So what is the effect on the brain from working out – how does it fit into the equation?
On one hand, our brains are such complex organs that scientists who study the field of neuroscience can’t even accurately define what intelligence, consciousness or the essence of personality are.
The circular irony of this is fascinating; the concept that we don’t know where ideas and thoughts originate from on a base level is a fact that could drive you simultaneously to insanity and enlightenment. Thinking about thinking, when it comes down to it, is essentially an exercise in futility.
On the other hand, the brain is just another organ, and a very demanding one at that. A good portion of your Resting Metabolic Rate (RMR) – around one-fifth, or 20% – is dedicated to fuelling the brain. RMR is the energy it takes simply to exist over the course of a day.
Of the 63 watts your body uses, 12.6 watts can be allocated to your brain power
You can assume about 1300 kilocalories (or just calories) are burned every day to keep your basic functions going. And that’s before you add any one of the numerous physical and mental activities you might pursue over the 24 hour period.
An article in Scientific American went as far as converting this into units of power. Of the 63 watts your body uses, 12.6 watts can be allocated to your brain power. From this, we can infer that our whole body runs on the same amount as an average light bulb, and the brain a fifth of that.
So, your brain is efficient relative to other power consuming technology, but it’s pretty hungry in comparison to the rest of your body, considering its size. The brain weighs roughly 2% of your total bodyweight, but it saps 20% of its power.
Calorie Burning Brains
Scientists more or less understand how the brain uses the roughly 260 calories it burns to ensure the life-preserving processes are ticking over:
Blood transports glucose – the primary form of fuel that our diet is converted to – across the blood-brain barrier, and it is then converted to Adenosine Triphosphate (ATP).
ATP is the fuel that all of the cells in the body use to produce energy. The brain is in this sense no different to any other organ, muscle or metabolic process we have working away at any given moment.
The base activity the ATP fuels in this case is the firing of neurons. And, when the neurons of a region of the brain fire more than others, the blood vessels which transport the glucose to that region dilate, and in doing so, feed the active area with more as required.
The natural conclusion is that the harder we think, the firing rate of neurons will increase and so too will the consumption of glucose – and calories – in order to stoke it. Follow that train of thought and here you have the concept that thinking harder will help you burn more fat.
It shouldn’t be a stretch to imagine that if an arduous mental task can exhaust you, then why couldn’t it also help you lose weight?
Well, there actually seems to be a strange relationship between mental fatigue and brain usage. The example most often used is that of an academic exam.
Generally speaking, students come away from tough exams tired, and more inclined to hit the sack than go out and party. Studies suggest this might be more to do with the stress levels and the effect of different hormones on a physiological level than a mental one.
The reasoning behind this is that other studies where people have completed a challenging mental game or puzzle like Sudokus and Crosswords before heading off to work or performing other daily tasks are in fact more cognitively ‘fresh’ than they would otherwise be.
This goes against the premise that more brain activity should tire you out. It seems that the brain can handle most activity from the amount of fuel it already gets, and that using different areas of the brain will fire more neurons and get the brain ’ticking over’ more readily than if you tried to reserve it for the important tasks of the day.
The studies with Sudoku puzzles and Crosswords highlight another interesting theory. The brain responds differently when you are engaging it for fun rather than ‘duty’. Say it how you like but when you have an important work deadline to hit, you are under duress, whether or not you get off on that.
As mentioned earlier, the cocktail of stress hormones, tiredness and any number of other variables, probably equate to the end result of being haggard and exhausted at the end of the day, project, exam period or whatever.
When we regularly engage and challenge our cognitive abilities for enjoyment, however, our brains respond by performing better on a short and long-term basis.
In addition to the fun exercises we can give our grey matter, it appears to really appreciate some physical activity as well.
Most people can testify to this; there isn’t much that clears the head and freshens you up mentally better than a workout.
That said, the studies supporting this state that sub-maximal aerobic exercise no more than 60 minutes is optimal for brain function. If you start dehydrating yourself and overdoing it, the cognitive and physical recovery required will cancel out any positive effects.
Also, on the flip-side of that coin, mental fatigue can impair physical performance. Of course this is true, your brain is the primary recipient of blood glucose. If that starts to wane then your muscles aren’t going to get much attention as their contractions are triggered by the very neurotransmitters that are being used up.
Perception and Expectation
Still though, none of this fully explains why you can feel mentally drained without the stimulus of stress to contribute to your physiological exhaustion. If there is enough fuel, and no other obstacle then surely the brain should be adequately prepared to deal with anything.
The answer seems to lie in our pre-determined expectations of mental fatigue and what we might even perceive as exhausting cognitive work. Simply put: if we think it is going to be tough, or we think it ought to be tough, we will feel it.
The old sports coach mantra that it’s “all in your head, kid” could hold some scientific weight after all. Pro sports players and Olympic athletes are always talking about the mental game being far more important on the big day. Physical training can get you so far, but then it might all be in the mind. (read bout nootropics and bodybuilding)
Fuelling the brain with optimum supplementation could be the ticket to success in many aspects of life, not the least of which is your desired physical composition.
Mental Endurance and Fitness
Not many studies have looked at mental endurance and whether longer tasks will dip into the calorie reserve more than a duration no longer than 2 hours. It may well be the case that subjecting the brain to long periods of arduous usage will elicit some deeper energy consumption and in-turn fat-burning, but the applicability to every day life is rather low.
Mental fitness is an interesting concept, however. It’s possible that the more active a brain is in generally, the more of its capacity is used and therefore the more overall energy it needs to consume.
So What About Burning Fat?
It’s not difficult to see that both Body and Mind are heavy users of energy and that aside from day to day nutritional intake, fat reserves are of course one of the sources of calories they can use.
To say that harder thinking or tougher cognitive tasks will burn a huge amount of surplus fat would be silly. However, it does seem that the more active we can be, both Cognitively and Physically, the higher our chances of not only getting in shape quicker, but experiencing a plethora of other benefits and successes in life.
Are there ways in which we can enhance the cognitive side of this equation? Arguably, yes there is. And that is precisely why there are another two parts to this group of articles. Make sure you check them out as well.
From a little research and common sense, we know these things:
- Cognitive power is fuelled by glucose in our diets
- We use more or less the same fuel for cognition, whatever our brain activity
- Cognitive performance is enhanced by fun puzzles and games
- Cognitive performance is enhanced by physical activity
- Physical performance is impaired by mental fatigue
- Stress can be mistaken for mental exhaustion
- Both Cognitive and Physical performance can be negatively impacted by our perception and expectation of fatigue
- Supplemental nutrition for both Body and Mind can lead to optimal performance and physical composition
Example Information Resources
- Scientific American – Why the brain needs constant power
- Scientific American – Thinking Hard
- Parks RW et al (1988) – Cerebral metabolic effects of a verbal fluency test: a PET scan study
- Andrei G et al (2006) – Human brain glucose metabolism may evolve during activation: Findings from a modified FDG PET paradigm
- Scholey AB et al (2001) – Cognitive demand and blood glucose
- Fairclough SH et al (2004) – A metabolic measure of mental effort
- Gerald E. Larson et al (1995) – Evaluation of a “mental effort” hypothesis for correlations between cortical metabolism and intelligence
- Claude Messier (2004) – Glucose improvement of memory: a review
- Tomporowski PD (2003) – Effects of acute bouts of exercise on cognition
- Hillman CH et al (2009) – The effect of acute treadmill walking on cognitive control and academic achievement in preadolescent children
- Chambers ES (2009) – Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity
- Samuele M. Marcora et al (2009) – Mental fatigue impairs physical performance in humans
- Chaput JP et al (2008) – Glycemic instability and spontaneous energy intake: association with knowledge-based work