Knowing what, how much and when to eat are key aspects of nutritional support for training. Appreciating the complexity of energy production and the effect different foods have on the body can make a huge difference to how you perform, to your body composition and to the maintenance of good health.
It’s not just a question of “calories in” v “calories out”
Different foods may have the same calorific content but can have radically different effects on the body; e.g. protein provides similar calories per gram as carbs but only 10% of protein is used for energy.
Carbs provide the body’s primary source of fuel but the fibre and starch content and the glycaemic load all affect the rate of conversion to energy.
Fat can be used as a source of fuel but the conversion of fat to energy is much slower and occurs mainly in aerobic conditions, i.e. low intensity exercise when plenty of oxygen is available. ‘Training on empty’ and limiting fat in the diet are more likely to result in the breakdown of muscle tissue for conversion to glucose than the use of fat for fuel.
The complex process of converting food to energy also requires vitamins and minerals from a wide variety of sources, i.e. plenty of fruit and vegetables.
Glycaemic index (GI) and glycaemic load (GL)
The GI was created as a measure of the rate of conversion of carbs to glucose. The lower the GI the more sustained the release of energy from carbs. The picture is incomplete without looking at the GL too, i.e. the amount of carb contained in the food: e.g. watermelon is high on the GI as conversion to glucose is rapid, but the GL of watermelon is very low, as it is mostly made up of water.
Blood sugar balance
The fat, protein and fibre content of a meal affects the release of glucose into the bloodstream. Foods high in sugar. Such as cakes, sweets, etc will cause a rapid increase in blood sugar compared with those containing more fibre, fat or protein e.g. a bowl of porridge.
A bowl of porridge will take about 1.5-2hours to digest – during this time much energy is being used up in the digestive process. Conversely, a high sugar food or drink causes a big spike in blood sugar, resulting in the production of large amounts of insulin, which brings blood sugar down below normal levels. Both of these scenarios result in insufficient energy being available to train for a period of time following consumption.
The importance of fruit
Along with glucose, fructose found in fruit is another simple sugar used for fuel. It is metabolised differently and is absorbed more slowly, thus triggering much smaller amounts of insulin. Including fruit or fruit juice in a pre-training meal or on the bike serves as another source of energy without upsetting blood sugar balance.
Water and electrolytes
All the body’s cells contain and are surrounded by water and all cellular processes take place in a watery medium. Without sufficient water, the function of the cell (and so energy production) is impaired. Body fluids contain electrolytes and minerals that carry an electric charge-which are involved in nerve and muscle function. Exercise causes loss of body fluids and electrolytes with it. In addition, dehydration causes a reduction in blood volume which causes the heart to work harder. Loss of electrolytes means the nerves and muscles that propel you forward start to suffer.
So what do I eat – and when do I eat it?
Before you train you should ideally have plenty of stored glucose (glycogen) and circulating glucose available to your working muscles. Consumption of protein limits muscle fatigue and speeds the recovery process; and a small amount of fat provides free fatty acids as an additional fuel source. This means a well-balanced meal eaten at least 1.5hours before training to allow digestion to take place and blood sugar to return to normal levels. Recent evidence suggests that training on empty helps to build new mitochondria (the ‘batteries’ of the cell that produce energy) but this is only recommended for low-intensity, short-term training.
Research shows that around 200-300 calories 1-1.5 hrs before training at a rate of 4:1 carbs:protein provides sufficient fuel to support one hour of intense exercise, i.e. the equivalent of 200g potatoes and half a chicken breast or 1 large egg. Training very early in the morning may not allow enough time to prepare or eat solid food (and you may not have the appetite for it!): something like a smoothie containing banana, apple juice and some protein powder will be more easily digested and can be consumed an hour prior to training time. What you eat the night before is also important.
If you’re planning a lunchtime or evening session at the Lab, you should be prepared and take a pre-training snack with you to work and have it 1-1.5 hrs beforehand.
Glycogen will last on average for only 90 mins of exercise – for any training session longer than 90 mins you need to start taking on carbs well before the 90 min mark to avoid hitting the wall or ‘bonking’. An easily digestible source of glucose such as energy gels or drinks (commercial or home-made) are ideal; if you prefer solid food such as flapjacks and energy bars work well but bear in mind these take longer to digest and release their valuable glucose.
Research shows that an exercising adult (regardless of size, age or gender) can consume no more than 60g of carbs per hour so ideally you should be aiming for 40-60g of carbs plus 500-750ml of water (depending on heat and sweat rate) per hour of training to maintain energy levels.
As soon as you stop training your body ceases to secrete hormones that encourage the breakdown of fuel sources into energy and recovery and the rebuilding of muscles and tissues and restoration of glycogen reserves starts to occur. For the first 30-45 mins the rate of uptake of fuel into cells is about 10 times higher, providing a window of opportunity to kick-start the recovery process and maximise the use of nutrients. Miss this window and you’re missing a trick and will leave you feeling hungry for the rest of the day, increasing the likelihood of overeating. A 500ml recovery drink containing carbs, protein and electrolytes (again, 4:1 carbs:protein) will do the trick (unfortunately most commercially produced recovery drinks contain too much protein and insufficient carbs).
Boost your performance
Recent research is showing that certain foods can increase time-to-fatigue in cycling trials: caffeine is well-known but foods high in nitrates such as beetroot and watercress have been shown to increase oxygen delivery whilst the high-oxygen capacity of the blue-green algae spirulina is showing promising results in time trials.