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October 2009 Highlights of This Issue
Consumption of a Vegan Diet Related to Small Decrease in Bone Density
Background The maintenance of healthy bones requires adequate intake of many nutrients including calcium, phosphorus, and protein.
Although these nutrients are found in plant-based foods, their concentration in animal foods is much greater per unit of energy consumed. Consequently,
there has long been concern that individuals who eat little or no meat, dairy, fish, and eggs might be at increased risk of developing bone disease,
especially as they age. Osteoporosis, the loss of bone mineral density (BMD) that typically occurs over time, is a major public health problem worldwide,
with a prevalence between 17% and 30% in older women. Because BMD can be influenced by a variety of factors including dietary patterns, there is continued
interest in whether vegetarianism might be a risk factor for osteoporosis. Using data combined from 9 previously conducted studies, researchers from
Vietnam and Australia studied this particular question. Their results, as well as an accompanying editorial by Lanham-New from the University of Surrey,
United Kingdom, can be found in the October 2009 issue of The American Journal of Clinical Nutrition.
Study Design Public databases were searched to identify all original studies related to vegetarianism and BMD measured by dual-energy
X-ray absorptiometry in adults. From 922 articles initially identified, 9 were deemed eligible for this investigation, and these studies were gleaned for
relevant data such as mean age, sex, degree of vegetarianism, and BMD. In all, data from 2749 individuals (1880 women and 869 men) were pooled for this
analysis, and the differences between BMD in omnivores and vegetarians were statistically evaluated.
Results Statistical analysis showed that vegetarians had a 4% lower femoral neck BMD than did nonvegetarians. A similar effect was
observed at the lumbar spine. Further analysis suggested that this effect was significantly more pronounced among vegans, who exclude all animal foods,
than in lactoovovegetarians, who eat milk, dairy products, and eggs. These differences were greater in white than Asian women; being vegetarian did not
appear to influence BMD in men. However, only 2 of the studies included men.
Conclusions The authors concluded that the results of this meta-analysis support a slight detrimental effect of vegetarianism,
particularly a vegan diet, on BMD. However, they caution that this appears to be a relatively small effect that is unlikely to result in increased risk of
bone fracture. In her associated editorial, Lanham-New lauds this report as “a most timely and important piece of work” particularly because of its careful
selection and inclusion of studies. Nonetheless, she points out that several key confounding variables such as overall nutrient intake, dietary calcium
intakes, vitamin D, body weight, physical activity levels, and smoking were not fully controlled for in the analysis; nor does it provide any insight into
physiologic mechanisms by which the different dietary patterns influence BMD.
Reference Ho-Pham LT, Nguyen
ND, Nguyen TV. Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis. American Journal of Clinical Nutrition
2009;90:943–50.
Lanham-New SA. Is “vegetarianism” a serious risk factor for osteoporotic fracture? American Journal of Clinical Nutrition 2009;90:910–1.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/943
To contact the corresponding author, Tuan Nguyen, please send an e-mail to
tuan.nguyen{at}unsw.edu.au.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/910
To contact the corresponding author, Susan Lanham-New, please send an e-mail to
s.lanham-new{at}surrey.ac.uk.
Weight-Loss Maintenance Success May Be Related to Brain’s Response to Seeing Food
Background There is overwhelming agreement that the recent increase in the prevalence of obesity is alarming, and efforts to prevent
unhealthy weight gain across the lifespan are widespread. Whereas these initiatives are aimed mainly at prevention, it is also crucial to understand how
overweight people can most effectively lose their excess weight and then keep it off. To understand lifestyle and biological factors associated with
individuals who have succeeded in maintaining weight loss after dieting, the National Weight Control Registry has, since 1993, been tracking persons
who have maintained a weight loss of 
30 lb for 1 y. In a study
led by Jeanne McCaffery from Brown Medical School and described in the October 2009 issue of The American Journal of Clinical Nutrition, data from
this registry were used to investigate whether the brains of individuals who are able to maintain successful long-term weight loss respond differently to
food pictures than do those of their obese counterparts. An accompanying editorial by Macdonald provides additional insight.
Study Design These investigators studied 3 groups of weight-stable individuals: normal weight (NW; n = 18) with body mass index
(BMI; in kg/m2) between 18.5 and 24.9; obese (n = 16; BMI 30); and National Weight Control
Registry participants with successful weight-loss (SWL) maintenance of 30 lb for
3 y (n = 17). After a 4-h fast, participants were shown a series of pictures that included low-energy
foods (eg, salads), high-energy foods (eg, cheeseburgers), and nonfood objects (eg, shrubs). Neuroimaging was conducted using a magnetic resonance imaging
scanner to document brain responses to each image.
Results As hypothesized, SWLs responded somewhat differently to these pictures than did obese and NW individuals. Specifically, SWLs
showed greater activation in the left superior frontal and right middle temporal regions than did NW and obese controls. These changes are generally thought
to be related to greater inhibitory control in the SWLs, which might result in greater ability to resist overeating. The results also supported the
possibility that SWLs might experience greater visual attention to food images than do their obese and NW counterparts.
Conclusions The authors concluded that individuals who are especially successful in keeping weight off after it is lost may be able to
do so, in part, because they experience greater inhibitory control and greater visual attention to food cues. Macdonald lauds this study for providing
interesting data but cautions that it does not prove whether these differences are inherent within an individual or subject to change. He urges further
longitudinal studies following obese individuals before, during, and after weight loss.
Reference McCaffery JM,
Haley AP, Sweet LH, et al. Differential functional magnetic resonance imaging response to food pictures in successful weight-loss maintainers relative to
normal-weight and obese controls. American Journal of Clinical Nutrition 2009;90:928–34.
Macdonald IA. In search of the basis of successful maintenance of weight loss. American Journal of Clinical Nutrition 2009;90:908–9.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/928
To contact the corresponding author, Jeanne McCaffery, please send an e-mail to jeanne_mccaffery{at}brown.edu.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/908
To contact the corresponding author, Ian Macdonald, please send an e-mail to ian.macdonald{at}nottingham.ac.uk.
Fish Consumption during Pregnancy—Balancing the Risks with the Benefits
Background Fish, which are excellent sources of protein, minerals, and omega-3 (n–3) fatty acids, have long been considered an
important part of a healthy diet, especially during pregnancy, when these nutrients are critical for development of the fetal neurological system. However,
some types of fish are sources of environmental contaminants, such as mercury, which can be especially damaging to the growing fetus. In response, pregnant
women are often advised to limit and carefully choose the type of fish they eat. Balancing the benefits and risks of fish consumption remains a challenge.
To better understand the holistic effects (or lack thereof) of fish consumption during pregnancy, researchers recently studied the relations between fish
consumption, prenatal mercury exposure, and birth outcomes in a group of mothers and infants in Spain. Their results are published in the October 2009 issue
of The American Journal of Clinical Nutrition..
Study Design A total of 554 maternal-infant pairs were studied beginning in pregnancy, when maternal fish intake was assessed using a
100-item semi-quantitative food-frequency questionnaire. This survey documented detailed information concerning specific types and frequency of fish eaten.
Infant (umbilical cord) blood was collected immediately after birth and analyzed for its mercury content. Infant birth weight and length were determined.
Results Average fish consumption was found to be 55 g/d. This is equivalent to consuming 1 serving of canned tuna or two-thirds serving
of baked salmon every day. Seventy-two percent of newborns had cord blood mercury concentrations above levels deemed safe by the US Environmental Protection
Agency. Women who consumed large amounts of canned tuna, lean fish, and large oily fish (eg, swordfish) had infants with the highest blood mercury
concentrations. Newborns with the highest concentrations of mercury weighed an average of 144 g less than those with the least mercury (P for
trend = 0.02) regardless of the mother’s fish consumption. Conversely, greater consumption of canned tuna was related to increased birth weight (P
for trend = 0.03). Cord blood mercury concentration was positively related to risk of being born “small-for-gestational-age” (SGA) in terms of length, but
not weight. Mothers who consumed 2 servings of lean fish/wk had the lowest risk of having an infant that was
SGA for length (P = 0.09). Conversely, women who consumed 2 servings of large oily fish/wk were at
greater risk of having an SGA infant than were those who rarely or never consumed this type of fish (P = 0.03).
Conclusions The data from this study highlight the complexities inherent in making public health recommendations concerning fish intake
during pregnancy, especially given the risks and benefits related to some types of fish. The authors conclude that “maternal fish consumption plays a
different role in fetal growth depending on the amount and type of fish consumed” and urge further studies designed to better understand the effects of
prenatal mercury exposure on fetal growth and development.
Reference Ramón R,
Ballester F, Aguinagalde X, et al. Fish consumption during pregnancy, prenatal mercury exposure, and anthropometric measures at birth in a prospective
mother-infant cohort study in Spain. American Journal of Clinical Nutrition 2009;90:1047–55.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/1047
To contact the corresponding author, Rosa Ramón, please send an e-mail to
ramon_rosbon{at}gva.es.
Nature Is Important, but Can It Be Trumped by Nurture?
Background Despite intense scientific and public interest, the etiology of obesity is still poorly understood. The recent discovery of
“obesity genes,” however, is adding important insight as to why some individuals may be more susceptible than others to weight gain. Scientists are learning
that variations—known as polymorphisms—in a large number of human genes can alter the risk of obesity. One such obesity gene codes for the
melanocortin-3 receptor (MC3R), which has been shown to play an important role in energy homeostasis in rodents; some studies also suggest that MC3R
polymorphisms may also be related to obesity in humans. In 3 studies published in the October 2009 issue of The American Journal of Clinical
Nutrition, scientists investigated the link between genetics and obesity risk; in one study, the possibility that increased physical activity levels
might trump unfortunate genetics was also assessed.
Study Designs In a collaboration of US scientists led by Jack Yanovski at the National Institutes of Health, the presence of
polymorphisms in the MC3R gene was assessed in 416 healthy children (6–19 y of age). The associations between MC3R polymorphisms and energy intake,
energy expenditure, and adiposity were then determined. In another study, Dutch researchers led by Yvonne van der Schouw evaluated the presence of
polymorphisms in several obesity genes in 1700 Dutch women. They then assessed whether having these polymorphisms was related to abdominal obesity, energy
intake, and food preferences. In the third study, a collaboration of Finnish and Danish scientists led by Karri Silventoinen studied whether physical
activity and the proportion of energy as protein in the diet might modify a person’s inherited risk of obesity in 1034 pairs of twins. Twin studies, such
as this one, are powerful because their use of both identical (monozygotic) and fraternal (dizygotic) twins can help tease out the independent and
interactive effects of genetic and environmental factors.
Results Yanovski and colleagues found that children with one particular polymorphism in the MC3R gene had significantly higher body
mass index and fat mass than did those without this genetic alteration (P = 0.001); this appeared to be driven by greater energy intake rather than
lower energy expenditures. The Dutch researchers found polymorphisms in several genes to be associated with general adiposity. Additionally, they uncovered
possible links between some polymorphisms and food choices, such as increased fat or carbohydrate intake. Results from the twin study confirmed the
importance of genetics in altering the risk of obesity. Moreover, the authors found evidence that increased physical activity can counteract the action of
at least some of the genes responsible for a predisposition to obesity. High protein intake had no such effect.
Conclusions Together, these studies support the long-held hypothesis that genetic factors can increase one’s risk of obesity, perhaps
by altering a person’s preference for high-fat or high-calorie foods and ultimately overall food intake. Importantly, however, the study of Finnish and
Danish twins suggests that high levels of physical activity can help nullify the effects of these risky gene polymorphisms.
Reference Savastano DM,
Tanofsky-Kraff M, Han JC, et al. Energy intake and energy expenditure among children with polymorphisms of the melanocortin-3 receptor. American Journal
of Clinical Nutrition 2009;90:912–20.
Bauer F, Elbers CC, Adan RAH, et al. Obesity genes identified in genome-wide association studies are associated with adiposity measures and potentially
with nutrient-specific food preference. American Journal of Clinical Nutrition 2009;90:951–9.
Silventoinen K, Hasselbalch AL, Lallukka T, et al. Modification effects of physical activity and protein intake on heritability of body size and
composition. American Journal of Clinical Nutrition 2009;90:1096–103.
For More Information For the complete article by Savastano et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/912
To contact the corresponding author, Jack Yanovski, please send an e-mail to jy15i{at}nih.gov.
For the complete article by Bauer et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/951
To contact the corresponding author, Yvonne van der Schouw, please send an e-mail to
y.t.vanderschouw{at}umcutrecht.nl.
For the complete article by Silventoinen et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/90/4/1096
To contact the corresponding author, Karri Silventoinen, please send an e-mail to
karri.silventoinen{at}helsinki.fi.
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