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June 2009 Highlights of This Issue
Understanding Energy Balance—Not as Simple as One Might Expect
Background There is no disagreement that the burgeoning obesity epidemic is of great concern. Scientists continue, however, to
struggle with understanding its causes. For instance, are obesity rates increasing because of greater caloric intake, decreased energy expenditure, or
both? In addition, how does the increase in energy requirements caused by increased body weight fit into this equation? One term used recently to describe
the difference between energy intake and energy expenditure needed to return our population to a healthy weight is “energy gap,” and there are two
variations on this theme. An “energy imbalance gap” is a small difference between energy intake and energy expenditure that leads to weight gain
over time. Conversely, “energy flux gap” describes an overall increase in average energy intake (and expenditure) that occurs in a population
experiencing an obesity epidemic because obese individuals require more energy for day-to-day activities than do their lean counterparts. To understand how
these two types of energy gaps are related to the current obesity epidemic, an international group of researchers reanalyzed the collective results of
previously conducted studies to develop a mathematical equation relating energy flux (which is approximately equal to energy intake and energy expenditure
when weight is stable) to body weight. Their results, along with an accompanying editorial, are published in the June 2009 issue of The American Journal
of Clinical Nutrition.
Study Design Only data from studies (n = 8) that had measured energy expenditure by using the “gold standard” doubly labeled
water technique were included. This resulted in the investigators having information about body weight (the dependent variable), energy expenditure (the
main independent variable; equal to energy flux), height, age, and sex for 1399 adults. These data were then used to develop an equation describing the
relation between energy flux and body weight.
Results As expected, there was a strong, positive relation between body weight and energy flux. In other words, larger people were
found to expend more energy than did their smaller counterparts. The overall flux gap related to the current obesity epidemic was estimated to be
400 kcal/d, a value substantially higher than what has been proposed previously (100 kcal/d).
Conclusions These data confirm what has long been suspected: substantial increases in energy intake (as opposed to energy expenditure)
have likely largely driven the increases in body weight seen over the past 3 decades. In his critical analysis of this article, Heymsfield reminds us that
scientifically rigorous evaluation of energy intake and expenditure was not technically possible prior to the current obesity epidemic—making this
article of particular importance to the field. He also compares and contrasts estimates of the “energy gap” proposed previously and comments on why these
differences might exist.
Reference Swinburn BA,
Sacks G, Lo SK, et al. Estimating the changes in energy flux that characterize the rise in obesity prevalence. American Journal of Clinical
Nutrition 2009;89:1723–8.
Heymsfield SB. How large is the energy gap that accounts for the obesity epidemic? American Journal of Clinical Nutrition 2009;89:1717–8.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1723
To contact the corresponding author, Boyd Swinburn, please send an e-mail to
boyd.swinburn{at}deakin.edu.au.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1717
To contact the corresponding author, Steven Heymsfield, please send an e-mail to
steven_heymsfield{at}merck.com.
DNA Shortening May Be Lessened by Multivitamin Supplements
Background Scientists, psychologists, and philosophers have long pondered whether aging can be slowed or even reversed. Indeed, the search for the “fountain of youth”
is unique neither to nutrition nor any other scientific discipline. Researchers have shown that increased intake of some nutrients, such as those with
antioxidant or anti-inflammatory properties, might help slow some forms of age-related decline. Although the mechanisms are probably complex, these
nutritional effects might be partially due to a protective effect on telomeres (the end portions of chromosomes). In general, telomeres are shortened
slightly during cell division, and research suggests that preventing this may protect the function of the new cells—thus reducing the effects of
biological aging. To investigate whether nutrition might affect this, researchers from the National Institutes of Health and the University of Utah
examined whether multivitamin use is associated with telomere length. Their results are published in the June 2009 issue of The American Journal of
Clinical Nutrition along with an editorial by Aviv.
Study Design This epidemiologic study was conducted using a subset of early participants (n = 586; mean age: 54 y) in The
Sister Study, an ongoing cohort study of 50,000 breast cancer–free sisters of women who have had breast cancer. Participants were asked whether they used
vitamin supplements regularly during the past 12 mo, and those who answered “yes” were then asked to categorize the products they consumed and provide
detail concerning the frequency and duration of their use. Dietary intake was also assessed. Blood samples were collected, and DNA was extracted from whole
blood. Telomere length was determined by using standard methods.
Results Most (65%) women used multivitamins at least monthly, and about 89% of “users” took a once-a-day type preparation. After
accounting for potentially confounding factors, these researchers found an association between multivitamin use and longer telomeres. Compared with
non-users, daily users had 5.1% longer telomeres (P = 0.002). This corresponded to an estimated 9.8 y less age-related telomere length loss in
supplement users. After adjustment for multivitamin use, intakes of vitamins C and E from foods were also associated with longer telomeres.
Conclusions These scientists concluded that “This study provides the first epidemiologic evidence that multivitamin use is associated
with longer telomere length among women,” but that further study is needed to translate these results to health outcomes. In his accompanying editorial,
Aviv points out several shortcomings of the study, including its cross-sectional nature and the fact that the supplement users had systematically healthier
lifestyle characteristics than did the nonusers. Nonetheless, he concludes that these findings point to a potentially important health-promoting effect of
dietary supplements, especially in terms of iron supplementation, that deserves further scientific attention.
Reference Xu Q, Parks CG,
DeRoo LA, Cawthon RM, Sandler DP, Chen H. Multivitamin use and telomere length in women. American Journal of Clinical
Nutrition 2009;89:1857–63.
Aviv A. Leukocyte telomere length: the telomere tale continues. American Journal of Clinical Nutrition 2009;89:1721–2.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1857
To contact the corresponding author, Honglei Chen, please send an e-mail to
chenh2{at}niehs.nih.gov.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1721
To contact the corresponding author, Abraham Aviv, please send an e-mail to avivab{at}umdnj.edu.
Optimal Protein Intake in Infancy Still Debated
Background Consumption of adequate protein during infancy is crucial to support the growth and development that occur during this time.
Most infant formulas are made from cow’s milk proteins, which are compositionally different from those in human milk, and protein intake by formula-fed
infants is substantially higher than that by breastfed infants. There continues to be debate concerning the adequacy of infant formula protein content and
form in terms of promoting healthy weight gain, especially in light of recent findings that rapid growth during the first year might be related to
increased risk of later obesity. In 2 separate studies published in the June 2009 issue of The American Journal of Clinical Nutrition, German
researchers report the results of studies they conducted in this area. In a companion editorial, Kalhan considers whether or not, on the basis of the
available data, we are ready to prescribe low-protein infant formula.
Study Designs Both studies were conducted as randomized, double-blind, controlled clinical trials. Koletzko and colleagues enrolled
1138 formula-fed infants and assigned them to receive cow milk–based formulas with lower (1.77–2.2 g protein/100 kcal) or higher (2.9–4.4 g protein/100
kcal) protein contents for the first year of life. Weight and length were followed for 2 y and compared with those of 619 breastfed infants. Rzehak from the
Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Epidemiology and his group studied 1044 infants fed partially
hydrolyzed whey, extensively hydrolyzed whey, extensively hydrolyzed casein, or standard cow-milk formula containing 2.1–2.8 g protein/100 kcal. Growth was
monitored for 6 y and compared with that of 796 breastfed infants.
Results At 2 y of life and after adjustment for length, the infants fed the higher-protein formula in the study by Koletzko et al
weighed more than did those who consumed the lower-protein formula; this was related to differences in energy intake. However, there were no significant
differences between either of the formula-fed groups and the breastfed group. In the study conducted by Rzehak et al, there were only minor effects of type
of formula protein and weight gain in the first 12 mo of life, such that infants consuming the extensively hydrolyzed casein formula were smaller. This
effect disappeared after 12 mo.
Conclusions Although the investigation by Koletzko et al suggests the possibility that lower protein intake during the first 2 y of
life might slow early weight gain, neither of the formula-fed groups in this study differed significantly from the breast-fed reference group. Results from
the study by Rzehak et al suggest a short-lived effect of protein type on early growth but no measurable effects on long-term growth, at least at 6 y of
life. In his editorial, Kalhan reviews the somewhat limited literature on determination of optimal protein intake during infancy and points to the
complexity of interaction among protein intake, satiety, and growth during this critical period of the lifespan.
Reference Koletzko B, von
Kries R, Closa R, et al. Lower protein in infant formula is associated with lower weight up to age 2 y: a randomized clinical trial. American Journal of
Clinical Nutrition 2009;89:1836–45.
Rzehak P, Sausenthaler S, Koletzko S, et al. Short- and long-term effects of feeding hydrolyzed protein infant formulas on growth at
6 y of age: results from the German Infant Nutritional Intervention Study. American Journal of Clinical
Nutrition 2009;89:1846–56.
Kalhan SC. Optimal protein intake in healthy infants. American Journal of Clinical Nutrition 2009;89:1719–20.
For More Information For the complete article by Koletzko et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1836
To contact the corresponding author, Berthold Koletzko, please send an e-mail to
office.koletzko{at}med.uni-muenchen.de.
For the complete article Rzehak et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1846
To contact the corresponding author, Peter Rzehak, please send an e-mail to
peter.rzehak{at}helmholtz-muenchen.de.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1719
To contact the corresponding author, Satish Kalhan, please send an e-mail to
sck{at}case.edu or kalhans2{at}ccf.org.
Researchers Determine That Golden Rice Is an Effective Source of Vitamin A
Background Vitamin A is essential for a plethora of functions including eyesight, reproduction, growth, and immune function. Despite
current interventions, vitamin A deficiency (VAD) remains a serious problem worldwide. Rice-consuming populations are especially vulnerable to VAD because
regular rice does not contain vitamin A or its precursors, and intake of vitamin A–containing meat is low. An alternative to animal products as a source of
vitamin A is the provision of provitamin A carotenoid-rich foods, because the body makes vitamin A from some of these compounds. Unfortunately, results
from several recent studies in which the effects of increased consumption of selected carotenoid-rich food on vitamin A status were measured suggest very
little effect on vitamin A status. Golden Rice is genetically modified rice created to address VAD-related morbidity and mortality in rice-consuming
populations. However, the extent to which ß-carotene from Golden Rice can be converted to vitamin A was not known until researchers very recently
studied this in humans. Their results are published in the June 2009 issue of The American Journal of Clinical Nutrition.
Study Design Golden Rice plants were grown hydroponically in water enriched with deuterium, the naturally occurring, nonradioactive
isotope of hydrogen. This resulted in the incorporation of small amounts of stably labeled hydrogen atoms in the rice’s ß-carotene molecules. This
state-of-the-art technique allows researchers to “follow” nutrients as they are absorbed by and used in the body. When the rice was mature, it was
harvested and processed. Five healthy volunteers (2 men and 3 women; mean age: 59 y) were then recruited for a 36-d trial consisting of 2 main parts. First,
they consumed a supplement containing stably labeled vitamin A along with a rice-based breakfast. Eight days later, they consumed a similar breakfast
except that stably labeled Golden Rice (providing 0.99–1.53 mg ß-carotene) was used instead of regular rice. Blood samples were then taken repeatedly
for measurements of stably labeled ß-carotene and vitamin A (retinol), and conversion rates were calculated.
Results The data from this study indicate that, after consumption, the stably labeled ß-carotene from the Golden Rice was
absorbed intact in the gastrointestinal tract. Subsequent conversion of ß-carotene to vitamin A was estimated to occur at a rate of 3.8 to 1. This is
much better than the rates of 10:1 to 27:1 estimated previously for colored vegetables such as spinach and carrots.
Conclusions These results show the potential for a much more advantageous bioconversion rate than achieved from any other known
crop-based source of ß-carotene. Furthermore, they imply that Golden Rice could probably supply 50% of the Recommended Dietary Allowance (RDA) of
vitamin A from a very modest amount—perhaps a cup—of rice, if consumed daily. This amount is well within the consumption habits of most young
children and their mothers.
Reference Tang G, Qin J,
Dolnikowski GG, Russel RM, Grusak MA. Golden Rice is an effective source of vitamin A. American Journal of Clinical Nutrition
2009;89:1776–83.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/6/1776
To obtain more information, please send an e-mail to Christine Fennelly, Tufts Director of Public Relations,
christine.fennelly{at}tufts.edu.
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