Fuel Sources During Exercise
Professional athletes must eat many calories each day. Consequently, they can be lax with the quality of their diet. They will not gain weight even if they eat burgers and fries and a bunch of sugared energy bars. However, weight gain is not the only factor that must be considered when it comes to an athlete’s diet. If the athlete does not eat enough healthy nutritious foods, his or her performance will suffer and eventually lead to injury and a long, difficult recovery.
At rest and during normal activities, fats contribute 80–90% of our energy; carbohydrates provide 5–18% and protein 2–5%. During exercise there are four major endogenous sources of energy: muscle carbohydrate stores (glycogen), blood sugar, blood fatty acids, and intramuscular triacylglycerols. The extent to which these substrates contribute energy for exercise depends on the intensity and duration of exercise, the level of exercise training, the initial muscle glycogen levels, and supplementation with carbohydrates during exercise.
Protein can be used by the body for fuel or for anabolic processes. Anabolic processes are those that build up the body, whereas catabolic processes are those that break down the body. Please note that not all protein is equal in its ability to be anabolic vs. catabolic within the body. Protein is used as an energy source if calories are insufficient. However, with sufficient calories, the break down of amino acids (the building blocks of protein) contributes only minimally to the total amount of energy used by working muscles. When a person begins a moderate endurance exercise program, they initially lose more protein than they ingest; that corrects itself within 2–3 weeks without dietary intervention.
In order to promote increases in muscle size (hypertrophy) and increase in strength, it is an absolute requirement that athletes be in a positive nitrogen status (ingesting more protein than is lost). Ingesting more protein than needed, however, does not lead to increased protein synthesis over a certain level and too much protein can result in dehydration, loss of urinary calcium, and stress on the kidneys and liver. Recommended protein intake is .8–2 gm protein/kg body weight per day or 12–20% of total energy intake.
|TABLE OF PROTEIN INTAKE RECOMMENDATIONS FOR PHYSICAL ACTIVITY
|Body Weight in lbs and kg
|0.8 g/kg RDA
|0.9 g/kg Light Exercise
|1.0 g/kg Moderate Exercise
|1.2 g/kg Moderate/Heavy Exercise
|1.4 g/kg Heavgy Exercise
|110 lbs (50 kg)
|130 lbs (59 kg)
|150 lbs (68 kg)
|170 lbs (77 kg)
|190 lbs (86 kg)
|210 lbs (95 kg)
|230 lbs (105 kg)
Fat is the major fuel for light-intensity to moderate-intensity exercise, such as jogging, hiking, dance, cycling, and recreational swimming. Half of the energy for these activities comes from the aerobic (using oxygen) breakdown of muscle sugar stores (glycogen) and the other half comes from circulating blood sugar and fatty acids. It is recommended that athletes consume 20–30% of calories as fat. These fats should include the “good” fats, such as the essential fatty acids EPA, DHA that are found in fish, flax, avocados, and olive oil as well as typical meat/dairy fats. Intake of trans fatty acids (from partially hydrogenated oils) should be avoided entirely and saturated fats should be limited but not completely restricted.
Carbohydrates are the main source of fuel for athletes, especially those participating in endurance sports. It is more beneficial to eat a low glycemic carbohydrate (oatmeal, yams, brown rice, 100% whole grains) meal 3–4 hours before exercising or athletic competition. A high glycemic carbohydrate meal (refined sugars in soda, candy, cake, muffins, white bread, Gatorade) will result in a rapid release of insulin and ultimately reduced blood sugar, suppressed release of fatty acids from fat stores, and inhibition of liver glycogen breakdown.
Carbohydrate intake during intense exercise should average 25–30 gm/30 minutes of activity. Carbohydrate solution should not exceed 6–8%; otherwise the athlete may experience cramps, nausea, and diarrhea. (To determine the concentration in a sports drink, the grams of carbs in a serving is divided by the weight of the serving of the drink, which is usually 240gm.) Post-exercise, it is important for the individual to restore muscle glycogen or carbohydrate stores by eating a source of carbohydrate mixed with a small amount of protein. (Refined carbohydrates work best at this time—small baked potato, yogurt, or Gatorade.) For the average exerciser this is not a crucial step and is in fact where a lot of people are mistaken when they start an exercise program. They tend to fuel themselves more than they actually need and end up gaining weight.
Water intake is a crucial part of our diet that is often overlooked due to its lack of “substance”. However, if the importance of a nutrient is judged by how long we can do without it, water ranks as the most important. A person can survive only eight to ten days without water, whereas it takes weeks or even months to die from a lack of food. Water circulates through our blood and lymphatic system, transporting oxygen and nutrients to cells and removing wastes through urine and sweat. Water also maintains the natural balance between dissolved salts and water inside and outside of cells. Our joints and soft tissues depend on the cushioning that water provides for them. While water has no caloric value and therefore is not an energy source, without it in our diets we could not digest or absorb the foods we eat or eliminate the body’s digestive waste.
Water absorption is maximized when sugar concentrations range from 1–3 %. Again, to determine this, the number of grams of carbs in a serving is divided by the weight of the serving of the drink, which is usually 240gm. It is also necessary to have sodium for sugar to be absorbed. Rehydration alone in endurance athletes (i.e., those who are active for over 60 minutes) is not as efficient. Too much water dilutes the blood rapidly, increases its volume and stimulates urine output. Blood dilution lowers both sodium and the volume-dependent part of the thirst drive (making one less thirsty). Sufficient amounts of electrolytes need to be ingested with the water in endurance athletes. After one hour of intense exercise, sports drinks (or something similar that contains electrolytes in a good proportion) are highly recommended.
VITAMINS AND MINERALS
Strenuous exercise can produce free radicals that cause damage to all of our cells. Antioxidants such as beta-carotene, vitamin E, and vitamin C all decrease the free radical damage, improve recovery time, decrease muscle damage and help with immune response. Athletes are at risk for developing some common nutrient deficiencies/health problems including:
- The B vitamins (thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, folate, B12)—The increased energy metabolism seen with athletes creates a need for more of the B vitamins that serve as helpers in the energy production cycle.
- Iron-deficiency anemia is not frequently seen among athletes, but suboptimal iron stores are common. Athletes at risk are the rapidly growing male adolescent, the female athlete with heavy menstrual losses, the person who restricts energy intake (wrestlers, dancers, young girls in general), the distance runners who have increased GI iron loss, and those training heavily in hot climates with heavy sweating.
- Osteoporosis can become a problem in females who exercise strenuously enough. Women with amenorrhea stop having menstrual cycles. Low estrogen associated with this can inhibit calcium absorption from the gut.
- Intense and lengthy exercise (thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, folate, B12)—The increased energy metabolism seen with athletes creates a need for more of the B vitamins that serve as helpers in the energy production cycle.
- Food allergies and asthma
- IBS aka Runners “Trots”
- Higher susceptibility to microbial imbalances or dysbiosis
- Frequent colds and coughs
All of these can be treated or prevented by simple dietary interventions. Sometimes, however, some athletes may need intravenous nutrients to keep their bodies at optimal performance.
The main point to remember is that exercise is very important for good health. Our bodies are meant to move, and most chronic pain is due to a lack of proper movement of our tissues. When we exercise, our muscles are broken down, and it is the rebuilding process after the fact that is most crucial. You have to break it down to build it up stronger. The quality of food you choose to put in your body should be your highest priority because that is what your body uses to repair itself.
“Dis-moi ce que tu manges, je te dirai ce que tu es” translates to “Tell me what you eat and I shall tell you what you are.” This quote was written by a French doctor, Anthelme Brillat-Savarin, back in 1826. It may also be translated as “You are what you eat.” He knew that the food we eat is what our bodies use to build and repair itself. But, he also believed that the type of food that you choose to consume is a reflection of the kind of person you are. So, next time you eat, take a moment before and decide, “Is this really the person I am?” If it is not, then choose to make the change to be the person you want to become.
If you or someone you know would like to learn more about nutrition and/or the health, hope, and healing offered at the Riordan Clinic, call 316-682-3100 to make an appointment or contact us here.