PED 291 - Chapter 9 Notes

Active Americans, including those involved in high intensity endurance activities, consume the same diets in composition to those consumed by people who do not work out regularly, except that athletes eat more of the same foods to support the extra energy required by exercise.

Attention to proper diet does not mean an athlete must take supplements (vitamins). Synthetic supplements like vitamins do not get broken down in your system as food does.

Table 9.1 compares the amount of carbohydrates, lipids, and protein intake of male and female athletes and non athletes.

A physically active person should consume 60% of their diet in carbohydrates, preferably complex carbohydrates. This is because of the glycogen synthesis in liver and muscle for energy depends on dietary carbohydrates.

Food guide pyramid- a model for good nutrition for Americans aged 2 and over (figure 9.2).

Diet quality index- looks at the healthfulness of one’s diet (table 9.2, page 210). We will use the diet decoders to help you score this.

Creeping obesity- calorie intake usually exceeds daily expenditure. It can take months or even years.

Because of extensive workouts, energy intake often falls short of energy expenditure, and malnutrition develops. The athlete often ends up training and competing in a carbohydrate depleted state. Some athletes then do turn to supplementation to try to meet nutrient balance.

Very active men and women who eat considerably more on a daily basis will weigh less than those who do not exercise or exercise at a lower total caloric expenditure (eat more, weigh less). They also maintain a leaner (more muscle, less fat) body and a more healthful heart.

Athletes often compete in the morning following an overnight fast. Carbohydrate reserves significantly drop over a 8 to 12 hour period without eating.

A precompetition meal is significant: it provides the athlete with adequate carbohydrate energy and ensures hydration (proper amount of liquids consumed).

Fasting is bad because it rapidly depletes liver and muscle glycogen and impairs exercise performance.

Lipids and protein should not be consumed in high quantities on competition days because they digest slowly and stay in the digestive tract longer than carbos, so they don’t provide energy as quickly.

Generally 3 hours provides enough time to digest and absorb a carbohydrate precompetition meal. High protein can actually hinder performance (steak and eggs). Note: the night before eating steak is a good idea because it provides a substance called alcarnine. Also: eating a lot of protein for a precompetition meal causes dehydration because the byproduct of amino acid breakdown require water for urinary excretion.

Ideal precompetition meal: contains 150 to 300 grams of carbohydrates in either solid or liquid form consumed 3-4 hours before competing. However: that meal cannot make up for existing nutritional deficiencies (Doritos and a diet soda) during the weeks before competition.

Liquid meals are good if athletes are not interested in eating on competition day, supplies fluids and digests rapidly.

Carbohydrate intake before, during and after intense exercise.

One hour of intense exercise depletes 55 % of liver glycogen, and 2 hours almost completely depletes it. It does not have to be continuous: it can be 1 to 5 minute intervals of work with rest.

One line of research on consuming before exercise is a quick sugar fix before, but this actually increases glycogen depletion and negatively affects performance by:

a.     causing an overshoot of insulin release, causing low blood sugar called rebound hypoglycemia. This can affect central nervous system function during exercise (unable to catch a ball during a game)

b.     high insulin levels inhibit Lipolysis-which reduces fatty acid release from adipose (fat) tissue during exercise, causing fatigue.

The body does not digest and absorb all carbohydrates at the same rate.

Glycemic index- an indicator of how well ingested carbohydrates raise blood sugar levels, usually over a 2 hour period. Each food has a maximum value of 100%, and the higher the number the worse the food is: if you ingest something that has a glycemic index of 80, that means blood glucose concentration goes up 80%, and more insulin has to be made to push this glucose to cells or stored as liver and muscle glycogen.

Also: consuming fats and proteins with carbohydrates will drop the total glycemic index of a food (truth: a snickers bar has a lower glycemic index than an orange). White rice and potatoes have higher indexes than apples and peaches.

A lot of vegetables have a low glycemic index because the fiber in them slows down digestion (eat broccoli with your rice and chicken).

Some glycemic index food numbers:

Kellogg’s all bran cereal: 51

Corn flakes: 84

Oatmeal: 49

Brown rice: 55

White rice: 72

Fettuccine: 32

Spaghetti: 43

Taco shells: 68

Bagel: 72

Rye bread: 76

Blueberry muffin: 59

Crisp bread: 81

Vanilla wafers: 77

Oatmeal cookies: 55

Carrots: 49

Baked potato: 93

Sweet corn: 55

Green peas: 48

Baked beans: 48

Lentils: 30

Navy beans: 38

Apples: 38

Dried apricots: 31

Cantaloupe: 65

Grapefruit: 25

Mango: 55

Pineapple: 66

Raisins; 6

Watermelon: 7

Whole milk: 22

Skim milk: 32

Ice cream: 61

Orange juice: 46

Gatorade: 78

Corn chips: 72

Peanuts: 14

Pretzels: 83

Power bars: 58

Jelly beans: 80

Snickers: 41

Twix bars: 44

Honey: 58

Consuming low glycemic index foods before competition allows for a slow rate of glucose absorption into the blood, providing a steady release of glucose from the digestive tract during exercise.

During exercise: consuming about 60 grams per hour (biking, hiking, hockey, basketball: high intensity, aerobic exercise that utilizes a lot of glycogen) can help continue exercise.  Why?

a.     it spares muscle glycogen because the ingested glucose powers the exercise.

b.     It stabilizes blood glucose: preventing headaches, lightheadedness, nausea

c.     Supplies the muscles with glucose when glycogen reserves deplete late in the activity.

Consuming carbos can postpone fatigue for up to a half hour, great for marathon runners.

An activity that is below 50% of exercise intensity relies primarily on fat oxidation and only a small demand for carbohydrate breakdown: (jogging). Consuming carbos offers no benefit during such activity.

Fluid intake:

Determining the optimal fluid/carbohydrate mixture and volume to consume during exercise is very important when the objectives are to reduce fatigue and prevent dehydration.

1.    consuming a large dilute (no carbs) fluid volume may lessen carbohydrate uptake

2.    consuming concentrated sugar solutions actually diminish fluid replacement.

3.    the rate of stomach emptying greatly affects the absorption of fluid and nutrients by the small intestine.

How much fluid should we drink before exercise to ensure the most beneficial passages of nutrient into the intestine?

400 to 600 milliliters

How much fluid should we drink every 15 minutes during exercise continuously replenishes the fluid passed into the intestine?

250 milliliters

How much fluid is passed per hour to the small intestine to meet an endurance athletes needs?

1 liter

Don’t drink fluids with alcohol or caffeine-they are diuretics that enhance water loss

Negative effects of sugar drinks on water absorption from the digestive tract: stomach emptying is slow when you consume a liquid over 8% sugar (how full do you feel when you drink a lot of Pepsi?). This can be very dangerous in hot weather, because increased sugar in a fluid means that fluid is not leaving the digestive system to get throughout the body. Any fluid from 3-8 percent replenishes your system and maintains glucose in your system, which spares liver and muscle glycogen.

What is the benefit of sodium (salt)?

It keeps an athlete from getting hyponatremia (water intoxication and dilution of sodium) and maintains plasma sodium concentration. It also reduces urine output.

How do you figure out what percentage sugar is in your drink?

If a drink has 80 grams of carbohydrate in 1000 milliliters of water- it is 8 percent sugar.        

                             __.8__

The math:   1000/80.00          or 8 percent

In hot weather you need to drink a lower percentage solution (less than 5 percent) In cold weather you should can drink a more concentrated beverage of about 15%

See page 220 to compare drinks.

After a hard workout consume high glycemic carbohydrates to speed glycogen replacement (50-75 grams every 2 hours). No milk, beans and fructose sugar drinks (not as fast absorption into the system)

If you do it correctly, glycogen replenishes at about 5 percent per hour (working out twice a day hard is not recommended). That is 20 hours for total replacement.

Staleness-a physiological state from gradual depletion of glycogen reserves, even if they are putting carbohydrates back in (don’t run 10 miles 3 days in a row).

Carbohydrate loading-the packing of muscle glycogen by maintaining a high carbohydrate diet. Enhanced muscle glycogen levels can be maintained for 3 days by eating 60% carbohydrates each of those 3 days. It only applies to intense and prolonged exercise (marathon). Otherwise no loading is necessary, a normal intake is fine.