DIETICIAN FAQ


Are foods with a low glycaemic index better? 


Is exercising on an empty stomach better for weight loss? 

Which supplements enhance the immune system?

How can dehydration be avoided? 

What is considered safe/ harmful weight loss?

Should protein be added to sports drinks? 

Do high fat diet to increase fat-burning capacity or to increase training adaptations?

How much caffeine is necessary to enhance performance?

1. Are foods with a low glycaemic index better?
The type of carbohydrate in food or drinks can have varying affects on blood glucose levels. High glycaemic carbohydrates provide a rapid release of glucose into the blood stream which is short lived while low glycaemic carbohydrates provide a slower release of glucose which is sustained over a longer period of time. It is assumed that low glycaemic carbohydrates consumed in a pre-exercise meal are more useful during exercise as they provide a more sustained release of glucose which delays the onset of hypoglycaemia (low blood glucose levels). However, research on the performance benefits is inconclusive and athletes need to be aware of their body’s response to high or low glycaemic carbohydrates before exercise.

Reactive hypoglycaemia occurs when insulin levels increase in response to the blood glucose level. Insulin clears glucose from the blood into muscle cells and when this coincides with the start of exercise, blood glucose levels dip. However, very few athletes experience reactive hypoglycaemia as the body will quickly correct this dip without any symptoms. Athletes who are more sensitive to this drop in blood glucose levels and feel that their performance is affected can overcome these symptoms by:
  • experimenting to find the best time to eat or drink before exercise.
  • consume smaller amounts of carbohydrate to reduce the insulin response.
  • consume a low glycaemic carbohydrate before exercise such as a fruit smoothie, rye toast, small amount of pasta, original Pronutro
  • consume small amounts of carbohydrate, regularly during exercise.
  • It is important to remember that many low GI options foods such as muesli, All Bran Flakes, wholegrain bread, baked beans are high in fibre and are more likely to cause stomach discomfort during exercise.

2. Is exercising on an empty stomach better for weight loss?
Exercising in a fasted state can result in a larger proportion of fat being used as fuel to your exercising muscles. However, eating before exercise may help you to exercise for longer or to a greater intensity enabling you to use up more energy (kilojoules) in the exercise session. Your exercise goals can help you to decide whether you should to eat before exercise, if your goal is to improve performance you should consume a carbohydrate but if your goal is to loose weight and you do not feel fatigued you should avoid eating before exercise.

3. Which supplements enhance the immune system?
In general, the immune system is suppressed by intensive training, with many parameters being reduced or disturbed during the hours following a work-out. This may place athletes at risk of succumbing to an infectious illness during this time. Many nutrients or dietary factors have been proposed as an aid to the immune system - for example, vitamins C and E, glutamine, zinc and most recently probiotics - but none of these have proved to provide universal protection. The most recent evidence points to carbohydrate as one of the most promising nutritional immune protectors. Ensuring adequate carbohydrate stores before exercise and consuming carbohydrate during and/or after a prolonged or high-intensity work-out has been shown to reduce the disturbance to immune system markers. The carbohydrate reduces the stress hormone response to exercise, thus minimising its effect on the immune system, as well as also supplying glucose to fuel the activity of many of the immune system white cells.

4. How can dehydration be avoided?
Losing only 2% of body weight can impair performance (i.e. only 1.4kg for a 70kg cyclist). The longer the ride, the greater the risk for developing dehydration which can impair performance. This is critical on race day but also a disadvantage to a good training ride. The key is to drink enough fluid to match sweat losses which is different for each individual cyclist and the environmental conditions. A good guideline is to measure your fluid losses by weighing yourself immediately before and after a cycle and take into account the fluids you have consumed during the ride. 1kg weight loss is approximately equivalent to 1L sweat losses.


To replace lost fluids, you should drink approximately 1.5 times the volume of fluid lost i.e. if you lost 1 kg on the cycle, you should drink approximately 1.5 Litres during recovery.

Tips:
  • Drink 1.5 to 2 Litres of water or non-caffeinated tea per day.
  • During a ride, start drinking early on in the ride and regularly in amounts that are comfortable.
  • Try to perfect your hydration strategy on a training ride that mimics race day conditions.

 

5. What is considered safe/ harmful weight loss?
This following weight loss techniques are may result in rapid weight loss but are likely to impair performance weight loss methods:
  • Completing long training rides without consuming carbohydrates or under consuming carbohydrates,
  • Consuming carbohydrate during a long ride but neglecting the recovery drink/ meal,
  • Suppressing appetite with diet drugs,
  • Restricting food intake during the day in between rides.

To avoid these performance problems in the pursuit of leanness, weight loss should be achieved by a long term program that creates a small calorie deficit (decreasing caloric intake or increasing energy output from training or both). Weight loss of 0.5 to 1kg per week can be achieved by creating a calorie deficit of approximately 500 kcal to 1000kcal, provided the diet is well balanced nutritionally adequate. Of course each cyclist requires an individual approach depending on the amount of weight to be lost, the stage in their training program, their existing diet, race day nutrition strategy, rate of recovery, existing medical conditions etc. A more conservative approach to weight loss is more likely to result in long term maintenance of the weight lost. 

6. Should protein be added to sports drinks?
The potential effects of a combined carbohydrate-protein sports drink during endurance exercise remain controversial. The main reasons for using a sports drink for endurance exercise is to spare glycogen stores (with the carbohydrate) to prolong the time to fatigue as well as reducing the risk for dehydration (fluid and electrolytes). Protein in combination with a carbohydrate sports drink does not appear to contribute significantly to these factors to enhance performance. However, some studies have shown that adding protein to a carbohydrate based sports drink may promote post-exercise recovery. The protein in the sports drink appears to reduce markers of muscle damage thereby enhancing recovery which could potentially improve performance in subsequent exercise. This is effect is the desired effect which can be achieved with a post-exercise, recovery drink/meal. The case remains open and can both sides are supported. 

7. Do high fat diet to increase fat-burning capacity or to increase training adaptations?
Short term “high fat, low carbohydrate” diets appear to have a negative effect on performance given the depletion of glycogen stores. However, long term adherence to a “high fat, low carbohydrate” diets are associated with adaptations that enhance fat oxidation during moderate to sub-maximal exercise. Theoretically, this is the answer for improved performance in endurance and ultra-endurance exercise but clear evidence in a practical setting is lacking. It is suggested that some athletes may be considered “responders” and others “non-responders” to the “high fat, low carbohydrate” dietary manipulation and further studies are required. 

8. How much caffeine is necessary to enhance performance?
The optimum dose of caffeine for enhancing exercise performance is 200 mg (or approximately 3 mg per kg body weight). Caffeine should be taken 45-90 min before exercise and the performance enhancing effects are evident for 2 to 4 hours of exercise. The mechanism for these ergogenic (performance enhancing) effects appear to be related to the central nervous system by reducing the perception of pain, exertion and fatigue. If exercise continued beyond 4 hours, lower doses of caffeine are necessary for a similar benefits to performance. It appears that the brain is more sensitive when fatigued and less caffeine is needed. Studies have shown that there are very few negative side-effects (such as anxiety, dizziness, nausea, tremors, dehydration etc) when taking caffeine at a dose of 200 mg although athletes should remain cautious.



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