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Dietary Protein and Bone Health:
A New View
Karl Insogna, M.D., Rebecca Sullivan, M.S., R.D., Yale University
Anne Kenny M.D., Jane Kerstetter, Ph.D., University of Connecticut
O
steoporosis is a disease in which the (0.7 grams of protein per kilogram of body weight
bones in our body thin so much that per day) to high normal (2.1 grams of protein
even a minor injury can cause a per kilogram of body weight per day) the
fracture. Simply lifting a heavy bag of ability of the body to absorb calcium from
groceries out of the trunk of the car can the diet improved by more than 35%.
cause a spine fracture in a person with We also found that the rate at which
osteoporosis. Osteoporosis is a “si- the skeleton was being broken down
lent” disease until a fracture occurs. was not increased by the increase in
Thinning bones do not hurt until dietary protein. Finally, we found
they break. Our skeletons are living that the increase in urine calcium
tissue and our bodies are constant- that had troubled other investiga-
ly building new bone and remov- tors was caused by the increase in
ing old and damaged bone tissue calcium absorption from the intes-
from our skeleton. As we age and tinal tract. The body was getting rid
particularly in women after meno- of some of the extra calcium it had
pause, more bone is broken down absorbed through the urine. It was
than is replaced, leading to a net loss not due to bone breakdown at all.
of bone. This causes thinning of the Another research group from the Uni-
bones, so called osteopenia. versity of North Dakota has recently re-
Osteoporosis and osteopenia are ported similar findings to ours. They also
very common problems and affect almost found that increasing dietary protein was
44 million Americans over the age of 50, not bad for bones but actually helped bones
most of whom are women. This number is ex- hang on to calcium particularly when the level
pected to grow to 52 million by 2010. While new of dietary calcium was low. Another report from the
drugs to prevent bone loss and treat osteoporosis are being Framingham Osteoporosis Study has shown that in both men
developed, these drugs are expensive and can have signifi- and women, a higher level of dietary protein was associated
cant side effects. It is clear that we need other approaches with better bone mineral density and a slower rate of bone
to help maintain bone health. Since bone is living tissue, it loss with aging.
makes perfect sense that nutrition is very important to skeletal Despite what one might think, there are actually a large
health. Despite this, a detailed understanding of how nutri- number of women and men in the U.S who consume a low
tion influences the skeleton is still lacking for many nutrients. protein diet on a daily basis. Between 32% and 41% of women
Two of the most intensively studied nutrients are calcium and over the age of 60 years consume a diet that contains less than
vitamin D. It is very clear now that adequate amounts of both the recommended dietary allowance for protein (0.8 grams/ki-
are important for slowing the rate of bone loss as we age and logram of body weight per day). It is important to realize that
reducing the risk of fractures. increasing dietary protein does not mean a person necessarily
One of the dietary factors that traditionally had not been has to eat more fat. Skim milk, fish, egg whites and soy are all
thought to be good for skeletal health is dietary protein. It examples of sources of low fat, high quality protein.
had been thought that dietary protein leached calcium from Although our work suggests that dietary protein may be
the skeleton and caused thinning of the bones. Many sci- helpful in preventing bone loss in individuals who are con-
entists still believe this because when dietary protein intake suming a low level of dietary protein, the only way to prove
increases, the amount of calcium in the urine goes up. It has this is to do a scientific controlled study. We are currently con-
been assumed that this extra calcium in the urine was coming ducting a multi-center trial, funded by the National Institutes
from your bones. of Health, to determine the effect of a natural protein supple-
Ten years ago our research group at Yale University and ment on bone health in women over the age of 60 and men
the University of Connecticut, began investigating the effect over 70 who have low levels of dietary protein intake and thin
of dietary protein on bone health. To our surprise, we found bones. Help us find alternative, safe and effective therapies for
that dietary protein causes a significant improvement in the the prevention of osteoporosis! See our advertisement about
efficiency with which our body absorbs calcium from the diet. the SPOON Study on the opposite page.
When we increased dietary protein intake from low-normal
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