Carbohydrates have a wide range of functions, but they are most known for providing kilocalories (i.e., energy) and a storage form of energy in the body. Simpler carbohydrates are known to have the empirical formula (CH₂O) _n , hence the name “hydrate of carbon” [8]. Carbohydrates are usually classified into three major groups: monosaccharides, disaccharides, and polysaccharides.

Monosaccharides are single sugar molecules and include glucose, fructose, and galactose. Monosaccharides can bond to form disaccharides and polysaccharides. Disaccharides, as the prefix suggests, are two sugar units and include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose). Monosaccharides and disaccharides are better known as simple carbohydrates or simple sugars. Polysaccharides are commonly referred to as complex carbohydrates. Important polysaccharides include starch, fiber, and glycogen. Glycogen is also the storage form of glucose in the body and is found primarily in the liver and skeletal muscle.

Over the last few decades, simple carbohydrates have received an overwhelming amount of negative attention. Beverages such as sodas, fruit juices, energy drinks, and functional waters are sweetened with simple sugars [9], and these sugar-sweetened beverages are associated with an increased risk of weight gain, metabolic syndrome, and type 2 diabetes in both children and adults [10–12]. Furthermore, simple carbohydrates have also been associated with a greater risk for certain cancers [10]. It may sound like simple carbohydrates are vastly inferior to complex, but a mix of carbohydrate types is beneficial for supplying athletes with energy. While the majority of the sedentary population should cut back and even avoid sugar-sweetened beverages, the athletic population has better use of short-term simple sugar-containing beverages to enhance training adaptations and exercise performance during competition [13]. With that said, athlete should consume simple sugars before, during, and after exercise training (this will be further discussed in the nutrient timing section).

Polysaccharides are generally promoted because of their ability to be absorbed more slowly and provide greater nutrient value overtime. Starch is the storage form of carbohydrate in plants, and starch can be found in grains, nuts, legumes, and vegetables. It is a viable energy source because it digests slowly and provides energy for longer periods than does simple carbohydrate. Fiber on the other hand, is indigestible, and is useful in slowing the digestive rate of food, adding bulk to the feces, reducing appetite and is associated with health benefits [14, 15]. It is found in foods such as vegetables, fruits, nuts, and legumes. Current recommendations suggest that ~20–40 g/day, depending on age and gender, of dietary fiber be consumed for proper health [16].

Although first developed for use with diabetics, the glycemic index (GI) provides a useful tool for helping athletes with food choices. The GI is a measurement of the response of blood glucose concentration after a 50-g bolus of a carbohydrate-containing food [17, 18]. The values are based on a standard of 100, which is the value for glucose or white bread (common food found globally). Often, people mistake the GI as a function of whether foods are simple or complex. However, some complex carbohydrates (e.g., baked potatoes) may increase glucose levels similarly to glucose. These values can be helpful for athletes to determine food choices when they quickly want to increase glucose/glycogen levels. A food is considered to have a low GI when its value is less than 55, a medium GI when it is 55–70, and a high GI when its value is over 70 [19].

Glycemic load (GL) is often confused with the glycemic index. Although GL is related to GI, the latter is thought to be a better indicator of dietary insulin demand [20]. GL is related to GI, yet its value represents the effect it will have on blood sugar after an average serving of a particular food [19]. It is calculated by dividing the product of the grams of carbohydrate in a typical serving of a food and its GI value by 100 [19]. A low, medium, and high GL is represented by a score of 10 or less, 11–19, and 20 or more, respectively [19]. Table 4.2 lists common foods and data derived from subjects with normal glucose tolerance [21].

Lipids are a broad group of energy dense compounds made up of carbon, hydrogen, and oxygen that are insoluble in water. Often, the terms fat and lipid are used interchangeably, although they are indeed different―all fats are lipids, but not all lipids are fats. Lipids include triglycerides, sterols, and phospholipids. Triglycerides are the primary fat found in our food and our body. They are the primary storage form of fat within the human body. Sterols are found in both plant and animal sources. In animal and plant sources, sterols are referred to as cholesterol and plant sterols, respectively. Although many associate cholesterol with negative health outcomes, it plays an import role as a structural component of all cell membranes and is a precursor of bile acids, steroid hormones, and vitamin D. Phospholipids are the predominate lipids of cell membranes. Phospholipids play a role in intracellular communication as well as structural support of the cell membrane. Many other lipids exist and are significant in the diet. For the purposes of this chapter, the terms fat/fats will be used to refer to dietary lipids.

Weight gain is often attributed to dietary fats because they contain far more energy per gram than does carbohydrate or protein. Dietary fats provide 9 calories per gram, while carbohydrates and proteins provide 4 calories per gram. Fats are often viewed in a negative light due to the association with weight gain and their role in disease development. However, fats serve many functions in the body. These include providing energy for tissues and organs as well as playing a role in cell membrane makeup, nerve signal transmission, vitamin transport, and cushioning and insulation for internal organs. In addition, for endurance athletes, they are a vital fuel source for skeletal muscles.

The primary fats found in large quantities in foods are triglycerides. Triglycerides are composed of three fatty acids and one glycerol molecule. Fatty acids can be grouped by the amount of hydrogen they contain, otherwise known as saturation. Saturated fatty acid chains contain no double bonds; monounsaturated fatty acids contain one double bond; and polyunsaturated fats have two or more double bonds. The fatty acid makeup of the triglycerides is important to its metabolism in the body. For example, saturated fats may increase cholesterol in the body, while unsaturated fats may have no effect or lower cholesterol.

Cholesterol is found in food and even synthesized by the body. High-density lipoproteins (HDLs) are a type of cholesterol composed of a high protein-to-fat ratio. HDL is typically known as good cholesterol because of its protective nature against heart disease, while elevated low-density lipoproteins (LDLs) are a risk factor for heart disease. LDL is primarily fat with lower amounts of protein. However, recent research suggests that lipoprotein size, regardless of whether the lipoprotein is high or low density, is more important to cardiovascular health [22]. Small particle LDL and HDL may both have a negative effect on the cardiovascular system [22]. A recent prospective study of 26,332 initially healthy women evaluated the association between HDL particle size, determined via nuclear magnetic resonance spectroscopy, and the risk of coronary heart disease (CHD) [23]. Researchers observed a positive association in CHD and both small and very small HDL particles.

Dietary fats also provide a source of essential fatty acids. These fatty acids are essential as the body cannot synthesize them from endogenous sources. There are two types of fatty acids to pay special attention to in the diet. The essential fatty acids are linoleic (omega-6) and linolenic (omega-3), both 18-carbon fatty acids. Linoleic acid is found in oils of plant origin, while marine oils are a good source of linolenic acid. Although both linoleic and linolenic are essential fatty acids, they have very different roles in the body. Linoleic acids are generally associated with the promotion of inflammation [24] and certain cancers [25], while linolenic are anti-inflammatory and associated with a decreased risk of heart disease [26] and cancers [25].

Trans fatty acids should receive considerable attention as well due to their relationship with health status. Trans fats, as they are commonly known, are often oils that are solidified through a process known as dehydrogenation, although some amounts are found naturally. Dr. Paul Sabatier, a French chemist, received the Nobel Prize in Chemistry in 1912 for developing a method to convert oils, via hydrogenation, to saturated fats. Trans fats are now used in foods such as margarine, shortening, and some dairy products. These fats are beneficial to the food industry as they are inexpensive to make and promote product shelf life. The reduction of trans fats has become a point of public scrutiny in places such as fast food and packaged foods because, although they are unsaturated fats, they behave like saturated fats in the body. Trans fatty acids have been shown to have a negative effect on blood cholesterol markers of health, increase inflammatory markers, and promote endothelial dysfunction [27]. Research suggests that trans fatty acids should have no place in our food supply as they have no health value and pose substantial health risks [28]. In 2013, the Food and Drug Administration took their initial steps to potentially eliminate trans fats from our processed-food supply as ample evidence suggested that trans fats are no longer safe for consumption.

Generally, fruits and vegetables contain little fat. Animal products such as meat, milk, cheese, and eggs, as well as baked goods, generally contain high amounts of saturated fats. Nuts and peanut/canola oils can be good sources of monounsaturated fats. Polyunsaturated fats, including the essential fatty acids, can be found in fish, nuts, corn, soy, and sunflower oils. Lastly, margarine, shortening, cookies, pastries, and fried foods have high levels of trans fats.

Paramount to understanding sport-specific eating and proper food decisions is a basic knowledge of the metabolic usage of the macronutrients within the body. This chapter will give only a cursory overview of the bioenergetics of activity and exercise, yet these principles are essential to a proper nutritional design. The discussion here will be limited to energy production from carbohydrates and fats.

The primary energy systems used during exercise depend on the intensity and duration of the exercise. Most exercise activity can be categorized as power–strength events (e.g., discus throw), speed events (e.g., 100-m sprint), and endurance events (e.g., triathlons). Short quick bursts such as a discus throw and vertical jump are fueled by the phosphagen system (adenosine triphosphate [ATP] system and creatine phosphate [CP]). The glycolytic system is mainly responsible for supplying energy derivative during speed events such as a 100-m and 400-m sprints. Endurance events are mainly supported by the substrates metabolized by the oxidative phosphorylation system. It is important to realize that all of the energy systems work in unison, but under certain conditions, one energy system may be more dominant in providing energy substrates. In terms of energy metabolism for exercise, it is agreed that fats provide the dominant energy source during low- to moderate-intensity exercise [29]. As exercise intensity increases, there is a greater reliance on carbohydrate (e.g., muscle and liver glycogen; blood glucose; blood, muscle, and liver lactate) oxidation for fuel. In addition, the longer the duration, the more fat will be utilized. This means that even activity that begins at high or moderate levels will taper off due to glycogen depletion, and fat will be the primary fuel derivative after 20–30 min of continual exercise. These basic concepts are essential to determine proper dietary guidelines for an activity or event.

When comparing energy reserves, the human body has far more fat than glycogen stores. Skeletal muscle glycogen stores approximately 400 g for an 80-kg individual, with an additional 100 g stored in the liver. In comparison, that same 80-kg individual may have over 12,000 g of fat stored in adipose tissue! When factoring in the fact that fat is more than twice as calorie dense than carbohydrate, the energy stores are quite unbalanced. However, while each fatty acid provides 147 ATP and each triglyceride provides 460 ATP, glucose metabolism (36 ATP/molecule) is more efficient per unit of oxygen at providing energy. In addition, it takes roughly 20 min for free fatty acids to be liberated for use through lipolysis. Therefore, per unit of time glucose is more efficient and thus the preferred fuel for high-intensity exercise. These data help to briefly detail the merits of both fats and carbohydrates as fuel sources. The importance of both of these fuels should not be underestimated by the athlete, when considering intake or expenditure.

Possibly, the most important piece of the nutritional puzzle for athletes is the understanding of how to determine the right amount of calories and macronutrients to consume. After all, what good is an understanding of what the nutrients are for an athlete if they do not know how much they need to take in?

The initial consideration when determining macronutrient needs is to determine the goal of the nutritional design. Is the goal to improve muscular strength and power, lose fat mass, or simply improve body composition? Secondly, one must then consider the bioenergetics of the event or training required to meet the established goal. For example, a high-intensity, high-frequency resistance training will require higher dietary protein intake than other forms of exercise. Finally, physiologic factors such as size, age, and gender will play a role in caloric needs as well as the macronutrient distribution of those calories. For example, older athletes may need higher protein intake to prevent muscle loss and/or bone resorption, while highly active women at risk for amenorrhea may need to increase caloric intake and fat consumption.