FN 225: Nutrition
Teresa McFerran, M.S., R.D.
Health Professions Division
Lane Community College
Eugene, Oregon


LECTURE 10A
Nutrients, Physical Activity and the Body's Responses
 

First look through the major headings of this lecture.

Now use the following information to fill in Week 10 lecture outline.

I  Benefits of Exercise
Your lecture outline lists the following benefits:
  1. improved mental outlook
  2. feeling of vigor
  3. sound sleep
  4. reduced body fat
  5. greater bone density   
  6. reduced risk of heart disease & some cancers
  7. improved blood sugar control
I find that often times people's primary reason for exercising is to reduce body fat.  Usually people measure their progress of reducing body fat by the scale, which does not distinguish between muscle and fat.  When the number on the scale does not go down, or maybe even initially goes up, people are not motivated to continue exercising.  This is a shame because more research is showing that fitness is more important than fatness.  So you don't necessarily need to lose body fat to gain benefits. 

Nancy Clark, the author of, "Nancy Clark's Sports Nutrition Guidebook" discusses the myth that starting an exercise plan leads to a reduction of body fat.  The reason why exercise alone with no dietary changes does not necessarily result in a reduction of body fat is because appetite tends to keep up with Calories burned through exercise.  She states that this is especially true for women.  We also tend to reward ourselves with food after exercise.

  1. Cardiorespiratory
  2. Musculoskeletal (muscular strength & muscular endurance)
  3. Flexibility
  4. Body composition
III  Benefits of regular AEROBIC (use oxygen) activities

Aerobic activities like jogging or brisk walking lead to lung/respiratory muscles getting stronger so you can breathe in more oxygen.  Heart/cardiac muscles also get stronger so there is more oxygen-carrying blood pumped by the heart for every beat. (Cardiac Output increases).

With regular exercise, blood volume also increases so there are more red blood cells to carry oxygen.

All of this has the effect of decreasing an athlete's resting heart rate because the heart doesn't have to work as hard.  The cardiorespiratory system is more efficient at delivering oxygen to cells.

Regular aerobic exercise can also raise HDL levels, which can decrease risk of heart disease.  This has no impact on resting heart rate.
IV  Benefits of regular ANAEROBIC (without oxygen) activity

ANAEROBIC activity is defined as all-out exertion lasting less than 3 minutes.   Examples include 100 meter dash and lifting heavy weights.

Anaerobic activity increases muscle strength. Activities like lifting weights can  increase muscle endurance if lifting lighter weight with more repetitions, but then the activity would likely be aerobic.

Which of the 4 components of fitness would NOT be achieved if on a regular basis you jogged one day and lifted weights the next? ______________________

Note:  The answer to this is flexibility, but I recently read a research article which found that strength training DID improve flexibility. However, the researchers did conclude that stretching is still an important component to an exercise program (and remember how science works - this experiment and results would need to be replicated to be accepted as scientific truth.) 


 


V  Energy Use
What does the purple arrow represent in the image below?  

Does it represent glycolysis, or does it represent the Krebs cycle?

Click here if you think it represents glycolysis.

Click here if you think it represents the Krebs cycle.


You can click on the image if you want to see a larger version.

What does the blue to green to yellow spiraled arrow represent?
 

Click here if you think it represents glycolysis.

Click here if you think it represents the Krebs cycle.

VI  Fuel Use during AEROBIC activity


The image below shows that fat and glucose (blood glucose and muscle glycogen) are the primary fuels used during aerobic activities like walking, cycling, and jogging. 



You can click on the image if you want to see a larger version.

At the beginning of this bike ride, the rider is using glycogen & fat, but slightly more _________________. 

As time goes on, the rider is using more ________ than glycogen.

When does glycogen run out for this bike rider?

 

One of the advantages of relying on fat for an energy source is that it is abundant, even in lean people.  For example, a man who weights 154 lbs who has a body fat level of 10% has approximately 15 lb of body fat, which is equivalent to more than 50,000 Kcal of energy!  This is significantly more energy than can be provided by his stored muscle glycogen (800-2,000 kcal)*

* Information taken from Thompson, M & Manore, M & Vaughan L. (2011). The Science of Nutrition.



Two ways you can manipulate what you do to make glycogen last as long as possible is to:
  1. Train so you build up the number of fat-burning enzymes you make.  That means you can burn more fat for energy, conserving glycogen for as long as possible.  More highly trained individuals also make more and larger mitochondria.  The mitochondria is the powerhouse of the cell where aerobic metabolism takes place.

  2. Eat plenty of whole foods with carbohydrate so you have glucose to make glycogen.
 



Activities like fast running that are high in intensity and short in duration (30 seconds to 3 minutes) need an energy source that can be used quickly to provide ATP.  The breakdown of carbohydrates (muscle glycogen as well as blood glucose) provides this quick energy through glycolysis. 

Fat is not a fuel that is used during anaerobic activities because fat is relatively slow to breakdown, and it requires oxygen.

During glycolysis, the six-carbon glucose is converted to two molecules of three-carbon pyruvate. When oxygen is present pyruvate can continue through Aerobic metabolism, or the Krebs cycle.  When oxygen is not present (like in the case of sprinting), pyruvate gets converted into lactic acid.  Click here to see an animation on the glycolysis process.
 

 

Summary of Fuels Used for Activities of Different Intensities and Durations

Activity Intensity

Activity Duration

Preferred Fuel

Oxygen Needed?

Activity Example
Maximal
 3-15 sec.
 ATP-CP
 No
 Sprint start

Very High

15 sec. – 3 min.

 Glucose

No 

  Running (fast)

High to moderate

3 min. – 4 hours

 Glucose

 Yes

 Running, jogging

Moderate to low

> 4 hours

 Fat

 Yes

 Walking


VIII  Protein as Fuel
Proteins (or more specifically amino acids) are not major energy sources during exercise.  Depending upon the intensity and duration of the activity, amino acids may contribute 1% - 6% of the fuel used during activity. (Information taken from Thompson, J. & Manore, M. (2015). Nutrition, an Applied Approach).

Protein is not a major fuel source, but is used to build and repair muscles.  The protein needs of different athletes are listed in the table below. 
 
The rule of thumb I use is to double the RDA if you are active, which would mean your protein needs would be 1.6 g/kg/day.  (Remember the RDA is 0.8g/kg) 
 
The majority of Americans get plenty of protein and don't need to eat special foods to get adequate amounts of protein.

RECOMMENDED PROTEIN INTAKES FOR ATHLETES


Type of Individual
 Recommendations
(g/kg/day)
 Protein Needs
for a 70 kg male
(g/day)
 Protein needs
for a 55 kg female
(g/day)
Endurance Athlete, adult
 1.2-1.5
 84-105
 66-83
Strength athlete, adult
 1.3-1.8
 91-126
 72-99
  Source: Thompson, J. & Manore, M. (2015). Nutrition, an Applied Approach
 

If you are an athlete, the extra protein you need is mainly needed to build and maintain muscle and other lean tissue.  If you want to gain 1 pound of muscle per week, you only need 14 grams of extra protein per day, the amount in 2 ounces of meat (Bernardot 1992).  Exercise, not extra protein, is the key to developing bigger muscles.  Any excess protein that you take in beyond the above recommendations is burned for energy or, stored as glycogen or fat (depending on Calorie intake).  Humans do not store excess protein as muscle, protein, or amino acids.
 

COMMON QUESTIONS REGARDING PROTEIN*

1. What’s the concern of too much protein?  You’ll crowd out carbohydrates which fuel your muscles.  When athletes focus too much on protein, and not enough on carbohydrates they often sacrifice endurance.

2.  Do I need to eat as soon as I finish exercising?  There is a 45 min. post exercise window to nourish, repair, and build muscles.  You can switch out of the muscle breakdown mode by eating a combination of carbohydrate and protein as soon as tolerable after you exercise.  Good examples of this are a yogurt and fruit, or a peanut butter sandwich.

3.  Do I need to eat protein every 3 to 4 hours to support muscle growth?  Yes, when amino acid levels are above normal, the muscles take up more, enhancing muscle growth.

4.     Are protein supplements better than real food?  Protein supplements are a mindless way to get protein, and are often quick and convenient, but they don't offer any benefit over whole foods.  The advantage of getting protein from whole foods is that protein comes packaged the way nature intended, and whole foods also contain phytochemicals and other yet-unknown bioactive compounds that might influence muscle growth.  Whole foods are also typically less expensive than protein supplements.

*The above information was taken from Nancy Clark's Sports Nutrition Guidebook, 2008.

IX  Fluids and Temperature
Sweat helps protect you from overheating because it absorbs a lot of heat before it changes from a liquid to a gas (evaporation).

Your lecture outline has a chart comparing
Heat EXHAUSTION and
Heat STROKE

Heat STROKE is more dangerous because the high temperature can denature body proteins, which can lead to loss of brain function and death.
 


X  Sports Drinks

Water is all you need if exercising less than about one hour.

What sports drinks offer besides fluid, to those exercising over one hour:
  1. Electrolytes like sodium- may accelerate glucose & water absorption from digestive tract. About 225 mg per 12 oz. (150 mg per cup) is enough.
  2. Glucose: no more than 7%, which is about 23 grams per 12 oz. (15 grams per 1 cup).  More sugar than that delays fluid going from the stomach to the small intestine where it can be absorbed.
  3. Psychological edge  
  4. Taste

Homemade sports drink: 1 qt. water, 1 cup sugar-sweetened fruit juice, 1/3 tsp. salt









END of Lecture 10A















 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Correct.  The purple arrow represents glycolysis.  Click here to return to the lecture.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Incorrect.  The purple arrow does not represent the Krebs cycle. Click here to return to lecture.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Correct.  The blue to green to yellow spiraled arrow represents the Krebs cycle.  Click here to return to the lecture.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Incorrect.  The blue to green to yellow spiraled arrow does not represent glycolysis. Click here to return to the lecture.