The human
body needs a continuous supply of energy to be able to perform its many complex
functions. As a person’s energy demand increases with exercise, the body should
be provided with extra energy, but energy and
nutrient (carbohydrates, proteins and fat) requirements from each individual to
another differ depending on weight, height, age, gender, and metabolic rate and
also the type, frequency, intensity and duration of training and performance.
Active individuals
such as recreational athletes or light trainers (train or exercise
30-40mins/day, three times/week) can meet their energy requirements by eating
their everyday meals provided that it is within the normal total energy
requirements for adults: 25-35kcal/kg/day (1800-2400 calories/day). But the
more engaging the training is and the longer the individual trains; more than 2
hours at a time per day, will require an extra 600-1200 calories/day and depending
on the type, frequency, intensity and duration of training, it can reach up to
150-200kcal/kg/day, roughly 7500-10’000 calories/day.
Carbohydrate is the main energy source when
exercising, especially during lengthy or high-intensity sessions. The body
stores carbohydrate as glycogen in the muscles and liver, but in small amounts
and this is used within seconds of exercise. When these carbohydrate stores are
not enough to meet the fuel needs of an athlete’s training program, the results
include fatigue, reduced ability to train hard, impaired competition
performance, and a reduction in immune system function. Therefore requirements
depend on intensity level of the exercise; the lowest being 3-5g/kg and
highest, most extreme intensity requires 8-12g/kg per day.
Protein is an essential nutrient in the diet
that has many functions in the body; it is needed to build connective tissue,
cell membranes and muscle cells. Proteins are made up of about 20 different
amino acids. Eight of these amino acids are essential and must come from the
diet. Some amino acids are used as a minor fuel source during exercise. As
mentioned, athletes enjoy the advantage of increased energy requirements therefore
they are allowed larger amounts of protein and other nutrients than the average
non-active person. On average, 0.8-1g/kg/day is recommended. For athletes the
need is greater;1-1.7g/kg/day, and greatest for growing adolescents; up to
2g/kg/day but females require 10-20% less compared to males. In general,
protein intake less than 2g/kg/day do not cause any side-effects.
During exercise the body focuses on protein
breakdown, while during the recovery period after exercise the opposite happens
and the body starts building muscle. By consuming protein immediately after
exercise it helps with muscle uptake. The beneficial effect of post-exercise
protein intake is best when the protein is combined with carbohydrate, bringing
about an increase in stimulation of the hormone insulin, which stimulates the
muscle to absorb proteins.
Points to consider about the high protein,
low carbohydrate diet:
·
High protein intake requires increased
fluid intake (potentially leads to dehydration)
·
High protein intake involves more animal
protein (high in saturated fat and cholesterol)
·
High protein intake puts pressure on
kidney function (kidney diseases)
·
High protein intake decreases the
appetite (reduced energy intake)
·
High protein intake increases calcium
loss through the urine (osteoporosis)
·
Low fruit and vegetable intake
(vitamin and mineral deficiencies)
·
Low fibre intake (constipation is likely
to follow)
·
Low glycogen refueling in muscles (can
lead to muscle breakdown)
·
Low carbohydrate is replaced by high
fat intake (causing ketone bodies buildup)
·
Ketones in urine – anorexic effect (decreasing
the appetite even more)
·
Low insulin levels initially, can lead
to water loss (higher potential of dehydration)
In
order to ensure that you are getting in enough energy from each nutrient, and
that you achieve your optimum performance level, see a sports dietitian who can
plan out a meal plan specific to your needs and training program.
This
article was written by Salaamah Solomon, a HPCSA registered dietitian.
*References
available on request.
