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Marc Francaux and Jacques R. Poortmans

Context:

Allegations about side effects of creatine supplementation by athletes have been published in the popular media and scientific publications.

Purpose:

To examine the experimental evidence relating to the physiological effects of creatine supplementation.

Results:

One of the purported effects of oral creatine supplementation is increased muscle mass. A review of the literature reveals a 1.0% to 2.3% increase in body mass, which is attributed to fat-free mass and, more specifically, to skeletal-muscle mass. Although it is unlikely that water retention can completely explain these changes, increase in muscle-protein synthesis has never been observed after creatine supplementation. Indirect evidence based on mRNA analyses suggests that transcription of certain genes is enhanced. Although the effect of creatine on muscle-protein synthesis seems irrefutable according to advertising, this allegation remains under debate in the scientific literature. The kidneys appear to maintain their functionality in healthy subjects who supplement with creatine, even over several months.

Conclusion:

The authors, however, think that creatine supplementation should not be used by an individual with preexisting renal disease and that risk should be evaluated before and during any supplementation period. Even if there is a slight increase in mutagenic agents (methylamine and formaldehyde) in urine after a heavy load of creatine (20 g/day), their excretion remains within a normal range. No data are currently available regarding the potential production of heterocyclic amines with creatine supplementation. In summary, the major risk for health is probably associated with the purity of commercially available creatine.

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Jacques R. Poortmans and Olivier Dellalieux

Excess protein and amino acid intake have been recognized as hazardous potential implications for kidney function, leading to progressive impairment of this organ. It has been suggested in the literature, without clear evidence, that high protein intake by athletes has no harmful consequences on renal function. This study investigated body-builders (BB) and other well-trained athletes (OA) with high and medium protein intake, respectively, in order to shed light on this issue. The athletes underwent a 7-day nutrition record analysis as well as blood sample and urine collection to determine the potential renal consequences of a high protein intake. The data revealed that despite higher plasma concentration of uric acid and calcium. Group BB had renal clearances of creatinine, urea, and albumin that were within the normal range. The nitrogen balance for both groups became positive when daily protein intake exceeded 1.26 g · kg−1 but there were no correlations between protein intake and creatinine clearance, albumin excretion rate, and calcium excretion rate. To conclude, it appears that protein intake under 2.8 g·kg−1 does not impair renal function in well-trained athletes as indicated by the measures of renal function used in this study.

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Dirk Aerenhouts, Marcel Hebbelinck, Jacques R. Poortmans and Peter Clarys

Purpose and Methods:

To investigate dietary habits of Flemish adolescent track and field athletes using a 7-d weighed-food record. Besides adequacy for growth, development, and physical performance, dietary health aspects were considered.

Results:

Twenty-nine girls and 31 boys, with minimum 2 yr of track and field training practice, were recruited. All participants had daily breakfast (girls 22.5% ± 5.5% of total energy intake [TEI]; boys 19.8% ± 7.3%). Fruit in girls and juices and sports drinks in boys were consumed mostly between meals (girls 21.3% ± 8.1% of TEI; boys 24.3% ± 10.1%). Soft drinks contributed considerably to energy intake between meals in both sexes. Protein intake (1.5 ± 0.3 g · kg–1 · d−1 for both sexes) was within the recommended daily intake (RDI) for strength athletes. Mean daily carbohydrate intake in girls was lower than in boys (girls 5.1 ± 1.1 g/kg; boys 6.0 ± 0.9 g/kg), with mono- and disaccharides contributing 26% to TEI in both sexes. Total fat intake was above 30% of TEI in more than half the participants, and only 10 participants had a saturated-fat intake below 10% of TEI. Fiber intake (girls 23.7 ± 7.9 g; boys 29.1 ± 11.2 g) was far below the Belgian RDI. Intake of vitamins and minerals were generally low, despite micronutrient supplementation in 37.5% of the participants.

Conclusion:

Few athletes reached all nutrient RDIs. Unhealthy food habits with regard to refined sugars, fat, and micronutrients were observed. These adolescent sprinters should be encouraged to consume more nonsweetened beverages, fruits, and vegetables.