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9.20.1 Basic Nutrition Primer




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This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.

9.20.1 Basic Nutrition Primer

Nutrition in athletics is a very controversial topic. However, for
an athlete to have confidence that his/her diet is beneficial he/she
must understand the role each food component plays in the body's
overall makeup. Conversely, it is important to identify and understand
the nutritional demands on the physiological processes of the body
that occur as a result of racing and training so that these needs
can be satisfied in the athlete's diet.

For the above reasons, a basic nutrition primer should help the athlete
determine the right ingredients of his/her diet which fit training and
racing schedules and existing eating habits. The body requires three
basic components from foods: 1) water; 2) energy; and 3)nutrients.

WATER

Water is essential for life and without a doubt the most important
component in our diet. Proper hydrations not only allows the body to
maintain structural and biochemical integrity, but it also prevents
overheating, through sensible heat loss(perspiration). Many cyclists have
experienced the affects of acute fluid deficiency on a hot day, better
known as heat exhaustion. Dehydration can be a long term problem,
especially at altitude, but this does not seem to be a widespread
problem among cyclists and is only mentioned here as a reminder(but
an important one).

ENERGY

Energy is required for metabolic processes, growth and to support
physical activity. The Food and Nutrition Board of the National
Academy of Sciences has procrastinated in establishing a Recommended
Daily Allowance(RDA) for energy the reasoning being that such a daily
requirement could lead to overeating. A moderately active 70kg(155lb)
man burns about 2700 kcal/day and a moderately active 58kg(128lb) woman
burns about 2500 kcal/day.

It is estimated that cyclists burn 8-10 kcal/min or about 500-600
kcal/hr while riding(this is obviously dependent on the level of
exertion). Thus a three hour training ride can add up to 1800
kcals(the public knows these as calories) to the daily energy demand
of the cyclist. Nutritional studies indicate that there is no
significant increase in the vitamin requirement of the athlete as a
result of this energy expenditure.

In order to meet this extra demand, the cyclist must increase his/her
intake of food. This may come before, during or after a ride but most
likely it will be a combination of all of the above. If for some
reason extra nutrients are required because of this extra energy
demand, they will most likely be replenished through the increased
food intake. Carbohydrates and fats are the body's energy sources and
will be discussed shortly.

NUTRIENTS

This is a broad term and refers to vitamins, minerals, proteins, carbohydrates,
fats, fiber and a host of other substances. The body is a very complex product
of evolution. It can manufacture many of the resources it needs to survive.
However, vitamins, minerals and essential amino acids(the building blocks of
proteins) and fatty acids cannot be manufactured, hence they must be supplied
in our food to support proper health.

Vitamins and Minerals

No explanation needed here except that there are established RDA's for most
vitamins and minerals and that a well balanced diet, especially when
supplemented by a daily multivitamin and mineral tablet should meet all
the requirements of the cyclist.

Proper electrolyte replacement(sodium and potassium salts) should be
emphasized, especially during and after long, hot rides. Commercially
available preparations such as Exceed, Body Fuel and Isostar help
replenish electrolytes lost while riding.

Proteins

Food proteins are necessary for the synthesis of the body's skeletal(muscle,
skin, etc.) and biochemical(enzymes, hormones, etc.)proteins. Contrary
to popular belief, proteins are not a good source of energy in fact they
produce many toxic substances when they are converted to the simple sugars
needed for the body's energy demand.

Americans traditionally eat enough proteins to satisfy their body's
requirement. All indications are that increased levels of exercise do
not cause a significant increase in the body's daily protein
requirement which has been estimated to be 0.8gm protein/kg body
weight.

Carbohydrates

Carbohydrates are divided into two groups, simple and complex, and serve
as one of the body's two main sources of energy.

Simple carbohydrates are better known as sugars, examples being fructose,
glucose(also called dextrose), sucrose(table sugar) and lactose(milk sugar).

The complex carbohydrates include starches and pectins which are multi-linked
chains of glucose. Breads and pastas are rich sources of complex
carbohydrates.

The brain requires glucose for proper functioning which necessitates a
carbohydrate source. The simple sugars are quite easily broken down to
help satisfy energy and brain demands and for this reason they are an ideal
food during racing and training. The complex sugars require a substantially
longer time for breakdown into their glucose sub units and are more suited
before and after riding to help meet the body's energy requirements.

Fats

Fats represent the body's other major energy source. Fats are twice as
dense in calories as carbohydrates(9 kcal/gm vs 4 kcal/gm) but they are
more slowly retrieved from their storage units(triglycerides) than
carbohydrates(glycogen). Recent studies indicate that caffeine may help
speed up the retrieval of fats which would be of benefit on long rides.

Fats are either saturated or unsaturated and most nutritional experts
agree that unsaturated, plant-based varieties are healthier. Animal
fats are saturated(and may contain cholesterol), while plant based fats
such as corn and soybean oils are unsaturated. Unsaturated fats are
necessary to supply essential fatty acids and should be included in the
diet to represent about 25% of the total caloric intake. Most of this
amount we don't really realize we ingest, so it is not necessary to heap
on the margarine as a balanced diet provides adequate amounts.

 

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