Right Time, Right Place – the Importance of Nutrient Timing, Part II

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In the last blog I wrote, I talked about how and when to utilise carbohydrates when trying to turn your body into a fat burning machine. In this blog I will be talking about how to take advantage of carbohydrate timing to improve your performance.

This blog will be very science-based because in order to maximise your abilities and smash your targets – whether that be to improve your 5k time or to beat your marathon time – you need to understand how to utilise carbohydrates properly.

The goals of carbohydrate ingestion in relation to performance are to:

  • Maximise the glycogen stores pre-exercise
  • Maintain carbohydrate supply during
  • Maintain blood glucose during
  • Replenish the stores of glycogen post-exercise

So in order to cover all of these goals I will be breaking this down into 4 sections:

  1. Introduction
  2. Pre-exercise carbohydrates
  3. During exercise carbohydrate intake
  4. Post-exercise carbohydrate intake

Introduction

Carbohydrates are needed to fuel almost every type of activity, and the amount of glycogen (this is the stored form of carbohydrates in the muscles and liver) has a direct effect on your performance.

A high muscle-glycogen concentration will allow you to train at your optimal intensity and achieve a great training effect. A low muscle-glycogen concentration, on the other hand, will lead to early fatigue, reduced training intensity and sub-optimal performance, which is not what we want!

Research has shown that athletes on high carbohydrate diets store twice as much muscle glycogen than those on a moderate carbohydrate diet, and SEVEN times more than those on a low carbohydrate diet. 

So how much should you eat a day?

I won’t spend too much time on this, as I want to focus on more on the timings of carbohydrates rather than the overall intake. However, that being said, here are some general guidelines based on your activity level and your bodyweight (the carbohydrate amounts are represented as g/kg which means grams per kilogram of bodyweight):

-Very light exercise (less than an hour a day) – 3-5g/kg

-Moderate (around 1 hour a day) – 5-7g/kg

-Moderate to High (1-3hrs a day) – 7-12g/kg

-Very High (over 4 hrs a day) – 10-12g/kg

Now let’s move onto pre-exercise carbohydrates.

Pre-exercise

What, when and how much you eat before you exercise will affect your performance, strength and endurance. Multiple studies have shown that when you consume carbohydrates before exercise, your performance is increased when compared to exercising on an empty stomach.

When is best to eat before exercise?

The general guideline on this is that you should eat 2-4 hours before exercise, leaving enough time for your stomach to settle so you are neither too hungry nor full. This helps increase your liver and muscle glycogen stores and enhance subsequent performance.

If you leave too long an interval between eating and exercising, you will be at risk of hypoglycaemia – a state of low blood glucose. Being in this state will impair your performance, leaving you feeling light-headed and fatigued, and can put you at risk of an injury. 

How much should I eat?

In general, the closer you are to exercising the smaller the meal should be, and vice versa, the further away you are the larger the meal can be. There have been multiple studies conducted testing the optimal amounts of carbohydrate to consume in conjunction with how far out before exercising to consume them; the majority of that research suggests consuming between 1-4g/kg 1-4 hours before exercise.

You may need to experiment with these timings and amounts to see what works best for you.

What types of carbohydrates should I consume?

In the last blog I talked about something called the GI (Glycaemic index) of foods, something I’m sure most have heard of. It basically tells us how fast a carbohydrate is digested and its affect on our blood glucose levels. A high GI food will be rapidly digested and cause a spike in the blood glucose levels, whereas a low GI food is digested at a slower rate and causes a lower, steadier increase in blood glucose (shown below). The reason this is important, is because both types will have different effects on performance.

screen-shot-2016-09-08-at-12-59-05

Research suggests that eating a low GI meal before exercise can increase endurance performance. This is because the low GI meal leads to a better maintenance of blood glucose levels and increases the amount of fat burnt, which in turn leads to less glycogen being used and performance increasing.

During Exercise

For most activities, anything other than water isn’t necessary, providing your pre-exercise muscle glycogen levels are high. However, it has been clearly shown that consuming carbohydrates during prolonged periods of exercise (>1 hr) can help performance. 

Let’s go through when carbohydrates during exercise can be beneficial.

Less than 45 minutes

Any exercise lasting less than 45 minutes is unaffected by consuming carbohydrates during exercise.

45-75 minutes

Interestingly, research has shown that just by simply rinsing your mouth with a carbohydrate solution can improve your performance. This is thought to be down to the carbohydrate receptors in the mouth sending signals to the brain telling it that food is on its way. This is meant to override the perception of effort and fatigue so you can continue longer and perform better.

Over 1-2 hours

Consuming carbohydrates during this duration of exercise can help maintain blood glucose levels and delays fatigue, enabling you to perform for longer.  When we exercise for this amount of time we slowly but surely start to deplete our muscle glycogen, liver glycogen and blood glucose levels. The combination of depleted muscle and liver glycogen stores with low blood glucose levels will make everything feel 100 times harder, your muscles feel weak and tired, you become light-headed and eventually you either decrease the intensity dramatically or you stop entirely. This point is known as ‘hitting the wall’ in marathon running.

When exercising for this duration it is recommended to consume 30-60g per hour. This is the maximum rate of absorption. You can combine different types of carbohydrates (e.g. glucose and fructose) at different ratios to help increase the absorption rate, but we will leave that for another time. 

Post-exercise

After exercise we want to: replenish, rehydrate & support and remodel, all of which can be done through post-workout carbohydrate consumption.  The reason we want to refuel so much is because we want to be ready for the next session so that we can get the biggest training effect possible.

The rate which it takes to refuel depends on several factors and can take anywhere between 20 hours and 7 days! 

During the first 2 hours after exercise, replenishment is most rapid at around 150% of the normal rate; this is because we are very sensitive to insulin post-exercise, so when we consume carbohydrates we spike our insulin, which drives the carbs into the muscles.

Four hours after exercise and the rate of replenishment has slowed but is still higher than normal, so when we are looking to maximise the effects of carbohydrate intake we want to get them in during the 2-hour window post-workout, especially if you are an athlete who trains every day or even twice a day.

There is also a large amount of research showing the benefits of consuming a carbohydrate and protein drink on recovery. It has been shown that the protein exacerbates the insulin response, causing a faster refuelling of the body’s carbohydrate stores, as well as increasing protein synthesis and blocking cortisol function.

The figure bellows shows the effects of consuming more carbohydrates each day on the rate of replenishment per day. It displays the importance of consuming enough carbohydrates to refuel the body ready for the next session.

screen-shot-2016-09-08-at-13-01-38

Summary

It is clear that carbohydrate timings can have massive implications on performance. So in order to maximise your performance and smash your goals you must:

  • Maximise the glycogen stores pre-exercise
  • Maintain carbohydrate supply during
  • Maintain blood glucose during
  • Replenish the stores of glycogen post-exercise

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