The current recommendations for sports nutrition: A risk factor for health?

No matter if recreationally active or performing at an elite level, the common recommendation for athletes is mostly the same and relies on a diet that is composed of 6g to 12g of carbohydrates per kg bodyweight per day (Vitale et al., 2019).  These recommendations are based on the demands of elite endurance athletes but seem to be universally accepted for most athletes (Burke et al., 2011).  This habitual recommending of a high carb intake across a wide spectrum of fitness levels and disciplines could be the cause of unexpected health consequences, which this article will try to highlight. 

The recommendation of high levels of dietary carbohydrates stems from the athletic world where milliseconds decide over defeat or victory.  In a long standing history of scientific research it has been proven that this form of diet seems to be superior when it comes to performance outcomes (Brewer et al., 1988; Williams et al., 1992).  And as these high-performance athletes are seen as the epitome of healthy humans, it seems to be logical to recommend the same way of eating to humans that are not even close to high level athletic performance, if at all.  If eating like this helps people to run fast, and fast running humans must be healthy humans, then everybody who is somewhat physically active must eat the same way to be equally healthy and performant.  But there might be a problem with that assumption.  Elite athletes are per definition blessed to have (acquired through years of training and genetical predisposition) physiological properties that are superior to the rest of the population.  Properties like lean muscle mass/ low body fat, high capacity to utilise oxygen, tendons with a high capacity to store kinetic energy, high levels of explosive strength, and a high capacity to store energy as muscle glycogen, to name just a few.  Clearly not every athlete or human has the same properties, yet the dietary recommendation seems to be the same for everyone who is physically active.  To make matters worse it even seems as if some of these high-performance athletes are also not that healthy after all.  So was revealed that among marathon runners outcome measures like all-cause mortality and cumulative six-year cardiac events were not different, and markers like CAC score and myocardial fibrosis were indeed higher than in the non-athletic control group (Noakes, 2014).  Another interesting investigation by Needleman (2013) found that the dental health of Olympic athletes was poor which resulted in substantial negative impacts on training and performance.  Add to the previous two points these reports of individuals being active their entire life and still developing insulin resistance (which is a condition that can develop into type-2 diabetes) in their mid-life and it becomes clear that there might be something afoot (Coaching, 2021).  Central to all these health problems is sugar and the dietary intake of carbohydrates, and the point can be made that the recommended intake thereof might be in a causal relationship to the conditions described here.  Complex carbohydrates are just long chains of single sugars, and the body utilises them by breaking these chains into single sugars known as glucose.  This happens to rice, pasta, potatoes, and bread (all complex carbs), which all end up as glucose in the bloodstream.  The resulting blood glucose is directed into the cells through insulin secretion.  This is necessary because under normal conditions the amount of glucose in the blood is not higher than 4g in total or 70–100 mg/dL and is tightly controlled by the pancreas (insulin secretion) and the liver (glucose secretion) (Murray & Rosenbloom, 2018).  The storage capacity of a typical 70kg man consists of 300g muscle glycogen and 100g liver glycogen (Maughan & Gleeson, 2010).  According to sports nutrition recommendations though, a moderately active man (1 hour per day) of 70kg is supposed to ingest up to 490 grams of carbohydrates per day, which is the equivalent of 2.88kg of boiled potatoes (Vitale et al., 2019).  This will lead to an acute temporary increase of blood glucose and insulin levels, probably several times a day, which can lead to several unexpected health consequences.

The most obvious consequence of this type of diet is the potential to develop insulin resistance which, if undiagnosed, will lead to type-2-diabetes mellitus (Ma et al., 2014).  As a result of the constant presence of insulin in the bloodstream, muscle cells and other tissues lose their sensitivity to the insulin signalling, which results in a delayed removal of blood glucose, and the pancreas tries to compensate by secreting more insulin until the pancreatic β-cells literally burn out (Malone & Hansen, 2019).  Additionally, the constantly elevated insulin levels provoked by blood glucose have a hypertrophic effect, especially on fat cells (lipohypertrophy) (Chowdhury & Escudier, 2003).  Another detrimental effect of a very high carbohydrate diet as recommended for sports is the widely accepted problem with dental health in athletes following such diet (Ashley et al., 2015; Bryant et al., 2011; Sirimaharaj et al., 2002).  These dental problems are not just inconvenient but can often have negative impact on performance and overall health (Needleman et al., 2013).  Most astonishing though is the oddity of the occurrence of heart disease among marathon runners which seems paradoxical at first (Schwartz et al., 2014), until the following is understood.  Emerging evidence shows that the associated risk of high levels of LDL cholesterol for heart disease is more closely related to the amount of ingested carbohydrates than fat (Alique et al., 2015).  This paper from Alique (2015) explains how the glycation (glucose sticking to the surface of other molecules, especially proteins) of lipo-proteins leads to a malfunctioning of signalling molecules (ApoB) on their surface, with the result that the immune system has to respond in order to remove them (macrophage).  These glycated molecules are called advanced glycation end products (AGEs) and lead to heart disease as a result of systemic inflammation, and a host of other problems.  For example, the prevalence of tendinopathy in long distance endurance athletes and team sport athletes is high, with a majority affecting the larger tendons like the Achilles, and patella tendon (Lagas et al., 2019; Maffulli et al., 2003).  The current view on the occurrence and development of these injuries is that excessive loading, insufficient recovery and sudden changes in training or match intensity is causing the collagen fibres of the tendon to lose their parallel orientation, to separate, to decrease in diameter, and to lose overall density and thus the ability to tolerate load (Maffulli et al., 2003).  It is also characteristic for proliferation of capillaries arterioles and sensory nerve innervation which is responsible for the pain in people affected by tendinopathy (Maffulli et al., 2003).  In addition to mechanical loading and intensity management it seems that also the presence of AGEs in the body can have an effect on tendon health.  High levels of blood glucose leads to AGEs formation which can interfere with the collagen matrix reconstruction of tendons, through a process of non-enzymatic glycosylation of collagen with AGEs formation according to Abate (2013).  The result is that AGEs that are being embedded in the tendon lead to a disorganised collagen matrix which causes inferior biological and mechanical function:  AGEs already engulfed within the tendon can only be removed together with the collagen they are attached to, which is a slow process already (natural slow turnover rate within tendon tissue), but is further negatively affected by higher levels of blood glucose (Abate et al., 2013).  This could be crucial information for the prevention and rehabilitation of people affected by tendinopathy especially in cases where the pathology shows frequent occurrence or slow rates of improvements. 

Considering all the above one has to decide whether it is worth following the common recommendation of a high carbohydrate diet for sports performance.  If the pure performance is paramount then this might be the right thing to do, even though high performance in endurance athletes seems not to be affected, even when only a minimum of carbohydrates are ingested (Cao et al., 2021).  With that, and the detrimental effects of high blood glucose levels in mind, it is questionable if this form of eating is the right thing for all people that are physically active.  It might be the case that high carbohydrate diets should be exclusively prescribed to elite athletes and even then only with full disclosure of the possible health consequences.

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