The effects of resistance exercise and post-exercise meal timing on the iron status in iron-deficient rats

Effect of the Energy Intake on the Iron Status of Resistance Exercises Performed in Rats

In many cases, athletes compensate for nutrient deficiencies due to a reduced dietary intake by taking supplements or other means. However, in what ways nutrients are utilized by the body when it is deficient in energy and yet receives adequate amounts of the required nutrients are unclear. We therefore examined the effect of the balance between available energy and iron intake on the iron nutritional status of athletes. The experiment was conducted in two parts. Four-week-old male rats were divided into two groups based on energy and iron sufficiency: Experiment 1 was energy-sufficient and iron-sufficient (ES-FeS) and energy-sufficient and iron-deficient (ES-FeD). Experiment 2 was energy-deficient and iron-sufficient (ED-FeS) and energy-deficient and iron-deficient (ED-FeD) groups. All rats were made to perform climbing exercises 3 days a week at 5 P.M. The results showed that a significantly higher hematocrit, hemoglobin, plasma iron concentration, and TfS were found in the iron-sufficient group than in the iron-deficient group, TIBC was significantly lower in the iron-sufficient group than in the iron-deficient group, and TfS was significantly higher in the iron-sufficient group than in the iron-deficient group, irrespective of energy intake. It was suggested that restricting both iron and energy intake may significantly decrease the amount of iron in the liver and accelerate the metabolic turnover of red blood cells, while restricting iron intake but providing adequate energy intake suggested that resistance exercise-induced tissue iron repartitioning was not altered by iron sufficiency or deficiency.

Impact of resistance training and basic ferritin on hepcidin, iron status and some inflammatory markers in overweight/obese girls

BACKGROUND

Exercise can reduce hepcidin, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 and improve the iron status, but the intensity of exercises is very important. This study will compare the effect of resistance training (RT) intensity on hepcidin levels, iron status, and inflammatory markers in overweight/obese girls with and without iron stores deficient.

MATERIALS AND METHODS

In this quasi-experimental study, 40 students of the University of Isfahan (18-22-year old, with 35 > body mass index [BMI] ≥25) voluntarily participated in the study. Participants were divided into two groups with 20 participants, based on serum ferritin (>30 ng/ml or ≤30 ng/ml). Participants in each group were randomly and equally assigned to one of the moderate or high-intensity training groups. RT was performed 8 weeks, 4 days a week, and each session for 1 h, with an elastic band. The iron levels, hepcidin, total iron-binding capacity, ferritin, hemoglobin, TNF-α, and IL-6 before and after intervention were collected with the blood samples. Two-way analysis of variance was used to assess the impact of exercise and ferritin level and their interaction, and the paired test was utilized for test changes from baseline.

RESULTS

There are no significant interactions between ferritin levels and exercise intensity for the main outcomes (all P > 0.05). The significant impact of the mode of exercise was observed in TNF-α (P < 0.05), and a significant difference between low and high levels of ferritin was observed in hepcidin (P = 0.002). Besides, in all four groups, significant decreases were observed in BMI (28.00 ± 3.00 to 27.00 ± 3.00), hepcidin (1234.02 ± 467.00 to 962.06 ± 254.00), and TNF-α (223.00 ± 99.00 to 174.00 ± 77.00) compared to the baseline measurements (all P < 0.05).

CONCLUSION

Basal ferritin levels appear to be effective on hepcidin levels, TNF-α, and IL-6 after the intervention. RT with two different intense can reduce BMI, hepcidin, ferritin, and TNF-α in all groups. It seems that performing RT reduces inflammation and hepcidin in obese/overweight participants with different iron stores.

Chronic Iron Overload Restrains the Benefits of Aerobic Exercise to the Vasculature

Physical exercise is a well-recognized effective non-pharmacological therapy for cardiovascular diseases. However, because iron is essential element in many physiological processes including hemoglobin and myoglobin synthesis, thereby playing a role on oxygen transport, many athletes use iron supplement to improve physical performance. Regarding this, iron overload is associated with oxidative stress and damage to various systems, including cardiovascular. Thus, we aimed to identify the vascular effects of aerobic exercise in a rat model of iron overload. Male Wistar rats were treated with 100 mg/kg/day iron-dextran, i.p., 5 days a week for 4 weeks, and then underwent aerobic exercise protocol on a treadmill at moderate intensity, 60 min/day, 5 days a week for 8 weeks. Exercise reduced vasoconstrictor response of isolated aortic rings by increasing participation of nitric oxide (NO) and reducing oxidative stress, but these benefits to the vasculature were not observed in rats previously subjected to iron overload. The reduced vasoconstriction in the exercised group was reversed by incubation with superoxide dismutase (SOD) inhibitor, suggesting that increased SOD activity by exercise was lost in iron overload rats. Iron overload groups increased serum levels of iron, transferrin saturation, and iron deposition in the liver, gastrocnemius muscle, and aorta, and the catalase was overexpressed in the aorta probably as a compensatory mechanism to the increased oxidative stress. In conclusion, despite the known beneficial effects of aerobic exercise on vasculature, our results indicate that previous iron overload impeded the anticontractile effect mediated by increased NO bioavailability and endogenous antioxidant response due to exercise protocol.

Timing of ergogenic aids and micronutrients on muscle and exercise performance

The timing of macronutrient ingestion in relation to exercise is a purported strategy to augment muscle accretion, muscle and athletic performance, and recovery. To date, the majority of macronutrient nutrient timing research has focused on carbohydrate and protein intake. However, emerging research suggests that the strategic ingestion of various ergogenic aids and micronutrients may also have beneficial effects. Therefore, the purpose of this narrative review is to critically evaluate and summarize the available literature examining the timing of ergogenic aids (caffeine, creatine, nitrates, sodium bicarbonate, beta-alanine) and micronutrients (iron, calcium) on muscle adaptations and exercise performance. In summary, preliminary data is available to indicate the timing of caffeine, nitrates, and creatine monohydrate may impact outcomes such as exercise performance, strength gains and other exercise training adaptations. Furthermore, data is available to suggest that timing the administration of beta-alanine and sodium bicarbonate may help to minimize known untoward adverse events while maintaining potential ergogenic outcomes. Finally, limited data indicates that timed ingestion of calcium and iron may help with the uptake and metabolism of these nutrients. While encouraging, much more research is needed to better understand how timed administration of these nutrients and others may impact performance, health, or other exercise training outcomes.

International society of sports nutrition position stand: nutrient timing

The International Society of Sports Nutrition (ISSN) provides an objective and critical review regarding the timing of macronutrients in reference to healthy, exercising adults and in particular highly trained individuals on exercise performance and body composition. The following points summarize the position of the ISSN:

Nutrient timing incorporates the use of methodical planning and eating of whole foods, fortified foods and dietary supplements. The timing of energy intake and the ratio of certain ingested macronutrients may enhance recovery and tissue repair, augment muscle protein synthesis (MPS), and improve mood states following high-volume or intense exercise.

Endogenous glycogen stores are maximized by following a high-carbohydrate diet (8–12 g of carbohydrate/kg/day [g/kg/day]); moreover, these stores are depleted most by high volume exercise.

If rapid restoration of glycogen is required (< 4 h of recovery time) then the following strategies should be considered:

aggressive carbohydrate refeeding (1.2 g/kg/h) with a preference towards carbohydrate sources that have a high (> 70) glycemic index

the addition of caffeine (3–8 mg/kg)

combining carbohydrates (0.8 g/kg/h) with protein (0.2–0.4 g/kg/h)

Extended (> 60 min) bouts of high intensity (> 70% VO₂max) exercise challenge fuel supply and fluid regulation, thus carbohydrate should be consumed at a rate of ~30–60 g of carbohydrate/h in a 6–8% carbohydrate-electrolyte solution (6–12 fluid ounces) every 10–15 min throughout the entire exercise bout, particularly in those exercise bouts that span beyond 70 min. When carbohydrate delivery is inadequate, adding protein may help increase performance, ameliorate muscle damage, promote euglycemia and facilitate glycogen re-synthesis.

Carbohydrate ingestion throughout resistance exercise (e.g., 3–6 sets of 8–12 repetition maximum [RM] using multiple exercises targeting all major muscle groups) has been shown to promote euglycemia and higher glycogen stores. Consuming carbohydrate solely or in combination with protein during resistance exercise increases muscle glycogen stores, ameliorates muscle damage, and facilitates greater acute and chronic training adaptations.

Meeting the total daily intake of protein, preferably with evenly spaced protein feedings (approximately every 3 h during the day), should be viewed as a primary area of emphasis for exercising individuals.

Ingestion of essential amino acids (EAA; approximately 10 g)either in free form or as part of a protein bolus of approximately 20–40 g has been shown to maximally stimulate muscle protein synthesis (MPS).

Pre- and/or post-exercise nutritional interventions (carbohydrate + protein or protein alone) may operate as an effective strategy to support increases in strength and improvements in body composition. However, the size and timing of a pre-exercise meal may impact the extent to which post-exercise protein feeding is required.

Post-exercise ingestion (immediately to 2-h post) of high-quality protein sources stimulates robust increases in MPS.

In non-exercising scenarios, changing the frequency of meals has shown limited impact on weight loss and body composition, with stronger evidence to indicate meal frequency can favorably improve appetite and satiety. More research is needed to determine the influence of combining an exercise program with altered meal frequencies on weight loss and body composition with preliminary research indicating a potential benefit.

Ingesting a 20–40 g protein dose (0.25–0.40 g/kg body mass/dose) of a high-quality source every three to 4 h appears to most favorably affect MPS rates when compared to other dietary patterns and is associated with improved body composition and performance outcomes.

Consuming casein protein (~ 30–40 g) prior to sleep can acutely increase MPS and metabolic rate throughout the night without influencing lipolysis.

Effects of resistance exercise on iron absorption and balance in iron-deficient rats

We have previously reported that resistance exercise improved the iron status in iron-deficient rats. The current study investigated the mechanisms underlying this exercise-related effect. Male 4-week-old rats were divided into a group sacrificed at the start (week 0) (n = 7), a group maintained sedentary for 6 weeks (S) or a group that performed exercise for 6 weeks (E), and all rats in the latter groups were fed an iron-deficient diet (12 mg iron/kg) for 6 weeks. The rats in the E group performed climbing exercise (5 min × 6 sets/day, 3 days/week). Compared to the week 0 rats, the rats in the S and E groups showed lower tissue iron content, and the hematocrit, hemoglobin, plasma iron, and transferrin saturation values were all low. However, the tissue iron content and blood iron status parameters, and the whole body iron content measured using the whole body homogenates of the rats, did not differ between the S group and the E group. The messenger RNA (mRNA) expression levels of hepcidin, duodenal cytochrome b, divalent metal transporter 1, and ferroportin 1 did not differ between the S group and the E group. The apparent absorption of iron was significantly lower in the E group than in the S group. Therefore, it was concluded that resistance exercise decreases iron absorption, whereas the whole body iron content is not affected, and an increase in iron recycling in the body seems to be responsible for this effect.