The Science of STAMINA
From Gatorade to creatine, a dietary supplement used by baseball sluggers Sammy Sosa and Mark McGuire, ingredients and formulated products targeting weekend warriors, as well as professional athletes, have grown in popularity.
As with so many market statistics, estimates of the size of the sports nutrition market vary widely, depending on types of products included and distribution channels monitored. Nutrition Business Journal, for example, reported that sports nutrition products—in the form of supplements, bars and drinks—racked up $4.7 billion in consumer sales in 1999, a 10% rise over 1998. Slightly over half of this category consists of sports beverages.
In contrast, a Frost & Sullivan report places revenues from the U.S. sports and fitness nutrition market at nearly $2 billion in 2000, and projects it to reach nearly $4.5 billion by 2007.
Catering to the needs of athletes and active individuals looking for a performance edge, some isotonic beverages deliver quick rehydration. Others offer specialized protein, peptide and amino acids for muscle development and repair. Yet others claim to have a cluster of or the "magic bullet" to enhance performance. Such substances are called ergogenic aids and theoretically enhance performance by improving energy production, hormone-related anabolism and recovery.
Rehydration & 'Carbo Loading'
Athletes strive to obtain both fluid (if needed) and energy at the highest possible rate before and during exercise. Sports drinks should be formulated to provide a supply of substrate (energy), furnish electrolyte replacement, prevent dehydration, and provide pre-exercise hydration and post-exercise rehydration.1
During exercise, sweat loss can exceed two liters per hour. The negative consequences of dehydration include reduced oxygen supply to muscle cells and impaired heat exchange.2 This negatively impacts both health and performance.
In rehydration beverages, increasing carbohydrate (CHO) concentrations, to a point, translates to a faster rate of water absorption since solutes are more easily absorbed than pure water.
However, a beverage's osmolality also increases as the concentration of any particular CHO increases, which counters rehydration by enhancing osmotic fluid secretion into the gut. This is why soft drinks with over 100g CHO/l are less effective sports drinks. Larger CHO molecules, such as maltodextrins or glucose polymers, are generally preferred because they produce beverages of lower osmolality. Thus, higher concentrations of these ingredients can be used (e.g., 6-8%).
Higher CHO contents (e.g., solutions containing >5% glucose (w/v)) can also slow rehydration rates because they, like proteins and fats, delay release of materials from the stomach to the small intestines where absorption occurs. Overall, optimum rehydration occurs if the beverage is formulated to be less than 400 mOsm/l.2 But what about energy needs? Much evidence exists for the effectiveness of "carbohydrate fueling."3 Athletes "top off" or "carbo load" before an event to maximize carbohydrate (glycogen) storage in the muscle, to supplement carbohydrates during an event and replenish quickly after.
In formulating sports bars, for example, product developers have found the glycemic index concept useful. Glycemic index refers to a food's ability to increase (or undesirably spike) blood glucose levels. (See www.preparedfoods.com, type in "glycemic index" in search field.)
Products with a moderate to low glycemic index (GI) evenly sustain blood glucose release and maintain fat oxidation, which spares muscle glycogen. The lower the GI, the better the blood glucose is sustained. This is especially important for pre-event fueling. Eating a high glycemic index product less than an hour prior to an athletic event may run the risk of hypoglycemia at the start of the event. Adding fiber, especially soluble fibers, protein and fat, lower GI.
Products on the market often claim that simple sugars are for quick energy and complex carbohydrates are slow carbohydrates for sustained energy. However, this is an oversimplification. Fructose, a simple sugar with a low glycemic index compared to glucose, is absorbed and metabolized relatively slowly in the body. Maltodextrin, a more complex carbohydrate, has a higher GI more similar to glucose.
Products with a high glycemic index are recommended both for fueling during and after an event.4 During intense exercise, muscles require quick, readily available energy and hypoglycemia is not a concern since insulin release is down, regulated during exercise. High GI products are thought to speed recovery post event. It is important to drive anabolic processes to replenish glycogen and protein, especially for multi-event competitions. A three-to-one ratio of CHO to protein speeds up glycogen anabolism.
Proteins and Peptides
Proteins, peptides and amino acids aid in muscle growth and repair. They are also beneficial in that a chronic shortage may lead to a net amino-nitrogen loss in tissues, resulting in poorer performance and muscle wasting. During extreme physical exercise, oxidative energy production uses more amino acids, particularly when there's a shortage of glycogen. From a product developer's point of view, protein quality, not quantity, should be important. This is captured in a protein's "Protein Digestibility Corrected Amino Acid Score" or PDCAAS, which individual suppliers provide. Regulations (21 C.F.R. Â§ 101.9(c)(7)(i)) set forth instructions on how to determine the "Percent of Daily Value (PDV)" of protein for the Nutrition Facts panel. The PDV, in turn, is calculated from an equation involving the PDCAAS.
Manufacturers often tout the presence of whey protein concentrates and isolates on their ingredient legends. "Analytical tests of some of our own products have shown their PDCAAS to be as high as 1.14," says Polly Olson, director of marketing & sales with Davisco Foods. "However, federal regulations say that 1.00 is the maximum that can be declared."
PDCAASs are based on our current understanding of human amino acid requirements, notes Olson. Interestingly, some researchers have begun to question exactly what our essential amino acid requirements are, she adds.
Individual amino acids, such as tryptophan, arginine and those that are branched-chained, can attract consumers. The thought is that benefits range from an ability to influence fatigue development to stimulate the release of human growth hormone or insulin. Amino acids challenge formulators, however, because they add cost, are often bitter and are generally not absorbed as swiftly as peptides.
Of the ergogenic aids, the strongest scientific evidence exists for the efficacy of carbohydrates, caffeine (e.g., from coffee beans or guarana seeds), and creatine. For example, one researcher found 2 to 5 mg caffeine/kg increased performance.
Items with more conflicting support include L-carnitine, the mentioned amino acids, glycerol and antioxidants in general. Other popular items that still require the most research include bee pollen, Co-enzyme Q10, ginseng, inosine, medium-chain triglycerides (MCTs) and Ciwujia, also known as Eleuthera or Siberian ginseng.
"We have new research on MCTs and their ability to provide a dense source of readily available energy for sports products," says Andy Estal with Stepan Food Ingredients. "MCTs are metabolized differently than traditional fats and provide seven calories per gram versus the four obtained from a carbohydrate."
When considering adding an ergogenic aid to a product, a three-step process has been suggested:
- Investigate the performance claim based upon a physiological and biochemical understanding of exercise. Does it make sense?
- Investigate supportive evidence and use care when the evidence is not published research from peer-reviewed journals.
- Determine safety, ethical, and legal consequences of taking the ergogenic aid.
Such advice contributes to sports products in the marketplace with a strong performance of their own.
1 Maughan, R.J. 1998. Proceedings of the Nutrition Society. 57:15-23.
2 Brouns, E., and Kovacs, E. 1997. Functional drinks for athletes. Trends in Food Sci. and Tech. 8:414-421.
3 Fallowfield, J. et al. 1995. The influence of ingesting a carbohydrate-electrolyte beverage during 4 hours of recovery on subsequent endurance capacity. Int. Sports Nutr. 5:285-299.
4 Browns, E. 1997. Functional Foods for Athletes. Trends in Food Sci. and Tech. 8:358-363.
5 Smith JC, et al. 1998. Effect of oral creatine ingestion on rate-time relationship and time to exhaustion in high-intensity cycling. Eur J Appl Physiol. 77:360-5.
6 Zawadzki, et. al., 1992. Carbohydrate-protein complex increases glycogen storage. The American Physiological Society.
7 Pasman, W.J. et al. 1995. The Effect of Different Dosages of Caffeine on Endurance Performance Time. Int. J. Sports Me. 16:225-230.
8 Butterfield G., 1996. Ergogenic aids:
Evaluating sport nutrition products. Int. J. Sport Nutr. 6:191-197.
Also see: Applegate, E. 1999. Effective Nutritional Ergogenic Aids, Int. J. of Sports Nutrition. 9:229-239.