Workout Supplements: Do They Really Boost Performance?

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Dietary supplements are widely utilized by athletes of all levels and this reflects their widespread usage in society. Approximately half of adults in the US use some type of dietary supplement and many other countries likely have a similar prevalence, despite regional, cultural, and economic differences. Athletes have various reasons for choosing specific supplements and these products can serve different purposes in their performance plans. This includes promoting good health by providing necessary nutrients, addressing micronutrient deficiencies, and meeting energy and macronutrient needs that may be challenging to attain through food alone. Athletes also use supplements for direct performance enhancement or for indirect benefits such as supporting intense training, manipulating their physique, relieving musculoskeletal pain, recovering quickly from injuries, and improving mood.

This review aims to provide information to high-performance athletes and their support team (coach, trainer, nutritionist, physician) in making informed decisions about the use of supplements. It discusses the issues faced by athletes and emphasizes the importance of supplements that are effective, safe, permitted for use, and suitable for the athlete’s age and sports maturation. Some sporting bodies now endorse the pragmatic use of supplements following a risk-versus-benefit analysis.

What is a supplement?

There is no specific definition for a dietary supplement in either legal or nutritional science. One example is how the US Congress defined a dietary supplement when creating the Dietary Supplement Health and Education Act of 1994.

A product, aside from tobacco, is utilized alongside a nutritious diet and consists of one or more of the following dietary components: a vitamin, mineral, herb or other botanicals, an amino acid, a dietary substance for human consumption to enhance the daily intake or a concentrate, metabolite, constituent, extract, or combinations of these components.

The provided definition is inadequate because it relies on whether or not one consumes a ‘healthy diet.’ Therefore, to establish clarity in this overview, we define a dietary supplement as follows:

A specific health and/or performance benefit is sought by purposefully ingesting a food, food component, nutrient, or non-food compound that is consumed in addition to the habitual diet.

Additionally, we acknowledge that there are various forms in which dietary supplements are available, including the ones listed below:

functional foods, foods enriched with additional nutrients or components outside their typical nutrient composition (e.g., mineral-fortified and vitamin-fortified, as well as nutrient-enriched foods)
formulated foods and sports foods, products providing energy and nutrients in a more convenient form than normal foods for general nutrition support (e.g., liquid meal replacements) or for targeted use around exercise (e.g., sports drinks, gels, bars)
single nutrients and other components of foods or herbal products provided in isolated or concentrated forms
multi-ingredient products containing various combinations of those products described above that target similar outcomes.

Prevalence of, and rationale for, use by athletes

Given the widespread use of supplements among the general population and the emphasis of athletes on reaching optimal performance, it is expected that there is a high prevalence of supplement use reported in most athlete surveys. However, it is important to note that comparing these surveys is complicated by various factors such as variations in how dietary supplements are defined, the difficulty in accurately measuring sporadic supplement use, inadequate selection of study participants, and the utilization of survey instruments that have not been validated or standardized. Nonetheless, surveys generally indicate that supplement use is common.

varies across different sports and activities
increases with the level of training/performance
increases with age
is higher in men than in women
is strongly influenced by perceived cultural norms (both sporting and non-sporting).

Athletes use supplements for various reasons, including taking advantage of the intended/claimed effects or benefits.

to correct or prevent nutrient deficiencies that may impair health or performance
for convenient provision of energy and nutrients around an exercise session
to achieve a specific and direct performance benefit in competition
to gain a performance improvement indirectly accrued from outcomes such as allowing more effective training (i.e., higher intensity, greater volume), better recovery from training sessions, optimizing mass and body composition or reducing risks of injury and illness
for financial gain (sponsorship) or because products are provided free of charge
as a ‘just in case insurance policy
because they know or believe that other athletes/competitors are using the supplement(s).

Some supplements serve multiple purposes. For instance, zinc can be taken to help heal wounds and repair tissue, or to lessen the severity and duration of symptoms from an upper respiratory tract infection. Carbohydrate supplements are used to enhance performance in various events by providing fuel, supporting the immune system, or improving the effectiveness of other supplements, such as creatine. Similarly, creatine supplementation can directly improve performance in strength and power events, as well as aid in training harder, building lean muscle mass, or maintaining muscle during periods of immobilization after an injury. Therefore, decisions about supplement usage should consider both the context of the situation and the specific guidelines being followed.

Assessing the evidence base for supplement use

Different approaches are required to assess the effectiveness of supplements since they target various scenarios of use. For supplements that aim to correct nutrient deficiencies, their ability to prevent or treat suboptimal nutrient status should be evaluated, taking into account the improvement in health, training capacity, or performance that arises from addressing the deficiencies. Determining the effectiveness of sports foods can be difficult when they are consumed as part of a regular diet to meet daily energy and nutrient requirements. However, their benefits may be more easily observed when they are specifically taken before, during, or after an event or training session, providing nutrients that are essential for performance, such as fuel for muscles or the brain, or to maintain homeostasis by replacing lost water and salt. Performance-enhancing supplements, which claim to provide direct or indirect benefits, present a greater challenge in terms of having a solid evidence base. There is a lack of research in this area, with only a few exceptions, and many of the available studies are of insufficient quality to support their use by elite athletes.

It is challenging to provide evidence to support the claims regarding the effectiveness of performance supplements and sports foods. Different audiences have varying definitions of “proof.” However, most of the information regarding the effectiveness of supplements in sports is based on less rigorous sources, such as anecdotes from athletes or scientific hypotheses that explain how a supplement could improve performance without solid evidence. The highest level of evidence comes from systematic reviews and meta-analyses, which consolidate the findings of multiple studies to reach a conclusive statement about efficacy. While these reviews offer general information about performance supplements, they are based on well-controlled and properly conducted scientific trials that also address specific questions about supplement use. Therefore, meta-analyses only reflect the quality and quantity of the studies available for review and may be influenced by the criteria used to include or exclude data.

To investigate the effects of supplements on sports performance, the most reliable method is to conduct a prospective, randomized, controlled scientific trial. In this trial, participants are randomly assigned to receive either an experimental supplement or a placebo (preferably in a double-blind manner). Alternatively, participants may be crossed over to receive both treatments in a counterbalanced order, all under standardized conditions. While some practical issues may lead to deviations from this ideal design, sports scientists are strongly recommended to incorporate the following elements in their studies if they want their results to be relevant to athletes in competitive settings.

adequate sample size and appropriate participant characteristics (e.g., event, training status, calibre) to allow the results to have statistical power and to apply to high-performance athletes
mimicking, as far as possible, the conditions (e.g., environment, nutrition preparation, event strategies) that exist in real-life competition
standardization, to the extent that is possible, of variables that might influence the results (e.g., pretrial exercise and diet, environmental conditions, external encouragement or distraction)—it is recognized that this conflicts to some extent with the above, and will limit the situations in which the results can be applied
use of a protocol of supplement use (e.g., specific product, dose, and timing of intake) that is likely to optimize any effects
independent verification of the contents of the supplement under investigation to ensure that the product is truly unadulterated, both to ensure the integrity of the study and to avoid inadvertent doping positives if the subjects are athletes
verification that the supplement was taken and induced a biological response (e.g., via muscle, blood, urine, or saliva sampling)
a performance protocol that is valid and sufficiently reliable to detect small but potentially meaningful changes/differences in performance outcomes
interpretation of results in light of the limitations of the study design and the change that would be meaningful to real-life sports.

Given the specific details that athletes and their support staff require to determine the effectiveness of a supplement (such as the specific event and conditions, the individual, and the combination with other strategies), it is unrealistic to always expect definitive evidence. It is important to prioritize research on issues that are not thoroughly studied, which includes measuring performance in real-life conditions, investigating the combined use of multiple supplements, and studying the repeated use of supplements in multi-day competitions or when there are closely scheduled events. In situations where there is limited literature or practical research, individual or small-group case studies may be necessary. These studies should consider using recommended methodologies such as conducting repeated baseline performances before using the supplement or alternating between presentations with and without the supplement.

For the purpose of this overview, we primarily rely on studies of healthy adults that are relevant to athletes. We acknowledge the limited availability of data from studies of elite athletes. We also acknowledge the usefulness of mechanistic studies on animal and cell culture models in identifying mechanisms, although proving a mechanism is not essential for demonstrating an effect that may be meaningful to an athlete. It is important to note that an individual’s habitual diet can impact gene expression and microbiota, which in turn can affect response to supplementation. While the variation in the genome between individuals is minimal (less than 0.01%), the variation in microbiota is significant (80%–90%). Emerging data suggest that both factors could influence athletic performance. The following sections present an overview of the use of supplements in sports nutrition, starting with the principles of use and then examining specific products that have solid or emerging evidence to support their use by athletes in specific situations.

Supplements used to prevent or treat nutrient deficiencies

Micronutrients are crucial for sports performance as they regulate various processes, including energy production and cell and protein synthesis. If an athlete lacks these nutrients, it can directly impact their performance, hinder training effectiveness, or increase the risk of illness or injury. Athletes are susceptible to inadequate eating habits and increased nutrient loss, which puts them at a higher risk of deficiencies. Additionally, subclinical deficiencies, which lack a clear metric for adequacy, pose a challenge and are subject to debate regarding their impact on performance. When suboptimal nutritional status is identified, using nutrient supplements can help reverse or prevent further deficiencies as part of the overall treatment plan.

To conduct a nutritional assessment of an athlete, systematic protocols are utilized to obtain, validate, and interpret evidence of nutrition-related issues, along with their causes and importance. An all-encompassing assessment should ideally consist of a comprehensive medical and nutritional history, evaluation of the diet, analysis of anthropometry and body composition, and biochemical testing. Unlike the sporadic use of nutrient supplements chosen by athletes as a precautionary measure, this nutritional assessment aims to guarantee that the athlete:

can address the factors that led to the nutrient deficiency, including ensuring that the athlete’s nutrition plan is adequate in energy, macronutrients, and micronutrients
would benefit from an acute or chronic period of supplementation to correct and/or prevent a nutrient deficiency and can understand the appropriate supplementation protocol
is not at risk for health issues associated with supplement use, including interactions with prescription or over-the-counter medications
has a baseline assessment against which future measures to assess progress can be compared.

In these situations, it is common to need to supplement nutrients such as iron, calcium, and vitamin D. However, individuals living in areas with low levels of iodine in their diet or not using iodized salt should also consider supplementing iodine. Women who might become pregnant should consider supplementing folate, and those following a vegan or near-vegan diet should consider supplementing vitamin B12. These recommendations do not specifically apply to athletes.

Supplements (sports foods) used to provide a practical form of energy and nutrients

Sports nutrition guidelines offer specific suggestions for the amount of energy and nutrients an athlete should consume in different circumstances. Sometimes, it is not feasible for athletes to rely on regular foods to meet their nutrition needs because there may be problems with preparing or storing the food, difficulty consuming it due to training schedules digestive discomfort, or difficulty meeting nutrient goals within their energy budget. In such situations, sports foods can offer a convenient but often pricier option for meeting these nutrient goals.

Supplements that directly improve sports performance

Currently, a small number of supplements have sufficient support to suggest that they may lead to slight improvements in performance. These supplements include caffeine, creatine monohydrate, nitrate, sodium bicarbonate, and possibly Beta-alanine. Before considering the use of performance-enhancing supplements, it is crucial to ensure that there is a strong evidence base to support their safety, legality, and effectiveness. Additionally, athletes should first focus on maintaining adequate dietary practices for sports nutrition. It is recommended that athletes thoroughly test supplements during training sessions that closely resemble competition conditions before using them in a competitive setting. To determine whether the potential gains from these supplements outweigh the risk of unintentional doping caused by contamination, athletes should carefully analyze the associated risks.

Supplements that improve performance indirectly

Dietary supplements are often claimed to indirectly enhance performance by promoting the athlete’s overall health, body composition, and ability to train hard, recover quickly, adapt optimally, prevent or recover from injuries, and endure pain or soreness. When training is interrupted or occurs at crucial moments, such as during selection events or major competitions, illness becomes a significant problem for athletes. Situations involving high training or competition volume, as well as intentional or unintentional deficits in energy intake (e.g., weight loss diets), macronutrient intake (e.g., train-low or sleep-low-carbohydrate), and micronutrient status (e.g., vitamin D insufficiency in winter), increase athletes’ susceptibility to illness. In such cases, athletes may find it beneficial to use nutritional supplements to boost their immunity and combat infections, both during common cold seasons and after extensive travel.

Vitamin C can be beneficial during intense physical activity and zinc lozenges can be helpful when symptoms first appear. However, taking high doses of individual antioxidants, particularly vitamins C and E, may hinder the beneficial effects of exercise on training adaptations. Probiotic supplements may decrease the occurrence of travellers’ diarrhea and gastrointestinal infections. Cochrane reviews have highlighted the inadequate quality of numerous studies on immune-boosting nutritional supplements, with common issues including small sample sizes, insufficient controls, and unclear methods for randomization and blinding. There is an urgent requirement for randomized controlled trials involving a substantial number of high-level athletes, stringent controls and protocols, appropriate supplementation plans, and meaningful measurements of immune function.

The use of supplements can enhance an athlete’s training, recovery, injury prevention, and return to play. Many products claim to provide these benefits. Manipulating body composition, such as gaining muscle and reducing body fat, can also improve performance in various sports. This explains the availability of weight gainers and fat burners in the supplement market, although many are banned in sports. Protein is considered the top ingredient in weight gain-promoting supplements and has been proven effective when combined with resistive exercise. However, the effectiveness of most fat-burning supplements is not well-established, and there is a lack of evidence for the majority of supplements in this category.

Popular workout supplements and what you should know about them

Creatine

According to Micheil Spillane, PhD, CSCS, an assistant professor at McNeese State University, creatine is a well-known workout supplement that is frequently recommended by sports scientists.

The Mayo Clinic states that creatine is a natural substance present in the muscles and brain. It has the potential to enhance energy production during high-intensity activities such as sprinting and weightlifting. Numerous athletes utilize creatine to enhance strength and muscle growth.

According to research and experts, a study conducted in June 2020 in Nutrients revealed that physically active young adults who received creatine supplements while engaging in six weeks of resistance training experienced notable enhancements in leg press, chest press, and overall body strength as opposed to the placebo group.

In a study published in Nutrients in November 2018, it was discovered that the inclusion of creatine supplements resulted in an increase in muscle strength and a decrease in muscle damage following four weeks of training.

Dr. Spillane emphasizes that creatine has a good safety profile and is one of the most thoroughly studied sports supplements, stating that most athletes’ bodies tolerate it well. He further adds that it is something that is typically administered to anyone.

Although there is a lack of research on the effectiveness of creatine, Spillane has observed that approximately 70 per cent of individuals benefit from the supplement.

According to the Mount Sinai School of Medicine in New York City, it is advised to consult with your doctor before consuming creatine if you are concurrently using nonsteroidal anti-inflammatory drugs (NSAIDs), caffeine, diuretics, Tagamet, medications that impact the kidneys, or probenecid (which is used for treating gout). Although generally safe, creaine usage may result in various side effects such as weight gain, muscle strains and cramps, upset stomach, high blood pressure, liver dysfunction, and kidney damage.

Leucine

The University of Rochester Medical Center explains that leucine, which is one of the three branched-chain amino acids (BCAAs), is utilized to provide energy for the skeletal muscles while engaging in physical activity.

According to Spillane, Leucine is one of the top sports supplements suggested by experts as it aids in repairing and building muscle, especially in older adults who may require assistance in maintaining muscle.

According to Spillane, individuals such as bodybuilders and athletes who aim to enhance their strength often rely on this supplement as it stimulates a particular pathway within the muscles that triggers growth and repair mechanisms.

You might not need to take this supplement since you can obtain leucine from your diet, which includes meat, fish, poultry, eggs, and milk.

Based on research conducted previously, BCAA supplements like leucine have been proven to be beneficial in enhancing the amount of lean muscle mass and reducing body fat percentage. A study involving a small group of 36 individuals aged 65 to 75 discovered that those who consumed a leucine-containing supplement two times daily experienced improvements in their lean muscle tissue and functional performance.

The University of Rochester Medical Center advises to exercise caution when considering high doses, as they can result in low blood sugar or pellagra. Previous research suggests that the safe daily upper limit for intake is approximately .53 grams (g) per kilogram of body weight. Moreover, it is important to avoid its consumption during pregnancy or breastfeeding and if diagnosed with maple syrup urine disease.

Protein

Protein provides numerous nutritional benefits and is highly valued in the context of fitness for its ability to enhance muscle growth, aid in muscle repair, and control appetite, as stated by Harvard Health. While most Americans consume sufficient protein in their diet, athletes who engage in high volumes of exercise may consider increasing their protein intake to maximize the benefits of muscle repair. This is why some athletes choose to supplement with protein in the form of powders, either derived from plants (such as pea or rice protein) or animals (such as whey). These powder supplements can be conveniently added to workout smoothies.

According to the National Institutes of Health’s Office of Dietary Supplements (ODS), athletes require 0.5 to 0.9 grams of protein per pound of body weight daily, with the potential for an increase during periods of vigorous training.

It is safe to consume high amounts of protein without any health risks for most healthy individuals. However, surpassing the recommended quantities does not provide any additional benefits, as stated by the ODS. In a review published in May 2018 in Current Nutrition Reports, the authors advised obtaining protein from natural food sources whenever possible and resorting to supplements only when dietary intake is insufficient.

Marie Spano, RD, CSCS, who is based in Atlanta and coauthor of Nutrition for Sport, Exercise and Health, concurs, stating that if one consumes an adequate amount of protein from food, there is no need for supplementation.

Beta-Hydroxy Beta-Methylbutyrate (HMB)

At the Memorial Sloan Kettering Cancer Center, it is stated that HMB is produced when leucine is broken down in the body. HMB is known to prevent or delay any harm to muscle cells caused by exercise. Thus, some individuals who engage in exercise take HMB as a supplement to assist in enhancing muscle development and enhancing strength and stamina.

Based on research and expert opinion, a study released in the Journal of Human Kinetics in 2019 has indicated that HMB has the potential to decrease muscle damage after exercise and enhance recovery time, all while enhancing strength.

Spano suggests that HMB might be especially beneficial to individuals who are in the process of recuperating from an injury. For instance, in the case of a 70-year-old who has fractured their hip and is currently admitted to the hospital and confined to bed rest, HMB can aid in avoiding the deterioration of muscles, which is likely to occur during such a period. However, for young and normally active individuals who regularly engage in exercise at the gym, the utilization of HMB is unnecessary.

Memorial Sloan Kettering Cancer Center emphasizes the necessity for further research to support the potential advantages of exercise.

Caffeine

The function of caffeine extends beyond waking you up in the morning and may enhance your performance during exercise. A review published in December 2020 in Frontiers in Sports and Active Living revealed that 75% of athletes, including triathletes, marathoners, tennis players, and weight lifters, consumed caffeine before or during sports competitions. The review suggests that caffeine’s performance-enhancing benefits may involve preserving muscle glycogen or positively affecting the nervous system.

According to research and experts, caffeine is a beneficial workout supplement. In January 2021, The Journal of the International Society of Sports Nutrition examined studies on caffeine and determined that it primarily enhances aerobic endurance. It is recommended to consume caffeine in doses ranging from 3 to 6 milligrams (mg) per kilogram (kg) of body weight.

Spillane says that although caffeine supplements may not reach your upper limit, they can still potentially cause severe cardiac arrest in certain individuals.

According to MedlinePlus, excessive consumption of caffeine can also result in less severe yet still worrisome side effects like insomnia, headaches, dizziness, and an elevated heart rate.

To ensure safe consumption, the ODS suggests limiting caffeine intake to 500 mg per day, with a maximum of 100 mg for teenagers. If a person takes a single dose of 10,000 mg, equivalent to 1 tablespoon of pure caffeine powder, it can lead to fatality.

Kaiser Permanente advises being cautious about caffeine products mixed with ephedra, especially if you have a heart condition, hypertension, diabetes, or thyroid disease. This combination can raise heart rate and blood pressure and can be found in weight loss and energy supplements.

Practical implications and decision tree

Dietary supplements play a significant role in modern sports and are likely to continue doing so. Athletes who use supplements often lack a clear understanding of their potential effects, but it is important to carefully consider the costs and benefits before using them. On one side, the benefits include correcting nutrient deficiencies, achieving nutritional goals, and improving performance through physiological/biochemical enhancements. On the other side, there is the risk of using an ineffective supplement, potential health hazards, and the possibility of violating anti-doping regulations.

When deciding whether to use a supplement, athletes should consider all aspects of their training and preparation for their event. They should ensure that the supplement provides an advantage that cannot be addressed by any other strategy. Additionally, athletes should assess whether the supplement is practical to use, including factors such as availability, affordability, tolerability, and compatibility with their other goals. It is important to consult with an athlete’s coaching team and medical/science support network. Athletes without access to such a network should consult an independent sports nutrition expert and a physician when making decisions about supplement use. Analyzing the evidence regarding the effectiveness and safety of supplements can be challenging. A complete nutritional assessment may offer a valid justification for using specific nutritional supplements and sports foods. Some sports supplements have good evidence of performance benefits or indirect advantages for certain athletes in specific situations, with minimal risk of negative outcomes. It is crucial to seek professional advice to ensure that athletes have sufficient knowledge about the appropriate protocol for using these supplements. However, individual athletes may respond differently to a particular supplement, with some experiencing significant benefits while others may see no improvement or even a decline in performance. Additionally, the context in which an athlete wants to use a supplement may differ from its scientifically proven use. Repeated trials may be necessary to determine if a true effect, rather than random variation, is observed when using a new intervention. Some trial and error may also be involved in adjusting the supplement protocol to suit the specific needs of the situation or the individual athlete.

The available evidence to support the effectiveness and safety of many supplements targeted at athletes is lacking. Those selling supplements may not have a strong incentive to conduct detailed scientific evaluations of their products due to the substantial costs involved. Even when some evidence does exist, it may not be relevant to high-performance athletes due to limitations in the study design, the participants, or the context of use. Failing to verify the composition of supplements can also lead to misleading results. Therefore, caution should be exercised when using supplements, as any compound that can potentially enhance health or exercise performance may also have adverse effects on certain individuals. Athletes should require substantial evidence of performance or other benefits, as well as confidence in the lack of harm to health, before investing in supplements and accepting the associated risks. Additionally, athletes should ensure that they have done sufficient research to source low-risk products that do not contain any prohibited substances if they choose to use supplements or sports foods.