Potential
Hazards of Low Carbohydrate Diets
While most of the criticisms
I have heard about a low carb intake are scientifically invalid, I wanted
to diligently
search for any real potential hazards before committing myself and my
husband to such a diet for an indefinite period of time.
There
is a significant lack of study about this type of diet, especially in
relation to searching for adverse consequences. I based my research, then,
on any studies that could relate to the same metabolic processes taking
place as those in the low carb diet, looking for any negative effects
that might extrapolate to this diet.
The criticisms
that have potential scientific validity are the following:
(a) excessive
protein in the diet can lead to loss of calcium in the urine, which
comes from the bones, resulting in osteoporosis
(b) ketosis
can be hazardous if it is ongoing for long periods
Excessive
Protein
When
the body uses protein for energy it does so by breaking the chemical bonds
between its components, which are amino acids and nitrogen. The amino
acids can be recycled for later use, but with
high protein intakes, some of the amino acids are also disposed of. This
process creates some molecules that are acids, or have a positive electrical
charge, which must be excreted via the kidneys. There are also inorganic
ions in meat which are acidic and which circulate to the kidneys for disposal.
The body
likes chemical neutrality overall, so it compensates for an acid load
by releasing both bicarbonate and calcium from the bones, which are known
to be the body's buffering system. As
the kidneys restore balance in the system by excreting the acids, some
of the calcium ions will get excreted along with them. The net result
then can be loss of calcium from the bone mass, which can result in osteoporosis,
or thinning of the bones.
This
topic was discussed in depth at the symposium of the Nutrition Working
Group of the American Society for Bone and Mineral Research, in Cincinnati,
OH on September 10, 1997, and numerous scientific studies were presented.
As typical with "gray" areas of science, the answer to the question,
"Does excess dietary protein adversely affect bone?" was given
as both "Yes" and "No".
The researcher
who answered "No " rephrased the question to, "Are protein
intakes at the upper end of the range likely to be found in the population
harmful?" and provided evidence that In most
observational studies, as protein intake went up, so did calcium intake.
When adjustment for calcium intake was made, most of the time the positive
association between protein intake and fractures disappeared.
More
specific evidence was given by the "Yes" camp.
My final
conclusion is that an unlimited protein intake that satisfies an individual's
hunger in a low carb diet should not be hazardous, however, there is no
benefit, and can be a potential hazard, to ingesting large amounts of
additional protein (beyond that which satisfies normal hunger) such as
with supplemental pills or powders.
Ketosis
A ketogenic
diet has been used for nearly 70 years to treat seizures in children -
initially before medications were available, and currently for those cases
in which medications are not effective. In articles relating the use of
this diet, no adverse effects are indicated, however, no specific adverse
effects are looked for either.
Interestingly,
calcium loss and osteoporosis as noted in (a) above is likely a greater
concern with ketosis than it is with excessive protein. I base this statement
both on scientific knowledge and the results of one small study I encountered
in my research.
First
of all, the loss of calcium due to ketosis is complex but scientifically
sound. Ketosis is a state in which up to five times the normal nighttime
levels of ketones are present in the bloodstream. Ketones are acids, which
are molecules with a positive charge. As explained above, the body likes
chemical neutrality overall, so it compensates by producing more bicarbonate,
which has a negative charge. The presence of bicarbonate in turn may
cause release of other positively charged molecules, which includes calcium,
and which may come from the bones. (Again, the emphasis indicates
this statement is based on theory).
At the
kidney, which selectively excretes charged molecules (ions) to restore
neutral balance, calcium ions may be excreted along with the ketones.
The overall result is a loss of calcium from the bones which, over extended
periods of time, can lead to osteoporosis or thinning of the bones.
I found
only one study which appears to confirm this process, and this is a very
small study in which six adolescents who had weights greater than 200%
of ideal body weight were placed on a very low calorie diet which produced
ongoing ketosis. Specific testing at regular intervals revealed all six
subject to have an increase in calcium excretion in the urine as
well as a decrease in total body bone mineral content, despite
the intake of calcium and vitamin D supplements. Bone mineral content
was measured by a DEXA scanner, which is a reliable method.
When
these same subject were provided 90 grams of carbohydrate daily, frequent
testing revealed the absence of ketosis, and urinary calcium at normal
levels. After a short period of time the bone mineral density also returned
to baseline.
This
finding does not tell us whether the same effect would be seen in individuals
who were consuming a normal quantity of total calories. However, since
the calcium loss is apparently associated with ketosis, we must consider
the possibility that an ongoing state of ketosis with any dietary intake
could likely cause the same result.
Admittedly,
this is a single study of a very small population, which limits its scientific
relevance. However, when it comes to scientific evidence, absence of proof
is not proof of absence. As
a scientist, I must consider that even such a small study should be considered,
especially because its outcome agrees with what in theory could occur.
It is for this reason that I believe that ongoing ketosis should be avoided.
This
is especially important for women, because many of them will experience
calcium loss from the bones and resulting osteoporosis after menopause.
This process is well documented and is somehow related to the lack of
estrogen.
It has
long been advised that women in their 30's ensure that they receive 1200
mg of calcium daily, with supplements if necessary, in order to maintain
their bone mass prior to undergoing menopause. DEXA scans to measure bone
density are recommended for women within the first five years of menopause
in order to assess their risk of osteoporisis. This is especially important
now that treatments are available to prevent and even reverse bone loss.
Because
of the indication that ketosis may be a factor related to bone loss, I
believe it is advisable for any woman on a maintenance low carb diet to
consider having a DEXA scan. Just because these studies have not been
performed yet does not mean we must ignore the possibilities, especially
with a condition that may already be a risk for many women.
Conclusion
- How to avoid potential hazards of low carb diets
In "DIET
TRUTHS REVEALED: The IDEAL DIET for Human Health" the
known scientific facts about human nutrition and metabolism are presented
in layman's terms, explaining why low carbohydrate diets are the healthiest
for most people.
The issue
of ketosis is discussed in detail, and is the basis for the recommendation
of an intake of 90 grams of carbohydrate daily. Detailed explanations
are provided as to why this still allows for weight loss, appetite control,
and healthy cholesterol levels in most persons. More
information about the book
In addition,
you can download
articles that appeared in The IDEAL DIET Newsletter on the topics of ketosis
and osteoporisis. Check out the following:
Pub.
22. "Valid and Invalid Criticisms of Low Carbohydrate Diets -- Protein
Intake and Bone Loss; Osteoporosis - Risk Factors, Screening, Treatment
and Prevention"
Pub.
23. "Ketosis - Safe or Not?"
You can
also get information on many other topics about the low carb diet and
the controversy that surrounds it.
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copyright 2000 Jan McBride, M.D.
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