 |
What is a Low-Carbohydrate Diet? | Nutritional
Concerns | Typical Menus | Nutrient
Analysis | Health Concerns | Misunderstandings
and Deceptive Statements | High-Protein
Registry Established
Health Risks of Low-Carbohydrate Diets
Recent media reports have publicized the short-term weight loss
that sometimes occurs with the use of low-carbohydrate weight-loss
diets. Some of these reports have distorted medical facts and have
ignored the potential risks of such diets. Past experience with
the fen-phen drug combination and other weight-loss regimens has
shown that some people may disregard even serious long-term health
risks in hopes of short-term weight loss.
The American Heart Association,1,2 American Dietetic
Association,3 and the American Kidney Fund4 have all
published statements warning about the various dangers associated
with low-carbohydrate, high-protein diets.
We would like to notify you of (1) the potential risks from the
long-term use of low-carbohydrate, high-protein diets, (2) currently
circulating misunderstandings and deceptive statements made in support
of such diets, and (3) the establishment of a registry for individuals
who feel they may have been harmed as a result of following a low-carbohydrate,
high-protein diet.
What is a Low-Carbohydrate Diet?
The theory behind low-carbohydrate diets is that if dieters avoid
foods containing carbohydrate—that is, starches or sugars—they
will shed pounds. Such diets eliminate or dramatically restrict
the intake of fruit, fruit juice, starchy vegetables, beans, bread,
rice, cereals, pasta and other grain products, and all other foods
containing carbohydrate, leaving a limited diet of foods that contain
primarily fat and protein: meat, cheese, nonstarchy vegetables,
and very little else. As the diet proceeds, the carbohydrate restriction
relaxes somewhat, but fatty, high-protein foods continue to dominate
the dieter’s plate.
Despite anecdotal accounts of seemingly dramatic weight loss,
the effect of low-carbohydrate diets on body weight is similar
to that of other weight-reduction diets. In research studies at
the University of Pennsylvania and at the Philadelphia Veterans
Affairs Medical Center, the average participant lost weight during
the first six months on a low-carbohydrate diet, but regained some of this weight during the
next six months so that the net weight loss after one year (15.8
pounds in the University of Pennsylvania study and 11.2 pounds in
the VA study) was not significantly different from that seen with
other diets used for comparison.5,6 This degree of weight
loss is not greater than that which occurs with programs using low-fat,
vegetarian diets. In Dean Ornish’s program for reversing heart
disease, for example, a combination of a low-fat, vegetarian diet
and exercise led to an average weight loss of 22 pounds in the first
year, along with dramatic reductions in cholesterol levels and reversal
of existing heart disease.7 Five years later, much of
that benefit had been retained.8 Studies of whether weight
loss from low-carbohydrate diets is maintained for more than one
year have not been performed.
In a one-year clinical trial reported in JAMA in 2005,
researchers randomly assigned 160 overweight individuals to one
of four popular diets. Participants assigned to the Atkins diet
lost 2.1 kilograms, while Weight Watchers dieters lost 3.0 kilograms, Zone
dieters lost 3.2 kilograms, and dieters following the Ornish program
lost 3.3 kilograms.9
A review of 107 research studies on various low-carbohydrate,
high-protein weight-loss diets concluded that weight loss on these
diets is not due to any special effect of restricting carbohydrate;
rather, weight loss depended on the extent to which the dieters’ caloric
intake fell and how long they continued with their regimens.10
Other reports have also found calorie reduction to be the most
important factor in weight loss, with no special weight-loss advantage
from the restriction of carbohydrates.11,12
A review on the safety of low-carbohydrate diets notes
that Atkins-type diets are at a greater risk for being nutritionally
inadequate and raise the issue of potential long-term health
effects.13
Some low-carbohydrate diet books, such as those promoting the
Atkins diet, describe how a diet devoid of carbohydrate forces
the body to turn to other fuels for energy. That means getting
energy from fats and protein in the diet or from body fat. When
fats in the diet or in body fat are used for energy, they produce
compounds called ketones, and low-carbohydrate dieters sometimes
check for the presence of ketones in their urine as a sign that
they have managed to eliminate carbohydrate. It turns out, however,
that, in controlled trials, the degree of ketosis does not appear
to influence weight-loss speed.12
Nutritional Concerns
Low-carbohydrate diets typically include quantities of cholesterol,
fat, saturated fat, and protein that exceed the recommended safe
limits set by the National Academy of Sciences, and are often
low in fiber and other important dietary constituents.11
The Nutrition Committee of the Council on Nutrition, Physical Activity,
and Metabolism of the American Heart Association states, “High-protein
diets are not recommended because they restrict healthful foods
that provide essential nutrients and do not provide the variety
of foods needed to adequately meet nutritional needs. Individuals
who follow these diets are therefore at risk for compromised
vitamin and mineral intake, as well as potential cardiac, renal,
bone, and liver abnormalities overall.” 1
A nutrient analysis is presented below for the sample menus for
the three stages of the Atkins diet as described in Dr. Atkins'
New Diet Revolution (M. Evans & Co., 1999), pp. 257-259, using
Nutritionist V., Version 2.0, for Windows 98 (First DataBank, Inc.,
Hearst Corporation, San Bruno, CA). The menus analyzed were as follows:
Typical Induction Menu
Breakfast
Bacon slices, 4 slices
Coffee, decaf, 8 ounces
Scrambled eggs, 2
Lunch
Bacon cheeseburger, no bun
Bacon, 2 slices
American cheese, 1 ounce
Ground beef patty, 6 ounces
Small tossed salad, no dressing
Seltzer water
Dinner
Shrimp cocktail, 3 ounces
Mustard, 1 teaspoon
Mayonnaise, 1 tablespoon
Clear consommé, 1 cup
T-bone steak, 6 ounces
Tossed salad
Russian dressing
Sugar-free Jell-O, 1 cup
Whipped cream, 1 tablespoon
Typical Ongoing Weight Loss Menu
Breakfast
Western Omelet:
Eggs, 2
Cheddar cheese, 2 ounces
Bell peppers, 1 tablespoon
Onion, 1 tablespoon
Ham bits, 1/10 cup
Butter, 1 tablespoon
Tomato juice, 3 ounces
Crispbread, 2 carbo grams (1/4 slice)
Tea, decaf, 8 ounces
Lunch
Chef's salad with ham, cheese, and egg with zero-carb dressing
Iced herbal tea, 8 ounces
Dinner
Subway seafood salad, 1 item
Poached salmon, 6 ounces
Boiled cabbage, 2/3 cup
Strawberries, 1 cup
4 tablespoons cream
Typical Maintenance Menu
Breakfast
Gruyere and spinach omelet:
Eggs, 2
Gruyere cheese, 2 ounces
Spinach, 1 cup cooked
Butter, 1 tablespoon
1 cantaloupe
Crispbread, 4 carbo grams (1 slice)
Coffee, decaf, 8 ounces
Lunch
Roast chicken, 6 ounces
Broccoli, 2/3 cup, steamed
Green salad
Creamy garlic dressing
Club soda
Dinner
French onion soup, 1 cup
Salad with tomato, onion, carrots
Oil and vinegar dressing
Asparagus, 1 cup
Baked potato, 1 small with sour cream (2 tablespoons) and chives
Veal chops, 1 serving
Fruit compote, 1+ cups (generous cup)
Wine spritzer, 16 ounces
Nutrient Analysis of Atkins Sample Diets
| |
Atkins Induction |
Atkins Weight
Loss |
Atkins Maintenance |
| Energy, kcal |
1759
|
1505
|
2173 |
| Protein, g (% energy) |
143 (33%) |
120 (32%) |
135 (25%) |
| Carbohydrate, g (% energy) |
15 (3%) |
36 (10%) |
116 (22%) |
| Fat, g (% energy) |
125 (64%) |
97 (58%) |
110 (45%) |
| Alcohol, g (% energy) |
0 |
0 |
26 (8%) |
| Saturated fat, g |
42 |
45 |
38 |
| Cholesterol, mg |
886 |
885 |
834 |
| Fiber, g |
2 |
7 |
18 |
| Calcium, mg (% DV) |
373 (37%) |
952 (95%) |
1019 (102%) |
| Iron, mg (% DV) |
15 (86%) |
10 (54%) |
13 (70%) |
| Vitamin C (% DV) |
20 (33%) |
140 (234%) |
242 (404%) |
| Vitamin A, RE (% DV) |
799 (80%) |
1525 (153%) |
2521 (252%) |
| Folate, µg (% DV) |
143 (36%) |
268 (67%) |
584 (146%) |
| Vitamin B-12, 5g (% DV) |
11 (191%) |
8 (132%) |
5 (80%) |
| Thiamin, mg (% DV) |
0.7 (48%) |
1.1 (76%) |
1.0 (64%) |
*% Daily values are based on a 2000-kcal diet deriving 30%
of total energy from fat (10% each from saturated, monounsaturated,
and polyunsaturated fats), and 15% total energy from protein.
In addition to having very high protein content and low carbohydrate
content, the menus at all three stages are very high in saturated
fat and cholesterol. The menus are also low in fiber. In addition,
these sample menus do not reach Daily Values for calcium and iron.
The Induction menu does not meet the Daily Values for vitamin C,
vitamin A, folate, and thiamin. The Weight Loss menu is low on folate
and thiamin.
Health Concerns
No published studies have addressed the long-term effects of low-carbohydrate
diets. The longest studies have followed dieters for only 12 months,
which is not sufficient to assess whether dieters are at risk for
the problems seen in studies of general populations consuming large
amounts of meat, fatty dairy products, and the cholesterol, saturated
fat, and animal protein they contain. However, long-term studies
of the general population following a variety of diets and short-term
studies of individuals on low-carbohydrate diets raise important
concerns, which are outlined below:
1. Colon cancer. Colon cancer
is one of the most common forms of cancer in North America and
Europe and is among the leading causes of cancer-related mortality.
Long-term daily intake of meat, particularly red meat, such as
beef, pork, or lamb (as is common in Western countries), is associated
with approximately a three-fold increased risk of colon cancer.14,15
The 1997 report of the World Cancer Research Fund and American
Institute for Cancer Research, entitled Food, Nutrition, and the
Prevention of Cancer, concluded that, based on available evidence,
diets high in red meat are probable contributors to colon cancer
risk.
Studies of large populations published in subsequent years
arrived at similar conclusions.16 In addition, meat-heavy
diets are often low in dietary fiber, which protects against cancer.17 Low-carbohydrate
diets typically include red meats among their foods recommended
for daily consumption, but no studies have yet been conducted
to see whether low-carbohydrate dieters do indeed have the same
increased long-term cancer risk seen with other populations eating
meat-heavy diets.
2. Heart disease. Generally
speaking, weight loss tends to reduce cholesterol levels, while
saturated fat and cholesterol tend to raise them.18,19
Consequently, the effect on cholesterol levels of a low-carbohydrate
weight-loss diet that includes saturated fat and cholesterol can
vary from person to person.5,20-23 In some studies,
about 30% of people on low-carbohydrate diets showed an increase
in cholesterol levels, despite their weight loss.21,23
In a low-carbohydrate diet study conducted at Duke University,
funded by the Atkins Center for Complementary Medicine, LDL (“bad”)
cholesterol levels fell in 29 of the 41 study completers, as
would be expected from weight loss along with the various supplements
used in the study. However, LDL levels rose in 12 participants
by an average of 18 mg/dl (the increases ranged from 4 to 53
mg/dl). One participant had an LDL increase from 123 mg/dl to
225 mg/dl (normal LDL values are typically described as <100
mg/dl, although some investigators have called for lower limits).
The participant was then treated with a “cholesterol-lowering
nutritional supplement,” and the LDL dropped to 176 mg/dl,
which is still far above recommended levels.21 In
a subsequent Duke University study, two low-carbohydrate diet
participants dropped out of the study because of elevated serum
lipid levels (one had an increase in LDL cholesterol from 182
mg/dl to 219 mg/dl in four weeks; the second had an increase from
184 mg/dl to 283 mg/dl in three months), and a third developed
chest pain and was subsequently diagnosed with coronary heart
disease. In 30 percent of participants, LDL cholesterol increased
by more than 10 percent.23
The effect of the diet on HDL (“good”) cholesterol
levels is not consistent.5,6,20
We recommend caution when reading favorable press accounts of
the effect of low-carbohydrate diets on cholesterol levels. The
two Duke University studies cited above are sometimes cited as
evidence that low-carbohydrate diets reduce LDL (“bad”)
cholesterol and increase HDL (“good”) cholesterol.
However, these studies did not test a low-carbohydrate diet alone.
Rather they tested the diet along with regular exercise and various
nutritional supplements, including flax oil, borage oil, fish
oil, vitamin E, chromium picolinate, and a “multivitamin
formula” containing
niacin, vitamin C, and other nutrients. Exercise and supplements
would be expected to influence cholesterol levels on their own,
apart from the effects of the diet.21,23
One particular danger of the press promotion of low-carbohydrate
diets is the suggestion that meats and dairy products that are
high in saturated fat and cholesterol do not pose the risks that
scientists have long said they do. However, abundant evidence
shows the risks of such foods.19 In fact, some evidence
suggests that even a single fatty meal (e.g., a ham-and-cheese
sandwich, whole milk, and ice cream) may adversely affect the
compliance of arteries, increasing the risk of heart attacks after
meals.24 Low-carbohydrate
diet promoters have argued that the risks of diets high in saturated
fat and cholesterol may be disregarded when the diet is also very
low in carbohydrate. However, no long-term studies have tested
this conjecture.
Furthermore, a study of nearly 30,000 women followed
for 15 years found that coronary heart disease death was associated
with intakes of red meat and dairy products when substituted
for servings of carbohydrates. Coronary heart disease death was
significantly reduced when animal protein was replaced with vegetable
protein, leading the authors to conclude that "Long-term
adherence to high-protein diets, without discrimination toward
protein source, may have potentially adverse health
consequences."33
3. Impaired kidney function.
Studies of the Atkins diet and other low-carbohydrate, high-protein
diets have not been of sufficient duration to evaluate their
potential to affect kidney function. However, reason for concern
comes from studies of the general population, in which diets
high in animal protein are associated with reduced kidney function
over time. Harvard researchers reported that animal protein
intake is associated with decline in kidney function, based
on observations in 1,624 women participating in the Nurses’ Health
Study.24 The
good news is that the damage to the kidneys was found only in those
who already had reduced kidney function at the study’s
outset. The bad news is that as many as one in four adults
in the United States may already have reduced kidney function,
and the percentage is considerably higher for those over forty
or who have hypertension. Mild kidney impairment is also found
in approximately 40% of individuals with diabetes.25 This
suggests that many people who have kidney problems are unaware
of that fact and do not realize that high-protein diets may
put them at risk for further deterioration. The kidney-damaging
effect was seen only with animal protein. Plant protein had
no harmful effect.24
The American Academy of Family Physicians notes that high animal
protein intake is largely responsible for the high prevalence
of kidney stones in the United States and other developed countries
and recommends protein restriction for the prevention of recurrent
kidney stones.26
4. Complications of diabetes.
In diabetes, kidney and heart problems are particularly common.
The use of diets that may further tax the kidneys and may reduce
arterial compliance is not recommended.
No studies of low-carbohydrate diets have been of sufficient duration
to assess their potential long-term effects on individuals with
diabetes. Because controlling blood cholesterol levels and protecting
kidney function are essential for individuals with diabetes, health
authorities recommend choosing diets that are rich in vegetables
and fruits, while limiting saturated fat, cholesterol, and animal
protein.27
5. Osteoporosis. High intake
of animal protein is known to encourage urinary calcium losses
and has been shown to be associated with increased fracture risk
in research studies involving various populations.28,29
Two studies have examined the effects of low-carbohydrate diets
on calcium losses. A Duke University study showed that urinary
calcium losses rose significantly in individuals following a low-carbohydrate,
high animal-protein diet for six months.15 Similarly,
the loss of calcium was demonstrated in a low-carbohydrate diet
study at the University of Texas. In the maintenance phase of
the diet, urinary calcium losses were 55% higher than normal.
The researchers concluded that the diet presents a marked acid
load to the kidney, increases the risk for kidney stones, and
may increase the risk for bone loss.30 No studies
of low-carbohydrate, high-protein diets have yet been of sufficient
duration to measure long-term bone loss.
6. Other adverse effects. The following adverse
effects were noted in a six-month study of a low-carbohydrate
diet, in addition to the effects on cholesterol levels noted above:23
Constipation 68%
Headache 60%
Bad breath 38%
Muscle cramps 35%
Diarrhea 23%
General weakness 25%
Misunderstandings and Deceptive
Statements
Some individuals may be confused or misled about important dietary
issues based on the following inaccurate claims:
1. “High-protein diets cause dramatic weight
loss.”
The weight loss typically occurring with high-protein diets—approximately
11-16 pounds over the course of a year5,6—is not significantly
different from that seen with other weight-reduction regimens or
with low-fat, vegetarian eating patterns.
2. “Fatty foods must not be fattening, because
fat intake fell during the 1980s, just as America's obesity epidemic
began.”
Some news stories have encouraged the public to discount health
warnings about the amount of fat (especially saturated fat) in
the diet, suggesting that fat intake declined during the 1980s,
an era during which obesity became more common. However, food
surveys from the National Center for Health Statistics from 1980
to 1991 show that daily per capita fat intake did not drop during
that period. For adults, fat intake averaged 81 grams in 1980
and was essentially unchanged in 1991. While the American public
added sodas and other non-fat foods to the diet, forcing the percentage
of calories from fat to decline slightly, the actual amount of
fat in the American diet did not drop at all. What did change
was portion size. A report in the Journal of the American
Medical Association confirmed
that meal sizes have steadily risen over recent decades.31
A notable contributor to fat and calorie intake in recent years
is cheese consumption. Per capita cheese consumption rose from 15
pounds in 1975 to more than 30 pounds in 1999. Typical cheeses derive
approximately 70 percent of energy from fat and are a significant
source of dietary cholesterol.
3. “Fat and cholesterol have nothing to do with
heart problems.”
Abundant scientific evidence establishes that dietary fat and cholesterol
are associated with increased cardiovascular disease risk.19 Nonetheless,
some popular-press articles have incorrectly suggested that evidence
supporting this relationship is weak and inconsistent.
In addition, the late diet-book author Robert Atkins claimed in
interviews that, despite his having followed a fatty, high-cholesterol
diet for decades, he did not have artery blockages. The net result
may be that dieters believe they can safely disregard well-established
contributors to heart disease. After Dr. Atkins’ death, his
widow and his personal physician revealed that Dr. Atkins had indeed
had coronary artery blockages, although they have maintained that
these blockages had nothing to do with his death.
4. “Meat doesn't boost insulin; only carbohydrates
do that, and that's why they make people fat.”
Popular books and news stories have encouraged individuals to avoid
carbohydrate-rich foods, suggesting that high-protein foods will
not stimulate insulin release. However, contrary to this popular
myth, proteins stimulate insulin release, just as carbohydrates
do. Clinical studies indicate that beef and cheese cause a bigger
insulin release than pasta, and fish produces a bigger insulin
release than popcorn.32
Also, it is important to realize that different carbohydrate-rich
foods have very different effects. Most cause a gradual, temporary,
and safe rise in blood sugar after meals. Beans, green leafy vegetables,
and most fruits are in this healthful category. The main exceptions
are large baking potatoes, white bread, and sugary foods, which
can cause an overly rapid rise in blood sugar.
5. “People who eat the most carbohydrates tend
to gain the most weight.”
Popular diet books point out that cutting out carbohydrate-containing
foods may lead to temporary weight loss. This fact has been misinterpreted
as suggesting that carbohydrate-rich foods are the cause of obesity.
In epidemiological studies and clinical trials, the reverse has
been shown to be true. Many people throughout Asia consume large
amounts of carbohydrate in the form of rice, noodles, and vegetables
and generally have lower body weights than Americans—including
Asian Americans—who eat large amounts of meat, dairy products,
and fried foods. Similarly, vegetarians, who generally follow diets
rich in carbohydrates, typically have significantly lower body weights
than omnivores.
High-Protein Diet Registry Established
In order to assist patients and consulting clinicians, the Physicians
Committee for Responsible Medicine has established a registry
for individuals who have begun low-carbohydrate, high-protein diets
or who may have been prescribed them by practitioners. Individuals
signing onto the registry may report their experience with such
diets.
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