Chapter 3 Nutrition

CHAPTER CONTENTS

Energy for exercise

Energy production

Energy values

Energy intake

Ingredients for energy

Carbohydrates

Timing of carbohydrate intake

‘Hitting the wall’

Proteins

Protein supplementation

Fluids

How much is enough fluid?

Planning your drinking

What type of drink?

The others

Minerals and vitamins

Vitamins

Minerals

Going the extra mile

Targeted supplementation

Glucosamine and chondroitin

Maximising performance

ENERGY FOR EXERCISE

We all need energy for exercise. Energy is the basic requirement for any form of activity.

It comes from the food we eat and fluids we drink but how much is enough? Too little and we run the risk of under-performing and getting fatigued, too much and we gain weight. What form of exercise we perform also plays a role. Whether we are involved in endurance or explosive activities or whether we are watching our weight, or male or female, we all need energy to exercise but the balance of that energy requirement varies from one to the other.

How quickly we need that energy is also a factor. If we need the energy over a 20 s sprint, then it has to be quickly and freely available as opposed to the slow drip feed supply of a marathon runner. Where that energy is stored and available is important and this reflects the form of energy we take in.

Energy production

The unit of energy is ATP (adenosine triphosphate) which when broken down releases energy. There are three systems of releasing energy from ATP which work together to provide the energy requirement depending on what exercise regime is being followed.¹

1. ATP-CP

• ATP is linked with creatine phosphate (CP) as a small store in muscles readily available for fast activity. It is used for short sharp explosive activity and only lasts 5–7 s before the muscle store is depleted. This system is used for sprinting where the energy is needed instantly and therefore does not require oxygen nor distant stores of ATP that would take too long to get to the muscle (Fig. 3.1).

2. Anaerobic energy

• This provides 100 s of power-based energy. This system produces more energy than the ATP-CP system, and for longer, but is still too quick for oxygen to be involved. In the ATP-CP system, energy is instantly available but here it requires glucose to be broken down to ATP and lactic acid, releasing the ATP for energy. The by-product, lactic acid, can result in muscle cramps and so is not the most efficient energy system for, e.g. a 400 m runner (Fig. 3.2).

3. Aerobic energy

• This is a slower, more efficient, system of producing ATP and releases 20 times the amount of ATP than the anaerobic system. Glucose is broken down with oxygen to produce the majority of ATP but fat can also be used to produce ATP. This is what happens with training where fat is used preferentially thus conserving the glucose/glycogen stores and reducing the chances of glucose deficiency that happens when an endurance runner ‘hits the wall’. Protein is also a source of ATP but not as efficient as when glucose is metabolised, e.g. in the long-distance runner (Fig. 3.3).

Figure 3.1 Energy production ATP-CP.

Figure 3.2 Energy production: anaerobic energy.

Figure 3.3 Energy production: aerobic energy.

Some athletic events require purely one energy system to be utilised but most require a combination of all three (Fig. 3.4). Training fine tunes the efficiency of each system appropriate to the event which is being trained for.

Figure 3.4 The three energy production systems.

Reproduced courtesy of Brian Mackenzie

Energy values

Energy in the form of ATP is derived from carbohydrates (glucose), fats and proteins but which energy system is used is determined by the following factors:

• Type of activity performed

• Intensity of activity

• Duration of activity

• Frequency of activity

• Fitness level of the athlete

• Diet of the athlete.

If you intensify the level of activity then the body transfers from a fat source to a glucose source of energy. However, the longer you exercise, more fat is metabolised in preference to glucose in an attempt to conserve the limited supply of glucose within the muscles and liver. The balance of fat and glucose, therefore, depends on the exercise training you are undertaking. A sprinter has no need for fat as a store, as his event is over very quickly. They will therefore have very little lean body fat, whereas a marathon runner, although thin, may need fat as a source of energy, as will a swimmer who may benefit from some fat to act as buoyancy. Therefore, rather than looking at the weight of an athlete, we should be measuring the percentage body fat and muscle mass as a true measure of how well we are shaping up to our energy needs.

Energy intake

So how much is right? If we take in too much carbohydrate or protein, then the excess is stored as glycogen and the protein is excreted. Taking in too much fat means that this will be stored within the body. To reduce the body fat we need to reduce the intake and increase the fat burning activity in the form of longer durations of exercise. To increase the protein in lean muscle mass we need to increase the protein and carbohydrate in our diet and increase our exercise and resistance exercise regimes.

Take home points

• Tailor your energy intake to your exercise needs.

• Not all the fat in your diet is bad.

• Muscle mass and percentage lean body fat are better measures than body weight.

• Fatigue may be dietary in origin, not just as a result of over-training.

INGREDIENTS FOR ENERGY

The different types of energy sources and their sub-divisions can be confusing and distracting. The three sources of energy are as follows ²:

1. Carbohydrates

• Essentially, this is glucose which is stored as glycogen in muscles and the liver. Carbohydrates exist in our diet in two forms:

a Sugars (mono or disaccharides): sugar, fruits, honey, vegetables, sugar cane

b Starches (polysaccharides): these are larger molecules which take the body more time to break down and release the glucose, e.g. pasta, potatoes (Fig. 3.5).

• It is not always helpful to describe foods as simple or complex carbohydrates, as often foods contain a mixture of different types.

2. Proteins

• These are the building blocks for life. The units for protein, the amino acids, are stored in muscles where there is a limited capacity and any excess is either stored as fat or carbohydrate.

• Amino acids are divided into those essential ones (which are found in all animal sources of proteins) and the semi-essential and non-essential ones.

• Protein rich foods include:

Milk

Yoghurt

Fish (especially tuna and salmon)

Eggs (boiled, scrambled or in omelettes)

Meat (beef, lamb, ham)

Poultry (chicken)

Grains and nuts, especially muesli (Fig. 3.6).

• Proteins are also the building blocks for increasing muscle size and are therefore essential dietary components for those athletes wishing to gain muscle bulk or strength from weight training or resistance exercise.

3. Fats

• These are essential as a fuel for endurance training, and consist of fatty acids and vitamins A, D, E and K. It is important not to avoid all fats, as the body will use other sources as an energy source, such as carbohydrate, resulting in residual fatigue when the body’s store of carbohydrate is so low that fatigue and lethargy result.

• Fats are divided into saturated and unsaturated (mono-unsaturated and poly-unsaturated) fats. It is important to avoid saturated fats and enhance the unsaturated ones as these reduce the total cholesterol and LDL-cholesterol levels that are harmful in atherosclerosis and heart disease.

• Fats are also a source of essential fatty acids in the form of omega-3 (salmon, tuna, mackerel, linseeds and soya bean oil) and omega-6 (sunflower seeds and oil, and nuts). Omega-3 food sources are also the most ‘protective’ against heart disease (Fig. 3.7).

Figure 3.5 Carbohydrates.

Figure 3.6 Proteins.

Figure 3.7 Fats.

Take home points

• Eat a variety of foods and enjoy what you eat.

• Eat more carbohydrates, especially cereals and starchy foods.

• Don’t be afraid of fats but choose unsaturated ones.

• Eat moderate protein – more is not better and oily fish is best.

Carbohydrates

Glucose is stored in the form of glycogen in muscles and in the liver and is the preferred and most efficient source of energy. Glycogen stores are relatively small and run out after a few days of exercise if not replenished. The amount needed to be re-stocked depends on the exercise regime that is being followed.

The bulk of carbohydrate should come from cereals or starchy food sources such as:

The remainder is gained from sugar, fruits and juices.

You should tailor your intake to your energy expenditure, so if you have a high daily load of intensive exercise you should have an equally high carbohydrate intake, with regular snacks in-between feeds.

The speed with which the glucose is absorbed into the blood stream and hence its availability as a substrate for energy release is also a factor in your choice of carbohydrate foods. The glycaemic index (GI)³ is a measure of this. Highly absorbed carbohydrates have a high GI index and poorly absorbed ones have a low GI index. The high GI foods are useful to take as recovery after exercise when carbohydrate stores need to be re-stocked quickly, and low GI foods, which have higher fibre contents, release their energy sources more slowly. Examples of high and low GI foods are shown in Table 3.1.

Table 3.1 High and low GI foods

	High GI	Low GI
Breads	Bagel, wholemeal	Granary, rye bread
Cereals	Bran flakes, Weetabix	Muesli, All-bran
Starches	Baked/mashed potato	Pasta, lentils
Fruit	Watermelon	Apple, peach, pear
Snacks	Jelly beans, rice cakes	Sultanas, Mars bar
Drinks	Sports drinks (isotonic)	Apple/Orange juice