[PHNUTR-L] An Increase in Dietary N-3 Fatty Acids Decreases a
Marker of Bone Resorption in Humans
fivestar at nutritionucanlivewith.com
Mon Apr 2 20:35:41 PDT 2007
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Bone Resorption and Omega-3 Fatty Acids
Rebecca Corwin, RD, PhD
Nutritional Sciences Department
The Pennsylvania State University
126 S. Henderson
University Park, PA 16802
(814) 865-6519 / (814) 863-6103 (FAX)
rxc13 at psu.edu
“An Increase in Dietary N-3 Fatty Acids Decreases a Marker of Bone
Resorption in Humans,”
Nutr J, 2007 Jan 16;6(1):2 [Epub ahead of print] 45647 (3/2007)
Kirk Hamilton: Can you please share with us your educational
background and current position?
Rebecca Corwin: I received my BA in Education, University of
Florida, 1972; BS in Clinical Dietetics, Texas Woman’s University, 1978;
MS in Biopsychology, University of Houston-Clear Lake, 1981; and PhD in
Biopsychology, University of Chicago, 1989.
KH: What got you interested in studying the role of plant omega-3
fatty acids and bone loss?
RC: Converging evidence suggested a beneficial effect of omega-3
fatty acids on bone health, but very little was known about the
plant-derived omega-3s. Furthermore, a controlled feeding study in
humans had never been done. By conducting this kind of study, we knew
exactly what the participants ate. This made it easier to determine what
contributed to the beneficial effect.
KH: Why did you not use fish oil (eicosapentaenoic (EPA) and
docosahexaenoic (DHA)) as your source of omega-3s versus ALA
(alpha-linolenic acid) from walnuts and flaxseed?
RC: Previous studies had shown beneficial effects of marine-based
omega-3 fatty acids (EPA, DHA) on bone health, but little was known
about the effects of plant-based sources. The omega-3 fatty acid in
plants (ALA) can be converted to EPA and DHA in the body, albeit not
very efficiently. Since we wanted to use whole food sources instead of
oil supplements, and many Americans do not like to eat fish, we decided
to assess the effects of the plant-derived omega-3s in this study.
KH: How much of bone loss is an inflammatory condition?
RC: The importance of inflammation to bone loss varies according to
the individual case. Inflammation probably plays a major role in bone
pathology associated with inflammatory conditions such as rheumatoid
arthritis and systemic lupus erythematosus, but may be important in
conditions such as post-menopausal osteoporosis, as well.
KH: What markers do you follow with regards to inflammation and bone
RC: Several markers of inflammation have been associated with bone
loss including, but not limited to, TNF-alpha, interleukin-1 and
KH: Can you explain what the NTx (N-Telopeptide) test is and why it
is valuable as a marker of bone loss?
RC: Bone is made of several different types of cells including
osteoblasts (bone forming cells), osteoclasts (bone breakdown or
resorbing cells), and collagen (a protein matrix within which the
osteoclasts and osteoblasts are located). Healthy bone is constantly
being broken down and built back up again, a process that keeps bone
strong. However, when breakdown exceeds formation, bones become weak and
bone disease occurs. When the osteoclasts break bone down, some of the
collagen is also dissolved. NTx is a product that is produced when the
collagen is broken down.
KH: What were the main differences between the Average American Diet
(AAD), the Linoleic Acid Diet (LA) and the Alpha-Linolenic Acid Diets
(ALA) with regards to fatty content? Was total fat content the same?
RC: The LA and ALA diet contained a higher percentage of total fat
compared to the AAD diet. However, the LA and ALA diets were higher in
polyunsaturated fatty acids (PUFA) and lower in saturated fatty acids
than the AAD. The ALA diet contained the highest amount of alpha
linolenic acid (the plant-based omega-3 fatty acid), compared to the
other two test diets.
KH: Were more walnuts and flaxseed consumed in the ALA diet or were
these fatty acids consumed in oils? How did you get the quantity you
desired? Were the “fatty acids” given with meals or away from meals? In
single doses or divided doses?
RC: Walnuts and walnut oil, which are particularly rich sources of
both n-6 and n-3 PUFA, represented half of the total fat in the LA and
ALA diets. Sources of walnuts in the diet included walnut granola, honey
walnut butter, walnut pesto, and plain walnuts as a snack. Flaxseed oil,
also was used to increase the ALA content of the ALA Diet. The fatty
acids were incorporated into the food that the subjects ate; they were
not given as supplements. For each of the three experimental diets,
eight calorie levels (1800 - 3900 kcal) were developed to meet different
energy needs of the subjects. Unit foods (muffins) containing the same
macronutrient profile of each of the test diets were used during each
diet period to provide incremental adjustments of 100 kcal/day as needed
to maintain body weight.
KH: Can you tell us about your study and the basic results?
RC: Subjects (n=23) consumed each diet for 6 weeks in a randomized,
3-period crossover design. NTx levels were significantly lower following
the ALA diet relative to the AAD. There was no change in levels of a
marker of bone formation across the three diets. Concentrations of NTx
were positively related to the pro-inflammatory cytokine TNF alpha for
all three diets. The results indicate that plant sources of dietary n-3
PUFA may have a protective effect on bone metabolism via a decrease in
bone resorption in the presence of consistent levels of bone formation.
KH: Were there any side effects to the different fatty acid diets?
How was the patient compliance?
RC: No side effects were reported. Patient compliance was excellent.
KH: Are there any other components of flaxseed or walnut oils, aside
from their omega-3 fatty acid content, that might account for this
RC: Flaxseed is also a source of lignans, a type of phytoestrogen,
and walnuts have a high antioxidant content; however, the effects of
these compounds on bone health have not been fully determined.
KH: How would you incorporate your findings on these omega-3 fatty
acids into public health recommendations for the prevention and/or
reversal of bone loss that frequently include calcium, magnesium, zinc,
copper, manganese, vitamin D, vitamin K, weight-bearing exercise and
strength training recommendations?
RC: Our findings are really too preliminary for public health
recommendations to be made. However, the results of our study certainly
are consistent with recommendations already in place for prevention of
heart disease, i.e. to include sources of omega-3 fatty acids in your diet.
KH: How often would you recommend the NTx test over a year or between
DEXA tests, and what level are you trying to lower this marker to
document success in slowing or preventing bone loss?
RC: Bone density measurements, such as the DEXA scan, provide
information about the current skeletal mass, but do not provide
information about metabolic activity. One of the most commonly used
markers to assess bone turnover is the serum NTx measurement. Various
studies have shown that for a 1 SD increase in a bone marker value above
that of a premenopausal woman, there is a 1.5 to 2.5-fold increase in
bone loss over the next year. Therefore, the higher the bone marker
(i.e. serum NTx), the greater the risk of bone loss over the next year.
The goal in a patient with osteoporosis is to drive the NTx below these
values, to a NTx seen in premenopausal women. Bone markers can also be
used to monitor therapy for osteoporosis. This has been demonstrated for
hormone replacement therapy, bisphosphonates, calcitonin, and the
selective estrogen receptor modulators. As far as how often this test
should be done, that would really be up to your doctor. The tests we ran
are not the only tests for bone breakdown and build-up. Your doctor can
recommend which tests would be best for you.
KH: Is it worth doing fatty acid profiles on bone loss patients to
assess for omega-3 fatty acid status? Were any fatty acids profiles done
in this study? Did they correlate with bone loss or inflammation?
RC: Fatty acid profiles are not used clinically to assess bone
status. It is important to appreciate that plasma fatty acids represent
short-term dietary consumption practices. Consequently since people
don’t eat exactly the same thing day after day, the plasma profiles
would not be informative of tissue or bone levels of fatty acids over
the long term, and it is likely that these longer-term changes in the
bone levels are what’s important. Serum fatty acids were assessed in
this study, with the omega-3 fatty acids being highest when the ALA diet
was consumed. They did not correlate strongly with the NTx; however,
other work from Dr. Kris-Etherton’s group has shown correlations with
markers of inflammation.
KH: Do you have any further comments you would like to make on this
interesting subject? This work is so important!
RC: Most of the participants in this study were middle-aged men. The
presence of osteoporosis in men is increasing, but they generally are
not included in studies of bone health. This report, as well as others,
suggests that men may benefit from adjustments to the fatty acid
composition of the diet, not only because of benefits to their
cardiovascular systems, but also because of benefits to their bones.
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
"Ask the Parkinson Dietitian" http://www.parkinson.org/
"Eat well, stay well with Parkinson's disease"
"Parkinson's disease: Guidelines for Medical Nutrition Therapy"
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