Carbohydrates: performance AND health

The new year brings with it many goals to “lose weight”, well, normally people do mean fat mass but I digress. This has resulted in many gyms/PT’s offering “nutrition challenges” to their clients which tend to promote their own adaptation (miscomprehension) of the paleo diet. Many of these challenges suggest reducing carbohydrate (CHO) intake to extremely low levels and this then affects both health and performance. With this in mind, I want to take some time to discuss the effect that CHO has on health, namely, on immune function. I believe this is timely not just because of the “new years resolutions” but because at this time of the year many of us get ill which affects our training and probably just pisses you off full stop.

1.1 Exercise and Immune Function

The relationship between the risk of infection from a pathogen and exercise has been modeled as a “J” shaped curve. This model suggests that periods of prolonged and strenuous exercise may impair immune function. This exercise-induced immune dysfunction appears to be linked to the immunosuppressive action of stress hormones such as cortisol. It has been suggested that a decrease in blood plasma glucose during exercise leads to an increase in the stress hormone cortisol which leads to a decrease in T-lymphocyte function.

1.1.1 Carbohydrate, Exercise and Immune Function

It is clear that an adequate amount of carbohydrate (CHO) availability is a key factor for maintenance of heavy training schedules and successful athletic performance. Glucose is an important substrate for immune cells because metabolic rates of immune cells are extremely high. High levels of stress hormones such as cortisol and catecholamines (epinephrine, norepinephrine) not only occur during high intensity exercise but also depend on glucose availability. Low levels of blood glucose concentration during prolonged exertion are associated with higher levels of cortisol and epinephrine. The immunosuppressive effects of acute and chronic stress and high levels of stress hormones are well established. Thus, the underlying rationale is that adequate CHO availability and stable blood glucose concentration may limit stress hormone responses, provide glucose as energy substrate for immune cells and help to maintain immunity.

1.1.2. Availability of Dietary Carbohydrate

It has been shown that exercising on a high-CHO diet vs a low-CHO diet leads to an increase or stable blood glucose level. Plasma cortisol levels may be decreased and the post-exercise glutamine level may rise or stays unaffected. A high-CHO diet during times of intensified training for six days may have a favorable effect on immunity.

Training on low levels of CHO availability may raise the magnitude of exercise-induced immune alterations, such as higher plasma and salivary cortisol levels which ultimately leads to impaired performance.

Although limited evidence exists, it should be highlighted that exercising in a carbohydrate-depleted state, results in higher levels of circulating stress hormones, greater perturbations of immune cell subsets and an impaired immune function. Putting this in to context, if you begin to train in a CHO-depleted state you will experience an increased heart rate, you will fail to increase muscle mass as your body will be in a catabolic state and you will have a much greater chance of becoming ill which is detrimental to both health and performance. Keeping the muscle and liver glycogen stores full is therefore a crucial factor.

So, if you want to be able to optimise your training and remain healthy for as long as possible this year then do not exclude CHO from your diet. CHO is the fuel for athletic performance and immune system health.

References

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