You are probably not in control of your food choices.
This paper was written by a professor of economics who specialises in decision-making. It looks at how factors of which we are normally unaware can significantly influence the decisions we make. In particular, the focus is on how our hormones are intricately linked with our food choices.
In this two-part article, I will cover the basic ideas proposed in the paper, but expand on them to include how the individual foods we eat can also affect our decisions, as well as how things change in diabetes and obesity. To begin with, though, let’s consider the problems we face when we’re juggling the “health” benefits of salad versus the unadulterated joy of cake.
The paper I mention focuses on the three main “decision-making circuits” that function side-by-side whenever we make a decision. These are particularly relevant when we’re deciding what we should eat, or whether we should eat something put in front of us. They are:
Pavlovian control: Named for Pavlov and the famous experiment where he showed that dogs would salivate at the sound of a buzzer, after being trained to hear the buzzer when food was served. Pavlovian control is the most basic response, and can be heavily influenced by environmental cues such as restaurant signs or the smell of food. Your pavlovian control loves cake.
Habitual control: As the name suggests, this circuit is heavily influenced by what you have experienced in the past or have done repeatedly. It works by assigning value to previous experiences that are similar to the one you are about to encounter. The decision is then made based on positive or negative results from previous situations. If you regularly have cake with your afternoon coffee (and enjoy it), you are more likely to have cake with your next cup.
Goal-directed control: This is the most flexible circuit, and the one that is heavily influenced by conscious thought. Unlike habitual control, the values assigned to food can include future benefit. For instance, you can affect your goal-directed control by thinking about the long-term consequences of eating cake instead of having a salad.
The main downside of having multiple circuits is that they will often favour different outcomes. Goal-directed control is what we rely on when we’re trying to eat better, or make any lifestyle changes to improve overall health. Unfortunately, this circuit is the one that is most heavily affected by what you eat, hormonal changes, and the stresses of daily life. This is the reason that, even though most people want to eat better or exercise more, it is very difficult for us to make long-term changes.
In the past, we ate when we were genuinely hungry, or needed to fuel whatever daily activities were required, be that hunting sabre-toothed tigers or conquering neighbouring countries. Decisions were made based on how much energy we had available, and how much we were likely to need. Therefore, the cues to start and stop eating were controlled by:
- The environment (whether or not there was food to eat).
- Hormones, which affect how hungry we are.
Though there are many, insulin, leptin and ghrelin tend to be the most important hormonal regulators of eating. Generally, their levels change such that they make us hungry when energy reserves are low, and send signals to stop eating when we have refuelled sufficiently. However, these hormones can also affect the way we perceive pleasure from food. This pleasure tends to be signalled by groups of “opioid” neurons. In a parallel manner, dopamine neurons help us assign the value to foods, and control our actions.
Insulin: When we digest the carbohydrates we eat, glucose is released into the blood. Increased glucose causes the release of insulin. By transporting glucose into the liver and muscles, or storing extra glucose as fat, insulin acts to stabilise levels of glucose in the blood. Insulin also increases the effects of leptin.
Leptin: Leptin is released from our fat stores. Higher leptin levels decrease “pleasurable” opioid signalling, telling the brain that we have a good amount of energy available in reserve. After a meal, insulin and leptin increase our feeling of satiety, reduce the pleasure we get from food, and prevent further eating.
Ghrelin: The traditional “hunger” hormone, ghrelin is released by cells in the stomach when the stomach is empty, or energy reserves are low. Ghrelin peaks just before a meal and decreases after we’ve eaten. Ghrelin augments dopamine signalling. This increases our pavlovian and habitual drives to eat by increasing the "value" of food.
Putting the first two sections together, we find that we have three main decision-making circuits. These circuits are made up of varying amounts of neurons that involve pleasure (opioid neurons), and those that encode “value” to foods, or help guide actions (dopamine neurons). Depending on our physical state and energy levels, the key hormones can then come in and adjust those circuits to affect the decisions you make.
All pleasure, all the time
Though we like to consider ourselves complicated, intelligent, well-developed creatures, we are still at the mercy of our most basic circuitry. Deep down, we want to spend all of our time in a sweaty, naked, cheesecake-fuelled orgy. Because of this, when we don’t use our goal-directed control to take charge of our decisions, we are left with the more basic responses provided by the pavlovian system.
In order for us to make optimal food choices, we must then provide the best-possible situation for our goal-directed system to make those decisions. These are easily affected by a number of factors:
Hunger: Everybody knows that going shopping when you’re hungry will mean that chocolate and ice cream mysteriously make their way into your basket. When you are hungry, insulin and leptin are no longer dampening the effect of the pleasure-seeking opioid neurons. You are then driven by your pavlovian control to find something that will increase insulin and leptin, and provide maximum pleasure – cake.
Attention: Your level of attention plays a key role in self-control, and how much you eat. When you watch TV during a meal, your memory of the meal is poorly stored, and you are more likely to snack afterwards. In one study, participants were asked to either remember a long (9 digits) or short (1 digit) number, and then drink as much of a milkshake as they wanted. Those who were preoccupied with remembering the long number drank almost twice as much milkshake, as their attention was elsewhere.
We also know that focusing your attention on yourself and your personal goals will improve self-control. However, if you are in a situation where attention is taken away from you (such as in a group of people), there are a number of studies that have shown that you are much more likely to follow the actions of the group (all eating cake), regardless of your personal values.
Boredom: You are much more likely to eat poorly when you’re bored. When the mind is completely unoccupied, you will try to find pleasure for centres of the brain that take over when there are no other thoughts to occupy them. We have known for a long time that bored rats housed on their own in small cages are much more likely to voluntarily take morphine compared to those housed in large cages with other rats. The stimulation of social interaction is enough to satisfy the opioid circuitry that “craves” the pleasure of morphine. In your average person, this satisfaction is instead often brought by the act of eating high-sugar foods.
Exercise (and other pleasure substitutes): Rats that have access to an exercise wheel experience a greater response to leptin, which reduces their preference for a high-calorie diet. In this scenario, exercise acts as a “pleasure substitute”, and the need for a food-based reward is satisfied by the increased dopamine and opioid responses to exercise. I’m sure you can think of other activities that will have a similar effect…
We make food choices many times per day, and thus food is different from other sources of temptation (such as buying shiny new things). This is important, because more and more research is showing that we only have the capacity to make a finite number of decisions over a given period of time. After a certain point, our goal-directed control (which requires the most cognitive input) has to take a break, and habitual and pavlovian controllers take over. This is known as “decision fatigue”.
In possibly the most famous example of decision fatigue, a group of researchers examined how frequently judges on a parole board gave a favourable ruling for a prison inmate. Judges typically had three sessions in a day, with a break for a mid-morning snack and then a break for lunch. In all three sessions, the most likely chance of getting a positive result occurred if you were in the first three cases. After that, your chances of parole rapidly dropped off. This happened irrespective of the severity of the crime or the time already served, and was true even if a number of lengthy decisions preceded a particular case. It was not the total time the judge had spent during the session (indicating he or she might be getting bored/hungry/grumpy), but rather the number of decisions they had made since the last break.
The more decisions you make, the more likely you are to let habitual and pavlovian control take-over. Due to the nature of their work, a judge is more likely to deny parole than grant it, so this is the default response. By the end of a particular session, the likelihood of parole was 0%.
This is relevant in a world where we are constantly being bombarded with temptation, work pressure and general life stress. If you have spent your whole day making important decisions at work or within your family, you will be much more likely to succumb to the pavlovian drive for instant gratification when it comes to deciding on food. In fact, a similar effect is seen with self-control. Just one act of self-control (denying ourselves cake), reduces the likelihood that we will have self-control the next time our resolve is tested. When we are tired and stressed (as we all are on occasion), we are also much less likely to care about self-control, and will resort to ignoring any well-meaning goal-directed thoughts.
If we are constantly being pushed by the drive for pleasure, and at the same time our capacity for decisions and self-control is under continuous attack from the stress of modern life, it is no wonder that people are slowly gaining weight and becoming less healthy. It also becomes more obvious that telling the overweight and obese to “just eat less” is unlikely to make any difference, despite everyone’s best intentions.
To regain control of our food choices, a great place to start is by never mentioning or thinking about “diets” again. Constantly battling with your self-control is more than likely only going to fail. When people feel they are being restrained in their food choices and think they ate fewer calories, ghrelin levels don’t fall after a meal, regardless of what they ate. If you’ve spent all day denying yourself, the effect of “self-control fatigue” alongside persistently elevated levels of ghrelin is only going to lead to one thing. Cake.
However, some simple changes can make the whole process much easier:
- Pay attention to what you eat. Away from computers and the TV.
- Shop once per week when you have the time to do it and aren’t under time pressures.
- Write a list, and eat before you shop.
- Prepare meals in advance. This eliminates the need for food-related decisions at work.
- Make sure you allow yourself meals that are big enough to provide the energy you need.
- Partake in regular exercise. Not only will it increase energy expenditure, it will also satisfy the pleasure-craving areas of the brain.
All of these actions will help place your goal-directed control in charge of food choices. Rather than stressing about weight loss or “dieting”, invest some time in forming better habits. If sensible food choices become the rule rather than the exception, we know that habitual control will help keep the pavlovian drive at bay when you’re tired, hungry and stressed. Including good amounts of protein and fat rather than empty carbohydrate in your food will also make sure you don’t feel like you’re constantly denying yourself.
Finally, if you manage to put some good habits in place and remove the stress of eating well by planning in advance, then it’s ok to have some cake occasionally.
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