Every human on this planet needs energy: energy for chemical work, energy to produce body heat, and, especially for athletes, energy to perform physical work. Food is where we get this life-sustaining energy. More specifically, plants harness energy from the sun’s rays to convert a gas, carbon dioxide, and water into carbohydrate. Animals—cows, chickens, bison, ostriches—consume these plants and carbohydrates and convert some of them into fat. Ultimately, the carbohydrates and fats found in the plants and animals that we feed on are used to make a high-energy molecule—known as adenosine triphosphate (ATP)—that powers everything our bodies do. Although we can use protein to make ATP, our bodies prefer to save it for building muscle and other vital tissues and substances. Consequently, dietary carbohydrate and fat make up the largest sources of energy in humans’ diets and are the two fuels that our bodies prefer for manufacturing ATP.
The amount of daily energy you consume—relative to your body’s needs—has important implications when it comes to your gut’s function. Over the long run, consuming less energy than your body needs increases your chances of experiencing several gut symptoms; conversely, gut discomfort and problems can also arise if you are the type of athlete who needs to consume huge quantities of energy (e.g., more than 4,000–5,000 kilocalories per day) in order to meet training demands or to put on body mass. In this chapter, we explore what energy is, how to determine how much energy athletes need, and the consequences that can arise from under- and overconsuming energy in the diet.
MEASURING ENERGY
It may not be plainly obvious, but both underconsuming and overconsuming dietary energy can give rise to gut problems. Both scenarios are covered later in this chapter, but let’s take a minute to get on the same page when it comes to defining and measuring energy in foods. Even though ATP powers all your bodily processes, you likely already know that nutrition labels don’t list quantities of ATP but instead report energy in the form of calories (at least in the United States). Still, you might be wondering what in the world a calorie actually represents. The short answer is that a calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius.
Sounds fairly straightforward, but how do we apply this concept to quantify the calories in food? How many calories, for example, are in a Twinkie? A head of lettuce? A double cheeseburger? A pound of milk chocolate? To figure this out, a device called a bomb calorimeter can be used to measure the energy content of these and other foods. Scientists place a sample of food inside the bomb calorimeter, which consists of a sealed container surrounded by water. Then the sample is ignited, and the resulting combustion releases heat, which can be measured by the degree of temperature change of the surrounding water. Although this is a precise way of determining the energy content of foods, most manufacturers don’t go to these lengths. Instead, they calculate the calories in foods based on the amounts of carbohydrate, protein, and fat they contain, as the energy content per gram of each macronutrient is fairly consistent.
Before moving on to talk about the energy needs of athletes, there’s a brief point I need to make in regard to how energy is listed on the Nutrition Facts label in the United States. This may be a tad confusing, but the word calorie that’s used on the Nutrition Facts label doesn’t mean exactly the same thing as the definition I just gave you. Instead, 1 calorie on the Nutrition Facts label actually represents 1,000 calories, or 1 kilocalorie. As an example, 1 cup of cereal that lists 200 calories on its label actually contains 200,000 calories, or 200 kilocalories. I’ll use the term kilocalorie, or kcal for short, to describe energy concepts, and this will identify the same amount you’re used to thinking of as calories or seeing on Nutrition Facts labels.
ENERGY NEEDS AND ENERGY BALANCE
It’s a given that you need energy to survive, but exactly how many kilocalories should you consume each day to maintain your health and physical function? Even if you were to lie in bed all day and binge-watch your favorite TV show (I’d probably choose The Office), your body would still expend anywhere from 1,000 to more than 2,000 kcal over 24 hours. This is the energy required to keep your lungs breathing, heart pumping, kidneys cleansing, liver detoxifying, appendix appendicizing, and brain cogitating—it’s the energy needed to simply keep the lights in the building turned on. The technical term for this minimal energy requirement is resting metabolic rate, or RMR for short. (It’s also sometimes called resting energy expenditure or basal metabolic rate.) After adding in energy expended through physical activities (which, for nonathletes, is usually several hundred kilocalories), most people living in modern societies end up burning 2,000–3,000 kcal per day, or if you prefer to measure energy in candy bar form, about 8 to 12 Snickers’ worth.
Ultimately, if you eat fewer kilocalories than you burn, you’ll lose weight. Alternatively, if you eat more kilocalories than you burn, you’ll gain weight. If the number of kilocalories you ingest equals the kilocalories you burn, you’ll maintain your weight. The physics are simple, and meticulous feeding studies show us that this energy balance principle works.1 Outside the confines of a controlled lab, however, numerous factors complicate the application of this simple energy-balance equation by affecting your energy intake, energy expenditure, or both. For example, eating a 2,000 kcal diet that contains an abundance of protein, water, and fiber would blunt your hunger much more than eating a 2,000 kcal diet consisting entirely of sugar or oil. If you started eating a 2,000 kcal diet of pure sugar or oil, soon thereafter your ravenous brain would propel you to up your energy intake (perhaps to something like 2,500 kcal) due to persistent hunger. I recognize that all-sugar and all-oil diets are extreme, unsustainable examples, but they illustrate the point that the type and quality of food you eat impacts the dynamic processes that regulate energy intake.
Similarly, there are factors that subtly influence the expenditure side of the energy-balance equation. If you were to lose a considerable amount of weight over a few months (say, 30 pounds), your RMR and total energy expenditure would also decline (assuming you didn’t compensate by doing more physical activity). In fact, each pound you lose equates to about a 5 kcal drop in RMR. So, if your daily energy expenditure is 2,500 kcal and you follow a weight-loss diet of 2,000 kcal (equating to an initial negative balance of 500 kcal), your weight loss progress would slow to a crawl after several months because your RMR (and total energy expenditure) would decline over time. In order to continue to shed pounds, you’d need to either decrease your energy intake even further (maybe to 1,500 kcal) or boost your energy expenditure by doing more physical activity.
CONSEQUENCES OF HIGH ENERGY INTAKES
For the public, a failure to remain in a neutral energy balance has contributed to the explosive growth of obesity over the past half century, and today, almost 4 out of 10 American adults are obese. While most athletes don’t have to worry about suffering from the untoward effects of obesity in the midst of their playing careers, they do need to be conscious of how much energy they consume because consuming either too much or too little can have undesirable performance consequences. Excess intake can lead to body fat gain, while chronically underconsuming energy is a path toward metabolic and hormonal dysfunction.
Eating the appropriate amount of energy for weight maintenance can be challenging for athletes because, in comparison to couch potatoes, their total energy expenditures often vary much more from day to day. Amazingly, athletes training or competing for multiple hours each day routinely expend twice as much energy as their lazybones counterparts. A cyclist participating in one of the Grand Tours, as an example, can burn through 24 to 32 Snickers’ worth of energy (6,000–8,000 kcal) every day.2, 3 During the most extreme athletic endeavors—such as participating in a 24-hour adventure race—daily expenditures can swell to 15,000–20,000 kcal, or between 60 and 80 Snickers bars4 (see Figure 3.1).
It goes without saying, then, that many athletes have to eat almost nonstop during heavy training and competition periods in order to maintain energy balance, or at least prevent severe deficits. The sheer volume of food required to sustain this demand can undoubtedly be a source of gut discomfort. As a result, these athletes often choose foods and beverages that are energy dense, meaning they have more kilocalories crammed into each gram. Examples of energy-dense foods include butter, oils, nuts, sugar, sweets/desserts, and high-fat cheeses.5 Conversely, foods on the other end of the energy-density spectrum contain more energy-free or low-energy nutrients (such as water and fiber), with examples being vegetables, fruits, lean meats, and low-fat dairy products.
figure 3.1DAILY ENERGY NEEDS OF VARIOUS ATHLETES
The day-to-day energy needs of athletes can fluctuate drastically depending on their training volume and competition loads, with some athletes even burning 10,000+ kilocalories in a single day.
Cyclists competing in the Tour de France are prime examples of athletes favoring energy-dense foods. Case in point, a 1989 study of five cyclists competing in the Tour de France found that sweet cakes and a concentrated carbohydrate drink were the foremost contributors to the athletes’ energy intakes.2 Another study published about a decade later reported that biscuits and confectionery were the leading sources of dietary energy among 10 cyclists competing in the Vuelta a España (Tour of Spain).6 Returning to our Snickers bar system of measurement, a cyclist would need to consume 24 bars to achieve a daily intake of 6,000 kcal, and at a weight of 53 grams per bar, that adds up to 1.27 kilograms (or 2.8 pounds) of Snickers. As a point of comparison, 1 cup of cubed cantaloupe, coming in at 160 grams, contains only about 50 kcal, and that same cyclist would have to eat 120 cups’ worth of cantaloupe, or over 19 kilograms, to get those same 6,000 kilocalories! This is an outrageous example, but it demonstrates how energy density influences the amount of food that’s needed to meet an athlete’s energy demands.
A more realistic comparison is shown in Table 3.1. Although each menu provides roughly 2,500 kcal, the low-energy density version contains larger amounts of food. And remember that many athletes will need to eat much more than 2,500 kcal per day. In sum, athletes with high energy needs who attempt to get all of their energy from nutrient-dense, lower-energy foodstuffs can sometimes find themselves suffering from symptoms like excessive fullness, bloating, flatulence, and frequent urges to poo.
CONSEQUENCES OF UNDERCONSUMING ENERGY
While the massive volume of food that some athletes eat can sometimes lead to gut problems, eating too little energy over extended periods of time (days to weeks) can also be a source of digestive difficulties. As an example, individuals living with anorexia nervosa are often afflicted with symptoms affecting the upper portion of their digestive tracts (i.e., bloating, premature or excessive fullness, nausea, and stomach pain). The heightened prevalence of upper gut symptoms in anorexia stems, in part, from a delay in the release of chyme from the stomach; indeed, even a few days of severely undereating curtails gastric emptying.7 In a way, it’s as if the stomach forgets what it’s supposed to do after being off the job for a few days.
Obviously, not all athletes with small builds or very low body fat levels have anorexia. Yet, athletes are generally at greater risk of developing eating disorders like anorexia as well as disordered eating patterns (i.e., problematic but not necessarily diagnosable eating abnormalities). This is particularly true for those competing in sports where performance depends on having a low body weight or being lean. Despite evidence that upper gut symptoms are common in anorexia nervosa, there’s scarce data directly supporting the notion that athletes who subtly but chronically restrict energy intake are more prone to experiencing these problems. However, it’s logical that this would be the case, and while these symptoms may not directly impact the performance of every athlete, situations exist where slowed stomach emptying from chronic under-eating would be problematic. An example is a marathoner competing in a hot and humid environment, who, as a result of heavy sweating, needs to drink large quantities of fluid to stave off the effects of dehydration. If this athlete suffers from impaired stomach emptying because of disordered eating, they would be more likely to experience fullness and nausea if they try to maintain an appropriate level of hydration.
Just as with the upper half of the gut, long-term restriction of dietary energy can induce symptoms that affect the lower half of the digestive tract, most notably constipation. Interestingly, constipation may be an adaptive slowing of the digestive process that the body makes in response to a dwindling supply of incoming food, allowing it to squeeze out as many nutrients as possible.8 Again, anorexia nervosa serves as an extreme but illustrative example of this sort of functional change. In a study from Johns Hopkins Hospital, the time it took substances to transit the gut was nearly twice as long in individuals with anorexia (67 hours) than in controls (38 hours).9 Furthermore, this plodding transit is reversed when adequate nutrition is returned to an anorexic patient’s diet.10 Similar to the situation with upper gut symptoms, there’s not much research directly tying energy restriction to constipation in athletes, but the evidence linking disordered eating to constipation in nonathletes is robust.7
In the end, you need energy to run all your body’s systems, including your digestive tract. Cutting your caloric intake to slightly below your needs (a deficit of a couple hundred kilocalories) for a few days is unlikely to produce much in the way of gut problems, but more severe or prolonged restrictions could reduce gut motility and put you on a path to experiencing bloating, premature fullness, nausea, and constipation. The more severe the caloric deficit is and the more time that deficit is sustained, the more likely it is you’ll encounter these problems. Any athlete experiencing these symptoms—especially in the presence of other signs of disordered eating—should consult with a healthcare provider. Some signs and symptoms of disordered eating in athletes are listed below.11 On their own, none of these are 100 percent accurate for identifying disordered eating, but the presence of multiple signs and symptoms at the same time is cause for concern:
Dramatic/sudden weight loss
An irregular or absent menstrual cycle in females
Loss of sexual drive
Stress fractures
Memory loss or poor concentration
Low blood pressure or heart rate Heart palpitations
Fatigue
Inability to tolerate cold
Insomnia
Depression and/or anxiety
Poor healing
Reoccurring or frequent respiratory infections
Signs of frequent vomiting (e.g., swollen salivary glands, severe tooth erosion)
DETERMINING YOUR ENERGY NEEDS
In order to prevent the sequela of chronic low energy intake (especially if you expend more energy than the average person), it’s important to have an idea of how much energy you burn from day to day. How exactly would you go about figuring that out? Unfortunately, the most accurate methods of measuring energy expenditure are impractical, expensive, and mainly used in meticulous research studies. In reality, there are no exceptionally accurate, practical ways of measuring energy outputs in the real world. That being said, you could try a few different approaches to get a ballpark approximation of your energy needs.
The first approach is to purchase a wearable monitor that provides estimates of energy expenditure. Companies like Fitbit, Apple, Garmin, and Tanita make these devices, which are typically worn on the wrist, at the hip, or around the chest. The estimates generated by these monitors correlate pretty well with research-grade methods, but they still often end up being off by a few hundred kilocalories or more.12 As a rule of thumb, they are more likely to underestimate than overestimate energy expenditure. Also, the estimates are more inaccurate when you do a lot of physical activities other than straight walking or running. Examples include weight lifting, climbing stairs, yard-work (digging holes, raking, etc.), and swimming.
The second approach is to track all your activities using a website or smartphone app such as MyFitnessPal, Lose It!, or Cronometer. The key to getting a semiaccurate estimate from these sources is making sure to log every activity you do for 24 hours, whether it is watching TV, snoozing, or chopping wood like a lumberjack. At the same time, it’s also critical that you don’t overreport the time you spend exercising and doing other physical activities. For example, if you went to the gym for an hour but only spent 20 minutes of that hour actually lifting weights, you should log that as 20 minutes of weight lifting, not 60 minutes. Not surprisingly, most people overestimate the time they spend doing all sorts of activities, including housework, childcare, and walking; consequently, estimates derived from this method are often higher (sometimes grossly so) than the real values.
The final (and most crude) approach to estimating energy expenditure involves determining your resting metabolic rate (RMR) and multiplying it by a standard activity factor. You could contact your local university’s exercise science or nutrition department or a dietitian to see if they offer RMR testing, or you could use a published equation to estimate it. There are many equations available, but one that tends to be fairly accurate is the Mifflin-St. Jeor equation, shown here for each gender:
MALES
(10 × weight in kilograms) + (6.25 × height in centimeters) − (5 × age in years) + 5
FEMALES
(10 × weight in kilograms) + (6.25 × height in centimeters) − (5 × age in years) – 161
Once you determine your RMR, multiply that number by the most appropriate activity factor in Table 3.2 to obtain your projected daily energy expenditure.
One obvious shortcoming of this method is that the activity descriptions have relative meanings. Very high physical activity might be an hour of exercise for the average person, whereas it might be several hours for an athlete. For example, if an ultrarunner took his estimated RMR (say 1,800 kcal) and multiplied it by the factor for very high physical activity (2.0), he would get an estimated expenditure of 3,600 kcal. While that seems like a lot of energy to burn through, on a day that he trains 3–4 hours, his real energy expenditure is probably 4,000–5,000 kcal.
The fact that these methods have some inaccuracies doesn’t mean they’re completely useless. What it does mean is that it isn’t feasible to measure your energy needs with 100 percent certainty. Instead, figuring out if you’re chronically underconsuming energy is best achieved through a multipronged approach that includes an assessment of your energy intake and expenditure over several days, tracking your weight over weeks and months, and monitoring for the signs and symptoms of disordered eating.
table 3.2.TOTAL DAILY ENERGY NEEDS
ACTIVITY FACTOR |
DESCRIPTION |
EXAMPLE |
1.2 |
Little to no physical activity |
Sitting all day |
1.4 |
Light physical activity |
30 to 60 minutes of walking plus some housework |
1.6 |
Moderate physical activity |
60 to 90 minutes of walking plus some housework |
1.8 |
High physical activity |
60 minutes of jogging or playing soccer |
2.0 |
Very high physical activity |
90 minutes of jogging or playing soccer |
A rough estimate of your total daily energy needs can be estimated by multiplying your RMR by the physical activity factors in the left column.