What Does Glucose Have to Do with Public Speaking?

So – what does glucose have to do with public speaking? And have you ever thought about what your brain needs, to be able to think clearly under pressure?

Clients often talk about being unable to stay focused or coherent when faced with people looking at them. They struggle to string thoughts together, and sometimes go completely blank. If this has ever happened to you, you know how awful it feels…and you probably live in fear of it happening again.

What does Glucose have to do with Public Speaking?
What does Glucose have to do with Public Speaking?

Being unable to think clearly while speaking in public is very common, and there are always different factors which impact our mental agility in front of group. Everything from feelings of self-consciousness to full-blown panic; last-minute preparation or not being on top of the subject matter. But there’s one area which most people don’t consider – and that’s metabolic fuel. Our ability to think quickly and precisely, and to recall information when we need it, only lasts for a limited time.

And those abilities – to be quick, precise, with good recall –  are usually exactly what we need to call on when speaking to a group. Or indeed one-on-one under pressure.

When you speak in public, you’re mentally juggling a lot of balls at the same time:

You’re processing a lot of information in a short space of time.

You’re trying to stay focused and not be distracted by what else is happening in the room (the effort to focus can exhaust our brain’s limited resources). It’s worth knowing that attention is a lot more about suppressing distractions than about keeping your focus.

Talking of suppression: you might also be trying to suppress your fears and concerns – about who’s in the audience, what they think of you, how well or badly you’re doing.

If you’re a nervous speaker, you’ll be inhibiting your natural desire to flee the scene! (the flight/fight syndrome). Each time we inhibit an impulse, our capacity to inhibit for the next event reduces. (This is why our self-control tends to weaken as the day goes on.)

You may need to make decisions in the moment, such as during Q and A. Decisions such as: ‘what’s my best/most intelligent response to that tricky question?’ Or if you forget a key point, working out how you can get back to it without looking like you forgot!

How much fuel does our brain actually use?

While we’re doing all this, our brains use a lot of fuel; they’re like a battery which drains quickly if it’s not topped up. In fact while our brain accounts

What does Glucose have to do with Public Speaking?
What does Glucose have to do with Public Speaking?

for 2% of our body weight, it churns through 20% of our daily calories. It draws this up from the liver when needed. When you get really hungry, do you find your thinking seizes up? Or if you’ve been working for a couple of hours, that you slow down and find it hard to focus? Most people do. Hunger also tends to make us more impulsive or snappy.

And if you’ve ever tried to lose weight and reduce your food intake, you’ll probably know how distracted or bad-tempered you became! (So it wasn’t just that you were depriving yourself of your favourite snacks!)

And it’s our frontal cortex – the more recently evolved part of the brain  (where we do our thinking) -that’s so sensitive to falling glucose levels. The older part – the brain stem – which regulates vital functions is more resilient. Leigh Gibson of Roehampton University in England says: “When your glucose level drops, the symptom is confused thinking, not a change in breathing pattern.” 

So what does our prefrontal cortex need if we want to give ourselves the best chance of being quick-witted when we’re speaking in public?

In simple terms, we need to have enough (but not too much):

  • oxygen
  • glucose
  • water

The oxygen aspect obviously means that we need to breathe properly (which is also often overlooked), and our brains are roughly 73% water (we need to stay hydrated to stay sharp). But today we’re talking about glucose. The body’s overall need for glucose probably already makes sense to you, knowing how your energy and focus drops when you’re hungry. But were you aware of the brain itself and its glucose needs?

This was something new to me until a couple of years ago: and it’s made a big difference to how I approach all my work, not just my speaking assignments: I’ve learned to recognize that trying harder to focus when the fog sets in is counter-productive. I just need to stop briefly and refuel with food and water (remembering to breathe helps too!).

‘Save’ your brain for what matters

This also ties into the idea that if you have an important presentation, or one where you need to be sharp and ‘on the ball’, try not to use your brain for anything important beforehand. Save your prefrontal cortex for what matters that day. Remember that it’s a limited resource.

So what should we eat or drink to refuel and feed our brain?

Devour a large chocolate muffin or can of soft drink before we get up to speak? Well, ideally no! The bad news is that sugary food not only spikes our blood sugar, but also elevates our cortisol stress hormone. This obviously doesn’t help any anxiety you’re feeling – the last thing you need is to have more cortisol coursing through your bloodstream. The solution is to have some low glycemic food; your body breaks the carbs in lower GI food into glucose molecules more slowly, which gives your brain a steadier supply of energy. High fibre carbohydrates such as grainy dense bread are relatively low glycemic – this is good. But if you combine them with fat (good fat such a olive oil) or protein, this can slow absorption even more. Even better.

If you need a quick fix before you present, a banana or blueberries are great too. Michael Green of Aston University in the UK tells us that the brain works best with about 25 grams of glucose circulating in the blood stream —  you can get this amount by eating a banana.

So fuel up to protect yourself

Even if you’re one of those people who doesn’t feel like having breakfast or eating anything before you present, hopefully you can now see the wisdom of making sure that your brain has some fuel to run on. Protect yourself from running out of steam or going blank during your presentation!


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