Carbohydrates, glycogen and performance

One of the main reasons that carbohydrate is often removed from the diet when people are trying to lose weight is that, unlike certain fatty and amino acids found in dietary fats and protein, the body can survive without dietary carbohydrates. Therefore, it makes some sense to look to restrict calorie intake by manipulating carbohydrate whilst maintaining more essential nutrients in the diet.


However, is cutting carbohydrate from the diet completely necessary?

Well the answer to that is a resounding no… the fact is that for weight loss, although we need to be in a calorific deficit, that we can still achieve this with carbohydrates in the diet. In fact for those who take part in regular, high-intensity exercise, carbohydrate can be very beneficial. By keeping moderate amounts of carbohydrates in the diet we can hopefully keep our training output high, increase our calorie expenditure and preserve our strength, muscle mass and performance which is particularly important for competitive athletes and bodybuilders.


It should also be clear that under normal training conditions, for many sports when weight loss is not the goal, then carbohydrates are an essential part of a diet that is geared towards optimising performance… but why?


Why are carbohydrates are an essential part of a diet?

This comes back to how our body uses energy during exercise. At rest and during low-intensity exercise fat is the primary fuel source, with a small contribution coming from either glucose, or glycogen stored in the muscles. The reason why fat is the primary fuel source here is that we can provide the body with enough oxygen to use fat as a fuel. The process of using fat, or specifically fatty acids, as a fuel source is called beta-oxidation and this requires a steady and large supply of oxygen. As we increase our exercise intensity we start to switch more from fatty acid usage to carbohydrates as this requires less oxygen to ‘oxidise’ and produce energy (a process called aerobic glycolysis), in fact at very high intensities we can produce energy from glucose without the need for oxygen (anaerobic glycolysis).

 As we increase our exercise intensity we start to switch more from fatty acid usage to carbohydrates

Therefore, at higher intensity exercise we are reliant heavily on anaerobic glycolysis and the most readily available source of glucose is that stored as glycogen in the muscle cells that are doing all the work. Unlike aerobic glycolysis, not all the energy in the glucose released from glycogen is ‘used up’ as it does not get transported into the energy-producing parts of the cell which require oxygen to do their thing. Instead, it produces lactic acid which, although releases a small amount of energy, is normally an intermediary step in aerobic glycolysis. Unfortunately, as there is not enough oxygen present in the body to complete this step, lactate starts to accumulate and is then shipped outside the muscle cell into the blood stream. Despite lactate being seen as a waste product, it is in fact recycled back into glucose in the liver, to be recirculated back to the tissues that need it.


Obviously if we are training at higher intensities, and are going to be using muscle glycogen as a primary source of fuel, then by restricting carbohydrate we are not going to replenish stores, and eventually performance will likely be impaired and training output reduced. This is often an inevitability side-effect of dieting for physique competitions, as when trying to achieve levels of body fat, carbohydrate intake will have to be restricted at some point which will ‘flatten’ out the physique and optimise fat loss to get rid of the final few ounces of body fat. However, even in this situation, normally they will take part in weekly higher carb or refeed days, to restock glycogen, help to maintain performance and hopefully protect against loss of muscle tissue.


There is no good reason to remove carbs

For athletes who are concerned only with performance then there is no good reason, as far as I’m concerned, to remove carbohydrates from the diet as long as they are appropriate to a person’s energy requirements and tailored to the overall demands of the sport. Like protein intake, it is the overall carbohydrate intake over the course of the day that will influence glycogen storage levels. However, like protein there is also an argument to be made that consuming a good proportion of our carbohydrate post training will be of benefit. This is because our glucose transporters, which are normally activated by insulin to allow glucose to enter our cells, are also activated without the need for insulin for around 1 hour after exercise and this coincides with much greater rates of glycogen synthesis.

For athletes who are concerned only with performance then there is no good reason, as far as I’m concerned, to remove carbohydrates

What is the optimal glycogen refuelling?

It is suggested that for optimal glycogen refuelling that 1-2g per kg of bodyweight of carbohydrate are consumed post workout from fast digesting carbohydrate sources, such as Vitargo or highly branched cyclic dextrin for example, with the rest of the carbohydrate requirements being made up at a similar rate over the coming hours. Obviously, this will depend on the duration and intensity of exercise, a person’s goals and if any carbohydrate refuelling has taken place during the exercise itself. This also highlights that exercise is important for overweight people as it improves the body’s response to carbohydrates, which may be important for those with poor insulin sensitivity.


For those who don’t require massive amounts of carbohydrate to refuel, then ingesting protein from a fast digesting source, such as whey or EAA’s, can help with glycogen synthesis as this will stimulate the release of insulin and help with the uptake of glucose into the cells even more efficiently. This also highlights that we do not necessarily need to take carbohydrates with protein post-workout, as long as we have an adequate amount. This is because the insulinogenic (insulin producing response) from 30-40g of whey alone is enough to maximise protein uptake without the need for added carbohydrates. However, for the reasons we have discussed in this article, why wouldn’t we want to take on carbohydrate during this post-workout period is beyond me, as this is the time the body is primed for glycogen storage, refuelling and recovery.


For any nutrition or supplement advice feel free to contact us at CSN where we would be more than happy to help.