Are the Atkins, Zone, and South Beach Diets Slowing you Down?
by Kim Mueller, MS, RD
Many runners are jumping on the latest dietary crazes foregoing carbohydrate rich foods such as
pasta, bagels, fruits, vegetables, and good ole Cheerios to slim down and enhance their health.
Yet are these diets more destructive to their wellbeing? The truth about carbohydrate
composition and its effects on running performance are revealed.
Traditional guidelines posted by the American Dietetic Association recommend that 45-65% of
total calories be consumed in the form of carbohydrates, with guidelines for endurance athletes
focusing on the latter end of these recommendations during training and
competition.1 The carbohydrate intake of elite distance runners in the United
States2, Netherlands3, Australia4, and Southern Africa have
been measured at 49%, 50%, 52%, and 50%, respectively. Perhaps the most decorated distance
runners in the world, however, are the Kalenjin (Kenyan) runners who reportedly won a
staggering 40% of all major international middle- and long-distance competitions from
Interestingly, Kalenjin runners have a carbohydrate composition that tower over their
competition with measurements reporting 75+% or 10.4 grams carbohydrate per kg of body mass,
which may lead one to argue that running success and carbohydrate intake are directly
related.7 In fact, there is a plethora of sound research showing the profound
performance benefits associated with high carbohydrate intake, including optimal mental
functioning, muscle glycogen saturation, enhanced fat burning, protection against
protein/muscle breakdown, and improved immune function, just to name a few.8
Even so, such health authorities as Dr. Atkins (Atkins Diet), Dr. Barry Sears (Zone Diet), and
Dr. Agatston (South Beach Diet) question the efficacy of high carbohydrate diets for health and
performance. This has lead to an explosion of low carbohydrate products in the marketplace and
an adoption of new dietary habits by runners as means to shed body fat, enhance performance,
and optimize health. The information below gives you the low-down on the effects of low
carbohydrate dietary trends on running performance and ultimately sheds light on the top ten
reasons why a dietary focus on healthy carbohydrate sources (such as fruits, vegetables,
legumes, and whole grains) will always aid in health and running performance.
Here are the top ten reasons why high carbohydrate diets win the race.
#10: Low carbohydrate diets leave you mentally drained
Finding your motivation levels at an all time low? If you are following a low carbohydrate
regimen, it is no wonder since the minimal amount of carbohydrate grams suggested for optimal
mental functioning is listed at 130 grams or just over 500 calories. During the induction
phase, Atkins followers are encouraged to keep carbohydrate intake to no more than 20 grams per
day; if you are running enough, you can boost that up to 60-90 grams per day. You can see where
this may be a problem. Approximately 75-100 grams (300-400 calories) of carbohydrate can be
stored within the liver as glycogen. The energy stored within the liver helps maintain blood
sugars and also fuels both the brain and working muscles. With blood sugars naturally rising
and falling in 2-4 hour increments depending on metabolic efficiency, liver glycogen stores
constantly need to be replenished with snacks consisting of some carbohydrate. When inadequate
carbohydrates are consumed, liver glycogen levels fall quicker, causing blood sugars to drop; a
lack of fuel being sent to the brain triggers dizziness, fatigue, headaches, and an overall
feeling of sluggishness known as "bonking."
#9 Low carbohydrate diets trigger premature muscle fatigue during exercise
Do you find yourself flashing jealous looks at your competition as they blaze by you at the end
of that marathon while your muscles cramp and pace becomes slower than a turtle? Just like a
race car storing its fuel in a tank, the human body stores carbohydrates as glycogen in the
muscles and provides energy for muscle contraction and relaxation during activity. When
following the high carbohydrate diet recommended by the American Dietetic Association, the
average human body will store just over 2 grams (8-10 calories) of glycogen per pound of muscle
tissue, with a potential for super-compensation with carbohydrate loading protocols similar to
that seen with the Kenyan elite runners.9 This amount of muscle glycogen will supply
the energy needed to train for ~2-2.5 hours at a moderate-to-high intensity. Athletes following
lower carbohydrate regimens, however, have been shown to store approximately 45-75% less
glycogen as compared to their "carbo-loading" training buddies. Therefore, athletes
are more vulnerable to premature depletion of muscle glycogen, ultimately compromising muscle
function and leading to debilitating cramps, slowed pace, reduced power output, and diminished
endurance capacity, otherwise known as "hitting the wall."10-12 This is
not surprising considering Dr. Atkins suggests that athletes engaged in intense exercise for at
least 45 minutes consume an increased, though still limited, amount of carbohydrates in phase 2
of his program.
#8 Low carbohydrate diets compromise immune function
Ahhhh Chooo! Sound familiar? Prolonged intense exercise reportedly decreases the plasma
concentration of glutamine, an important fuel and precursor for DNA and RNA synthesis in cells
of the immune system, and may consequently depress immune function making runners more
vulnerable to infection in the 2 hours post workout.13 The immune suppression seen
in runners may also be attributed to elevated levels of the stress hormone cortisol and a
corresponding drop in lymphocyte production and T-cell activity seen after completion of hard
training. Interestingly, low carbohydrate diets, specifically those yielding carbohydrate
intakes less than 30 grams, seem to exacerbate this effect.14 Dr. David C. Nieman,
exercise physiologist, has conducted much of the research looking at immune function in runners
and has discovered that carbohydrate supplementation both during (~45 grams/hour) and
immediately after (~45 grams) intense, prolonged exercise helps reduce cortisol levels and
maintain lymphocyte production, thereby helping prevent infection.15
#7 Low carbohydrate diets affect mood
Yes, you may start to describe yourself as unpleasant to be around when following a low
carbohydrate diet! Many who are testing low-carbohydrate approaches like Atkins and the South
Beach Diet are reporting unusually elevated feelings of anger, tension and depression, enough
so that a new term 'Atkins attitude,' has been adopted to describe it. Judith Wurtman, director
of the Women's Health Program at the Massachusetts Institute of Technology and the Adara Weight
Loss Center, has conducted studies on rats showing a connection between low carbohydrate intake
and low levels of serotonin - a neurotransmitter that promotes feelings of happiness and
satisfaction. In her research, rats placed on a ketotic, or low-carbohydrate diet for three
weeks were found to have lower levels of serotonin in their brains. Wurtman believes that same
effect occurs in humans on low-carb diets, leading to pronounced feelings of depression and
sadness, even rage.16
#6 Low carbohydrate diets are often deficient in essential nutrients
With a lack of grains, fruits, and vegetables being consumed in low carbohydrate diets, runners
run the risk of developing dietary deficiencies of key nutrients including dietary fiber, which
can affect digestive health; vitamin C, which can compromise immune function; folic acid, which
may elevate risk for cardiovascular disease; and magnesium, which may elevate risk for cramping
and also compromise bone health. A lack of fiber also increases your risk for cancers of the
digestive track (because transit time is lengthened) and cardiovascular disease (because of
fibers effect on fat and cholesterol). Low carbohydrate diets lack in the phytonutrients /
antioxidants found in fruits, vegetables, legumes, and whole grains, all proven to aid in
prevention of cancer and heart disease. 17,18
#5 Low carbohydrate diets slow muscle recovery
Having trouble walking down those stairs after last night's killer track workout? Consumption
of carbohydrate-rich foods post-exercise will help enhance recovery from workouts.
Carbohydrate-rich foods cause a more rapid rise in blood glucose, which in turn triggers the
release of insulin or the "master recovery hormone." Insulin, the same hormone
knocked by Dr. Atkins (Atkins Diet), Dr. Barry Sears (Zone Diet), and Dr. Agatston (South Beach
Diet), actually facilitates the transport of carbohydrate, specifically glucose, from the blood
into the muscle cell where it can be metabolized to produce energy that will prepare the muscle
cell to do work again. Within 30-60 minutes post-exercise, consumption of a carbohydrate-rich
snack plus a small amount of protein (e.g., banana mixed in low-fat yogurt) has been shown to
triple the rate of muscle glycogen replenishment and muscle protein synthesis.19
Furthermore, as compared to a protein-only supplement taken post exercise, a
carbohydrate-protein solution has been shown to enhance rate of glycogen storage by 5 times,
thereby facilitating muscle recovery. 20
#4 Low carbohydrate diets increase risk for muscle injury during training
Do you find yourself constantly nursing little or big aches and pains? With a low carbohydrate
intake during endurance training, this is inevitable since there is increased protein breakdown
and consequent loss of lean body weight. Furthermore, the biomechanics of your running stride
may be negatively affected due to cramping and muscle fatigue (also associated with depletion
of muscle glycogen stores), aka "the wall", thereby causing a variety of new aches
and pains as well as muscle tightness. Finally, when insulin levels are chronically low, as
they often are with a very low carbohydrate intake, catabolism (breakdown) of muscle protein
increases, and protein synthesis is hindered.21
#3 Low carbohydrate diets increase risk for kidney stones
Ouch, it seems like something is stabbing me in the abdominal wall. I feel nauseous. Yes, these
are just some of the symptoms associated with passing a stone. Sound like fun? When following a
high protein, low carbohydrate meal plan, both uric acid and calcium oxalate stones are more
likely to form. In fact, one study found that consumption of a low carbohydrate, high protein
diet for 6 weeks delivers a marked acid load to the kidney, increasing the risk for stone
formation.22 Combine this with dehydration during a race and you are a prime
candidate for being stabbed by a "stone" - I guarantee that this won't aid athletic
performance. In 2003, former Ironman World Champion and pro triathlete Tim DeBoom unknowingly
passed a stone during the race, which lead him to pass out and be whisked off to the medical
tent, a medical DNF.
#2 Low carbohydrate diets can diminish bone health
Find yourself constantly dealing with stress fractures? Individuals consuming a higher ratio of
protein to carbohydrates run the risk of developing brittle bones or osteoporosis. When the
body digests protein, the kidneys work overtime to filter the toxic byproducts produced during
breakdown of protein. Once filtered, protein is excreted in the urine; however, along with
protein, there is increased urinary loss of calcium, which can ultimately compromise your bone
health, thereby increasing your risk for bone fracture. In fact, consumption of a low
carbohydrate, high protein diet over 6 weeks has been shown to significantly decrease estimated
calcium balance and may increase the risk for bone loss and stress fracture.22
Injury of the bone will definitely inhibit maximum fitness performance.
#1 Low carbohydrate diets can trigger joint pain
Protein-rich sources such as meats, poultry, seafood, and eggs commonly consumed as part of a
high protein regimen contain high levels of purines, which raise blood levels of a compound
called uric acid. An excess of uric acid in the body causes gout, which is a form of arthritis.
Elevated levels of uric acid in the blood may lead to needle-like uric acid crystals in joints,
triggering pain. A new study published in the New England Journal of Medicine has confirmed the
correlation between high protein intakes and gout. The researchers studied 47,150 men who had
no history of gout at the beginning of the study. During the 12 years of the study, they
documented 730 confirmed cases of gout. The relative risk of gout among men was highest among
men with the highest intake of meat and seafood. They concluded that higher levels of meat and
seafood consumption, like that seen in low carbohydrate meal plans, are associated with an
increased risk of gout.23
Low carbohydrate diets are not fun and certainly won't help aid running performance. So please
resist from jumping on the latest "fad diet" bandwagon and continue your high
carbohydrate ways, implementing such nutrient-rich foods as fruits, vegetables, whole grains,
and legumes. Your muscles and body will thank you. There are countless ways to incorporate
tasty, disease-preventing, sports-enhancing, carbohydrate-rich foods into your diet without
Get a jump on the day and try the following quick, healthy, tasty, and balanced
carbohydrate-rich breakfast: Blend ½ cup old fashioned oats, ¼ cup natural granola, 2 Tbsp
slivered almonds, ¾ cup mixed berries, and 1 cup nonfat milk. Cook in microwave for 3-4
minutes. Healthy carbohydrate trails!
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Info on Diet Trends
South Beach www.southbeachdiet.com
About the author: Kim Mueller, MS, RD, is a Registered Sports Dietitian and
competitive endurance athlete who provides nutritional counseling and meal planning to athletes
worldwide. You can contact her at email@example.com. Information on her services can be found