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GEORGE L. BLACKBURN,MD,PhD JUDY C.C. PHILLIPS, MS, RD SUSAN MORREALE,CHES
Associate Professor of Surgery and Nutrition, S. Daniel Program Manager, Center for Nutritional Research Project Manager, Center for Nutritional Research
Abraham Chair in Nutrition Medicine,Associate Director Charitable Trust; Content Manager, Centers for Obesity Charitable Trust; Program Coordinator, Centers for Obesity
of Nutrition, Division of Nutrition, Harvard Medical Research and Education,Wellesley, MA Research and Education,Wellesley, MA
School; Director, Nutrition Support Service, Director,
Center for the Study of Nutrition Medicine; Program
Director, Surgical Therapy for Severe Obesity; Chief,
Nutrition Metabolism Laboratory, Beth Israel Deaconess
Medical Center, Boston
Physician’s guide to popular
low-carbohydrate weight-loss diets
■ABSTRACT P OPULAR LOW-CARBOHYDRATE diets such
as those described in such best-selling
Low-carbohydrate weight-loss diets are very popular, but The Zone and Dr. Atkins’ New Diet
books as
the recommendations of many of these diets are Revolution can turn weight loss into a double-
diametrically opposed to those put forth by the US edged sword. These plans produce fast results
Department of Agriculture, the American Heart Association, relatively easily, without restricting intake of
and other national organizations.Their focus on foods high proteins and fats, but they can jeopardize
in protein, fat, and cholesterol has potentially serious health health in a variety of ways.
implications. Physicians need to be knowledgeable about Physicians treating patients for obesity-
the efficacy of these programs and to talk to overweight related conditions have a unique opportunity
patients about weight loss. to influence patients’ food choices by provid-
ing reliable, objective information about the
■KEY POINTS safety and efficacy of low-carbohydrate diets.
Low-carbohydrate diets fail because, like all fad diets, they See related commentary, pages 777-781.
do not deal with the underlying issues of being overweight, This paper addresses common claims made
nor do they teach better lifelong eating habits. by proponents of low-carbohydrate diets and
discusses what to tell patients who are already
An important first step in advising patients who are already on such a diet or may be thinking of trying one.
on a low-carbohydrate diet is to assess their readiness to ■ THE ’SUPER-SIZING’ OF AMERICA
question the merits of such diets.
Questions remain about the possible association of low- In 1980, 46% of US adults age 20 and older
carbohydrate diets with the risk of colon cancer, heart were overweight or obese; by 1999, the num-
1 This dramatic
disease, diabetes, and hypertriglyceridemia. ber had increased to 60%.
increase has coincided with several trends:
Each pound of body fat contains 3,500 kcal; therefore, a • Higher energy intake from larger portions
person who consumes 500 kcal less than he or she expends at home and at restaurants (“super-sizing”)
per day can lose only 1 lb of fat in 1 week.Any higher • Greater consumption of high-fat foods
• Widespread availability of low-cost, good-
initial weight loss with ketogenic diets is therefore due to tasting, energy-dense foods
more severe caloric restriction or water loss rather than to • Decreased physical activity at work, at
fat loss. home, and during leisure time.
A growing national preoccupation with
weight loss has accompanied these trends. At
any given time, 44% of women and 29% of
2 and Americans spend $33
men are dieting,
PATIENT INFORMATION billion a year on weight-loss products, pro-
What you should know about low-carbohydrate diets,page 775 3
grams, and pills.
CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 68 • NUMBER 9 SEPTEMBER 2001 761
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LOW-CARBOHYDRATE DIETS BLACKBURN AND COLLEAGUES
Not available for online publication.
See print version of the
Cleveland Clinic Journal of Medicine
Books on low-carbohydrate diets far out- Atkins Induction Diet to 170 g/day in the
3 Zone diet (
sell others books on weight loss. The two TABLE 1). This is in stark contrast to 60% of adult
books already mentioned seem to be the most the American Heart Association’s recommen-
popular; others include Sugar Busters, Protein dation that carbohydrates should account for Americans are
Power, Suzanne Somers’ Get Skinny on Fabulous 55% to 60% of total daily caloric intake: 275 overweight
Food, The Doctor’s Quick Weight Loss Diet (aka g/day for a diet of 2,000 kcal and 300 g/day for
5
the “Stillman diet”), and The Carbohydrate a diet of 2,500 kcal. or obese
3
Addict’s Diet.
CLAIM 2
■ FALSE CLAIMS A state of perpetual ketosis causes weight
OF LOW-CARBOHYDRATE DIETS loss, regardless of calories consumed
CLAIM 1 Low-carbohydrate, high-protein diets are
The main cause of obesity called “ketogenic” because they cause the
is the shift from foods that contain fat to body to eventually burn fat for energy. Ketosis
processed foods that replace fat with sugar is the accumulation in the blood of ketones,
byproducts of fat oxidation, and it represents
Proponents of low-carbohydrate diets claim the body’s adaptation to fasting or starvation.
that the main cause of accelerated weight gain The theory behind low-carbohydrate diets is
in the United States is the shift from foods that that inducing perpetual ketosis causes the per-
contain fat to foods that replace fat with sugar son to lose weight (fat) regardless of how many
(ie, processed foods), a substitution they say calories from protein and fat are consumed.
leads to high insulin levels and fat accumula- However, weight loss can occur only if
3 Not so: excessive energy intake—not
tion. caloric expenditure exceeds caloric intake.
4
diet composition—is the cause of weight gain. Furthermore, the level of carbohydrates need-
Low-carbohydrate diets restrict carbohy- ed to maintain ketosis is much less than either
drate intake to anywhere from 20 g/day in the the 275 g/day consumed by Americans on
CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 68 • NUMBER 9 SEPTEMBER 2001 765
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LOW-CARBOHYDRATE DIETS BLACKBURN AND COLLEAGUES
4
average or the American Heart Association’s gerated hyperinsulinemia and glucose
recommended 220 g/day (TABLE 1). The intolerance.
Ongoing Weight Loss Stage of the Atkins The glycemic index—a measure of the
diet, for instance, limits carbohydrate intake rise in blood glucose over a specified period of
to 20 to 40 g/day while allowing unlimited time (usually 2 hours) vs the response to an
amounts of meat, cheese, poultry, fish, eggs, equal amount of carbohydrate in a standard
salt, and fats, a recommendation that over- food (often white bread)—is a more pertinent
looks the total (or almost total) inability of way to assess how much insulin the body
the human body to convert fatty acids to glu- 10–12
secretes in response to various foods.
cose, the primary source of energy for the
6 CLAIM 6
human brain.
Low-carbohydrate diets
CLAIM 3 have specific cardiovascular benefits
Low-carbohydrate diets are new
Dr. Atkins claims that those who follow his
Most low-carbohydrate diets are touted as regimen appear to have lower cardiovascular
new, but they are not. English surgeon risk, lower blood pressure, and significantly
William Harvey prescribed such diets for the 13,14 No long-term
lower triglyceride levels.
7 studies substantiate this claim. In fact, any
treatment of obesity in 1872.
clinically significant weight loss (5% to 10%
CLAIM 4 of initial body weight) can have these
Ketogenic diets are safe effects.
Furthermore, animal and dairy products,
Ketosis from prolonged fasting in healthy peo- the main sources of protein in low-carbohy-
ple increases insulin resistance and glucose drate diets, usually contain fat. Even though
8 Insulin resistance—a state in
intolerance. some of the fat can be removed, as with skim
Key sources of which a given concentration of insulin is less milk, low-carbohydrate diets tend to be high
effective both at stimulating glucose uptake by in fat overall. The intake of fat with low-car-
protein in low- skeletal muscle and at restraining hepatic glu- bohydrate diets, particularly saturated fat,
carbohydrate cose production—plays a central role in many increases to 56% to 66% of total calories—
disease states (eg, insulin resistance/metabolic twice the 30% or less recommended in current
diets usually syndrome, type 2 diabetes, hypertension, car- national dietary guidelines. Excessive intake of
contain fat diovascular disease, atherosclerotic cardiovas- dietary cholesterol and, to a greater extent, sat-
cular disease) and is a major risk factor for the urated fat increases levels of low-density
development of coronary artery disease, the lipoprotein (LDL) cholesterol and the risk of
chief cause of morbidity and mortality in 15
heart disease and some types of cancer.
patients with type 2 diabetes. Glucose intoler- Consumption of large amounts of meat may
16
ance has been linked to hypertension and dys- also contribute to cardiovascular disease.
5,9
lipidemia.
CLAIM 7
CLAIM 5 Low-carbohydrate diets are high
Eating carbohydrates leads to overeating in protein and therefore are healthier
Promoters of low-carbohydrate diets main- Low-carbohydrate diets are not necessarily
tain that carbohydrates raise insulin levels high in protein, as claimed. A comparison of
more than other foods do, thereby causing dietary intake among persons who consumed
the overeating that leads to obesity. In fact, a low-carbohydrate diet vs those who con-
4 found scant
insulin is secreted in reaction to all foods, sumed a typical American diet
not only those containing carbohydrates. difference in protein intake (91 g/day vs 83
However, some responses are physiologic g/day). The low-carbohydrate group, however,
while others are pathologic; overeating consumed only about two thirds as many calo-
contributes to the latter by causing exag- ries as the group eating a typical American
766 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 68 • NUMBER 9 SEPTEMBER 2001
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LOW-CARBOHYDRATE DIETS BLACKBURN AND COLLEAGUES
diet (1,450 kcal vs 2,200 kcal), indicating that 19 and fiber, for
acid, indoles, isothiocyanates)
weight loss was due to reduced caloric intake, example, can only be obtained from foods.
4
not to high protein consumption. Due to poor intake of high-fiber breads, cere-
On the other hand, no direct link has yet als, and vegetables, dieters need to take fiber
been found between consumption of animal supplements or eat fiber-fortified foods to
protein and chronic disease. Though critics of avoid constipation and concentration of bile
high-protein ketogenic diets claim that the salts and chemicals that cause colon and
diets increase the risk of gout, osteoporosis, breast cancer.
and renal disease, they have no evidence to Complex carbohydrates. Carbohydrates
17 In fact, obese persons
back those claims. are generally classified as simple (sugars) or
with diabetes may benefit from high-protein, complex (starches). Simple carbohydrates
low-calorie diets. In a study that compared either occur naturally or are refined and added
the effects of high-carbohydrate (low-pro- to foods during or after processing. Foods high
tein) vs high-protein (low-carbohydrate) low- in complex carbohydrates (whole grains, veg-
calorie diets for hyperinsulinemic obese etables, beans, fruits) are rich in fiber and
patients, high-protein diets proved more other nutrients and are relatively low in calo-
effective at lowering insulin levels and body ries. Processed foods based on refined starch
18
weight. and simple sugars (sugar, soft drinks, cookies,
donuts, cakes, sweetened cereals, white bread,
■ COMPOSITION OF STANDARD pretzels) are generally high in calories and low
VS LOW-CARBOHYDRATE DIETS in fiber and other nutrients.
Diets deficient in complex carbohy-
Compared with national guidelines for drates are likely to be nutrient-poor. Weight-
healthy eating and weight loss, low-carbohy- loss plans that restrict high-carbohydrate
drate diets contain excessive amounts of cho- foods can lead to cravings for foods that are
lesterol, saturated fat, and animal protein. The high in sugar and fat.13 Diets high in simple
Atkins and Protein Power diets are particular- carbohydrates can lead to hypertriglyc-
Obesity-related TABLE 1 shows how the macronu- 20
ly high in fat. eridemia.
conditions trient composition of the leading low-carbo-
improve with hydrate diets differs from the American ■ POTENTIAL ADVERSE EFFECTS
Diabetes Association recommendations and OF KETOGENIC DIETS
a weight the American Heart Association’s dietary
5
loss of guidelines for the year 2000. Ketogenesis may cause the following condi-
tions:
only 5% to 10% Nutrients missing • Mild dehydration, which can cause dizzi-
from low-carbohydrate diets ness, headaches, confusion, nausea, fatigue,
Micronutrients. Cutting back on entire sleep problems, irritability, bad breath, and
food groups or restricting variety can lead to worsening of gout symptoms and existing kid-
deficiencies in vitamins, minerals, and other ney problems
3 Carbohydrate-rich
essential micronutrients. • Poor athletic performance from the
foods can be excellent sources of fiber, vita- depletion of stored glycogen: insulin is
mins (B, C, and E), carotenoids, and other required for protein synthesis, and without
beneficial phytochemicals. They also provide insulin, muscle protein synthesis after exercise
calcium, potassium, and the majority of trace 7
is impaired
minerals. Supplements can replace some but • Increased risk of osteoporosis from calci-
not all of these. um loss if protein intake remains high and cal-
21
Fiber. Low intake of fiber can cause con- cium intake is low ; a high ratio of animal to
stipation and may contribute to the develop- vegetable protein intake may increase bone
ment of hemorrhoids, diverticulosis, polyps, loss and the risk of hip fracture in elderly
22
colon cancer, heart disease, diabetes, and obe- women
sity. The health benefits of phytochemicals • Nauseamay at first suppress the appetite,
23
(eg, carotenoids, lycopenes, flavonoids, phytic but the effect might not be long-term
768 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 68 • NUMBER 9 SEPTEMBER 2001
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