Low
Carb Diet
(or Low Carbohydrate Diet)
Basics
A low
carb diet
restricts the amount of carbohydrates
you eat. The
Atkins and the
South Beach diets are two
examples. These
types of diets generally recommend somewhere between 20-60 grams of
carbohydrates per day. That comes out to about 20% of your daily
calories. To make up for having less carbs, these diets give you more
of your calories from fat and protein.
Most of the
low carb diet plans
have different phases. First, there is an initiation phase which has
the lowest amount of carbohydrates. Not eating many carbs will cause
your body to use fat and protein for energy. When fats are mostly used
for energy, your body enters a state called ketosis.
Your blood becomes more acidic and accumulates chemicals called
ketones. This state can be detected by checking your urine.
There may
be health consequences for going into ketosis, so you should discuss
this with your doctor. After the initiation phase, carbohydrates are
slowly added back to your diet until weight loss stops and you reach a
steady weight.
Some people
claim that these diets
cause weight loss from the effects of lowering carbohydrates in your
diet. However, these diets really end up being low calorie diets with a
high amount of protein. Protein makes you feel more full than
carbohydrates do. That makes it easier to eat less. In the end, weight
loss comes from eating fewer calories than you burn with these weight
loss plans.
Glycemic
Index
The
glycemic
index
is a way to rate foods based on how easily they are broken down into
sugars in your blood. The higher the glycemic index, the faster
carbohydrates are turned into blood sugar. Higher blood sugar levels
cause your body to release more
insulin.
This quick rise in insulin causes your body to overshoot and quickly
lower your blood sugar to a level that is lower than normal. While this
may not cause you to have a lot of symptoms, this might make you feel
hungrier and eat more.
Theoretically,
high glycemic index foods can
make you feel hungry after eating them, rather than feeling full. Also,
most foods with a low glycemic index are higher in fiber. Some of the
low carb diets restrict the amount on carbohydrates to 40% of your
daily calories and focus more on the glycemic index of foods.
Early
Weight Loss
Low
carbohydrate diets tend to
cause a quick early weight loss. When your body uses its own stored
carbohydrates for energy, the chemical reaction produces water. This
extra water then goes out in your urine. The ketosis state also causes
your body to get rid of more water. Therefore, much of this early
weight loss is just water weight.
If too many
carbohydrates are added
back, you can retain water and regain some of this water weight
quickly. This can cause swelling. This effect is called refeeding
edema.
How
Well Do They Compared to Other
Diets?
The studies on
low carb diets lasted
only up to one year. There is no scientific evidence at this time as to
how well people do on different diets after one year. After six months,
people generally lost more weight on low carb diets. After one year,
the weight loss was about the same between low carb and low calorie
diets.
One study looked specifically at
the Atkins (very low carbohydrate), Zone (low carbohydrate), LEARN (low
fat and high carbohydrate), and Ornish (very high
carbohydrate) diets.
It found that women on the Atkins diet lost more weight after one year
than women on the other three diets, who all lost about the same amount
of weight. It may be that people are able to stick to the low carb
diets more easily than the other diets because the extra protein fills
them up, which is probably why they are more successful at weight loss.
In
that same study that compare the four different diets, women on the
Atkins diet had better triglyceride
and
HDL
(or good cholesterol)
levels than those on the other diets.
LDL
(or bad cholesterol)
levels were the same after one year with all of the diets. Blood
pressure was also lower for women on the Atkins diet after one year
compare to the other diets.
Another study
lasting 2 years compared the Atkins diet, the Mediterranean diet,
and a low-fat diet.
It found that men lost the most weight with the Atkins diet (10.8 lbs)
and almost as much weight with the Mediterranean diet plan (8.8 lbs).
They only lost only 7.5 lbs on the low fat diet. Women in the study
lost 5.3 lbs on the Atkins plan, 13.6 lbs on the Mediterranean, and
only 0.22 lbs on the low-fat diet. It appears that Men do best on the
low carb diets and women do best on the Mediterranean diet.
Risks
The current
studies seem
to indicate that low carbohydrate diets are safe. However, there are
some theoretical risks to long term low carb dieting. They have a low
fiber intake. Fiber can help reduce the risk of
heart
disease,
stroke,
and
diabetes.
In spite of this, low carb diets have been shown to improve cardiac
risk factors, such as increasing HDL cholesterol and lowering
triglycerides. They do this better than low-fat diets.
There is also
a lower amount of magnesium, potassium, and vitamin C, as
well as an increase in the loss of calcium with these diets. This may
lead to osteoporosis. They are also low in
thiamine, folate, and iron,
as well as Vitamins A, B6, & E. You may need to take a vitamin
supplement. Low carbohydrate diets raise the levels of a chemical
called uric acid in the blood, which may worsen gout. The ketosis state
can cause bad breath. You should discuss all of these things with your
doctor.
Different
Low-Carb Diets
The
main low carbohydrate diets are the Atkins, South Beach, and Zone diets.
The
Atkins diet focuses on
low carbohydrate levels. The
South Beach diet is
more balanced and puts some limits on fat. The
Zone diet focuses on
eating the right ratio of carbohydrates to fat.
Return to
Diets
or the
Home
Page.
It is important you
discuss any weight loss or exercise plan with your doctor. Only you and
your physician can decide what is best for you. Some people have
certain conditions that prevent them from doing all exercises, and goal
body weights may be different for different people. You need to discuss
all these things with your physician before starting any weight loss or
exercise program.
This
article was written by
John
Vickery, MD.
References
American
Family Physician 2006;73:1942-8
Treatment Guidelines from The
Medical Letter 2003;1:101
“Dietary therapy for obesity”
Up To Date version 15.3
Journal of the American Medical
Association 2007;297:969-977
“Prudent diet” Up To Date version
15.3
Treatment
Guidelines from the Medical Letter 2008;6:23-28
N
Engl J Med 2008;359:229-41

Last updated 7/19/09
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