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Nutrition Performance
By Anssi H. Manninen
Low-Carb Ketogenic Diet: Friend or Foe?
The first law of thermodynamics describes one of the most important
principles related to biological work. The basic tenet states that energy cannot
be created or destroyed but, instead, transformed from one form to another.
That human beings obeyed the first law of thermodynamics was demonstrated
by Drs. Atwater and Benedict in 1903 and has been continually reaffirmed since
then. In accord with the first law of thermodynamics, the energy equation
dictates that body mass remains constant when caloric intake equals caloric
expenditure.
Any chronic caloric imbalance on the energy output or input side of the
equation changes body mass. Three factors can unbalance the energy balance
equation to produce weight loss: 1) reduce caloric intake below daily energy
requirement; 2) maintain normal caloric intake and increase energy expenditure
through additional physical activity above daily energy requirement; and 3)
decrease daily caloric intake and increase daily energy expenditure.
Year after year, “new and improved” diets appear on bookstore shelves
and circulate among friends. No matter what their names are, most fad diets
espouse essentially the same low-carbohydrate diet. If low-carbohydrate diets
were as successful as some people claim, consumers who tried them would
lose lots of weight and our obesity problems would be solved. Obviously, this is
not the case. Similarly, if low-carbohydrate diets were as worthless as others
claim, consumers would eventually stop pursuing them. Clearly, this is not
happening either. This article examines some of the science behind lowcarbohydrate ketogenic diets.
Basic Facts About Ketogenesis
The major function of adipose tissue (fat tissue) is storage of the
triglycerides (neutral fat) until they are needed to provide energy elsewhere in
the body. The first stage in using triglycerides for energy is hydrolysis of the
triglycerides into fatty acids and glycerol. Then, both the fatty acids and the
glycerol are transported in the blood to the active tissues, where they will be
oxidized (burned) for energy. Almost all cells, with some degree of exception for
brain tissue, can use fatty acids almost interchangeably with glucose for energy.
Under metabolic conditions associated with a high rate of fatty acid
oxidation (e.g., low-carbohydrate diet), the liver produces considerable
quantities of acetoacetate, β-hydroxybutyrate and acetone. These three
substances are collectively known as ketone bodies (also called [incorrectly]
ketones). Ketosis does not occur unless there is an increase in the level of
circulating free fatty acids that arise from lipolysis of triglycerides in adipose
tissue. Free fatty acids are precursors of ketone bodies in the liver. The liver, in
both fed and fasting conditions, extracts about 30 percent of free fatty acids
passing through it, so that at high concentrations, the flux passing into the liver
is substantial. Therefore, the factors regulating mobilization of free fatty acids
from adipose tissue are important in controlling ketogenesis (production of
ketone bodies).
When carbohydrates are not used for energy, almost all the energy of the
body must come from metabolism of fats. Lack of availability of carbohydrates
automatically increases the rate of removal of fatty acids from adipose tissue. In
addition, several hormonal factors, such as increased secretion of
glucocorticoids by the adrenal cortex, increased secretion of glucagon by the
pancreas, and decreased secretion of insulin by the pancreas, further enhance
the removal of fatty acids from the fat tissue. As a result, tremendous quantities
of fatty acids become available 1) to the peripheral tissue cells to be used for
energy and 2) to the liver cells, where much of the fatty acid is converted to
ketone bodies. The ketone bodies pour out of the liver to be carried to the cells.
The acetone that’s formed during ketosis is a volatile substance, some of which
is blown off in small quantities in the expired air of the lungs, often giving the
breath an acetone smell. This smell is frequently used as a diagnostic criterion
of ketosis.
Is the Low-Carb Diet a Friend?
According to Drs. Jeff Volek and Eric Westman, there is a lack of scientific
evidence for the criticisms commonly made against low-carbohydrate diets,
especially regarding metabolic mechanisms involved.2 Quite to the contrary,
they feel there’s a significant amount of scientific and anecdotal data
demonstrating favorable metabolic responses to very-low-carbohydrate
(ketogenic) diets (Table 1). Their recent review paper published in the
Cleveland Clinic Journal of Medicine included the following key points:2
1. Most studies have found that people lose more weight on very-lowcarbohydrate diets than on standard weight-loss diets.
2. Mechanism of weight loss on these diets may go beyond water loss and
include suppression of appetite, increase in metabolic rate, decrease in
metabolic efficiency, and shunting of nutrients away from fat storage.
3. Weight loss is usually associated with small to moderate reductions in
lean tissue, but low-energy, very-low-carbohydrate diets have a proteinsparing effect compared with low-fat diets.
4. These diets may also have favorable effects on specific risk factors for
cardiovascular disease.
Several short-term (under 12 weeks) trials have compared the effects of lowcarbohydrate and high-carbohydrate diets on weight loss when energy intake
was kept constant.10 These studies suggest that despite equal energy intakes,
initial weight loss during the first four weeks may be greater with a lowcarbohydrate diet than with a high-carbohydrate because a low-carbohydrate
diet induces a greater loss of water; however, weight loss between six and 12
weeks was the same with either diet.10
Many currently popular low-carb diets (e.g., Atkins Diet) restrict
carbohydrate intake, but allow unlimited intake of fat and protein. Some
potentially valid explanations for promotion of weight loss by low-carb diets,
despite unlimited fat and protein intake, include 1) initial diuresis (urine
excretion) associated with ketone and nitrogen excretion; 2) losses of up to 100
calories per day in urinary ketones; and 3) most important, decreased energy
intake, which may be related to ketosis, diet monotony, or other unknown
mechanisms.10
Although it has been suggested that the high-fat and high-protein intakes
associated with such diets may cause dehydration, electrolyte imbalance,
hyperuricemia, calciuria, kidney stones, glycogen depletion with easy fatigue
and hyperlipidemia, potential adverse effects of long-term ingestion of such
diets have not been carefully investigated. No serious side effects were
reported in a six-month trial involving 41 subjects receiving the Atkins diet.11
These subjects, in fact, showed a 43 percent decrease in plasma triglycerides,
an 18 percent increase in plasma HDL-cholesterol (“good cholesterol”), and a
seven percent decrease in plasma LDL-cholesterol (“bad cholesterol”).
However, the safety and efficacy of low-carbohydrate diets need to
evaluated in long-term studies using a randomized, controlled trial.10
Catabolism of proteins is reduced by ketone bodies, which probably explains
the preservation of lean tissue observed during very-low-carbohydrate diets. For
example, Dr. Volek and co-workers examined the effects of a six-week
carbohydrate-restricted diet on total and regional body composition and the
relationships with fasting hormones.9 Twelve healthy normal-weight men
switched from their habitual diet (48 percent carbohydrate) to a carbohydraterestricted diet (eight percent carbohydrate) for six weeks and eight men served
as controls, consuming their normal diets. Subjects were encouraged to
consume adequate dietary energy to maintain body mass during intervention.
Fat mass was significantly decreased (-3.4 kilograms [kg]) and lean body
mass significantly increased (+1.1 kg) at week six. However, there were no
significant changes in composition in the control group. Authors concluded that
a carbohydrate-restricted diet resulted in a significant reduction in fat mass and
a concomitant increase in lean body mass in normal-weight men. They
hypothesized that elevated β-hydroxybutyrate concentrations may have played
a minor role in preventing catabolism of lean tissue, but other anabolic
hormones were likely involved (e.g., growth hormone).
Table 1. Typical Day´s Menu on a Very-Low-Carb Diet
Breakfast
Ham and cheese omelet:
- whole eggs
- cheddar cheese
- ham
Bacon
Coffee
Cream
Lunch
Chicken salad
- tossed greens
- chicken breast
- mozzarella cheese
- ranch dressing
Almonds
Diet soda
Dinner
Grilled salmon
Green beans
3
2 ounces
2 ounces
2 slices
1 cup
2 tablespoons
2 cups
4 ounces
1.5 ounces
3 tablespoons
1 ounce
1 cup
4 ounces
1 cup
Tossed greens
Vinegar and oil dressing
1 cup
4 tablespoons
Sugar-free gelatin
Red wine
Daily Nutrient Content
Kilocalories
Carbohydrates
Fat
Protein
Alcohol
1 cup
4 ounces
2,000
10%
58%
28%
4%
Data from Volek and Westman, 2002
Is the Low-Carb Diet a Foe?
According to Dr. George Blackburn at Beth Israel Deaconess Medical
Center, lack of data on the long-term safety and effectiveness of lowcarbohydrate diets makes their medically unsupervised use very troubling,
especially by those who may have a preclinical or “silent” condition or illness.3
For example, Dr. Reddy and colleagues recently found that very-low-carb diets
delivered a marked acid load to the kidneys that increased the risk for kidney
stone formation and the potential for bone loss contributing to osteoporosis.4
As pointed out by Dr. Blackburn, a key point about low-carbohydrate
diets for weight loss is that the optimal weight loss diet is not necessarily the
same as the optimal weight maintenance diet that promotes health and long
life.3 Scientific studies that focus on foods eaten daily by people who are not on
weight loss diets provide considerable evidence that diets low in saturated fats
and high in fruits, vegetables and complex (low glycemic index) carbohydrates
are safe and effective for maintaining weight and health.5,6,7
Proponents of low-carbohydrate diets often blame the currently
recommended high-carbohydrate/low-fat diet for our obesity problems. They
claim the incidence of obesity is rising because we are eating less fat. True, the
incidence of obesity has risen dramatically over the past two decades. True, our
intake of fat has dropped from 36 to 34 percent of daily energy intake.8
However, the percentage declined only because average energy intake
increased by 200 calories a day. Actual fat intake increased by four grams a
day.8 Furthermore, fewer than half of us engage in regular physical activity.
Without vegetables, fruits and whole grain, low-carbohydrate diets lack
not only carbohydrate, but fiber, vitamins, minerals and phytochemicals— all
dietary factors protective against disease. To help shore up some of these
inadequacies, low-carb diets often recommend a daily supplement. However,
foods offer many more health benefits than any supplement can provide. Quite
simply, if the diet is inadequate, it needs to be improved, not supplemented. It’s
my view that low-carbohydrate diets do not support optimal health over time.
Table 2. Adverse Side Effects of Low-Carb Ketogenic Diets
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Nausea
Fatigue (especially if physically active)
Constipation (insoluble fibers such as cellulose [as in cereal
brans, fruits and vegetables] enlarge the stools, easing passage
and speeding the transit time)
Low blood pressure
Elevated uric acid (which may exacerbate kidney disease and
cause inflammation of the joints in those predisposed to gout)
Stale, foul taste in the mouth (bad breath)
In pregnant women, fetal harm and stillbirth
Modified from Whitney and Rolfes, 2002
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Guidelines for the Dieting Bodybuilder
In my opinion, energy restriction is best achieved with a low-fat diet and a
moderate carbohydrate intake. Protein intake should be about 1.5-2.5
grams/kilogram body weight. The upper level of protein is recommended
if energy restriction is substantial, as this may assist with the
maintenance of lean body mass and promote satiety.
Set a realistic rate of weight loss (i.e., 0.5 to 1.0 kilogram [about one to
two pounds] per week), including both short- and long-term goals.
Keeping a food record for a defined period (e.g., a week) is a useful task
that allows you to appreciate exactly what you are eating.
A moderate energy restriction of 500 to 1,000 kilocalories per day is
appropriate to produce a reasonable loss of body fat, but still ensure
adequate nutrient intake.
The meal plan for weight loss should not rely on skipping meals or
enduring long periods without food intake. Rather, food intake should be
spread over the day, particularly to allow for efficient refueling before and
after training sessions and to avoid hunger (which generally precipitates
overeating).
Meals and snacks can be made more “filling” with several strategies: Low
glycemic index carbohydrate choices (legumes, oatmeal, etc.) are
considered to have a higher satiety value than high glycemic index
choices (potatoes, white bread, etc.). Combine protein with
carbohydrate-rich meals to produce greater satiety than in carbohydraterich foods alone. Also, add low-energy-density vegetables and fruits to
meals to increase the volume of food you eat.
Consider a broad-range, low-dose vitamin-mineral supplement if you will
be restricting energy intake for prolonged periods.
A myth that’s circulating contends that in order to burn fat, you must
exercise at a lower percentage of your maximal oxygen uptake (VO2max).
This is certainly not the case. It is true that the percentage of energy
obtained from fat is greater at lower exercise intensities (e.g., 50 percent
VO2max) than at higher exercise intensities (e.g., 70 percent VO2max). At
the higher energy intensity, you will derive a lower percentage of your
energy output from fat, but the total energy expenditure will be greater,
and you will still burn about the same amount of fat calories as you would
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by exercising at the lower intensity, provided you are exercising for the
same amount of time. If you want to burn calories to lose body fat, your
objective should be to burn the greatest total calories possible within the
time frame you have to exercise.
Exercise, particularly intense exercise, may be used to curb appetite on a
short-term basis at an appropriate time. If you exercise before a meal,
your food intake may be reduced considerably. Try it and see if it works
for you. If you have the facilities available, a good half-hour exercise may
be an effective substitute for a large lunch.
Ephedrine and caffeine have been— and still are— used for weight
reduction in obese patients. Ephedrine at a dose of 150 milligrams daily
can produce weight loss, but best results are produced with the
ephedrine-caffeine combination. The doses used in studies were 20
milligrams ephedrine and 200 milligrams caffeine daily, and these were
effective when combined with reduced energy intake. However, caffeine
alone does not seem to be effective. The side effects of ephedrine are
tremor and nervousness, elevated blood pressure and increased heart
rate. While useful for those with asthma, ephedrine should not be used
by those with diabetes, hypertension or hyperthyroidism. Nor should
ephedrine-based products be used by patients taking Prozac and
related antidepressants. The International Olympic Committee (IOC)
prohibits use of ephedrine during competition. Also, taking an
ephedrine/ephedra-based product and applying for a new job is not a
good idea. The structure of the ephedrine molecule bears a very strong
resemblance to that of all of the other amphetamines. Most urine
screening tests will also detect ephedrine.
References
1. Guyton AC Hall JE (2000) Textbook of Medical Physiology. Philadelphia: W. B.
Saunders.
2. Volek JS, Westman EC (2002) Very-low-carbohydrate weight-loss diets revised. Cleve
Clin J Med, 69:849-862.
3. Blackburn GL (2002) Making good decisions about diet: Weight loss is not weight
maintenance. Cleve Clin J Med, 69:864-866.
4. Reddy ST, Wang CY, Sakhaee K et al. (2002) Effect of low-carbohydrate high-protein
diet on acid-base balance, stone-forming propensity, and calcium metabolism. Am J
Kidney Dis, 40:265-274.
5. Clinical guidelines on the identification, evaluation, and treatment of overweight and
obesity in adults: the evidence report. Washington, DC: National Institutes of Health,
1998. Available: http://nhlbi.nih.gov/guidelines/obesity/e_txtbk/index.htm
6. Anderson JW, Konz EC, Jenkins DJ (2000) Health advantages and disadvantages of
weight-reducing diets. Am J Clin Nutr, 19:578-590.
7. Fletcher-Mors M, Ditschuneit H, Johnson T et al. (2000) Metabolic and weight loss
effects of long-term dietary interventions in obese patients. Four-year results. Obes
Res, 8:399-402.
8. Whitney EN, Rolfes SR (2002) Understanding Nutrition. Belmont, CA:
Wadsworth/Thomson Learning.
9. Volek JS, Sharman MJ, Love DM et al. (2002) Body composition and hormonal
responses to a carbohydrate-restricted diet. Metabolism, 51:864-870.
10. Klein S, Romijn JA (2003) Obesity. In: Larsen PR, Kronenberg HM, Melmed S,
Polonsky KS, eds. Williams Textbook of Endocrinology. Philadelphia: Saunders, pp.
1619-1641.
11. Westman EC, Yancy WS, Edman JS et al. (2000) Effects of a very-low-carbohydrate
program on body weight: a pilot study (abstract). Obes Res, 8:(Suppl):73S.
12. Williams MH (2001) Nutrition for Health, Fitness and Sport. New York: WCB/McGrawHill.
13. O´Connor H, Sullivan T, Caterson I (2000) Weight loss and the athlete. In: Burke L,
Deakin V, eds. Clinical Sports Nutrition. Australia: McGraw-Hill Australia, pp. 146-184.
14. Karch SB (1999) The Consumer´s Guide to Herbal Medicine. Hauppage, NY: Advanced
Research Press.