Wednesday, 27 August 2014

Nutrition : What To Eat Pre-exercise

An awful lot has been written about how to fuel yourself during and after exercise, but there's not quite as much attention given to how to fuel yourself beforehand, especially the science aspect. I've learnt a lot on my Nutrition for Sport & Exercise module recently and have has some requests to share some of that knowledge.

The body fuels uses predominately muscle glycogen (from carbohydrate/CHO) and free fatty acids to fuel athletic activity. When you are exercising at a low intensity, fat is the main fuel you use. But, as you increase exercise intensity you rely more on glycogen. We only have around 2000kcal of CHO stored in the body, enough for around 2 hours of intense exercise, so it's important to have enough of it in our diet.

As a general rule of thumb our day-to-day CHO requirements are shown in the table below. For example, I'm working out for 6-7 hours a week at the moment and weigh roughly 60kg. This means I should be eating around 300g of CHO per day. As an idea of what that means in terms of real food, I could get 50g of CHO from 2 bananas, 6 jaffa cakes, 8 tbsp baked beans, 70g uncooked pasta, a small jacket potato, 70g muesli, 3 slices of bread or 50-60g of twiglets.

Activity Level (number of hours of moderate intensity exercise or sports) Grams of Carbohydrate/kg body weight per day
3-5 hours per week  5 grams per Kg body weight
5-7 Hours per week 5-6 grams per Kg body weight
1-2 hours per DAY  6-7 grams per Kg body weight
2-4 hours per DAY  7-8 grams per Kg body weight
More than 4 hours per DAY  8-10 grams per Kg body weight

Specifically, we should be aiming to eat 2.5g/kg body weight of CHO within the 2-4 hours before we exercise. So for me that would be 150g of CHO. So a lunchtime run might be well fuelled with a breakfast of muesli with a banana and dried fruit followed by elevenses of another banana or a couple of fig roll biscuits.

The type of food you eat matters. You'll probably be familiar with the Glycaemic Index (GI) which measures, on a scale of 1-100, how quickly sugar from the food is absorbed by the body. Anything up to 55 is classed as low GI, anything above 70 is classed as high GI. The lower the GI rating the longer it takes the body to absorb it which results in a more stable blood sugar level, reducing hunger pangs and cravings.

So you're better off eating low GI foods prior to workout, to give you that sustained energy. Examples of low GI foods are jacket potatoes and baked beans, spaghetti bolognese or muesli and semi-skimmed milk.

Trying to achieve this is almost certainly easier said than done but it's a guideline and you may find it can help your performance. You can find a lot more guidance on this online but I hope this has given you the basics and you've found this helpful. I plan to do a few more posts like this over the next few weeks so if there's anything you'd like me to write about specifically let me know.

How do you fuel before you exercise? Do certain things help or hinder you? Now I'm off to hunt out some twig lets, because I've not had them in years!


  1. My PT has advised me to only eat carbs AFTER exercise. This is because weight loss is my goal and given that if the carb stores in muscles and liver are already full, the only other place to store it is as fat, I should only eat carbs when I have depleted those stores (by exercising) and can refill them with yummy carby goodness.

    As a marathon runner used to carb loading as a ritual before running, this has completely blown my tiny mind.

    1. That's absolutely fair if weight loss is your goal... these guidelines are generalised and only what I've been taught on my courses. As long as you're not feeling any ill effects (lacking in energy on the run), which your PT will be making sure of, then you're good to go!