Nutrition for Sport

According to Greg Cox,  (De Castella, Clewes, & Dalgleish, 1996) there is a common perception that athletes eat appropriately to meet their exercise demands.  He contends that frequently, this is not the case.

The Effect of Good Nutrition

Carbohydrates

Most athletes today are aware that carbohydrate in their diet is essential for optimal sports performance during heavy training periods and busy competition schedules.  However, this awareness often fails to translate into appropriate eating strategies.  Athletes need to make informed food choices to ensure their carbohydrate intake keeps pace with their daily carbohydrate requirements.

Carbohydrates provide the most readily available source of energy to fuel working muscles during most types of exercise.  Eating adequate carbohydrate throughout the day is equally important for sprint and endurance athletes.  Insufficient carbohydrate in the diet results in decreased glycogen stores (Stored carbohydrate) which may jeopardise exercise performance and cause early fatigue.  Adequate glycogen stores in the muscle and liver are essential to maintain exercise performance during training and competition.  The more you exercise the greater your carbohydrate needs.  The amount of carbohydrate needed daily is determined by your level of activity and body weight.  Athletes who train daily (or twice daily) have the greatest requirements.

Those of you who are mathematically minded can calculate your own daily carbohydrate needs by using Table 1.  For example, the estimated daily carbohydrate requirements of an 85kg football player averaging 1 -2 hours of daily training, including weights, conditioning and team practice = 6 – 8 g/kg body weight.

 

General Exercise (up to 60 mins of daily exercise)	5 – 6 g/kg Body Weight
Moderate Exercise (1 – 2 hours moderate to high intensity training)	6 – 8 g/kg Body Weight
Endurance Exercise (more than 120 mins high intensity training)	9 – 10 g/kg Body Weight
Extreme Exercise (more than four hours of intense exercise)	11 – 13 g/kg Body Weight
Adapted from Louise Burke, The Complete Guide to Food for Sports Performance. 1995. Allen and Unwin, Sydney. (2nd Ed.)

Table 1 Estimated Daily Carbohydrate Requirements Expressed as Grams per Kilogram of Body Weight

Note this is expressed as per kilogram of body weight.  To work out total carbohydrate requirements you need to multiply carbohydrate requirements per kilogram by body weight.  In the case of the football player, body weight is 86kg.

6 – 8 g/kg x 86 = 510 – 680g of carbohydrate per day.

(De Castella, Clewes, & Dalgleish, 1996)

An infinitely more important reason for consuming adequate carbohydrates during the day, is to ensure our brain is functioning at its optimal level.  The brain, unlike other organs, can only use glucose as an energy source.  The glycogen that the body synthesises during the breakdown of carbohydrates, is the precursor to the brain’s sole source of energy, glucose. 

As a carbohydrate travel through the gastro-intestinal tract, it is broken down into simpler, and more easily distributed glycogen molecules.  The glycogen that can be immediately utilised by the muscles will be directed to those areas of most need.  The remainder will be either stored in the liver, continue to circulate in the blood stream until needed or, broken down further into glucose molecules.  The glucose molecules circulate in the blood stream and are drawn from the blood stream into the brain.  The brain’s reliance on glucose explains the “fuzzy head” phenomenon we experience when we become hypo-glycemic or, experience a “sugar flat”.

Protein – How Much is Enough?

Protein is essential for normal growth and development, plays a vital role in the repair and recovery of damaged tissues (such as muscle), and acts as a fuel source during exercise, especially when carbohydrate stores are depleted.  Athletes require more protein than the recommended daily intake for the sedentary population. 

It is generally agreed that athletes involved in light exercise require 1.0g of protein per kilogram of body weight.  Strength and endurance trained athletes require daily protein intakes of approximately 1.2g – 1.6g per kilogram of body weight.  So the approximate protein requirements for an elite 65kg middle distance runner training twice daily would be 78 – 104g of protein per day (65 x 1.2 – 1.6 = 78 – 104).  A 90kg weight-lifter training once a day in the gym would require approximately 108 – 144g of protein per day.

Despite their increased protein requirements, most athletes easily meet their daily protein needs simply by following a balanced diet.

(De Castella, Clewes, & Dalgleish, 1996)