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To eat, or not to eat (before exercise)? That is the question...

I have about 43 meals a day, and frankly some days I don’t have time to breathe I’m so busy eating. So for me, the answer is a very simple ‘yes’. I am SO in the ‘to eat’ camp. However, much as it pains me to say it, I’m not always right (ouch, that really did hurt), so here’s what some other folk think…

The Traditionalists believe that if you want to train hard, you should fuel your body (appropriately) beforehand. In a nutshell, you should always eat something before exercising so your body has enough fuel to power you through your workout.

Men’s Fitness mag put this into man speak:

“If you want your body to perform like a Lamborghini, then you've gotta put in the high-octane fuel”.

(Love it! But am now totally distracted by what sort of car I think my body performs like…I mention this meandering thought on the phone to my husband who gives me an answer I don’t like. I hang up, call him a few names under my breath, and carry on writing).

Foods that contain carbohydrate are a key energy source for exercise, as it's broken down into glucose, which is your body’s main fuel. BUPA explain that you can store a small amount of glucose in your muscles as glycogen until you need it. So if you eat sufficient carbohydrates before you exercise, you can keep your supplies replenished. If you don’t have enough glycogen, you won’t have the energy to exercise to the best of your ability. You might also start to lose muscle mass. This is because your body may need to break down protein in your muscles to use as an alternative energy source.

So how can it be then, that our next group of people actually advocate fasted training? NB: this practice is specifically for fat loss.

This band of merry wo/men dispute the traditional research that carbohydrate availability and muscle glycogen stores should be high for every training session. That carbs are important for performance is considered a given, but this new technique is known as the “train low, compete high” model. In the case of a runner, “this means choosing a number of running sessions to complete in a fasted state to optimise training adaptations, while actually racing with high carbohydrate stores and availability to maximise performance”.

Jill Leckey, Science in Sport’s senior nutritionist.

How it works is that the body gets better at using fat as a fuel source during exercise and saves the muscle glycogen for when it needs it most eg when the going gets tough in a race.

“However, on race day the body must also be able to use carbohydrate as a fuel source. This is why it is best to select certain shorter training sessions to complete fasted, while others should be completed in a carbohydrate-loaded state. This will ensure the body is well adapted to using both fat and carbohydrate for fuel during exercise”.

Points to note:

  • Hydration is still key.

  • Fasted training is best completed at an intensity and duration that does not require a great input from metabolism: typically training for around 60 minutes at a moderate intensity is recommended (which may well have an impact on your training schedule).

  • Repetitive fasted training can have negative effects: “Training with low muscle glycogen levels can also lead to a hormonal and metabolic environment that increases muscle protein breakdown and can impair immune function”.

We then have a third group of people, who still have fat burning as their objective, but they argue that men and women should behave differently despite sharing a common goal (nothing like a bit of sexism to spice up a blog).

An experiment was done for BBC2’s Trust me I’m a Doctor programme which demonstrated that men should eat after exercising to maximise fat-burning, while women should eat before.

Why? Because men and women burn fat and carbohydrate in different ways.

Men are more muscly, and as carbohydrates are stored in muscles, this is their bodies’ preferred fuel. If they eat before exercising, they have a store of carbohydrates available to their muscles, and they never make the 'big switch' to burning fat.

Dr Adam Collins (who was involved in the experiment) says: 'Men get a better effect if they exercise fasted as they're putting more stress on the muscle to burn more fuel, so the muscles burn more fat.'

Then, when they eat after exercising, they simply replace the carbohydrates that were used in the muscles.

Women's bodies, on the other hand, are programmed to burn fat in order to conserve glucose (sugar from carbohydrates) in the body.

Dr Collins says: 'This is probably an evolutionary advantage to do with pregnancy. If women are better at managing their fuels they have glucose to spare for the foetus'.

For women, most fat-burning occurs in the hours immediately after they stop exercising. By eating up to an hour and a half after exercise you’re forcing the body to use carbohydrate which gets in the way of the fat-burning.

He says this idea of metabolic flexibility, being able to switch between burning glucose (carbohydrates) and fat, is the key to good health.

'Most people who are obese are metabolically inflexible. They are constantly burning glucose and never make the switch to fat.

Exercise is healthy because it stresses the muscles and forces them to become better at managing fuels, and switching between fuels’.

So, by way of conclusion, there are clearly different approaches depending on your goal. If you fall into the category that the good old Americans call ‘fun lovin’ keep fitters’ (you gotta love it for its awfulness) then having a light bite pre-exercise is probably sensible.

But if you’re on a fat loss mission, then either the fasted approach or indeed addressing the timing of your ‘fuel’ intake might be of interest.

Anyway, enough chit chat, my Lamborghini’s running low on fuel. I’d better get it to the petrol station…the one with the drive-thru…


Jill Leckey, The Guardian

Dr Adam Collins, University of Surrey, BBC 2 Trust Me I’m a Dr


Men’s Fitness


I am not a dietician or a nutritionist, and make no claims to the contrary. What is written on this site should not be taken as fact or advice. It is merely an opinion blog.

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