Dietary intake and thiamin, iron, and zinc status in elite Nordic skiers during different training periods

Exploring the impact of age, and body condition score on erythrocytic B1-Dependent transketolase activity in cats: A comprehensive analysis of thiamine status

One of the key factors influencing aging and morbidity is the overall antioxidant status and regenerative capacity. In examining contributors to the antioxidant status, we analyzed the thiamine status in felines and the influence of age, gender, and body condition score. We measured erythrocytic B1-dependent specific transketolase (STKT) activity, an enzyme in the pentose phosphate pathway, in a group of 60 sexually intact, healthy, and specific pathogen-free felines (44 females, 16 males, aged 1-17 years) with thiamine diphosphate (TDP; 0.3 and 3 mM) and without it. Only two parameters (STKT activity with and without 0.3 mM TDP) decreased with age. After adjusting for age, statistical thresholds were established using these and other age-independent parameters, identifying 15 felines with subclinical thiamine deficiency. The red blood cell proteomics analysis revealed that the pentose phosphate shunt, glycolysis, and oxidative stress response were the most affected pathways in deficient felines, confirming the above diagnosis. Age emerged as the primary factor associated with thiamine deficiency, supported by the enrichment of neurodegenerative diseases with a proteotoxicity component; five young-adult felines showed marginal or acute B1 deficiency, and six were adult-mature with a more chronic deficiency, possibly linked to cognitive decline, all with an underweight to ideal body condition scores. Only three senior-adult felines were deficient and overweight-obese. Detecting thiamine deficiency emphasizes the need for more accurate reference values, the establishment of advanced preventive or therapeutic measures to enhance the well-being of aging companion animals, and potential extensions to human health, particularly concerning cognitive function.

Determination of Optimal Daily Magnesium Intake among Physically Active People: A Scoping Review

Little is known about the optimal daily magnesium (Mg) intake for individuals with high levels of physical activity. The aim of this study was to clarify the optimal dietary Mg intake for people with high levels of physical activity in a scoping review. In this review, we searched MEDLINE and Japan Medical Abstracts Society for studies published up to May 31, 2020. We conducted two searches, one for studies using gold standard measurement methods such as the balance method and factorial calculation (Search 1), and the other for studies using estimation from daily food intake (Search 2). We also performed a meta-analysis of studies that compared the Mg intake among physically active people with the Mg intake among controls. After the primary and secondary screening, 31 studies were included in the final review. All of the included studies examined professional or recreational athletes. We found no studies that examined the optimal intake of Mg using gold standard measurement methods. The Mg intake among physically active individuals was below the recommended dietary allowance in most studies. In five studies that conducted meta-analyses, physically active individuals had significantly higher intakes of Mg than controls, although these levels were still below the recommended dietary allowance. The present review revealed that evidence regarding the optimal daily magnesium intake is currently scarce, and further studies are needed.

Does Iron Supplementation Improve Performance in Iron-Deficient Nonanemic Athletes?

CONTEXT

Supplementing iron-deficient nonanemic (IDNA) athletes with iron to improve performance is a trend in endurance sports.

OBJECTIVES

To investigate the benefits of iron on performance, identify a ferritin level cutoff in IDNA athletes, and determine which iron supplementation regimens are most effective.

DATA SOURCES

A search of the PubMed, CINAHL, Embase, ERIC, and Cochrane databases was performed in 2014 including all articles. Citations of pertinent review articles were also searched. In 2017, the search was repeated.

STUDY SELECTION

Inclusion criteria comprised studies of level 1 to 3 evidence, written in the English language, that researched iron supplementation in nonanemic athletes and reported performance outcomes.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 3.

DATA EXTRACTION

The search terms used included athletic performance, resistance training, athletes, physical endurance, iron, iron deficiency, supplement, non-anemic, low ferritin, ferritin, ferritin blood level, athletes, and sports.

RESULTS

A total of 1884 studies were identified through the initial database search, and 13 were identified through searching references of relevant review articles. A subsequent database search identified 46 studies. Following exclusions, 12 studies with a total of 283 participants were included. Supplementing IDNA athletes with iron improved performance in 6 studies (146 participants) and did not improve performance in the other 6 studies (137 participants). In the 6 studies that showed improved performance with iron supplementation, all used a ferritin level cutoff of ≤20 μg/L for treatment. Additionally, all studies that showed improved performance used oral iron as a supplement.

CONCLUSION

The evidence is equivocal as to whether iron supplementation in IDNA athletes improves athletic performance. Supplementing athletes with ferritin levels <20 μg/L may be more beneficial than supplementing athletes with higher baseline ferritin levels.

Effect of magnesium supplementation on some plasma elements in athletes at rest and exhaustion

The effects of magnesium supplementation on plasma magnesium, zinc, and copper levels were determined in young adult tae-kwon-do athletes and sedentary controls at rest and exhaustion. After a 4-week supplementation period with 10 mg/day/kg Mg, the plasma magnesium, copper, and zinc levels significantly increased in sedentary and training (90-120 min training 5 days a week) subjects when compared to nonsupplemented controls (p < 0.05).

Methodology of dietary assessment in athletes: concepts and pitfalls

PURPOSE OF REVIEW

Evaluation of an athlete's diet is important in both clinical practice and research. The main purpose of this review is to provide health professionals with guidance regarding the special issues that are likely to be encountered when assessing the dietary intake of sportspersons.

RECENT FINDINGS

A number of methods may be used for the dietary assessment of individuals and/or groups of athletes, including retrospective (diet recall, food-frequency questionnaire, and diet history) and prospective (diet record, duplicate portion) techniques. A 3-4-day estimated diet record is the most widely used approach, but collection of single or multiple diet recalls is also common. Care must be taken, however, to ensure that days of diet monitoring accurately reflect usual food consumption during the period of interest. Under-reporting of habitual energy intake is widespread among athletes, and its magnitude should be carefully addressed when interpreting the results of dietary assessment. Other issues, specifically related to sportspersons, that are often neglected include adequacy of standard portion sizes, frequency of snacking, fluid intake, supplement use, weight-control practices, and seasonality of sport activities and food consumption.

SUMMARY

There are subtle methodological differences in the dietary assessment of athletes and non-athletes, which, when taken into consideration, may substantially increase the quality of intake data and optimise the outcome of dietary intervention.

Guidelines for daily carbohydrate intake: do athletes achieve them?

Official dietary guidelines for athletes are unanimous in their recommendation of high carbohydrate (CHO) intakes in routine or training diets. These guidelines have been criticised on the basis of a lack of scientific support for superior training adaptations and performance, and the apparent failure of successful athletes to achieve such dietary practices. Part of the problem rests with the expression of CHO intake guidelines in terms of percentage of dietary energy. It is preferable to provide recommendations for routine CHO intake in grams (relative to the body mass of the athlete) and allow flexibility for the athlete to meet these targets within the context of their energy needs and other dietary goals. CHO intake ranges of 5 to 7 g/kg/day for general training needs and 7 to 10 g/kg/day for the increased needs of endurance athletes are suggested. The limitations of dietary survey techniques should be recognised when assessing the adequacy of the dietary practices of athletes. In particular, the errors caused by under-reporting or undereating during the period of the dietary survey must be taken into account. A review of the current dietary survey literature of athletes shows that a typical male athlete achieves CHO intake within the recommended range (on a g/kg basis). Individual athletes may need nutritional education or dietary counselling to fine-tune their eating habits to meet specific CHO intake targets. Female athletes, particularly endurance athletes, are less likely to achieve these CHO intake guidelines. This is due to chronic or periodic restriction of total energy intake in order to achieve or maintain low levels of body fat. With professional counselling, female athletes may be helped to find a balance between bodyweight control issues and fuel intake goals. Although we look to the top athletes as role models, it is understandable that many do not achieve optimal nutrition practices. The real or apparent failure of these athletes to achieve the daily CHO intakes recommended by sports nutritionists does not necessarily invalidate the benefits of meeting such guidelines. Further longitudinal studies of training adaptation and performance are needed to determine differences in the outcomes of high versus moderate CHO intakes. In the meantime, the recommendations of sports nutritionists are based on plentiful evidence that increased CHO availability enhances endurance and performance during single exercise sessions.

Effect of physical activity on thiamine, riboflavin, and vitamin B-6 requirements

Because exercise stresses metabolic pathways that depend on thiamine, riboflavin, and vitamin B-6, the requirements for these vitamins may be increased in athletes and active individuals. Theoretically, exercise could increase the need for these micronutrients in several ways: through decreased absorption of the nutrients; by increased turnover, metabolism, or loss of the nutrients; through biochemical adaptation as a result of training that increases nutrient needs; by an increase in mitochondrial enzymes that require the nutrients; or through an increased need for the nutrients for tissue maintenance and repair. Biochemical evidence of deficiencies in some of these vitamins in active individuals has been reported, but studies examining these issues are limited and equivocal. On the basis of metabolic studies, the riboflavin status of young and older women who exercise moderately (2.5-5 h/wk) appears to be poorer in periods of exercise, dieting, and dieting plus exercise than during control periods. Exercise also increases the loss of vitamin B-6 as 4-pyridoxic acid. These losses are small and concomitant decreases in blood vitamin B-6 measures have not been documented. There are no metabolic studies that have compared thiamine status in active and sedentary persons. Exercise appears to decrease nutrient status even further in active individuals with preexisting marginal vitamin intakes or marginal body stores. Thus, active individuals who restrict their energy intake or make poor dietary choices are at greatest risk for poor thiamine, riboflavin, and vitamin B-6 status.

Magnesium, zinc, and chromium nutriture and physical activity

Magnesium, zinc, and chromium are mineral elements required in modest amounts to maintain health and optimal physiologic function. For physically active persons, adequate amounts of these micronutrients are needed in the diet to ensure the capacity for increased energy expenditure and work performance. Most physically active individuals consume diets that provide amounts of magnesium and zinc sufficient to meet population standards. Women tend to consume less of these minerals than is recommended, in part because they eat less food than men. Inadequate intakes of magnesium and zinc have been reported for participants in activities requiring restriction of body weight. Dietary chromium is difficult to estimate because of a lack of appropriate reference databases. Acute, intense activity results in short-term increases in both urine and sweat losses of minerals that apparently diminish during recovery in the days after exercise. Supplemental magnesium and zinc apparently improve strength and muscle metabolism. However, evidence is lacking as to whether these observations relate to impaired nutritional status or a pharmacologic effect. Chromium supplementation of young men and women does not promote muscle accretion, fat loss, or gains in strength. Physically active individuals with concerns about meeting guidelines for nutrient intake should be counseled to select and consume foods with high nutrient densities rather than to rely on nutritional supplements. The indiscriminate use of mineral supplements can adversely affect physiologic function and impair health.

Micronutrients: interaction between physical activity, intakes and requirements

The present literature review examines the following questions: (a) What is the evidence that micronutrient requirements are increased in physically active people? (b) Is there an association between physical activity and micronutrient intake? (c) Are there any significant differences between indices of micronutrient status between physically active and inactive people? The available data suggest that micronutrient requirements are increased in physically active people because of increased losses through sweat, urine and faeces, and an increased need for defence against free radicals. However the evidence is controversial, and it is not possible to make any quantitative estimations. Micronutrient requirements in moderately active people are not likely to be very much above the levels recommended for the general population. The intake of micronutrients increases with increasing energy intake. Therefore, physically highly active people (athletes) have higher micronutrient intakes than untrained subjects. However, moderate physical activity does not necessarily affect daily micronutrient intake. The available indices of micronutrient status do not support the belief that micronutrient status is compromised in highly trained athletes, even without use of dietary supplements. Hence, there are no reasons to believe that the situation would be different in people who are only moderately active. The results suggest that micronutrient status is adequate for health and functional performance in physically active people who follow a normal, mixed Western diet.

Effect of meal frequency and timing on physical performance

Two areas of sports nutrition in which the periodicity of eating has been studied relate to: (1) the habitually high energy intakes of many athletes, and (2) the optimization of carbohydrate (CHO) availability to enhance performance. The present paper examines how the timing and frequency of food and fluid intake can assist the athlete and physically-active person to improve their exercise performance in these areas. Frequent eating occasions provide a practical strategy allowing athletes to increase energy intake while concomitantly reducing the gastric discomfort of infrequent large meals. The optimization of CHO stores is a special challenge for athletes undertaking prolonged training or competition sessions. This is a cyclical process with post-exercise CHO ingestion promoting muscle and liver glycogen re-synthesis; pre-exercise feedings being practised to optimize substrate availability and feedings during exercise providing a readily-available source of exogenous fuel as endogenous stores become depleted. The timing and frequency of CHO intake at these various stages are crucial determinants for optimizing fuel availability to enhance exercise capacity.

Indicators of vitamin and mineral status in athletes' blood: a review

This review examines the hypothesis that vitamin and mineral status in athletes is inadequate for optimal sports performance. The review is based on indicators determined from blood and on studies published since 1980. Most of the studies did not find micronutrient status in athletes to be different from untrained controls. The serum ferritin concentration in females was lower than in males (27 vs. 78 micrograms.L-1), and the prevalence of low serum ferritin concentration was higher in female athletes than in untrained female controls (37 vs. 23%). Supplementation of water-soluble vitamins and iron was associated with an improvement in the corresponding indicators. Excluding a few studies with mildly anemic subjects, improvements in indicators of micronutrient status were not associated with enhanced athletic performance. Consequently, the levels of indicators of micronutrient status seen in athletes' blood were apparently compatible with optimal physical performance.

Micronutrients and exercise: anti-oxidants and minerals

Exercise has been shown to increase indirect measures of lipid peroxidation. However, exercise and training appear to augment the body's anti-oxidant defence system. Whether this augmented defence system can keep up with the increase in lipid peroxidation with exercise is not known. Iron depletion is experienced by many athletes, especially female endurance athletes and adolescents, but iron deficiency anaemia is rare. Iron depletion could affect the ability to train and recover from strenuous exercise, but this has not been examined. There is a concern that female athletes, especially adolescents, are not ingesting sufficient calcium, and this may affect the development of peak bone mass and increase the risk of bone fractures. Further research is needed on mineral and trace mineral intake and loss in athletes. It appears that most athletes have adequate status of chromium, zinc, phosphate and magnesium. Athletes who are restricting energy intake to achieve a low body mass (for example, endurance runners), may not have adequate vitamin or mineral status. More data are needed on vitamin/mineral status of athletes from underdeveloped countries. The general recommendation for athletes is that foods rich in anti-oxidants and minerals should be ingested rather than supplements.

Dietary intake and nutritional status of athletic and nonathletic children in early puberty

Dietary intakes, trace element status, and anthropometric measures were studied in 12- to 13-year-old boys (n = 49) playing ice hockey (AB) and in 11- to 12-year-old girls who were gymnasts, figure skaters, and runners (AG; n = 43). Thirty-five boys (CB) and 53 girls (CG) not involved in supervised sports were controls. After adjustment for sexual maturation, ABs had larger upper arm muscle circumference than CBs. The sum of four skinfolds was smaller in AGs than in CGs. The intake of energy and all micronutrients examined was higher in ABs than in CBs. Micronutrient intakes were not different between AGs and CGs. Compared to CBs, serum ferritin and copper concentrations were lower, but serum zinc concentration was higher in ABs. No differences in trace element status were found between AGs and CGs. Blood investigations did not indicate inadequate trace element status in any of the groups studied.

Trace mineral requirements for athletes

This paper reviews information pertaining to zinc, copper, chromium, and selenium requirements of athletes. Exercise increases zinc loss from the body, and dietary intake for some athletes, especially females, may be inadequate. Blood copper levels are altered by exercise, but there is no information to suggest that copper ingestion or status is compromised in athletes. Studies have shown that urinary chromium excretion is increased by exercise, but whether this leads to an increased requirement is still unknown. There is concern that athletes may not ingest sufficient quantities of chromium; however, there are inadequate data to confirm this. The limited data that exist show that athletes do not have altered selenium status. There is no conclusive evidence that supplementation with any of these trace minerals will enhance performance. A diet containing foods rich in micronutrients is recommended. However, for those athletes concerned that their diets may not be sufficient, a multivitamin/mineral supplement containing no more than the RDA may be advised.

Lack of association between indices of vitamin B1, B2, and B6 status and exercise-induced blood lactate in young adults

By means of a 5-week vitamin B-complex supplementation, associations between indices of vitamin B1, B2, and B6 status (activation coefficients [AC] for erythrocyte transketolase, glutathione reductase, and aspartate aminotransferase) and exercise-induced blood lactate concentration were studied. Subjects, 42 physically active college students (18-32 yrs), were randomized into vitamin (n = 22) and placebo (n = 20) groups. Before the supplementation there were no differences in ACs or basal enzyme activities between the groups. The ACs were relatively high, suggesting marginal vitamin status. In the vitamin group, all three ACs were lower (p < 0.0001) after supplementation: transketolase decreased from 1.16 (1.14-1.18) (mean and 95% confidence interval) to 1.08 (1.06-1.10); glutathione reductase decreased from 1.33 (1.28-1.39) to 1.14 (1.11-1.17); and aspartate aminotransferase decreased from 2.04 (1.94-2.14) to 1.73 (1.67-1.80). No changes were found after placebo. Despite improved indices of vitamin status, supplementation did not affect exercise-induced blood lactate concentration. Hence no association was found between ACs and blood lactate. It seems that marginally high ACs do not necessarily predict altered lactate metabolism.