Nutrients in sports training
An important aspect of nutrition is the daily intake of nutrients.
Nutrients consist of various chemical substances in the food that makes up each person’s diet.
Many nutrients are essential for life, and an adequate amount of nutrients in the diet is necessary for providing energy, building and maintaining body organs, and for various metabolic processes.
People depend on nutrients in their diet because the human body is not able to produce many of these nutrients—or it cannot produce them in adequate amounts.
THE THREE FUNCTIONS OF NUTRIENTS
• Lipids (fats and oils)
Promote growth and development
Regulate body functions
There are six major classes of nutrients found in food:
• Lipids (fats and oils)
• Vitamins (both fat-soluble and water-soluble)
Carbohydrates are the major source of energy for the body.
They are composed mostly of the elements carbon (C), hydrogen (H), and oxygen (O). Through the bonding of these elements, carbohydrates provide energy for the body in the form of kilocalories (kcal), with an average of 4 kcal per gram (kcal/g) of carbohydrates.
Carbohydrates come in a variety of sizes. The smallest carbohydrates are the simple sugars, also known as monosaccharides and disaccharides, meaning that they are made up of one or two sugar molecules.
The best known simple sugar is table sugar, which is also known as sucrose, a disaccharide.
Other simple sugars include the monosaccharides: glucose and fructose, which are found in fruits.
The disaccharides, which include sucrose, lactose (found in milk), and maltose (in beer and malt liquors).
The larger carbohydrates are made up of these smaller simple sugars and are known as polysaccharides (many sugar molecules) or complex carbohydrates. Nutrients in sports.
These are usually made up of many linked glucose molecules, though, unlike simple sugars, they do not have a sweet taste.
Examples of foods high in complex carbohydrates include potatoes, beans, and vegetables.
Another type of complex carbohydrate is dietary fiber. However, although fiber is a complex carbohydrate made up of linked sugar molecules, the body cannot break apart the sugar linkages and, unlike other complex carbohydrates, it passes through the body with minimal changes.
Although carbohydrates are not considered to be an essential nutrient, the body depends on them as its primary energy source.
The body utilizes most carbohydrates to generate glucose, which serves as the basic functional molecule of energy within the cells of the human body (glucose is broken down to ultimately produce adenosine triphosphate, or ATP, the fundamental unit of energy).
When the supply of carbohydrates is too low to adequately supply all the energy needs of the body, amino acids from proteins are converted to glucose.
Carbohydrates are an important fuel source. In the early stages of moderate exercise, carbohydrates provide 40 to 50 percent of the energy requirement. As work intensity increases, carbohydrate utilization increases.
Carbohydrates yield more energy per unit of oxygen consumed than fats.
Because oxygen often is the limiting factor in long duration and high intensity events, it is beneficial for the athlete to use the energy source requiring the least amount of oxygen per kilocalorie produced.
Depending on the intensity, duration, and frequency of exercise, in general athletes should consume between 6-10 grams of carbohydrates per kilogram of body weight per day. (A kilogram equals 2.2 pounds.).
Athletes training at high intensities for more than 3 hours per day may need to consume 7–10 or more grams of carbohydrate per kg body weight per day to meet their energy demands.
Smaller and lighter athletes such as gymnasts, divers and skaters may need as little as 4–5 grams of carbohydrate per kg of body weight per day.
Because these athletes are eating smaller amounts, they need to select especially nutrient dense carbohydrate foods.
Carbohydrate requirements are also affected by the athlete’s sex and body mass, as well as total daily energy expenditures and environmental conditions.
The main role of carbohydrates is to provide energy.
When they are digested, carbohydrates are broken down into glucose to provide readily available energy for the body to use quickly and effectively.
Carbohydrates are the most important form of fuel for exercise and sports activities.
The body can store carbohydrates in the muscles and liver as glycogen, and use these stores as a source of fuel for the brain and muscles during physical activity.
These glycogen stores are limited, so it is important to be fully fuelled at the start of any exercise. By not having adequate carbohydrate in your diet for exercise, you may feel tired and lacking in energy and not be able to perform at your best. So, regular intake of carbohydrate-rich foods is important to keep stores topped up.
The correct food choices can help ensure the body has enough energy for activity, as well as help aid recovery.
Which foods are good sources of carbohydrate?
Many everyday foods and fluids contain carbohydrate, but have different features. For this reason, carbohydrate-containing foods and fluids are often divided into categories for comparison.
Previously, carbohydrates were classified as either simple or complex, and more recently, the terms low and high glycemic index (GI) are being used.
From a sports nutrition point of view, it is more helpful to classify carbohydrates as nutrient-dense, nutrient-poor or high-fat.
|Category||Description||Examples||Use for athletes|
|Nutrient-dense carbohydrate||Foods and fluids that are rich sources of other nutrients including protein, vitamins, minerals, fibre and antioxidants in addition to carbohydrate||Breads and cereals, grains (e.g. pasta, rice), fruit, starchy vegetables (e.g. potato, corn), legumes and sweetened low-fat dairy products||Everyday food that should form the base of an athlete’s diet. Helps to meet other nutrient targets|
|Nutrient-poor carbohydrate||Foods and fluids that contain carbohydrate but minimal or no other nutrients||Soft drink, energy drinks, lollies, carbohydrate gels, sports drink and cordial||Shouldn’t be a major part of the everyday diet but may provide a compact carbohydrate source around training|
|High-fat carbohydrate||Foods that contain carbohydrate but are high in fat||Pastries, cakes, chips (hot and crisps) and chocolate||‘Sometimes’ foods best not consumed around training sessions|
Daily Needs for Fuel and Recovery:
|(body mass or BM)|
|Light||Low-intensity or skill-based activities||3–5 g per kg BM|
|Moderate||Moderate exercise programme (~1 hr / day)||5-7 g per kg BM|
|High||Endurance programme (i.e. moderate-to-high intensity exercise of 1-3 hr / day)||6-10 g per kg BM|
|Very High||Extreme commitment (i.e. moderate-to-high intensity exercise of >4-5 hr / day)||8-12 g per kg BM|
Sporting performance and glycaemic index
To determine the effect a certain carbohydrate will have on the body, nutritionists have developed the Glycemic Index.
This is a method for determining the response of blood-sugar levels to various carbohydrate-rich foods.
As a general rule of eating, foods with lower glycemic index values can help you maintain a more stable blood-sugar level.
In addition, these foods help prevent the overproduction of the hormone insulin, which is often associated with a rapid decrease in blood-sugar levels followed by a feeling of physical or mental fatigue.
The glycemic index rating system is important for athletes for two main reasons:
• First, it indicates the metabolic consequences that different foods can have on the body.
• Second, it helps to determine which foods should be consumed in relation to exercise sessions.
Glycemic index explains how carbohydrate containing foods, when eaten alone, affect the body’s blood sugar level.
The glycemic index is a measure of how fast a carbohydrate food is digested, absorbed and used by the body.
Some carbohydrate foods supply glucose slowly over time while other foods increase blood glucose level quickly.
High glycemic index foods increase blood sugar levels faster than low glycemic index foods.
Glycemic index applies only when single foods are eaten.
Adding other foods containing carbohydrate, fibre, protein, or fat changes how slowly or quickly glucose enters the blood stream.
Athletes can choose carbohyd rates with a low glycemic index in the following situations:
• In the meal hours before or after exercise, a low glycemic index carbohydrate food provides energy over a long time.
• Because blood sugar level influences appetite, foods with a lower glycemic index satisfy you longer, delaying hunger.
Athletes may choose carbohydrates with a high glycemic index for the following situations:
• A high glycemic index food eaten within 60 minutes before exercise increases the blood glucose level. To benefit, the athlete must keep the blood glucose level high by consuming a sport drink until exercise starts.
• During exercise, high glycemic index foods are digested and absorbed quickly, increasing blood glucose.
• In the first couple hours after exercise, high glycemic index foods are useful for rapid muscle glycogen storage.
This is important for multiple training days or between events or games.
While the recommendations provided above consider the overall carbohydrate needs over the day. It is also important to consider the timing of carbohydrate around training and competition.
Carbohydrate ingestion before exercise should assist in topping up blood glucose levels as well as glycogen stores in the muscle and liver. This is especially important if the competition or training is undertaken first thing in the morning or if the event is high intensity or will continue beyond 90 mins in duration.
Carbohydrate intake after exercise is essential for optimum recovery of glycogen stores. Often athletic performance is dependent upon the ability to recover from one session and do it all again in the next session. Incomplete or slow restoration of muscle glycogen stores between training sessions can lead to a reduced ability to train well and a general feeling of fatigue.