In the United States, a summary definition of dietary supplements as defined by the DSHEA of 1994 [1] can be stated as “a product (other than tobacco) intended to supplement the diet that bears or contains one or more of the following dietary ingredients: (a) a vitamin, (b) a mineral, (c) an herb or other botanical, (d) an amino acid, (e) a dietary substance for use by man to supplement the diet by increasing the total dietary intake, or (f) a concentrate, metabolite, constituent, extract, or combination of any ingredient described in clauses a, b, c, d, or e.” It should be noted, additionally, that any claims a manufacturer or individual makes about a supplement might change its classification. Dietary supplements claimed to cure, mitigate, or treat disease would be considered to be an unauthorized new drug rather than a supplement. Researchers have also differentiated “nonvitamin, nonmineral supplements” (NVNM) as those primarily consisting of herbal, botanical, protein/amino acid, brewer’s yeast, and shark cartilage and a variety of other plant-based and nonplant dietary supplements such as enzymes and fish oil [3, 4]. Finally, in the arena of competitive sport specifically, it should be noted that there are both “accepted” and “illegal/banned” substances, including some supplements. Making this distinction somewhat difficult, various sport governing bodies do not necessarily agree about which supplements should constitute banned substances, with inconsistencies appearing between the IOC, WADA, USOC, and the NCAA [5].

In an interesting quandary for the field of performance enhancement, many supplements marketed to athletes may contain banned substances—either overtly or because of impurities in these supplements. Geyer and colleagues’ [6] IOC-commissioned study examined nonhormonal supplements to determine the prevalence of anabolic–androgenic steroids (AAS) in these products not listed on the label. Researchers bought supplements from 215 suppliers in 13 different countries testing 634 nonhormonal supplements. A meaningful percentage of the supplements (14.8 %) contained substances that would lead to a positive drug test. These results indicate that a proportion of supplements would be considered drugs; further, they would be considered drugs with potentially deleterious side effects. The difficulty for many athletes and the various sport governing bodies is that it is difficult to determine which supplements may truly be supplements and which contain substances that would be considered drugs.

Despite the possibility for failed doping tests, athletes typically take supplements because they want an advantage over their competition. Supplement use should not be surprising considering that some athletes are willing to take illegal/banned drugs to improve performance. Thus, it would appear that the desire for money, fame, and feelings of achievement associated with athletic success are driving forces for the use of sport supplements. Yet not all athletes use supplements, and some are extremely cautious about the substances they ingest. Perhaps there are more subtle psychological factors at work that should be considered.

Problems also abound for individuals who supplement in order to achieve added weight loss and/or muscle gain (or even improved recovery post-workout) from their exercise programs. Products of dubious efficacy are plentiful, and little is known about drug/supplement or supplement/supplement interactions which may be hazardous to the user’s health [7, 8]. Substances such as brindleberry (Garcinia cambogia/indica), capsaicin, caffeine, l-carnitine, chromium picolinate, and Ginkgo biloba have purported weight loss benefits; however, not all of these substances have research support in the published literature [9]. Considering a worldwide ongoing obesity epidemic [10] and problems in particular in the United States, it is not surprising that many individuals are seeking new ways to lose weight. Supplements promise, though probably seldom deliver, a magic bullet of sorts—easy, hassle-free weight loss with little in the way of dietary sacrifice. Motivation for users of weight loss supplements, however, is likely not simple or straightforward. A range of issues ranging from body image concerns to obsessive tendencies may be important to consider.

There have been several large-scale surveys of supplement use among US citizens. The Slone Survey [11] used random digit dialing to survey 2,590 US citizens to determine commonly used herbals/supplements (nonvitamin, nonmineral: NVNM) and vitamins and minerals. The ten most commonly used substances in these categories are reported in Tables 2.1 and 2.2, respectively. Additionally, 14.0 % of individuals reported use of a herbal/supplement over the previous 7-day period. Popular reasons given for the use of herbal/supplements included health (16 %), arthritis (7 %), memory improvement (6 %), energy (5 %), and immune booster (5 %). Recent analysis of NHANES data from 2003 to 2006 [12] found that of the 18,758 individuals included in the analysis, 49 % reported supplement use, with multivitamins being the most commonly consumed (33 %) followed by botanical supplements (14 %). Over 70 % of adults over 71 years indicated using at least one dietary supplement [12].

Other large surveys have been conducted to examine supplement use and find, generally, greater usage rates among older individuals, nonobese, Caucasians, females, nonsmokers, physically active individuals, those with higher levels of educational attainment, as well as those with higher fruit and fiber intake [3, 13, 14]. In a study of 1,000 university students, Perkin and colleagues [4] found that 26.3 % indicated use of a NVNM supplement and 16 % had used in the past. ginseng, echinacea, protein powder/amino acids, and Ginkgo biloba were the most frequently used supplements. Reasons for use included to improve energy (61.2 %), to promote weight loss (38 %), to burn fat (36.1 %), to supplement inadequate diet (35 %), to build muscle (27.8 %), and to relieve stress/improve mood (24.7 %). It appears the reasons for use in the university population are more performance- and appearance-driven than the reasons for the general US population, which are more health-focused [11].

Examining the literature as a whole, it is well-established that supplement use is high among athletic populations and those who want to either build muscle or lose weight. What existing theoretical paradigms, however, might inform our future study of this area concerning reasons for use and potential abuse? To answer this question, it is perhaps best to consider three specific categories—supplement use to produce athletic performance benefits, supplement use to build muscle for aesthetic purposes or body image concerns, and supplement use to lose weight for aesthetic purposes, body image concerns, or health. Each of the three reasons for use likely has different motivational underpinnings. Therefore, in our description of theoretical paradigms that may be applied to understand supplement use, we have tried to identify the areas where each theory may be particularly effective for understanding supplementation. Overall, it should be considered that there are likely to be multifaceted, overlapping motivations for supplement use. Table 2.3 gives an overview of psychological/motivational theories and constructs that may be related to supplement use. As is obvious upon examination of this table, little direct inquiry has been conducted to explain motivation to use supplements in sport and exercise settings.

Certainly, there is a behavioristic explanation possible for the use of supplements in that athletes’ use may lead to reward contingencies (e.g., more prize money) thus driving future behavior. Similarly, supplements that build muscle or promote weight loss could produce rewarding results. Also, there are undoubtedly social influences at work considering that coaches, parents, athletic trainers, and peers have been reported as influential to the decision to take supplements [17, 19, 20]. Finally, other extant motivational theories may be useful to predict supplement use and abuse. Most of these potential explanations have received limited research, if any, in the context of supplement use, so our primary purpose is to describe how theory or previous research would predict the stated constructs’ explanatory ability and direct future inquiry to understand motivation for supplementation.

Among theories adopting the concept of normative influence on behavior, the theory of planned behavior (TPB) may be useful for understanding motivation to use supplements. This theory proposes the existence of three psychological constructs which are believed to influence behavior through the mediator of intent: normative influences, attitude, and perceived behavioral control (see Fig. 2.1) [27]. Within normative influences, it is important to consider what one believes concerning what others feel you ought to do, known as the injunctive norm, in addition to the actual, descriptive norm relating to what others do themselves [27, 28]. Attitudes pertain to the degree that a behavior is positively or negatively valued. Specifically, in this context, would taking supplements be considered “good”? Perceived behavioral control pertains to one’s beliefs about factors that might facilitate/impede performance of a behavior. Factors such as cost and availability of supplements would be expected to influence perceptions of behavioral control. No known study has focused on supplement use among athletes/exercisers using this theory, though it has shown very good predictive ability examining supplement use in other populations. In a study of 400 randomly selected women from the UK Women’s Cohort Study including 15,000 participants who completed variables pertinent to TPB constructs and supplement use, Conner and colleagues [28] found that intent very accurately predicted supplement use (82.9 % accuracy) and that attitude was the strongest predictor of intent, though subjective norm and perceived behavioral control were also significant predictors of intent. The latter three variables predicted an astonishing 70 % of variance in intent to use supplements. Certainly, these findings suggest that attitudes, normative beliefs, and perceptions of control are important correlates of supplement use among women. What is not known, however, are the ultimate reasons for use in this sample (e.g., weight loss, health benefits, etc.). Future research examining the TPB’s predictive ability given different reasons for supplement use may be informative as these reasons may moderate the relative association of these predictors with intent to use and actual supplement use.

When trying to change attitudes about whether supplements are good or bad, it is likely that some individuals will be more persuasive than others. For example, individuals will be more persuasive if they are seen as trustworthy or having pertinent expertise [29]. The supplement industry often uses exactly such a strategy to help market their products. University research and “expert” sport and exercise nutritionists are increasingly being used to support the efficacy of performance-enhancing, muscle-building, or weight loss supplements. While this is a wise strategy on the part of the supplement industry from an economic standpoint, consumers should also consider that a company may contract with multiple universities to test their product and only report the results of the positive outcomes in their advertisements. Such a practice should be viewed as unethical, yet this is certainly a possibility. In recent years, certain research labs have even garnered a reputation for somehow always producing positive results for certain supplements. In some cases, these findings run contrary to a majority of previous research. Even in the published literature, there is likely to be a bias to the benefits of supplements as opposed to studies documenting no effects due to the file drawer problem in current scientific practice where significant results are published more frequently than nonsignificant results [30, 31]. Scientists conducting investigations in the area of supplements should attempt to publish nonsignificant and significant findings alike because of these issues.

Another theory that might inform persuasive efforts to effect attitude change is Heider’s [32] balance theory. According to this theory, people want to view the world in a consistent manner. In other words, if your favorite athlete has admitted using a controversial supplement but you do not generally approve of the use of performance-enhancing substances, you are likely to change either your opinion of the athlete or acceptability of substance use in order to achieve harmony of thought and action. In this manner, we might expect that overt or covert messages from well-liked or well-respected athletes that indicate their use of supplements will cause others to view use as acceptable even if they initially resist. This would also support supplement companies’ use of well-liked spokespersons to tout the use of their products. Similarly, using well-liked spokespersons to advertise supplements with purported weight loss benefits should have similar effects.

In a similar vein, it may be informative to look at disordered eating practices and supplement use. Examining the diagnostic criteria for bulimia [43], one of the notable symptoms is “recurrent inappropriate compensatory behavior in order to prevent weight gain, such as self-induced vomiting; misuse of laxatives, diuretics, enemas, or other medications; fasting; or excessive exercise” (p. 549). It might be expected that individuals suffering from bulimia, and perhaps anorexia nervosa, would have excessive or unhealthy supplementation practices. Research has shown that among women at risk for eating disorders, approximately 65 % engage in frequent use of “diet pills” [44], of which it is reasonable to assume a large portion would be considered supplements. Again, as the supplement industry has surged ahead promoting an ever-increasing range of products, researchers must try to determine how this may pose yet another risk for those who have eating disorders. It may also be that high levels of supplementation could be a warning sign of an eating disorder. More research simply needs to be done in this area. We do know that a warning sign of eating disorders is excessive exercise [43], and those working in exercise settings should be alert to this.

In one of the seminal works in this area, Pope and colleagues [46] interviewed 108 bodybuilders (55 steroid users and 53 nonuser controls) and found a higher than normal incidence of anorexia nervosa (2.8 % incidence) and a surprising incidence of “reverse anorexia” (8.3 % incidence) in which respondents believed they appeared small and weak despite a very large, muscular appearance. The latter finding indicated that some of these bodybuilders exhibited unusual preoccupations with their appearance. Such pathological preoccupations with muscularity have been termed muscle dysmorphia, and research concerning this issue has found it to be relatively common among adolescents and young males [45]. As an important link to potential supplement use or abuse, in Pope and colleagues’ [46] research, all of the bodybuilders indicating muscle dysmorphia (then termed “reverse anorexia”) were in the sample of steroid users, and many reported that the symptoms of muscle dysmorphia were a factor that led to steroid use. If these individuals are driven to use illegal substances, one might expect higher than normal use of any substance (i.e., muscle-building supplements) purported to promote strength or muscle mass gains. As an indication of the degree of this obsession, individuals with this affliction have reported lifting weights for hours a day while sacrificing other areas of their lives. For example, some of these individuals reported earning degrees in business, law, or medicine but did not pursue a career or gave up a career in these areas because they needed more time to lift weights [47].

Recent research indicates that bodybuilders suffering from higher levels of muscle dysmorphia are more likely to experience body dissatisfaction, social physique anxiety, and use muscle-building- or fat-reducing-targeted supplements [48]. While the association between “muscle dissatisfaction” and frequency of exercise has been questioned, indicating that incidence of muscular dissatisfaction is similar among frequent and infrequent exercisers [49], this study used perhaps an overly simplistic measure of muscular dissatisfaction likely not sensitive to indications of muscle dysmorphia. Nonetheless, further research is necessary to determine the incidence of muscular dissatisfaction or muscle dysmorphia and their impact on a variety of important outcomes such as supplement use. At present, there is some evidence that supplement use is greater among individuals with muscle dissatisfaction [49], muscle dysmorphia [48], or a high drive for muscularity [50]. It also appears that illegal supplement use may accompany muscle dysmorphia as data indicate that one million or more US males have used these substances (such as anabolic steroids) primarily to promote muscle growth as opposed to performance enhancement purposes [45]. Finally, it should also be noted that research finds that some men have become preoccupied with fat as opposed to muscle and, in contrast to attempting to gain weight, may develop eating disorders [45]. This suggests that body image concerns among males may drive some to obsessively attempt to build muscle mass, whereas others may obsessively work to lose fat—and in both cases, it is likely that legal or illegal supplementation is a common means to achieve such goals.