Technology. Isn’t it amazing? Well, actually – it’s only as amazing as the person using it. And for someone like me – who may be an early adopter of such things, but can’t read instructions or follow intuitive prompts – that limits the capability of the machinery. However, we all have the equipment that is the most sophisticated piece of machinery there is. Ourselves. The human body – how amazing is it? This is not a post that is an ode to our awesomeness in general (and, let’s face it – you are awesome) – it’s more a miniscule look at the requirements of our brain to maintain the level of amazing our body needs at the any one time in order to operate effectively. (Of course, the ability of the brain to do this varies on a day to day level…as anyone who has misplaced something, misspoke, or misstepped can attest – i.e. everyone).
That takes quite a bit of energy and it’s no wonder then, that humans have evolved to have an extraordinarily large brain in relation to the body – the adult brain takes approximately 20% of resting energy expenditure (or basal metabolic rate), and around 10% of total energy expenditure. Not bad for an organ that only accounts for 2% of overall body mass. An infant requires even more, with 50-70% of their BMR being used to support their brain function, and up to 9 years of age, their brain requires around 50% more energy than that of an adult brain. Blame the increased number and activity of synapses (the bridge between neurons in the brain, delivering messages) in their grey matter. Makes sense given the developmental phases that occur during childhood. Back to the size of our brain, though – this sets us apart from other mammals. As children, our body is actually really slow to develop compared to other infant mammals – it can take up to 15 years for human offspring (love that term? Me too lol) to reach puberty, something that is achieved in mere months in other mammals. The high energy requirements of our brains play some part in that. When measured against our predicted brain mass we (humans) punch above our weight. The encephalisation quotient (actual versus predicted brain mass) is off the chart at 6.5 – compare that to a cat (around 1). Hmm. Enough said. No wonder there are those amongst us who boast that we are the most intelligent species. I’ll leave that up for you to decide.
Given the myriad of functions required by the brain to maintain our most superior standing in the Animal Kingdom (that always makes me think of Rudyard Kipling), fuelling the brain is essential. The brain can effectively run off three different fuel systems. Predominantly – and in most people today – glucose is the preferred fuel source, and can use up to 120g of glucose a day. As you know, this will come from dietary carbohydrate (CHO). However, in times of CHO restriction/depletion – we can provide glucose from stored CHO (glycogen), our protein stores (gluconeogenesis – breakdown of protein), and from glycerol (the CHO backbone of triacylglycerol – a fatty acid). In fact, our evolutionary response to CHO restricted environment is to shut down the delivery system of CHO to other areas in the body and deliver it to the brain (i.e. insulin resistance). This isn’t to say that the brain can’t run on other fuel sources – indeed, if that were the case then we probably wouldn’t have survived the last gazillion years (or insert actual years here) if that was the case. The body is smarter than that – in fact the only part of our body whereby glucose is essential is the red blood cells. However, if you have a diet that is predominantly made up of carbohydrate – and therefore glucose is the preferred fuel source – the likelihood of glucose depletion and a subsequent energy crash, lack of concentration and overall brain fog is far greater.
The next main fuel source is from fat – ketone bodies derived either through the diet or through the breakdown of fatty acids in the body. This only really occurs in times of CHO restriction/depletion – this happened at a much more frequent rate throughout evolutionary times when food was scarce, which clearly isn’t the case in today’s modern world. An individual is able to tap into ketone bodies for the brain if they’ve gone through an extended period of carbohydrate restriction and a higher fat diet. The brain can then begin to utilise fat as a fuel source. Those who follow a ketogenic diet (whereby fat makes up 80% of overall caloric intake, with adequate protein and minimal (~5-10% calories) carbohydrate can shift the fuel preference from glucose to ketones. Lastly, the brain can also use lactate as a fuel source, and this is called upon during times of intense exercise when glucose is depleted – see this post by James Murphy for a detailed look on the use of lactate for the brain.
So the calorie requirements of the brain can be easily met in today’s environment of an abundance of food – however the metabolic consequence of the different fuel sources available can wreak havoc on the brain’s ability to function – both in the short and the long term. As I’ve often discussed – the metabolic breakdown of carbohydrate into glucose to use as a fuel is damaging – and the brain isn’t spared from this. An excessive amount of glucose in the brain can have a neurotoxic effect – increasing the oxidative stress, inflammation, and causing damage at the cellular level. There is robust evidence clearly showing the link between a high sugar diet and cognitive decline in adults, and cognitive impairment in both adults and children. More important than ‘where did I put my keys?’, it is also associated with serious neurological disorders such as dementia and Alzheimer’s, and stroke and epilepsy. Ketone bodies, on the other hand, are a clean burning fuel – causes less oxidative stress, less inflammation and better neuronal recovery can take place in an environment where ketones are used to fuel the brain. Indeed a ketogenic diet is used as a therapeutic tool for people with epilepsy, Alzheimer’s and to slow the growth of brain tumours.
Does that mean that you need to go on a ketogenic style diet to help protect the brain from oxidative stress caused by glucose metabolism? No. Certainly a reduction in glucose load by reducing overall carbohydrate (i.e. processed, refined foods) is the starting point. However, like all metabolic processes in the body, it takes more than just calories to enable the brain to function optimally – and I’ll talk more about that next week. Until then, look after the most sophisticated piece of equipment you have. And keep being awesome.