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May 2009 Highlights of This Issue
Diet and Colorectal Cancer—A Complex Case for Scientists
Background Cancers of the colon and rectum are the third most common type worldwide. However, risk increases with urbanization, and
although colorectal cancer has historically been more common in high-income countries, it is now increasing at all income levels. This suggests that
modifiable lifestyle factors, such as nutrition, are involved. Indeed, studies have shown decreased risk of colorectal cancer with increased intake of
fruit and vegetables, and others suggest increased risk with high red meat consumption. But not all studies support these associations, and there are
likely other variables that confound (eg, physical activity and obesity) or modify (eg, sex and smoking) these putative dietary effects. As such, research
in this area continues. The May 2009 issue of The American Journal of Clinical Nutrition includes 3 studies that investigated whether colorectal
cancer or colorectal adenoma, its premalignant precursor, might be linked to consumption of 1) animal fat or animal protein, 2) fruit and
vegetables, and 3) heterocyclic aromatic amines, which are found typically in grilled meat.
Study Design All of these studies were epidemiologic in nature. The investigation concerning animal fat and protein analyzed results
compiled from several previously conducted studies (ie, a meta-analysis approach). The research related to fruit and vegetable consumption was part of the
European Prospective Investigation into Cancer and Nutrition (EPIC; n = 452,755), encompassing 10 European countries. Data used to investigate
heterocyclic amines were drawn from a German subset (n = 25,540) of the same EPIC study.
Results Data from the meta-analysis provided no evidence for a relation between animal fat or animal protein and risk of colorectal
cancer. However, the German study suggested that consuming large amounts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP; the most abundant
dietary heterocyclic aromatic amine) was associated with a 47% increased risk of colorectal adenoma compared with consuming the lowest amounts of PhIP.
After control for intake of red and processed meats, the EPIC data showed an inverse association between fruit and vegetable consumption and colorectal
cancer, but this effect was only found in those who had never smoked or were former smokers. In fact, increased fruit and vegetable consumption was
positively related to colorectal cancer risk in smokers.
Conclusions Together, these studies support a complex relation between diet and colorectal cancer. Whereas animal fat and protein were
found to not be risk factors, PhIP was a risk factor for colorectal adenomas. In addition, although greater consumption of fruit and vegetables appeared to
be a beneficial lifestyle choice in those who did not smoke, these data suggest a very different picture for smokers. Clearly, unraveling these
interactions continues to necessitate careful and in-depth study. On the basis of the available scientific evidence, consuming a balanced diet, maintaining
a healthy body weight, increasing physical activity, and reducing smoking and alcohol may be the most effective ways to reduce risk of colorectal cancer.
In other words, there is likely no single magic bullet for preventing this disease.
Reference Alexander DD,
Cushing CA, Lowe KA, Sceurman B, Roberts MA. Meta-analysis of animal fat or animal protein intake and colorectal cancer. American Journal of Clinical
Nutrition. 2009;89:1402–9.
van Duijnhoven FJB, Bueno-De-Mesquita HB, Ferrari P, et al. Fruit, vegetables, and colorectal cancer risk: the European Prospective Investigation into
Cancer and Nutrition. American Journal of Clinical Nutrition 2009;89:1441–52.
Rohrmann S, Hermann S, Linseisen J. Heterocyclic aromatic amine intake increases colorectal adenoma risk: findings from a prospective European cohort
study. American Journal of Clinical Nutrition 2009;89:1418–24.
For More Information For the complete article by Alexander et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1402
To contact the corresponding author, Dominik Alexander, please send an e-mail to dalexander{at}exponent.com.
For the complete article by van Duijnhoven et al, please go to the following URL:
http://www.ajcn.org/content/full/reprint/89/5/1441
To contact the corresponding author, Fränzel van Duijnhoven, please send an e-mail to franzel.van.duijnhoven{at}rivm.nl.
For the complete article by Rohrmann et al, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1418
To contact the corresponding author, Sabine Rohrmann, please send an e-mail to
s.rohrmann{at}dkfz-heidelberg.de.
Researchers Conclude: Avoiding Sweetened Drinks May Help Weight Loss
Background The National Center for Health Statistics (NCHS) estimates that 67% of US adults are overweight or obese and that obesity
rates have steadily increased since the 1960s. This trend has been accompanied by an increase in mean caloric intake from 2450 to 2693 kcal/d. Because
research suggests that beverages account for almost half of this increase, there is considerable interest in understanding the overall effect of beverage
intake on obesity trends. For example, some studies suggest a positive association between intake of sugar-sweetened beverages (SSBs) and body weight.
Others propose that milk intake may help in weight loss. However, data are inconsistent and sometimes contradictory, likely due to the use of different
populations and failure to control for important confounding factors such as physical activity. To study this further, Caballero and colleagues analyzed
data collected in a prospective, longitudinal human nutrition trial, and their findings are published in the May 2009 issue of The American Journal of
Clinical Nutrition.
Study Design This research was a component of the PREMIER trial, an 18-mo randomized, controlled, behavioral intervention trial
originally designed to test the blood-pressure-lowering effects of two multicomponent lifestyle intervention programs in persons at risk for hypertension.
Because of this design, patterns in food and beverage consumption were altered from the beginning to the end of the study for many of its participants. The
analyses for the present study, however, were conducted by combining all participants and statistically controlling for intervention assignment. At the
beginning of the study and 6 and 18 mo later, dietary intake was measured by using two 24-h dietary recalls. Beverages were categorized on the basis of
their caloric content and nutritional composition as SSBs (eg, regular soda and fruit “drinks”), diet drinks (eg, diet soda and artificially sweetened
juices), milk, 100% juice, coffee and tea with sugar, coffee and tea without sugar, or alcoholic beverages. Weight, height, and physical activity were
assessed and controlled for in the statistical analyses.
Results The average age of participants (n = 810) was 50 y; most were non-Hispanic white with at least a college education.
Only 5% were classified as normal weight, whereas 65% were considered obese. Baseline mean energy intake from beverages was 356 kcal/d. This declined to
100 kcal/d at the end of the study, and this change was associated with a weight loss of ~0.25 kg (~0.6 lb) at 6 and 18 mo. The reduction in energy intake
from beverages was more strongly related to weight loss than was the reduction in energy intake from foods. A reduction in intake of SSBs, but not other
beverage types, was significantly associated with weight change.
Conclusions These results provide evidence that SSBs may be especially important contributors to our current obesity epidemic and that
a reduction in SSB intake of even 1 serving/d might help with weight loss. This study represents an important contribution to the current literature
because it provides the first documentation of the relative effects of calories from beverages compared with those from foods on weight loss in free-living
adults.
Reference Chen L, Appel LJ,
Loria C, et al. Reduction in consumption of sugar-sweetened beverages is associated with weight loss: the PREMIER trial. American Journal of Clinical
Nutrition 2009;89:1299–306.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1299
To contact the corresponding author, Benjamin Caballero, please send an e-mail to
caballero{at}jhu.edu.
Breastfeeding—Some Things Are Not Better in Moderation
Background Health professionals and related organizations have long agreed that breastfeeding is best for most healthy newborn infants.
However, there is still some debate as to how long exclusive breastfeeding should be recommended, and rates remain low throughout the world. One location
of particular interest in this regard is Africa, where exclusive breastfeeding is recommended to decrease the risk of HIV transmission. However, there have
been no studies documenting the benefits of exclusive breastfeeding for infants born to HIV-negative women in this region. To better understand this issue,
an international team of scientists studied the relation between breastfeeding practices and infant morbidity in Zimbabwe. Their results are published in
the May 2009 issue of The American Journal of Clinical Nutrition, as is an accompanying editorial written by Kline.
Study Design This study was conducted as part of a large trial (Zimbabwe Vitamin A for Mothers and Babies; ZVITAMBO) designed
originally to assess the health implications of vitamin A supplementation on maternal-infant health. At enrollment, women were tested for HIV. Only
non-HIV-infected women (n = 9207) and their children were included in the present study. It is noteworthy that the majority of the participants were
relatively well-educated urban women, and the vast majority had access to tap water, toilet facilities, and electricity. Follow-up visits were conducted at
6 wk, 3 mo, and every 3 mo thereafter until 2 y postpartum, during which time each mother was asked details concerning the health of her child.
Breastfeeding practices during the first 3 mo postpartum were classified as exclusive breastfeeding, partial breastfeeding, and mixed breastfeeding
according to World Health Organization standards.
Results The most common food items (aside from human milk) provided to partially and mixed breastfeeding infants were water, cooking
oil, juice, traditional medicines, and porridges. Infants who were exclusively breastfed between birth and 3 mo were approximately 8-fold less likely to
have diarrhea between 3 and 6 mo of life compared with those who were partially breastfed or experienced mixed breastfeeding. Similar results were found
for lower respiratory infections, but the results were not statistically significant.
Conclusions The authors concluded that “These findings, together with our earlier observations of reduced postnatal HIV transmission
among HIV-exposed infants whose mothers practiced early exclusive breastfeeding, indicate that universal promotion of exclusive breastfeeding is very
likely to improve infant health.” In his accompanying editorial, Kline concurred that exclusive breastfeeding for at least the first 6 mo of life remains
the cornerstone of child survival. Indeed, breastfeeding appears to be one niche in the world of nutrition in which “moderation” is not recommended
Reference Koyanagi A,
Humphrey JH, Moulton LH, et al. Effect of early exclusive breastfeeding on morbidity among infants born to HIV-negative mothers in Zimbabwe. American
Journal of Clinical Nutrition 2009;89:1375–82.
Kline MW. Early exclusive breastfeeding: still the cornerstone of child survival. American Journal of Clinical Nutrition 2009;89:1281–2.
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1375
To contact the corresponding author, Jean Humphrey, please send an e-mail to
jhumphrey{at}zvitambo.co.zw.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1281.
To contact the corresponding author, Mark Kline, please send an e-mail to
mkline{at}bcm.edu.
Replacing Saturated Fats with Polyunsaturated Fats Best Bet for Heart
Background Coronary heart disease (CHD) is the leading cause of death in the United States, and a first-line approach for decreasing
its risk is lowering saturated fatty acid (SFA) intake. However, whether dietary SFAs should be replaced with unsaturated fatty acids or carbohydrates
remains an area of active debate. Further, sex and age may influence the relation between SFAs and CHD, and it is difficult to measure precisely what
free-living people really eat. These factors, therefore, need to be accounted for, and this necessitates the use of a very large number of individuals in
studies related to this topic. To meet this challenge, a multinational group of nutrition researchers pooled data from several previously conducted human
studies to investigate the effect of replacing SFAs with unsaturated fatty acids or carbohydrates to prevent CHD. Their results are published in the
May 2009 issue of The American Journal of Clinical Nutrition. Accompanying their article is a discerning editorial by Katan.
Study Design Data from 11 American and European cohort studies were used to investigate associations between a lower energy intake
from SFAs and a concomitant higher energy intake from monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), or carbohydrates on risk of
CHD events. The final population consisted of 344,696 middle-aged and older women and men. Factors, such as sex and age, known to be important risk factors
for CHD were controlled for in the analyses.
Results These data indicated that, for a 5% lower energy intake from SFAs and a concomitant 5% higher energy intake from PUFAs, one
might expect a 13% lower risk of coronary events and a 26% lower risk of coronary deaths. Conversely, for a 5% lower energy intake from SFAs and a
concomitant 5% higher energy intake from carbohydrates, one might expect a modestly higher risk of coronary events. These relations were not influenced by
sex or age.
Conclusions Results from this large, epidemiologic study suggest that replacing SFAs with PUFAs rather than MUFAs or carbohydrates may
provide the best macronutrient mix for preventing CHD. In his companion editorial, Katan compares the effect of PUFA intake in this study with metabolic
trials on PUFA consumption and blood lipids and the scattered clinical trials on PUFA intake and CHD. He concludes that the 3 lines of research provide
remarkably consistent results. He also reminds us that data and conclusions obtained from cell culture and animal studies might not always be relevant to
humans. For example, although animal and in vitro studies have suggested that increasing PUFA intake might increase risk of CHD, the human data refute this
hypothesis.
Reference Jakobsen MU,
O’Reilly EJ, Heitmann BL, et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. American Journal
of Clinical Nutrition 2009;89:1425–32.
Katan MB. Omega-6 polyunsaturated fatty acids and coronary heart disease. American Journal of Clinical Nutrition 2009;89:1283–4
For More Information For the complete article, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1425
To contact the corresponding author, Marianne Jakobsen, please send an e-mail to
muj{at}dce.au.dk.
For the complete editorial, please go to the following URL:
http://www.ajcn.org/cgi/content/full/89/5/1283
To contact the corresponding author, Martijn Katan, please send an e-mail to
katan99{at}falw.vu.nl.
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