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Inflammation, Immune Function, The Diabetic Athlete & Overweight Athlete

Choosing the appropriate nutrition strategy can make a difference in ensuring the maximum success of the athletes in reaching their goals. Considering that the diet is unique to each individual, it varies according to age groups, gender, and diseases. In this article, nutritional strategies specific to the groups of inflammation, diabetic, and overweight athletes are mentioned. Moreover, information is given about the relationship of the immune system with athlete performance.

Exercise is important to maintain human health and is recognized by the American Sports Medicine Association and the American Heart Association as a drug used in the prevention and treatment of chronic diseases. It has been scientifically proven that regular exercise reduces the incidence of many cancers, especially breast and colorectal cancer, by 40-50% (Booth et al., 2002). The most significant decrease is seen in colorectal and breast cancers. Apart from these, it has been shown that the incidence levels of cancer types such as prostate, testis, ovary, endometrium, and lung are reduced significantly with regular exercise, and a significant amount of protection is provided against many types of cancer with exercise (Newton & Galvao, 2008). Regular physical activity reduces the risk of many chronic, non-communicable diseases and is negatively associated with chronic low-grade inflammation (Bruunsgaard, 2005). Both physical exercise and adequate nutrition can modulate myokine release, thereby potentially contributing to improving insulin sensitivity and reducing the risk associated with cardiometabolic diseases (Lombardo et al., 2020). In addition, moderate intensity regular exercise is predicted to reduce the suppression of the immune system caused by age and stress, as well as the incidence of cancer (Shek & Shephard, 1999). Physical activity is an energy-requiring process, and adaptations to regular exercise increase glucose homeostasis, energy metabolism, and weight control. In response to contraction, skeletal muscle produces and releases myokines that have immune and metabolic effects at the local and systemic level. Exercise induces an anti-inflammatory hormonal environment that contributes to the beneficial effects of exercise and chronic disease. As part of this hormonal environment, myokines can be seen as important mediators of the anti-inflammatory effect of exercise (Kraakman et al., 2013).

Figure 1: And then there were five. (Dave Simonds, 2015).

Prolonged and intense exercise has temporary but significant and far-reaching effects on the immune system (Gleeson, 2007; Nieman, 1997). Various nutritional agents have been tested for their capacity to reduce immune changes, oxidative stress, and inflammation following feeding (Gleeson et al., 2004; Nieman, 2008, 2010; Walsh et al., 2011). Such as N-3 PUFAs (fish oil) exert anti-inflammatory and immunomodulatory effects after exercise (Walsh et al., 2011). Moreover, herbal supplements such as ginseng and echinacea contain bioactive molecules that increase immunity and resist infection (Walsh et al., 2011). For example, carbohydrates maintain blood sugar during exercise, reduce the release of cortisol and epinephrine, and thus counteract adverse immune changes after exercise (Walsh et al., 2011). In fact, a study of marathon runners showed that athletes who consumed carbohydrates during the race tended to have lower rates of illness after a competitive marathon, compared with placebo drinks (Nieman et al., 2001). For example, fruit and vegetable extracts rich in polyphenols and flavonoids, e.g. green tea extract, black currant and blueberry extract, may reduce exercise-induced inflammation and oxidative stress (Walsh et al., 2011). In addition, probiotics improve intestinal microbial flora and intestinal and systemic immune function (Walsh et al., 2011). Apart from carbohydrates and probiotics, vitamin C suppresses exercise-induced reactive oxygen species (ROS) and increases immunity. In addition, vitamin C is known to be effective in suppressing ROS and reducing inflammation. (Walsh et al., 2011). Another element, glutamine, acts as an important immune cell energy substrate, which is reduced by prolonged exercise.

Diabetes mellitus, which develops as a result of insulin deficiency (Type 1 DM) or resistance (Type 2 DM), is a cause of morbidity and mortality all over the world. Before determining the diet of diabetic athletes, it is very important to determine the type of diabetes they have. There are several types of diabetes, but almost all fall into two broad categories; type 1 (T1DM) and type 2 (T2DM) diabetes. T1DM results from an absolute lack of insulin production secondary to the autoimmune destruction of the pancreas and typically presents acutely in childhood. T2DM develops due to insulin resistance and ultimately the inability of pancreatic beta cells to provide an adequate insulin secretory response. Inactivity is associated with obesity and family history and typically occurs later in life (DeFronzo, 2004). However, with the rise of obesity in younger age groups, children and young adults are increasingly being diagnosed with T2DM (Deckelbaum & Williams, 2001).

Figure 2: You're 'Prediabetic'? Join the Club. (David Plunkert, 2016).

Exercise increases insulin sensitivity and improves aerobic capacity and strength in individuals with diabetes. The biggest problem encountered during and after exercise in patients with type TD1M type is hypoglycemia. For this reason, it is very important to inform the athlete and his/her environment in predicting and treating hypoglycemia, and having enough CHO (carbohydrates) before, during and after activity is vital to maintain glycogen levels. Therefore, CHO consumption and the amount of insulin administered should be adjusted depending on the type, intensity, and time of day of exercise performed by athletes with T1DM (Gallen et al., 2011). On the other hand, before exercise, individuals with T2DM are often overweight and may develop risk factors for cardiovascular disease. Therefore, ahead of an exercise regimen, a medical examination should be performed (ADA, 2004). In such cases, diets can be regulated to reduce energy intake. In particular, by reducing saturated fats and trans fats, low GI (glycemic index) CHO can be consumed instead of high GI foods, both of which improve glycemic control (ADA, 2008; Willett et al., 2002). In general, more exercise and an improved diet can result in a negative energy balance, meaning decreased body weight, particularly fat mass, thereby reducing fatty acid metabolites at the cellular level and improving insulin sensitivity. Just prior to exercise, additional CHO should not be consumed to support a healthy diet, as the goal is to lose weight (ADA, 2008).

Many factors contribute to the amount of insulin an athlete needs. In general, 60% of the energy in an athlete's diet should come from CHO (Burke et al., 2004). However, a more practical method is to recommend the amount of CHO relative to activity and body mass (Burke & Deakin, 2003). In general, very light exercise usually requires 5 g CHO/kg body weight (BW)/day. Moderately intense exercise between 5-7 g CHO/kg BM/day is required, if performed 1-2 hours a day. Intense activity may require 12 g CHO/kg BW/day, if performed up to 4-5 hours per day. Therefore, the amount of insulin administered by athletes with T1DM needs to be adjusted depending on the type and intensity of exercise, the time of day and how much carbohydrate is consumed (Gallen et al., 2011).

Figure 3: Immunotherapy for type 1 diabetes: what’s in the pipeline? (Donough O'Malley, 2018).

In athletes, excessive CHO load the days before any competition, exercise, etc. may adversely affect glycemic control, and it is generally recommended that T1DM not load CHO (Gallen et al., 2011). Ideally, a low glycemic index meal high in CHO should be consumed 1-3 hours before exercise (Horton, 1988). If moderate exercise is performed, insulin adjustment should be considered, but if exercise is not planned and there is no capability for insulin dose adjustment, 20-30 g CHO should be consumed just before exercise and every half hour. If physical activity is planned early in the morning, medium or long-acting insulin should be reduced by 20-50% the previous evening and blood sugar should be checked before exercise in the morning. If it rises above 7-8 mmol/l, it may compromise long-term control, but levels below 10-12 mmol/l allow safe exercise. Conversely, levels below 6 mmol/l may increase the risk of hypoglycemia, even when exercise intensity is moderate (50-70% VO2 max). In the morning, the regular effective insulin dose should also be reduced by 30-50% before breakfast or even skipped, if exercise is performed before a meal. Otherwise, insulin should be taken 30-60 minutes before a meal, as usual. It is accepted that exercise should be avoided if the blood glucose measurement before exercise is above 17 mmol/l or in the case it is higher than14 mmol/l with the presence of ketones in the urinalysis. If blood glucose is between 5.5 and 6.0 mmol/l and exercise is expected to be vigorous, extra CHO should be taken (Peirce, 1999).

Elite athletes tend to exercise longer and at higher intensity, depending on the sport they are playing. The night before a scheduled morning session, intermediate to long-acting insulin should be reduced by 50-70%. It is also more likely to reduce insulin by 70-90% the morning before exercise. As long as the athlete is closely monitored, insulin can be skipped completely, especially for intense exercise approaching VO2 max. Insulin pumps are an option in this group and ideally need to be adjusted 30-60 minutes before exercise to stabilize the glucose level (Frohnauer et al., 2000), so CHO (20–30 g) can be consumed before exercise to increase blood glucose levels in this scenario.

Figure 4: As China puts on weight, type-2 diabetes is soaring. (Andrea Ucini, 2018).

Individuals with T2DM are often overweight and may have risk factors for cardiovascular disease, that’s why it is important to have a medical examination before starting an exercise regimen (ADA, 2004). Appropriate diets should be determined to reduce energy intake. In particular, saturated fats and trans fats should be reduced and low-GI CHOs should be consumed instead of high-GI foods, both of which improve glycemic control (ADA, 2008; Willett et al., 2002). In general, more exercise and an improved diet will result in a negative energy balance meaning decreased body weight, particularly fat mass, thereby reducing fatty acid metabolites at the cellular level and improving insulin sensitivity. Just prior to exercise, additional CHO should not be consumed to support a healthy diet as the goal is weight loss (ADA, 2008). Once again, consuming CHO during exercise is generally not recommended to athletes, when aiming to lose weight. Most overweight individuals will exercise at low to moderate intensity, and as a result, fat oxidation will fuel continued activity more than CHO oxidation (Maughan et al., 1997). Indeed, individuals with T2DM expend less energy than individuals without T2DM, due to generally weaker aerobic capacity. Insulin sensitivity increases after an acute exercise. Furthermore, exercise improves the efficiency of the IRS phosphorylation pathway, GLUT4 translocation, and hexokinase activity, thereby improving glycogen synthesis and reducing circulating plasma glucose. Improved glycogen stores will allow for greater endurance capacity and encourage longer exercise time in the future. Moreover, consumption of CHO immediately after exercise is not recommended to encourage greater energy use, and individuals with T2DM are advised to wait until their next regular meal (Jensen, 2004).

Figure 5: Much too fat. (Dave Simonds, 2014).

Athletes must train hard for competition and engage in strategies that will keep their immune systems intact and disease rates low despite the physiological stress they experience. The ultimate goal is to provide athletes with nutritional, ergonomic support and supplements consisting of carbohydrates and advanced supplements that will reduce the risk of infection, exert significant and measurable effects on their innate immune system, and alleviate exercise-induced oxidative stress and inflammation. Athletes can combine this strategy with other approaches that assist in the maintenance of immunity and health. While dieting and losing weight may seem commonplace in society, advice towards an athlete to lose weight or lose fat should be considered with caution. Restrictive diets can result in a number of adverse consequences for athletes, including inadequate nutrient intake or deficiency, and reduced immunodeficiency.

Bibliographical References

ADA (2004). Physical activity/exercise and diabetes. Diabetes Care 27, s58–s62.

ADA (2008). American diabetes association-nutrition recommendations and interventions for diabetes. Diabetes Care 31, S61–S78.

Bruunsgaard, H. (2005). Physical activity and modulation of systemic low‐level inflammation. Journal of leukocyte biology, 78(4), 819-835.

Burke, L. & Deakin, V. (2003). Clinical Sports Nutrition. The McGraw-HillCompanies, Inc, Sydney, Australia.

Burke, L.M., Kiens, B., & Ivy, J.L. (2004). Carbohydrates and fat for training and recovery. Journal of Sports Sciences 22, 15–30.

Defronzo, R.A. (2004). Pathogenesis of type 2 diabetes mellitus. Medical Clinics of North America 88, 787–835.

Deckelbaum, R. J., & Williams, C. L. (2001). Childhood obesity: the health issue. Obesity research, 9(S11), 239S-243S.

Frohnauer, M.K., Lin, K., & Devlin, J.T. (2000). Adjustment of basal lispro insulin in CSII to minimize glycemic fluctuations caused by exercise. Diabetes Research and Clinical Practice, 50, S80.

Gallen, I. W., Hume, C., & Lumb, A. (2011). Fuelling the athlete with type 1 diabetes. Diabetes, Obesity and Metabolism, 13(2), 130-136.

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Gleeson, M. (2007). Immune function in sport and exercise. Journal of applied physiology, 103(2), 693-699.

Horton, E.S. (1988). Role and management of exercise in diabetes mellitus. DiabetesCare, 11, 201–211.

Jensen, J. (2004). Nutritional Concerns in the diabetic athlete. Current Sports Medicine Reports, 3, 192–197.

Kraakman, M. J., Whitham, M., & Febbraio, M. A. (2013). Exercise, Nutrition, and Inflammation. The Encyclopaedia of Sports Medicine: An IOC Medical Commission Publication, 19, 466-477.

Lombardo, M., Bellia, C., et al., (2020). Effects of Quality and Quantity of Protein Intake for Type 2 Diabetes Mellitus Prevention and Metabolic Control. Current nutrition reports, 9(4), 329-337.

Nieman, D. C. (1997). Immune response to heavy exertion. Journal of applied physiology.

Nieman, D. C., Henson, D. A., et al., (2001). Cytokine changes after a marathon race. Journal of applied physiology, 91(1), 109-114.

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Maughan, R.J., Gleeson, M., & Greenhaff, P.L. (1997). Biochemistry of Exercise and Training. Oxford University Press, New York.

Peirce, N.S. (1999). Diabetes and exercise. British Journal of Sports Medicine, 33, 161–172.

Shephard, R. J., & Shek, P. N. (1999). Effects of exercise and training on natural killer cell counts and cytolytic activity. Sports Medicine, 28(3), 177-195.

Walsh, N. P., Gleeson, M., Pyne, D. B., Nieman, D. C., Dhabhar, F. S., Shephard, R. J., Oliver, S. J., Bermon, S., & Kajeniene, A. (2011). Position statement. Part two: Maintaining immune health. Exercise immunology review, 17, 64–103.

Willett, W., Manson, J., & Liu, S. (2002). Glycemic index, glycemic load, and risk of type 2 diabetes. American Journal of Clinical Nutrition, 76, 274S–280S.

Visual Sources

Figure 1: Simonds D., (2015). And then there were five. The Economist. [Photo]. Retrieved from

Figure 2: Plunkert D., (2016) . You're 'Prediabetic'? Join the Club. The New York Times. [Photo]. Retrieved from

Figure 3: O'Malley D., (2018). Immunotherapy for type 1 diabetes: what’s in the pipeline? The Pharmaceutical Journal. [Photo]. Retrieved from

Figure 4: Andrea Ucini, (2018). As China puts on weight, type-2 diabetes is soaring. The Economist. [Photo]. Retrieved from

Figure 5: Dave Simonds, (2014). Much too fat. The Economist. [Photo]. Retrieved from


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Hamit Can

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