Current knowledge about sports nutrition

Abstract

The scientific literature contains an abundance of information on the nutritional demands of athletes. However, designing the most suitable sports diet is very difficult.

The principal aim of this article is to summarize knowledge about sports nutrition, especially the intake of macronutrients and dietary supplements.

Introduction

Designing the most suitable diet for an athlete requires an intimate knowledge of the relevant scientific literature, the training and competitive demands of the sport, the social situation and the individual athlete's preferences.¹ Studies have demonstrated that the timed ingestion of carbohydrate, protein, and fat may significantlyaffect the adaptive response to exercise. Dietary supplements can also play a meaningful role in helping athletes consume the proper amount of calories, carbohydrate, and proteinin their diet. Many supplement products can improve performance.^{2, 3}

The aims of this article are to provide an overview of the current macronutrient requirements for athletes and provide some recommendations for dietary supplements intake.

Energy intake

The first component to optimize training and performance through nutrition is to ensure the athlete is consuming enough calories to offset energy expenditure. The components of energy expenditure are grouped in three categories: metabolic rate, thermic effect of feeding, and the energy spent in normal daily and exercise activities.¹ People who participate in a general fitness program (e.g. exercising 30-40 minutes per day, three times per week) can typically meet their nutritional needs following a normal diet (35kcals/kg/day).⁴ However, athletes involved in moderate levels of intense training (e.g. 2-3 hours per day of intense exercise performed 5-6 times per week) or high volume intense training (e.g. 3-6 hours per day of intense training in 1-2 workouts for 5-6 days per week) need to take 50- 80kcals/kg/day.^4,5 But the caloric needs for heavier athletes (e.g. 100-150 kg) are even greater.⁶

Maintaining an energy deficient diet during training often leads to weight loss (including muscle mass), illness, psychological and physical symptoms of overtraining and reductions in performance.⁴ Studies indicate that athletes tend to eat several times a day, most commonly on 5-9 occasions.⁷ Use of nutrient dense energy bars and high calorie carbohydrate/protein supplements provide a convenient way for athletes to supplement their diet in order to maintain energy intake during training.⁸

Carbohydrate

The fundamental component to optimizing training and performance through nutrition is to ensure that athletes consume the proper amounts of carbohydrate, protein and fat in their diet. Individuals engaged in a general fitness program can typically meet macronutrient needs by consuming a normal diet consisting of 45-55% carbohydrates (3-5g/kg/day), 10-15% proteins (0.81g/kg/day) and 25-35% fats (0.5-1.5g/kg/day).⁴ However, athletes involved in moderate and high volume training need greater amounts of carbohydrate and protein in their diet to meet macronutrient needs.² Athletes undertaking 2-3hours intense exercise per day, 5-6 times per week typically need to consume a diet consisting of 5-8g/kg/day of carbohydrate. Research has shown that athletes undertaking high volume intense training (e.g. 3-6 hours in 1-2 workouts for 5-6 days per week) may need toconsume 8-10g/kg/day of carbohydrate.^{2, 4} Some studies also suggest to the possibility of an even higher intake.⁹

The majority of dietary carbohydrate should come from complex carbohydrates with a low to moderate glycemic index (named “slow carbs”). Appropriate sources are whole grains, fruit, vegetables, legumes, etc. It is advisable to consume a carbohydrate-rich meal with a low glycemic index approximately 1-2 hours before training .⁴'⁹ Athletes should not exclude simple carbohydrates with high glycemic index (absorbed more quickly and faster) from their diet. These should be taken immediately after awakening and within two hours after training. Simple carbohydrates are important for faster glycogen replenishment after overnight fasting and intensive exercise.¹⁰

Protein

Research over the last decade has indicated that athletes engaged in intense training need to ingest about two times the usual recommended daily allowance (RDA) of protein in their diet to maintain protein balance.^{4, 9} An insufficient amount of protein in the diet leads to the negative nitrogen balance, which can increase protein catabolism and can slow post-workout recovery. This may lead to muscle wasting, training intoleranceand, certainly, overtraining.⁴

To ensure an even or positive nitrogen balance, it is necessary to consume sufficient amount of protein.^{11, 12} Competitive athletes require 1.5-2g/kg of protein daily.⁴ Resistance exercise athletes, and particularly bodybuilders, often receive even higher amounts of protein to maintain a certain daily energy intake (e.g. during low-carbohydrate diets).^{11, 13}

The type of protein consumed will determine the efficiency of the conversion into myofibrillar protein. The biological value of a protein is assessed by measuring the efficiency with which a given protein is absorbed and assimilated into the protein of an organism.⁴ The best dietary sources of low fat, high quality protein are light skinless chicken meat, turkey, beef, fish egg white and skimmed milk (casein and whey). The best sources of high quality protein found in nutritional supplements are whey, colostrums, casein, milk peptides and egg protein,¹² whereas plant sources (e.g. soy and soy products) have a relatively low value.^{15, 16}

Ideally, proteins should be consumed every 2.5-3 hours in portions of 30-40 g for 6-8 meals per day. It is sufficient to substitute individual food sources with protein drinks in those individuals who are not able to consume sufficient amount of proteins.⁴

Ingesting protein drinks following exercise may lead to greater training adaptations and protein synthesis. The best postworkout protein source is whey. Recent studies suggestthat the most suitable formulations contain whey hydrolysates with very short oligopeptide chains (contains 2-3 amino acid units, named di- and tripeptides).¹⁷ However, prior to sleeping consuming casein drinks (or curd) is preferable because casein is slowly digested. Thus it provides steady nutrition to the body during sleep.^{18, 19}

Fat

The dietary recommendations of fat intake for athletes are similar to or slightly greater than those recommended for non-athletes. Adequate consumption of essential fatty acids,^{1, 4} especially polyunsaturated fatty acids, are of great importance among athletes. The best sources of essential fatty acids are “fatty” fishes (salmon, tuna, mackerel), some seeds (flaxseeds, pumpkin seeds, walnuts) and oils (flaxseed oil, soy oil, olive oil).²⁰

It is recommended that athletes consume a moderate amount of fat (approximately 30% of their daily caloric intake). Higher-fat diets appear to maintain circulating testosterone concentrations better than low-fat diets. However, for athletes attempting to decrease body fat it has been recommended that they consume 0.51g/kg/day of fat.^{1, 4}

Intake of mainly healthy fats is very important for good physiological functioning of every organism.

Dietary supplements

Dietary supplements are defined as a product taken orally that contains a dietary ingredient “intended to supplement the diet”. Dietary ingredients may include vitamins, minerals, herbs or other botanicals, amino acids, and substances (e.g. enzymes, organ tissues, glandular, and metabolites). Dietary supplements may also be extracts or concentrates from plants or foods. They are available in the form of capsules, tablets, liquids, soft gels, powders and bars. But these dietary supplements are not drugs or replacements for a good diet.⁴

Supplements can generally be classified as convenience supplements, designed to provide a convenient means of meeting caloric needs, and/or managing caloric intake, which may be for weight gain, weight loss, and/or performance enhancement.¹⁹

We generally categorize nutritional supplements into three categories which are not strictly delineated, they are dietary supplements:

1. supporting muscle mass growth,

2. supporting weight loss and fat burning,

3. enhancing performance and endurance⁴

But not all dietary supplements are demonstrably effective.

Dietary supplements supporting muscle mass growth

The most effective supplements from this category are proteins (powders or ready to serve drinks) ,²¹ powders and drinks named “weight gainers” which have more carbohydrates than proteins (70-90% : 10-30%),⁴ creatine (monohydrate, ethyl-ester, kre-alcalyn),^{9, 22} essential amino acids (EAA),¹⁷ branched-chain amino acids (BCAA),^{18, 19, 21} and in young athletes also p-hydroxy p- methylbutyrate (HMB).^{22, 23}

The optimal intake of protein drinks is in the morning after awakening (whey), up to 30 minutes post-exercise (the best is whey hydrolysate) and prior to sleeping (casein).¹⁹ In the muscle mass increasing phase“weight gainers” are the best choice. They should be consumed up to 30 minutes postexercise.⁴ A typical creatine load consists of consuming at least 5g of creatine monohydrate 30 minutes before exercise and 5g post-exercise.^{9, 24} Recent studies have indicated that ingesting 3-6g of EAA,²⁴ 5-10g of BCCA⁴ and 1.5-3g of HMB prior to and/or following exercise stimulates protein synthesis.^{4, 22, 23}

Dietary supplements supporting weight loss and fat burning

In the general population, many people may attempt drastic diets and/or take “miraculous” tablets in attempt to lose weight and/or burn fat. Athletes also often do not have adequate knowledge of the theories underlying safe and effective weight loss and fat burning.

The most effective substances from this category of supplements are diet replacements with higher protein and fibre content and lower carbohydrate and fat content.⁴

Thermogenics are supplements designed to stimulate metabolism thereby increasing energy expenditure and promote weight loss. Thermogenesis supporting supplements are e.g. caffeine (300mg 30 minutes prior to exercise)¹⁹ and green-tea extract (1500mg two times per day). Some research suggest the positive effects of conjugated linoleic acid (CLA) and meals rich dietary fibre in weight loss.⁴

Dietary supplements enhancing performance and endurance

Effective supplements for enhancing performance and endurance are sports drinks with the ideal content and balance of carbohydrates and minerals,² and/or the above mentioned creatine,^{4, 9} caffeine,¹⁹ EEA,^{17, 25} and BCAA. Recent studies showed a sustained positive effect of p-alanine on athletes, performance.⁴ Better recovery and adaptation to training occurs after the intake of drinks containing protein and carbohydrate rather than after protein or carbohydrate drinks alone.²⁴

Hard-exercised athletes, of course, should not forget to an increased intake of vitamins and minerals.

Conclusion

This article demonstrates that designing the most suitable diet for an athlete is not impossible, or even difficult. Maintaining an energy balance and a nutrient dense diet, undertaking prudent training, appropriately timing nutrient intake, and obtaining adequaterest are the cornerstones to enhancing performance and/or training adaptations. Use of a limited number of nutritional supplements that research has supported can help to improveenergy availability (e.g. sports drinks, carbohydrate, creatine, caffeine, p-alanine, etc.) and/or promote recovery (carbohydrate, protein, essential amino acids, etc.) and thus can provide additional benefit in certain instances.

The topic of sports nutrition is very broad. Therefore it is necessary to seek resultsfrom a broad range of studies and to ensure these results are applicable to each individualsituation.