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July 2009 Highlights of This Issue
Nitrates and Nitrites—Naughty or Nice?
Nitrate and nitrite are small, inorganic, naturally occurring nitrogen-containing compounds. In the body, nitrate
(containing 3 oxygens) is converted to nitrite (containing 2 oxygens), which in turn can be converted to nitric oxide (NO). These reactions can also occur
in reverse. Nitric oxide helps regulate blood flow and blood pressure and thus is an important mediator in keeping the cardiovascular system in optimal
health. Nitric oxide also appears to be a critical component of the immune system because it helps regulate inflammation when a tissue has been injured or
infected. Approximately half of the nitrite and nitrate in the body comes from oxidation of NO, whereas the other half is obtained from dietary sources such
as spinach, lettuce, celery, and cabbage. Nitrate in the body is also converted to nitrite and NO by healthy bacteria residing in the mouth and
gastrointestinal tract. In addition, nitrate and nitrite are added to some cured and processed meats such as bacon and hot dogs. For decades, these
nitrogenous substances have been considered hazardous based on the contention that their consumption in high doses causes oxidation of iron (Fe) from the
Fe2+ (ferrous) form to the Fe3+ (ferric) form. This condition blunts the ability of the blood to deliver oxygen to cells. Although
epidemiological studies have provided limited evidence that consumption of some processed meats containing nitrite and nitrate might increase the risk of
certain forms of cancer, a causal relation between nitrite and nitrate and cancer has never been established. Are nitrate and nitrite really bad for you?
Conversely, should their status be completely altered to be that of "nutrients?"
Challenging the long-standing dogma that nitrate and nitrite are toxic, Hord et al from the University of Texas Health
Science Center and Michigan State University present intriguing evidence that consumption of these compounds is actually beneficial in the human body and
contributes to NO homeostasis. Their thesis and supporting arguments are published in the July 2009 issue of The American Journal of Clinical
Nutrition. Accompanying this account of the evolution of nutritional knowledge concerning these nitrogen-containing compounds is an editorial by the
Dutch researcher Katan.
Using a convenience sample of certain foods to quantify potential nitrate and nitrite consumption in the Dietary Approaches to Stop Hypertension (DASH)
diet, these researchers estimated that nitrate consumption from plant sources can easily exceed 1000 mg/d—an amount substantially higher than that
considered acceptable by the World Health Organization (222 mg/d). Furthermore they contend that the nitrate content and subsequent nitrite production may
be the mechanism of the health benefits and modest blood pressure–lowering effects ascribed to plant foods. They then question the rationale behind the
current nitrate and nitrite regulations and call for their thorough reevaluation. Katan concurs and concludes "A trial to investigate whether nitrate in
vegetables is healthy is feasible and would require a few months, a few hundred subjects, and less money than the bonus for a second-tier banker." This is
a timely argument indeed.
Reference Hord NG, Tang Y,
Bryan NS. Food sources of nitrates and nitrites: the physiologic context for potential health benefits. American Journal of Clinical Nutrition
2009;90:1–10.
Katan MB. Nitrate in foods: harmful or healthy? American Journal of Clinical Nutrition 2009;90:11–2.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/1/1
To contact the corresponding author, Nathan Bryan, please send an e-mail to
nathan.bryan{at}uth.tmc.edu.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/1/11
To contact the corresponding author, Martijn Katan, please send an e-mail to
katan99{at}falw.vu.nl.
Following the Dietary Guidelines May Slow Heart Disease in Women
Background The Dietary Guidelines for Americans (DGA) provide guidance to promote health and reduce risk of chronic diseases. However,
what evidence is there that following the DGA optimizes health? Is this advice useful for individuals already in poor health? To study these questions,
researchers at the USDA Human Nutrition Research Center on Aging at Tufts University and Wake Forest University devised a statistical model that assessed
adherence to the DGA and then related it to progression of atherosclerosis in women. Their results can be found in the July 2009 issue of The American
Journal of Clinical Nutrition.
Study Design Postmenopausal women (n = 224) with a history of heart disease were studied, and semiquantitative food-frequency
questionnaires were completed to assess dietary intake. The 2005 Dietary Guidelines for Americans Adherence Index (DGAI) was used to assess adherence to 20
key dietary recommendations put forth in the 2005 DGA. This index was modified so that each component had a continuous score from 0 to 1 instead of a
discrete score of 0, 0.5, or 1. In addition, the DGAI was further modified as a “weighted” DGAI (wDGAI) score by assigning a different weight on the basis
of the relation of each dietary component to atherosclerosis progress. Mathematical “penalties” were then applied to each component when intake was not
consistent with the DGA. The approach hybridized the existing dietary recommendations and the concept that not all recommendations are equally important in
preventing atherosclerosis. At baseline and 3 y later, severity of atherosclerosis was assessed by using coronary angiography.
Results No woman consumed a diet meeting all DGA recommendations, and statistical analyses showed no relation between DGAI and
atherosclerosis progression. However, wDGAI was inversely associated with disease risk, such that higher scores (associated with more compliance with the
DGA) were found in women who had experienced less progression of their atherosclerosis during the 3-y period. Specifically, the authors found that adherence
to recommendations for whole-grain, total fat, and cholesterol intake were most associated with decreased atherosclerotic progression.
Conclusions Imamura concluded, "Our study supports the concept that not all dietary recommendations are equally related to disease
progression." In her accompanying editorial, Kris-Etherton praises these researchers for developing their "hybrid" wDGAI and suggests that the concept and
approach will allow scientists to better evaluate additional associations between dietary practices and other health and disease outcomes. Of greater
importance are the findings that adherence to the DGA in individuals with atherosclerosis beneficially affects cardiovascular disease progression and that
certain foods play a more prominent role than others. This is further impetus for current efforts to develop the 2010 DGA.
Reference Imamura F,
Jacques PF, Herrington DM, Dallal GE, Lichtenstein AH. Adherence to 2005 Dietary Guidelines for Americans is associated with a reduced progression
of coronary artery atherosclerosis in women with established coronary artery disease. American Journal of Clinical Nutrition
2009;90:193–201.
Kris-Etherton PM. Adherence to dietary guidelines: benefits on atherosclerosis progression. American Journal of Clinical Nutrition
2009;90:13–4.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/1/193
To contact the corresponding author, Alice Lichtenstein, please send an e-mail to alice.lichtenstein{at}tufts.edu.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/1/13
To contact the corresponding author, Penny Kris-Etherton, please send an e-mail to pmk3{at}psu.edu.
Study Supports Benefits of Iron Supplementation in Females Soldiers
Background Although iron is likely the most well-studied nutrient, its deficiency remains common worldwide. Iron deficiency decreases
physical stamina and alters cognition, and premenopausal women are at especially high risk of iron deficiency because of monthly blood loss. The Centers for
Disease Control and Prevention estimates that iron deficiency anemia (IDA) affects up to 16% of premenopausal women in the United States. Women who are
physically active are at even greater risk because physical activity appears to have a negative effect on iron stores. Because the US military currently
comprises >15% women, preventing and treating iron deficiency might be particularly important in this population. In response, McClung and colleagues
studied the effect of iron supplementation in female soldiers during basic combat training. Their results can be found in the July 2009 issue of The
American Journal of Clinical Nutrition.
Study Design To test their hypothesis, these investigators studied 171 female soldiers (mean age: 20.6 y) randomly assigned to 1 of 2
treatment groups: control (cellulose) or iron (15 mg iron). Capsules were consumed daily for 8 wk. Before and after the treatment period, physiologic and
cognitive variables were evaluated by measuring the time needed to run 2 miles and administration of the Profile of Mood States (POMS) questionnaire. Iron
status was assessed before and after treatment periods, and women were classified as being iron deficient if they presented with
2 indicators of abnormal iron status. Those classified as iron deficient who also had low hemoglobin
concentrations were considered as having IDA.
Results During the study, subjects in both the control and iron groups experienced increased concentrations of hemoglobin, red blood
cell distribution width, and soluble transferrin receptor. However, serum ferritin concentrations (an indicator of iron stores) decreased only in the
placebo group. At the end of the study, the number of iron-deficient volunteers in the control group had increased by 100%, whereas the number in the
iron-treated group increased only by 36%. Similar results were found for other indicators of iron deficiency. In women who had IDA at the start of the
study, iron treatment had a beneficial effect on physical performance as assessed by speed of completing a 2-mile run. In general, mood was improved in
both groups over the course of the study. However, those in the iron supplementation group experienced greater improvement in "vigor" than did those in the
control group. No other indexes of mood were affected by treatment.
Conclusions The authors concluded that iron supplementation in female soldiers can attenuate the decline in iron status frequently
observed during military training. Furthermore, supplementation resulted in faster running time in women with IDA and improved vigor (an indicator of
cognitive state). The authors rightly urge heightened educational guidance regarding consumption of iron-rich foods to female soldiers, as well as
additional efforts to provide and identify iron-rich foods in military cafeterias. Clearly, our female soldiers deserve no less.
Reference McClung JP, Karl JP,
Cable SJ, et al. Randomized, double-blind, placebo-controlled trial of iron supplementation in female soldiers during military training: effects on iron
status, physical performance, and mood. American Journal of Clinical Nutrition 2009;90:124–31.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/1/124
To contact the corresponding author, James McClung, please send an e-mail to
james.mcclung{at}amedd.army.mil.
A Calorie Is a Calorie in Terms of Weight Loss but Maybe Not Heart Health
Background The Dietary Guidelines for Americans recommend consumption of a relatively low-fat (LF) diet composed primarily of
carbohydrates. Similarly, the Institute of Medicine recommends that we get 45–65% of our energy from carbohydrates and 20–35% from fats. This
dietary advice is based on the contention that a nutrient-dense, low-fat diet can decrease risk of many chronic diseases including obesity. Nonetheless,
there is much public and scientific debate regarding the best mix of macronutrients, and many advocate the consumption of a low-carbohydrate (LC)
diet—especially for weight-loss purposes. These types of dietary patterns, however, inevitably result in high saturated fat and protein intake, and
their long-term effects on cardiometabolic parameters are of concern. To help clarify both their weight-loss effects and effect on cardiac risk, a team of
Australian researchers conducted a 1-y, controlled trial in adults with preexisting risk factors for heart disease. Their results are published in the
July 2009 issue of The American Journal of Clinical Nutrition.
Study Designs Subjects (n = 107; mean age: ~50 y) were eligible if they had abdominal obesity and at least one additional risk
factor for metabolic syndrome. Those with diabetes, cancer, or cardiovascular, peripheral vascular, respiratory, or gastrointestinal disease were excluded.
Participants were assigned randomly to either an energy-restricted LC diet or one providing the same amount of energy (~1430 and ~1670 kcal/d for women and
men, respectively) but composed of LF foods. The LC diet provided 4%, 35%, and 61% of energy as carbohydrate, protein, and fat, respectively; the LF diet
provided 46%, 24%, and 30% of energy as carbohydrate, protein, and fat, respectively. Compliance with these dietary regimens was encouraged by attendance
at a clinic and individual guidance by a research dietitian. Subjects were also provided with a selection of appropriate foods and food vouchers (~$32/wk)
during the first 2 mo of the study. Body composition, blood pressure, and circulating concentrations of selected metabolites, inflammatory markers, and
blood lipids were measured at baseline and throughout the study until its completion 1 y later.
Results Compliance with both dietary interventions was good, and weight loss was similar between groups (–14.5 and –11.5 kg
for LC and LF, respectively). Similarly, both groups lost comparable amounts of body fat and fat-free mass. There was no effect of diet group on blood
pressure, fasting glucose, insulin, or C-reactive protein. However, total cholesterol, LDL cholesterol, and HDL cholesterol increased more in the LC diet
group than in the LF diet group; triglyceride concentration decreased to a greater extent in the LC diet group.
Conclusions These data provide convincing evidence that, calorie for calorie, there is no difference between LC and LF diets in terms
of weight loss. However, the LC diet was associated with greater increases in HDL cholesterol and decreases in triglycerides, which may be clinically
beneficial to persons with insulin resistance. These potential benefits may be counteracted by the detrimental effects of an increase in LDL cholesterol.
Reference Brinkworth GD,
Noakes M, Buckley JD, Keogh JB, Clifton PM. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after
12 mo. American Journal of Clinical Nutrition 2009;90:23–32.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/1/23
To contact the corresponding author, Grant Brinkworth, please send an e-mail to grant.brinkworth{at}csiro.au.
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