Transcript Fat For Fuel: Ketogenic Diet and Endurance Athletes

FAT FOR FUEL:
KETOGENIC DIET AND ATHLETIC PERFORMANCE
The Condition of Ketosis
DEPARTMENT OF HEALTH SCIENCES: DIETETICS
NUTRITION 482: NUTRITION AND METABOLISM FALL 2013
Ketosis is the abnormal accumulation of ketone bodies in the
blood as a result of excessive breakdown of fats caused by a
deficiency or inadequate use of carbohydrates. A ketone is a chemical
structure where oxygen is double-bonded to carbon and is between
at least two other carbons. Our body produces three kinds of ketone
bodies: acetone, acetoacetate and beta-hydroxybutyrate.1 When our
body runs out of glucose which is our body’s primary energy source
or when glucose levels are low, our liver can generate fatty acids
from fat and select amino acids and turn them into ketone bodies so
that our body can still function effectively. Fatty acids can not cross
the blood brain barrier and therefore this is the reason for which fatty
acids are converted to ketone bodies which can cross the barrier.
Ketone bodies then become the main source of energy for the body
instead of glucose.
Ketosis can be seen in starvation, and occasionally in pregnancy
if the intake of protein and carbohydrates is inadequate, and most
frequently in diabetes mellitus.2 Ketosis only becomes life
threatening in the case of diabetes. If a diabetic fails to receive
insulin, they go into a state of starvation. They may have glucose, but
without insulin which helps cells uptake glucose, the glucose cannot
get into the cells. The body will begin to make ketone bodies out of
fat which will continue to build up and will not stop because
diabetics can not produce insulin. PH imbalances begin to occur
when levels reach 15 to 25 mM and this can result in other metabolic
disorders and in severely ill persons. Nutritional ketosis however, is
not necessarily fatal.3
Ketogenic Diet
Nutritional ketosis is the result of a ketogenic diet, which is a high
fat, adequate protein, and low carbohydrate diet. A low carbohydrate
diet means a daily consumption of fewer than 50 grams of
carbohydrate, regardless of fat, protein or caloric intake.4 Switching to a
ketogenic diet is something that should be done gradually. Ketoadaptation is achieved through slowly reducing the amount of
carbohydrates in a diet so that the body can begin to learn to rely on fat.
The person will go from “glucocentric” (getting their primary fuel
source from glucose) to “adipocentric” (getting their primary fuel
source from fat/ketone bodies). On a ketogenic diet, fatty acids are
derived from dietary fat or adipose tissue if the diet does not meet
necessary daily caloric requirements. Ketone bodies mediate glucose
sparing effects by serving as the preferred energy source for active
tissues, such as in the heart and muscle.
Positive Effects:
Negative Effects:
•Low-carbohydrate/ high-fat diets consumed for more than 7 days decreases muscle glycogen content and
carbohydrate oxidation, which is compensated by increased rates of fat oxidation.1
•Patients following low carbohydrate diets usually complain about
lightheadedness, weakness, and fatigue.
•When muscle glycogen levels are low, the increase in the ability of skeletal muscle to oxidize fat after a lowcarbohydrate diet fails to alter or enhance exercise ability.1
• The participants from the elite gymnast study testing the effect of the
ketogenic diet versus high-carbohydrate diet done were unable to
continue and thrive off of the low carbohydrate diet for more than 2
weeks, but most maintained their low-carbohydrate diets for at least 7
days.6 This shows that a ketogenic diet may not be beneficial for athletes
whose sport requires short bursts of energy.
•If enhanced fat utilization is combined with increased carbohydrate availability, this would be
beneficial for endurance performance, especially in extremely long exercises such as marathon
running, where glycogen stores are likely to become minimal, and we can turn to fat as being
our primary energy source.1
•The capacity for fat oxidation and muscle glycogen sparing does not go away when
carbohydrates are introduced back into a person’s diet.1
•Examining the results of Stephen Phinney’s two ketogenic diet
performance studies together indicated that both groups experienced a lag
in performance across the first week or two of carbohydrate restriction,
after which both peak aerobic power and sub-maximal (60–70% of
VO2max) endurance performance were fully restored.8
•For example, if someone is training for a marathon and tried a ketogenic diet
for awhile, but then carbohydrate loaded before their actual marathon, their
body would still be able to use ketone bodies as an efficient fuel source.1
•There are no studies in today’s research that carefully examine the
optimum length of this “keto-adaptation” period, but it is longer than one
week and likely will advanced within 3–4 weeks.6
•Chronic low-carbohydrate/high-fat diets induce powerful metabolic adaptations to enhance fat oxidation.
When combined with short periods of carbohydrate intake, these adaptations have been shown to produce
superior results compared with other dietary strategies to enhance exercise performance, especially for ultraendurance exercise.1
•The adaptation process does not appear to happen any
faster in highly trained athletes than in overweight or
untrained individuals. This adaptation process also
appears to require consistent adherence to carbohydrate
restriction.
People
who
intermittently
consume
carbohydrates while attempting a ketogenic diet report
subjectively reduced exercise tolerance.6
•The body adapts to using a different energy source after a week.1
•Some of the metabolic and enzymatic changes are still unclear, but enzymatic adaptations are thought to
involve muscle fiber-type specificity and to depend on the increase in dietary fat.1
•Fat-adaptation increases resting muscle triglyceride stores and resting AMPK-α1 and -α2
activity.5
•This results in higher rates of whole body fat oxidation, reduced muscle glycogenolysis, and
attenuated the exercise-induced rise in AMPK-α1 and AMPK-α2 activity compared with highcarbohydrate diets.5
•This demonstrates that AMPK-α1 and AMPK-α2 activity and fuel selection in
skeletal muscle in response to exercise can be manipulated by diet and/or the
interactive effects of diet and exercise training.5
•These negative results in the scientific literature can be explained by the
cultures that traditionally lived by hunting.
•Therapeutic use of ketogenic diets should not require
constraint of most forms of physical labor or recreational
activity, with the one exception that anaerobic (ie, weight
lifting or sprint) performance is limited by the low muscle
glycogen levels induced by a ketogenic diet. This would
strongly discourage its use under most conditions of these
types of competitive athletics.7
Ketogenic Diet and Exercise
There are always athletes out there trying to get the edge in their
training, whether it be through steroids, supplements, or some
laboratory procedure (blood doping). All of these methods are ways to
become a more efficient athlete who can perform at higher levels. What
if there was a way to do this by just simply changing the diet that one
consumes? It is known that for endurance athletes, a higher percentage
of fat is burned during exercise for energy instead of carbohydrates. So
in theory, if an athlete trains their body to burn fat more efficiently, fat
stores will burn for a longer period of time and glucose stores will be
saved for later use. Therefore, scientific research has been done on
athletes to test if a ketogenic diet can be beneficial to athletic
performance. There have been other studies performed that counteract
the positive aspects showing that athletes have had side effects
hindering training and performance. Positive and negative effects of a
ketogenic diet on athletic performance are as follows.
Corey Crowe ‘14
Amanda Sperry ‘14
Jocelyn Tomsic ‘14
Brittany Shannon ‘14
Fig. 1. Simplified illustration of hepatic and cerebral metabolism of relevant substrates in ketosis. 10