When fuelling the body ready for activity, it is important to know what type of fuel your body is using, and where this comes from. Fuelling for training involves not only what you eat as your pre-training snack, but also what you eat across your day.
Nutrients that provide energy:
Nutrients that provide energy are referred to as ‘macronutrients’, and they provide our body with a source of energy in the form of calories or kilojoules. Our macronutrients are:
Proteins: We will cover proteins in a future blog on recovery post-exercise, but in short, proteins are vital for the repair and growth of muscle, bone and nerve tissue.
Fats: These are essential for cardiovascular health, joint health and the absorption of Vitamin D and calcium. Fats can also be broken down and converted to glycogen when carbohydrate intake is too low.
Carbohydrates: This is the form of energy in our blood (glucose) and muscles/liver (glycogen) and is the body’s preferred source of fuel as it is very easy to access. It is also the only form of fuel our brain can use, and this is the reason our body is able to break down muscle and other body tissues to make glucose if we go into starvation mode.
1 gram of protein = 4 calories (16.7 kJ)
1 gram of fat = 9 calories (37.6 kJ)
1 gram of carbohydrates = 4 calories (16.7 kJ)
As you can see, fat provides more than double the energy of carbohydrates, so we only need small amounts of it in our diet. Fat should make up approx. 25-30% of our total dietary intake. We do not need to consume this immediately prior to exercise, however, we should incorporate unsaturated fats into our diet on a regular basis.
Sources of unsaturated fats include: raw nuts, avocado, nut oils, olive oil, oily fish such as salmon/trout/tuna, and seeds. These can be incorporated with other foods during the day to ensure adequate intake.
Source: What Doctors Don’t Tell You
Immediately prior to training (approx. 45-60 mins prior) is a very important window of time for carbohydrate intake. There are two types of carbohydrates: complex and sugars. Carbohydrates should make up 50-60% of our diet, especially if we are engaging in regular training sessions. Throughout the day, it is important to include complex (slow-release) carbohydrates such as: whole grain cereals or breads, vegetables, fruits, legumes and low-fat dairy. This will ensure your stored carbohydrates (glycogen) in your muscles will be topped up and ready to go at training.
45-60mins prior to training is when we need to consume approx. 30g of carbohydrates in order to increase our ability to utilise our fuel stores effectively.
Examples of foods containing 30g of carbohydrates are: fresh fruit, fruit flavoured yoghurt, 300ml fruit juice, honey on a slice of toast or crumpet, museli bar, 400ml sports drink, handful of sultanas/dates/dried apricots. If all else fails, 3-4 jelly beans/lollies also work, however, these are best consumed within 30 minutes prior to exercise in order to avoid a crash in energy prior to training.
Source: Time To Run
How this links to training
The types of fuel you may be using during training are:
- Glycogen – which is the stored form of carbohydrates in your muscles and liver; and
- Fat – stored in your fat cells (called adipocytes).
During training sessions, a combination of glycogen and fat is used, the amount of which is dependent on what exactly we are doing in our training session.
This is generally low-intensity/low-heart rate exercise that can be maintained for a period longer than 45 minutes. The lower our heart rate during exercise, the higher our ratio of fat:glycogen used for fuel. The reason for this is because fat requires oxygen in its metabolism, and a very little bit goes a long way; i.e. it is an incredibly efficient source of fuel.
This type of exercise is performed at a high heart rate/high intensity for a short period of time, followed by a period of rest. During the intense phase, your main source of fuel will be glycogen from your muscles. Oxygen is not required in the process of metabolising glycogen into readily available energy, as it is a very quick process. However, this means it is also used up quickly, and is not a sustainable source of fuel. This is why we can’t run a marathon at the pace of Usain Bolt!
As this type of exercise does not require oxygen, we produce lactic acid a lot quicker than in anaerobic exercises. This is why we require periods of rest in between periods of intensity.
Every sport, whether endurance-based or speed-based will incorporate these aerobic and anaerobic exercises into training sessions. The reason is that they provide different benefits for our fitness and body composition.
Aerobic exercise does utilise a higher percentage of body fat for fuel than anaerobic exercise, however, per minute it is relatively low overall energy expenditure. In terms of overall calorie burn, it is quite conservative (unless performed for longer than 60 minutes). This is why we can maintain this type of exercise for extended periods of time.
Anerobic exercise does not utilise body fat as a source of fuel, however, the benefit is that during the intense phase the overall energy expenditure is very high, and post-exercise, RMR (resting metabolic rate) remains elevated.
If you think of it this way: aerobic exercise increases your stamina, whereas anaerobic exercise increases your cardiovascular fitness and energy metabolism. This of course, is subject to each individual’s VO² max, but that is another blog for another day!
Accredited Practising Dietitian