Diet & Nutrition

Balanced Diet and the Seven Classes of Food

A balanced diet provides an adequate intake of each of the seven classes of nutrients needed to maintain health, support energy demands and allow tissue growth and repair: carbohydrates, fats, proteins, vitamins, minerals, fibre and water.

Diet directly affects a performer's health, body weight and available energy levels, and elite performers must eat to meet the additional energy and repair demands placed on the body by training and competition.

Carbohydrates

• Simple carbohydrates are found in fruit and processed/refined sugary foods and are digested quickly; complex carbohydrates are found in plant-based foods such as bread, pasta, rice and vegetables and are digested more slowly
• Carbohydrate is broken down into glucose, which circulates in the blood and is stored as glycogen in the muscles and liver – a limited store that needs regular replenishment
• Carbohydrates are the body's main energy source across all intensities, and the only fuel that can be broken down anaerobically, making them essential for high-intensity/anaerobic exercise
• The glycaemic index (GI) ranks how quickly a carbohydrate raises blood glucose: low-GI foods (e.g. pasta, beans, cereal with milk) give a slower, sustained glucose release and are best eaten 3-4 hours before exercise; high-GI foods (e.g. fruit, smoothies, cereal bars) give a rapid, short-lived rise and are better suited 1-2 hours before exercise

Fats

• Saturated fats, mostly from animal sources, contribute to weight gain and raised cholesterol if eaten in excess, increasing the risk of coronary heart disease, high blood pressure and diabetes
• Cholesterol is carried in the blood as LDL ('bad' cholesterol, linked to fatty artery deposits and heart disease risk) and HDL ('good' cholesterol, which removes excess cholesterol via the liver)
• Trans-fats, largely created through hydrogenation, also raise blood cholesterol and should be limited to no more than 5g per day
• Unsaturated fats are a healthier alternative and are an important fuel source for prolonged, low-intensity aerobic exercise (e.g. jogging) – fat cannot be used at high intensity since it requires oxygen to be broken down. Fat also carries the fat-soluble vitamins A, D, E and K

Proteins

• Proteins are built from amino acids and are needed for muscle growth and repair, and for producing enzymes, hormones and haemoglobin
• Protein is only a minor energy source, used mainly by power athletes with high muscle-repair demands, or when glycogen and fat stores are depleted
• Good sources include meat, fish, eggs and dairy

Vitamins

• Fat-soluble vitamins (A, D, E, K) come mainly from fatty/animal foods (dairy, oils, eggs, oily fish) and are stored in the liver and fatty tissue for later use
• Water-soluble vitamins (B-complex and C) come from a wide range of foods (fruit, vegetables, dairy) but are not stored, so must be consumed daily – excess is simply excreted in urine
• Vitamin C protects cells and supports healthy connective tissue such as ligaments; Vitamin D supports calcium absorption for healthy bones and teeth (mostly produced via sunlight exposure)
• The B vitamins (B1/thiamin, B2/riboflavin, B3/niacin, B12) work together to release energy from carbohydrate and protein, support red blood cell formation and keep the nervous system healthy
• Good vitamin intake supports a strong immune system, allowing a performer to train at maximum capacity and recover quickly

Minerals

• Minerals dissolve in the body as ions, known as electrolytes, and support functions including nerve impulse transmission and effective muscle contraction
• Calcium builds strong bones and teeth and supports efficient nerve/muscle function
• Sodium helps regulate the body's fluid balance, but excessive intake raises blood pressure and stroke/heart attack risk
• Iron is required to form haemoglobin, supporting oxygen transport; a deficiency can cause anaemia
• Good sources of minerals include meat, fish, eggs, dairy, cereals, vegetables, fruit and nuts

Fibre and Water

• Fibre (found in wholemeal bread/pasta, potatoes, nuts, seeds, fruit and vegetables) slows digestion, producing a more sustained energy release, and prevents constipation by adding bulk to the digestive system
• Water makes up roughly 60% of body weight, transports nutrients, hormones and waste, and helps regulate core body temperature – sweat evaporation cools the body during exercise but also causes fluid loss
• Dehydration occurs when fluid loss exceeds intake and can cause: increased blood viscosity (reducing blood flow to muscles/skin), reduced sweating and rising core temperature, muscle fatigue and headaches, poorer nutrient transport/waste removal, raised heart rate with lower cardiac output, and reduced performance, reaction time and decision-making
• Fluid should therefore be taken on regularly before, during and after exercise – roughly 1.5 litres of fluid per kilogram of body weight lost is recommended for rehydration; sports drinks can raise glucose levels pre-competition while water rehydrates during competition

Glycogen Loading

Glycogen loading (carbo-loading) is a form of dietary manipulation used by endurance athletes to increase muscle glycogen stores above their normal capacity, delaying fatigue in prolonged events.

• Typical protocol: roughly six days before competition, a high-protein diet is combined with high-intensity exercise to deplete existing carbohydrate stores for around three days, followed by three days of a high-carbohydrate diet with lighter training – depleting stores first can allow glycogen to be super-compensated to around double the normal amount
• Positive effects – increased glycogen storage, delayed fatigue, increased endurance capacity
• Negative effects – water retention/bloating and heavy legs during carbo-loading; irritability and disrupted training during the depletion phase; potential digestive upset and weight gain
• Consuming a 3:1 to 4:1 carbohydrate-to-protein ratio (e.g. chocolate milk) within the first 20 minutes after exercise – when the body is most receptive to restoring glycogen – can further enhance recovery, and liquid nutrition also aids rehydration

Creatine Monohydrate

Creatine is a supplement used to increase stored phosphocreatine, the fuel for the ATP-PC energy system, which supplies rapid bursts of energy for up to around ten seconds of high-intensity work.

• Positive effects – helps provide ATP (energy), replenishes phosphocreatine stores, extends how long the ATP-PC system can be sustained, and can improve muscle mass – benefiting explosive event athletes (sprints, jumps, throws) most
• Negative effects – possible dehydration, bloating, muscle cramps, diarrhoea, vomiting and mixed evidence on benefit; can also hinder aerobic performance. Excess intake (over ~5g/day) is often simply excreted in urine rather than used by the muscle

Sodium Bicarbonate

Sodium bicarbonate ('soda loading') is an antacid supplement that increases the blood's buffering capacity – its ability to neutralise the build-up of hydrogen ions and lactic acid during high-intensity exercise, delaying fatigue.

• Most useful for athletes relying heavily on the anaerobic glycolytic (lactic acid) system, e.g. 400m runners, rowers and 100-400m swimmers
• Positive effects – reduces muscle cell acidity, delays fatigue, increases blood buffering capacity
• Negative effects – vomiting, stomach pain/cramping, diarrhoea, bloating – gastric side-effects mean many athletes choose not to use it despite the potential performance benefit

Caffeine

Caffeine is a stimulant that increases mental alertness and reduces the perception of fatigue, and is thought to increase the mobilisation of fatty acids, sparing glycogen stores – of particular benefit to endurance athletes relying on the aerobic system.

• Research suggests around 3mg of caffeine per kg of body weight produces the greatest performance benefit (roughly equivalent to three cans of cola per 100mg). Found in coffee, tea, cola, chocolate, energy bars and caffeinated gels
• Positive effects – increased alertness, reduced fatigue, greater use of fat as fuel (sparing glycogen), improved decision-making/reaction time, aerobic/endurance performance benefits
• Negative effects – loss of fine motor control, restricted in large quantities under many sports' rules, and possible dehydration (as a diuretic), insomnia, muscle/stomach cramps, vomiting, irregular heartbeat and diarrhoea