Sports Nutrition (Ch. 14) and
Eating Disorders (Ch. 15)
March 2015
Key Skills
• Identify major benefits of exercise.
• Distinguish between anaerobic and aerobic metabolism in
exercise (without oversimplifying)
• Discuss how exercise affects our carbohydrate, fat,
protein, and water/electrolyte needs.
• Explain how and when people should eat for exercise.
• Distinguish between the types of anorexia nervosa and
bulimia nervosa.
• Describe risk factors, health effects, and treatment
strategies for eating disorders.
Why Exercise?
What are the main reasons
that people exercise, in your
experience? Is it possible for
exercise to be an unhealthy
habit? Explain briefly.
Benefits of Exercise
Cardiovascular
Psychological
Fat/Muscloskeletal
Raises HDL, lowers
atherosclerosis risk
Reduces anxiety; endorphins
improve mood
Reduces fat
Reduces risk of hypertension,
stroke, and diabetes
Helps sleep quality
Maintains and builds muscle
Lowers resting heart rate
Improves self-esteem
Makes bones stronger and
reduces osteoporosis risk
Agree or Disagree?
“When trying to build muscle, you should perform
high-intensity exercise. When trying to
lose/maintain weight, you should perform longer
periods of low-intensity aerobic exercise.” Agree or
disagree, and why?
Exercise and Weight
Exercise helps with weight maintenance:
• Directly burns calories (to provide energy for
movement)
• Raises metabolic rate (since muscle burns more
calories than fat)
• Low-intensity exercise uses mostly fat for energy,
and high-intensity exercise uses mostly glycogen,
but…
• …either way, exercise increases calories out, so
both low- and high-intensity exercise can help
you lose weight!
Choosing Exercise Intensity
•
•
•
High-intensity exercise can be more
taxing, but does not take as long as
low-intensity exercise to burn
calories.
For good cardiovascular health,
moderate exercise 3-5 times a week
is recommended, 20-60 minutes
depending on intensity and weight.
Moderate = 55-70% of agepredicted maximum heart rate.
Age-predicted maximum heart rate
= 220 bpm – age. So a 30-year-old’s
maximum heart rate is 190 bpm,
and moderate exercise for them
would be ~105 – 133 bpm.
Exercising for Muscle-Building
•
•
There is no single way to build muscle.
There are many different muscle groups
and ways to train them! Repeated,
regular, gradually escalating exercise is
better than forcing yourself past your
limit.
It’s important to stretch and warm up
to prevent injury and reduce soreness.
Begin with light exercise and thorough,
but not forced, stretching on both sides.
Hold stretches, don’t “yank” your body
into place. Be especially careful with the
neck!
Aerobic vs. Anaerobic Exercise
What is the difference between aerobic and
anaerobic exercise?
Classify the following exercises as mainly aerobic or
anaerobic (or another category of your choice if you
do not think either term describes them well
enough):
Weightlifting
Long-distance swimming
Short-distance (50 m) swimming for speed
Exercise and Energy Systems
• Our muscles have a small amount of stored
ATP available, as well as a small amount of
phosphocreatine (PC), another energy storage
molecule. These reserves get used up very
quickly during intense activity.
• In intense exercise, we tend to use more
anaerobic respiration, as the energy demands
of muscles exceed the oxygen supply for
making ATP. Instead, muscles do lactic acid
fermentation.
• During longer-term exercise, aerobic
respiration kicks in and we use oxygen to make
ATP. This is less fatigue-inducing.
• We can and do use more than one pathway at
once in different muscle types!
Caloric Needs
• High physical activity increases our
caloric demands. Depends on weight and
activity level.
• Athletes often do better eating many
smaller meals, rather than a few large
ones, allowing them to keep their blood
sugar up.
• Athletes need enough protein to maintain
muscle mass and enough carbohydrates
to maintain blood sugar.
• Although athletes often try to gain
weight, this should be done gradually! ½
pound a week is a good rate for many.
Carbohydrate Needs
• For endurance athletes, eating foods that are rich in carbohydrates in a
pre-exercise meal (carb-loading 4 hours before exercise) can improve
performance. When eating directly before exercising, foods that raise
blood sugar can be helpful, but beware of “hitting the wall.”
• Assuming you have adequate carbohydrate reserves, your stored
glycogen will last for 60-90 minutes of exercise if you don’t eat or
drink any carbohydrate sources. For many people, sports drinks
containing sugar and electrolytes, or a homemade substitute, can help.
• Do not cut carbs excessively if you’re an athlete. While it is possible to
provide energy needs with a high protein diet, protein is not
metabolizes as efficiently.
• It’s also important to replenish carbs and protein after exercise with a
balanced meal.
Protein Needs
• Protein is not a great energy source due to
the time it takes to metabolize, but it’s
important for muscle building and repair.
We break down and build protein after
exercise!
• Athletes may need double the RDA for
protein… though most Americans already get
this much!
• Vegetarians can get enough protein for
exercise if they use protein complementation.
• Supplements can help in some cases, but as
we discussed in chapter 11, a balanced diet
will do fine.
Water and Electrolyte Needs
• Even in cold weather, we lose water
when exercising – especially if the air is
dry.
• As we saw earlier, dehydration and
electrolyte loss are both dangerous.
• Drink plenty of water and electrolytes,
with some sugar if exercising a long
time. Just drinking water alone does
not replace lost potassium and sodium.
• This is especially important for
prolonged exercise.
Exercise, Steroids, and Eating Disorders
• Some people suffer from body
dysmorphic disorders, a very negative
image of their own bodies. Men can
get these as well. Muscle dysmorphia
can lead to steroid abuse and its side
effects, such as heart disease, behavior
changes, and sterility.
• In female athletes, the female athlete
triad of amenorrhea, osteoporosis,
and disordered eating can combine to
result in bone damage.
True or False?
Bulimics are people
who eat and then
throw up. Anorexics
are people who
refuse to eat.
Types of Bulimia Nervosa
•
•
•
•
Bulimia nervosa is when a person
takes in a large amount of food
regularly, then engages in
compensatory activity, such as
purging or exercise to cope with
stress/guilt/etc. Different from bingeeating disorder, which doesn’t involve
compensatory behavior.
Not all bulimics induce vomiting!
Purging type: Use enemas, vomiting,
and/or laxatives
Non-purging: Uses fasting or exercise.
Bulimia Nervosa and Health
Types of Anorexia Nervosa
•
•
•
•
Anorexia nervosa is when a person
reduces their body weight to <85% of a
healthy weight for psychological reasons.
Sometimes overexercises. Often seen
with amenorrhea.
Restricting anorexia: Doesn’t bingeeat/purge.
Binge-eating/purging anorexia: In
addition to believing themselves
overweight even though underweight,
there are purging behaviors.
Not all disorders fit the anorexia or
bulimia patterns. EDNOS: Eating
Disorder Not Otherwise Specified.
Anorexia Nervosa and Health
Risk Factors for Eating Disorders
• Low self-image (depression, body dysmorphia)
• Stress
• Social pressures and cultural influences/unrealistic
expectations
• Teasing
• Crash dieting
• Be wary of stereotypes. Although there are
somewhat higher levels of anorexia nervosa in nonHispanic whites, there are similar prevalences of
most other eating disorders across ethnicities!
Prevention and Treatment
• Preventing eating disorders is challenging, and
treating them even more so.
• Ideals of body weight are formed early, and hard
to shift (“thinness schema.”)
• Treatment is multidisciplinary – requires
psychological support, nutritional support,
behavioral approaches, and patience.
• Things you can do: Respect diverse body types,
be a good role model, be supportive
• Things not to do: Do not treat weight and foods
as morally (rather than nutritionally) good and
bad, overcriticize, or enable.