Yesterday, my second article for Break Muscle was published. At the moment, there are hundreds of articles on the internet/in magazines telling you to avoid Christmas cheer and keep pushing with your training to avoid getting fat and ruining all your hard work. Most of this is nonsense. There are a number of very good reasons why you should eat more and train less this Christmas! Enjoy.
One of the most interesting scientific papers to have been published recently has managed to fly under the popular media radar, despite throwing up a very important thought:
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:
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.
While I won’t talk much more about these hormones this time, they become crucial later on, as their functions can change both based on what we eat, and in the case of diabetes and obesity.
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…
Bored of thinking
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:
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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Along with getting “ripped in 4 weeks”, there are a number of internet adverts floating around that promise to “increase your IQ”. The concept of increasing “intelligence” has become a hot topic recently, but this often seems to involve a combination of supplements that most of us will probably never buy, and technology that most of us may never be able to afford.
Also, I’m not sure anybody actually knows what “intelligence” is…
While I’m afraid nobody can realistically work on 4 week timescale, there is a simple (and free) way to help you think, learn and remember more effectively. Evidence is mounting, which suggests that both children and adults can improve their cognition simply by increasing their levels of activity.
The idea that exercise improves cognitive performance has been around for a while, but hasn’t really taken hold as much as you’d expect. In general, until recently, studies on the effects of exercise and cognitive performance have focused on adults. This is quite surprising, as certain areas of the brain associated with cognition continue to develop throughout childhood and adolescence. Therefore, the greatest capacity for change happens during this time. In fact, one key area, the pre-frontal cortex, doesn’t reach full (and largely final) function until your early 20s.
One aspect of cognition that has been studied with respect to exercise in both children and adults is “executive control”. Executive control involves:
Levels of executive control correlate better with academic performance than traditional IQ tests. Executive control has been shown to be higher in fitter children, as well as lower in children with higher body fat levels. As children in the Western world become more sedentary and overweight, we are seeing a parallel decrease in cognition and overall academic performance. Because of this, many areas of research are focused toward developing a picture of how activity might change the way we think.
To build on the above information, two studies investigating fitness and cognition in children have been published recently. Both of them suggest that fitter children will learn better and perform better academically.
The first study took children aged 9-10 and investigated how their fitness might affect their ability to first learn, and then remember. “Fitness” was assessed with a treadmill test measuring VO2max, as is done in athletes. The more oxygen your body can use when exercising at full effort, the higher your VO2max, and the fitter you tend to be. Forty-eight children were studied, half of which had above-average fitness for their age group, with the other half below-average. Over subsequent days, the children were asked to learn the names of regions on a fictional map, either by just studying the names, or using a system where they were tested during the learning period (which makes learning easier). They were then assessed by being asked to remember the regions they learned with either free-recall (harder), or with some prompting (easier).
Previous work has suggested that fitter children tend to have better memories, but this particular study found that the main difference between the two groups was that fitter children performed better when the test was at its hardest – remembering the map without any prompting, after learning the regions by studying only. They found that fitness had no effect on performance in the two different types of recall test (with or without prompting), which suggests that:
Fitter children learn (process and store) information better than unfit children, particularly in more challenging situations.
In the second of the recent studies on children, a meta-analysis (a study of many studies), examined how aerobic physical activity affects cognition, academic achievement and “psychosocial function” in children and teenagers. The idea was to review all of the available literature concerning how we can use exercise to help children perform better cognitively and socially, as well as provide optimum mental health.
Unsurprisingly, all of the eight studies included in the analysis showed that physical activity was beneficial. Overall, they found that:
The ways in which studies increased physical activity did differ greatly, including randomising children to receive 150% extra physical activity at school, with sports such as gymnastics and swimming. Another study changed regular physical education (“PE”) classes to a more structured programme of basketball, volleyball and jogging, for a total of 90 minutes per week.
The authors of the study then discussed in their conclusion that more rigorous studies are essential in order to determine the type of exercise, as well as intensity and duration of that exercise, which will provide the best benefit in the cognitive performance in children.
While further studies will no doubt take place, I would argue that it doesn’t matter!
In this meta-analysis, as little as 45 minutes of physical activity per week showed some cognitive benefit (not to mention many associated health benefits)! As so many different types of exercise “intervention” have been shown to work, there is only one essential take-home fact:
Getting children to move more, in any way, will make them think better and be happier!
Teaching old rats new tricks
OK, so you’re not in your teens anymore.... Does that mean you’ve peaked, and are destined to slowly, inexorably, lose your marbles over the coming years?
It is a sad fact that, as you get older, your hippocampi (you have one hippocampus on each side of the brain) shrink. Smaller hippocampi are associated with worsening memory, as well as a decrease in the ability to learn new tasks.
However, all is not lost…
Contrary to what many of us were told as children, you are not born with a fixed number of brain cells, which then slowly die off as we subject them to television, beer and contact sports. Certain areas of the brain can continue to produce new neurons (also known as neurogenesis) almost indefinitely. However, we need to keep providing a stimulus to make sure that neurogenesis continues into old age.
Simple things like sleeping more can help prevent cognitive decline but, regardless of age, aerobic exercise will also improve memory and cognitive function.
Over the years, we have learned a lot about memory and cognition from animal studies. Giving rats and mice access to exercise equipment and increasing their physical activity allows us to then test their memory, as well as study changes in the brain. From work in “aged” animals, we know that:
More sweat = More hippocampus
Whilst data from rodents is interesting, the reason we do those experiments is to try and learn about what might be happening in our brains as we get older. Luckily for us, we see very similar results in humans.
A recent study took 120 adults in their 60s and randomised them to either aerobic exercise, or a light stretching session, three times per week for a year. At the end of the trial period, the study found that:
Some say that “size doesn’t matter”. They’re lying. If you want your brain to stay fighting fit for as long as possible, you need a huge, pulsating, pair of hippocampi.
The effect of aerobic exercise was the equivalent of reversing 1-2 years of age-related decline in memory. Being fitter also protects your cognitive function. In the stretching group, those who were fitter to start with (as measured in a similar way to the treadmill test above), saw better retention of memory function over the year of the study.
In agreement with this, a study of older adults showed that those who exercised through life had less brain atrophy compared to those who had never regularly taken part in physical activity. Another study found that increased fitness in older adults is also associated with better performance in tests of learning, memory and executive function.
The best bit is that you don’t need to go running three times per week to see these benefits. After a gentle increase over the first two months, the exercise group simply performed 40 minutes of brisk walking, three times per week.
Similar improvements are seen in older adults who already show early signs of dementia. Sufferers of Alzheimer’s disease tend to have:
As moderate-intensity exercise (such as brisk walking) increases blood-flow to the brain, as well as levels of these pro-neuron growth-factors, exercise could be an important way to prevent and slow the progression of dementia.
In fact, exercise provides a better improvement in cognition than traditional “brain-training” type games and puzzles. A meta-analysis published this year showed that doing brain training games makes you better at brain training games, but so far they show little carry-over to other aspects of brain function.
“Be smart, exercise your heart”
The brain can often be ignored in favour of the more “obvious” organs that become diseased with age, as you can accommodate a lot of damage and neuronal loss before you notice a difference.
Though most of the brain is more or less finalised by your late 20s, all of these studies suggest that we can still have a huge influence on the areas of the brain that are involved with learning and memory as we age. Something simple like walking for a couple of hours per week appears to be enough to prevent most of the age-related decline in cognition. It’s also probably not a coincidence that keeping up this level of activity will reduce your risk of obesity, diabetes, heart disease, strokes and cancer.
As we enter the winter months, this is the perfect time to wrap-up warm and enjoy some long walks.
No matter how old or young you are when you start, doing so will keep your brain firing for many more years to come.
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