Purpose of Carbohydrates
Why eat Carbohydrates?
Carbohydrates are the predominant fuel for muscles as the majority of activity relies on glucose (carbs) for energy. There is no physiological function of carbohydrates for them apart from energy. It is also the preferred fuel for the heart, nervous system and brain that use ~130g daily.
How much do you need?
It depends on your goals, the amount of exercise and intensity you train at. The longer and harder you train the more you need. For example, if you do moderate activity (swim, run, cycle) for an hour a day then you should aim to consume 5-7g/kg of body weight daily for optimum nutrition.
What if you over or under eat Carbohydrates?
Under Eating
Low carbohydrate diets or exercising with low stores can result in early fatigue, reduced stamina and poor performance. I.e. Have you ever ran or swam on an empty stomach? If you eat too few after training recovery will be impaired and extended, symptoms of over training may become present.
Over Eating
Once eaten carbohydrates are converted into glycogen and stored in your liver and muscles. These stores are small and can only store around 100g (400calories) in liver and 400g (1600 calories) in muscles. Once your stores are ‘full’ the body converts excess carbs into fat. More carbs does not equal more energy, similar to overfilling a fuel tank won’t make your car go faster.
The Sugar Debate
Performance
Sugar can aid performance that lasts over 60minutes and muscles need quick fuel. Consuming a sports drink/banana/ dried fruit can help perform longer or maintain intensity. It is not necessary for shorter sessions. Eating too much or poorly timed intake can lead to too much insulin being created by the body, leading to lower blood glucose levels than before and feelings of tiredness, weakness and lightheaded. It is ‘safer’ to consumer a low GI meal 2-4hours before exercise or only consume small amounts of sugar prior to exercise.
Health
The main issue is that sugar leads to tooth decay. It also makes food and drink more palatable and therefore more easy to over-consume. It is not fattening, but can lead to over-consumption of calories. his is linked to obesity and type 2 diabetes, but main contributor of this is excess calories not sugar.
Glycaemic Index
Glycaemic Index is the ranking of foods from 0-100 based on their immediate effect on blood sugar levels in the bloodstream. Carbohydrates used to be classified as simple or complex according to number of sugar units in the molecule. But this tells little about the effect on the blood glucose level.
What use is GI?
You can use the GI of foods to plan intake around your training and competition. High GI means fast release and fast energy. Eat low or moderate GI meals in your day to day. This regulates blood glucose and insulin levels, promotes recovery and keep energy levels constant. Also lowers the risk of type 2 diabetes and cardiovascular disease.
GI does not take into account portion size. You can use Glycaemic load (GL) instead.
GL= (GI x carbohydrates per portion) / 100.
For optimal glycogen storage and minimal fat storage aim to achieve a small or moderate glycaemic load – eat little and often. Some foods may have a low GI, such as Crisps, but can easily be over eaten. While high GI such as Watermelon, you would need to eat 720g to raise blood glucose significantly, while he average portion is 120g and only provide 6g of carbs so has no effect.
Which GI and When
Low GI (<55)
Your main meals throughout the day should be low to moderate GI. This provides a smaller but longer rise in your blood glucose, providing energy throughout the day.
Examples of Low GI foods include:
Peanuts (14), Whole Milk (27), Skimmed Milk (32), Spaghetti (38), Milk Chocolate (43), Carrots (47), Banana (52), Crisps (54), Brown Rice (55)
Moderate GI (56-69)
Your main meals throughout the day should be low to moderate GI. This provides a smaller but longer rise in your blood glucose, providing energy throughout the day. Moderate GI meals will provide more energy that low GI meals and should be consumed when you have an activity packed day.
Examples of Moderate GI foods include:
Pitta bread (57), Porridge (58), Pizza (60), Tortillas (63), Couscous (65), Instant porridge (66), Croissant (67), Weetabix (74)
High GI (>70)
High GI food is ideal for when you need quick energy. Examples of such a situation include, just before a race or during an event that lasts over an hour. These foods provide a rapid rise in blood glucose. However, if you mistime or over-consume high GI food it can led to a rapid rise in insulin leading to lower blood glucose levels than before and feelings of tiredness, weakness and lightheaded. It is ‘safer’ to consumer a low GI meal 2-4hours before exercise or only consume small high GI snack prior to exercise.
Examples of High GI foods include:
White bread (70), Wholemeal bread (71), Watermelon (72), Cheerios (74), Chips (75), Cornflakes (81), Baked potato (85), Lucozade (95)