at car dealerships, specifically a car dealership in Germany.

The researchers surreptitiously observed real customers who were asked to make choices about their design options for their new sedan cars.


At first the customers took the choices they had to make very seriously. Here are some of the options they faced. There were:

~Four styles of gearshift knobs

~Thirteen kinds of tyres and rims

~Twenty-five combinations of the engine and the gearbox

~Fifty six different colours for the car’s interior.

Slowly the more difficult choices wore out the buyers’ energy, and they ended up choosing the habit-based, traditional route, and they thereby “settled for the path of least resistance.”

Levav and his researchers discovered:

# The salespeople seemed to consciously manipulate the potential buyers, by overloading them with information;

# the net result was that the buyers abandoned all apparent choices open to them, and left it up to the salesperson to decide what they should have; and

# the customer ended up being ‘given’ a more expensive option than they could have got, if they’s had the energy (glucose) to compute the available options.  ( And the average difference totalled more than fifteen hundred euros per car (which was about $2,000 dollars at the time of the observations).

Another example

Sometimes shoppers get fed up making decisions, and stop buying things. But this doesn’t stop the marketeers. Have you noticed that in supermarkets, after people have used up their decision-making energy – looking at the different special offers, price reductions and varied choices of food and drinks, etc. – they finally arrive at the checkout area, where they have another range of choices?


This is where the customers with decision fatigue (low glucose levels) are at their lowest ebb, and most vulnerable (especially if they have young children with them, clamouring for sweets). The sweets and chocolates are deliberately there at the checkout for anyone desperate for a glucose fix.

So what can we do in the face of this information about how our bodies and brains work – information which has been used, and will continue to be used, relentlessly by big (and small) businesses, to get our money? How can we get stronger?


Eat your way to willpower

As always, information is power, and Roy Baumeister and John Tierney (2012) make some very helpful suggestions so that we can benefit from their findings. They mention the key insights from all the willpower research that has taken place with thousands of people inside and outside the lab:

1. Firstly, we have a limited amount of willpower(which is fuelled by glucose!)

2.Secondly, we use the same store of willpower for a wide variety of tasks. So if you check your mobile phone about once every 4.3 minutes, as one recent study has found – (Sunday Times, October 30th, 2016,  Page 29) – then don’t expect to have much energy later on in the day for other decisions or uses of your willpower (like communicating with your loved ones at home at the end of the day!)

How can we use our store of willpower effectively?

Baumeister and Tierney recommend that you keep your level of glucose as constant as possible:

“Glucose depletion can turn the most charming companion into a monster. The old advice about eating a good breakfast applies all day long, particularly on days when you’re physically or mentally stressed.

“If you have a test, an important meeting or a vital project, don’t take it on without glucose. Don’t get into an argument with your boss four hours after lunch. Don’t thrash out serious problems with your partner just before dinner.”

(Very briefly, do not take this emphasis on the importance of glucose for willpower as advice to eat white sugar.  White sugar, and other sugary foods, like white bread and pasta, will give you a quick spike of glucose, but your insulin will then shoot up, and suck the sugar out of your system, leaving you with less blood glucose than you had before you had your quick sugar hit).

Making glucose work for you


In order to have a steady level of self-control, these authors advise people to eat foods which have a low-glycaemic index. This means that the food is converted into glucose at a slow and steady rate throughout the day. Suitable food examples are fish, meat, nuts, vegetables, complex carbohydrates, cheese, olive oil and other beneficial fats.

The evidence of the value of this type of diet is shown in the research findings from the behaviour changes of many teenagers held in detention centres. After the centres swapped sugary foods and refined carbohydrates with vegetables, fruits and wholegrains, there was a steep reduction in attempts to escape, violence and other behaviour problems.

Making sure you get enough sleep has a beneficial effect on your glucose level

If we don’t get enough sleep, we have less self-control and less ability to perform related processes like decision-making! Lack of sleep also interferes with the body’s ability to process glucose which can, over a longer period of time, create a higher risk of diabetes.


And by resting, we reduce the body’s need for glucose, and we improve our body’s ability to use the glucose that we have in our bloodstream.

Changing your habits

These authors recommend that if you want to make a big change in your life, keep it simple:.  This is what they say:

“Focus on one project at a time…if you  set more than one self-improvement goal, you may succeed for a while by drawing on reserves to power through, but that leaves you more depleted and more prone to serious mistakes later.

“People who are trying to quit smoking, for example, will have their best shot at succeeding if they aren’t trying to change other behaviours at the same time”.

Don’t make any New Year’s resolution lists!


The final insight from this book that I want to share with you is this wise advice:

“Above all, don’t make a list of new year resolutions…by February 1st people are too embarrassed to even look at the list.

“But instead of lamenting their lack of willpower, they should put the blame where it belongs – on the list! No-one has enough willpower for that list. Because you’ve only one supply of willpower, the resolutions all compete with each other. A better plan is to make one resolution and stick to it. That’s challenge enough.” (Page 38)



In this blog, I have looked at how our willpower depends upon our blood glucose levels; and how vested interests in the market use this against us.

I hope you find this information useful! Soon all of us will be exposed to intense and powerful marketing techniques and high-pressure sales bids, as we start to look for presents for our family and friends in the next month, leading up to Christmas. So don’t forget your glucose level, keep yourself as well-fed as you can afford, and it will keep your self-control strong!  (But always go for slow-burning fuel, and not quick spikes of refined sugar products!)

If you need support as you attempt lifestyle changes, contact me. Some changes are much harder to bring about in our lives than others. There’s no substitute for having a good coach, as I’m sure Andy Murray will agree.


That’s all for now.

Best wishes,


Renata Taylor-Byrne

Lifestyle Coach-Counsellor

The Coaching/Counselling Division

01422 843 629



Willpower: Rediscovering our greatest strength By Roy Baumeister and John Tierney, (2012) London, Penguin

‘Driven to Distraction’@joshglancy (30.10.2016, page 29) The Sunday Times, London.


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