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February 2010 Highlights of This Issue

• Australian Study: Sodium Contents of Processed Foods Decoded
  Australian researchers document sodium contents of hundreds of processed foods; database invaluable for future research on sodium consumption and health.
  
• An Optimal Diet: Is There Wisdom to Be Gleaned from Hunter-Gatherers?
  Study suggests that our hunter-gatherer ancestors likely ate more meat than previously thought, which begs the question of what our genetic make-up expects us to eat.
  
• Researchers Use Free-Access Vending Machines to Monitor Calorie Intake
  Human trial documents very high (but reproducible) caloric intake using free-access, computerized vending machine.
  
• Salt versus Salted Foods: Differential Relations with Cardiovascular Disease and Cancer?
  Japanese study finds that whereas total salt intake is positively related to cardiovascular disease, it is not related to cancer.
  

Australian Study: Sodium Contents of Processed Foods Decoded

Background  Sodium is essential for myriad biological processes including fluid balance and muscle contraction. However, too much sodium can have harmful effects such as increasing blood pressure. Consequently, reducing sodium intake is an important health message. Because processed foods contribute the majority of dietary sodium, reducing their sodium content and overall sodium consumption are often emphasized as public health goals. There is a wide range of sodium content among processed foods, however, which makes it difficult to monitor sodium consumption. In part to help solve this problem, researchers from The George Institute for International Health in Sydney, Australia conducted a systematic survey of the sodium contents of processed foods available in Australia. Their findings, as well as an editorial by Sonia Angell of the New York City Department of Health and Mental Hygiene, can be found in the February 2010 edition of The American Journal of Clinical Nutrition..

Study Design  Guided by previously published information concerning which food types contributed major amounts of salt to the diet of Australians, Webster and colleagues compiled brand-specific sodium content data for 7221 food products. Mean sodium values were then calculated for predetermined food groups, market share data were used to consider the proportion of products represented in each subgroup, and values were compared with national salt reduction targets established by the Food Standards Agency in the United Kingdom.

Results  The findings suggest wide variability in sodium content within and between most food categories. For example, there was a 14-fold difference in sliced meats (120–1720 mg/100 g). Food groups highest in sodium were sauces/spreads and processed meats; cereals, fruit, and vegetables had the lowest. Sodium contents of processed foods contributing the most sodium were 1283 mg/100 g for sauces/spreads, 846 mg/100 g for meat/meat products, 467 mg/100 g for bread/bakery products, and 353 mg/100 g for dairy foods. Almost half (44%) of the product groups had mean sodium contents that would be classified as high (>500 mg/100 g).

Conclusions  This database and descriptive data provide important tools and information needed for continued monitoring of food sodium content, and the authors challenge the Australian government to “take leadership and engage the food industry in a sector-wide, transparent reformulation effort that will progressively decrease salt intake in Australia.” In her accompanying editorial, Angell applauds these researchers for compiling such a database that can now be used to describe and track changes in sodium (and proposes the potential expansion to include other nutrients) in individual branded products for years to come. In addition, she notes that, in this global economy where food manufacturing is increasingly dominated by a limited number of corporations, the importance of this type of database goes well beyond the Australian borders.
   Reference  Webster JL, Dunford EK, Neal BC. A systematic survey of the sodium contents of processed foods. American Journal of Clinical Nutrition 2010;91:413–20.
Angell SY. Emerging opportunities for monitoring the nutritional content of processed foods. American Journal of Clinical Nutrition 2010;91:298–9.

For More Information  For the complete article, please go to the following URL: http://www.ajcn.org/cgi/content/full/91/2/413
To contact the corresponding author, Elizabeth Dunford, please send an e-mail to edunford{at}george.org.au.
For the complete editorial, please go to the following URL: http://www.ajcn.org/cgi/content/full/91/2/298
To contact the corresponding author, Sonia Angell, please send an e-mail to sangell{at}health.nyc.gov.

An Optimal Diet: Is There Wisdom to Be Gleaned from Hunter-Gatherers?

Background  Defining an “optimal” diet for humans continues to challenge nutrition scientists. One route of inquiry, however, involves the study of foods consumed by our ancestors who lived as preagricultural hunter-gatherers because, despite the millennia that separate us, we have the same core metabolic genetic makeup. Of particular interest is determining the proportions of plant and animal foods our ancestors ate, because this determines how much acid or base is produced during day-to-day metabolism. In response to recent evidence suggesting that hunter-gatherers consumed more animal-based foods than previously thought, scientists at Leibniz University (Hanover, Germany) and the University of California, San Francisco studied dietary habits of 220 recently examined forager populations. Their results, along with an editorial by S Boyd Eaton and colleagues, can be found in the February 2010 issue of The American Journal of Clinical Nutrition.

Study Design  The researchers used ethnographic data related to consumption patterns for 220 societies subsisting by hunting, gathering, and fishing. This information was then integrated mathematically and analyzed using established algorithms to calculate “net endogenous acid production” (NEAP), an indicator of the net acid or base load to the body from the food consumed. Lower NEAP diets are considered more health promoting than higher NEAP diets, and plant-based diets generally have lower NEAP values (ie, are less acid producing) than do animal-based diets. However, because NEAP values for animal foods are influenced by the diet’s fat content, the NEAP response to various dietary fat levels was also investigated.

Results  As expected, plant-based diets were associated with lower NEAP values, whereas diets high in animal protein were related to increased NEAP. However, for a given level of meat consumption, NEAP values were quite variable and were greatly affected by the diet’s animal fat content. When lean muscle tissue (3% fat by weight) made up the bulk of the diet’s animal food content, 70% of the diets analyzed were net acid producing. However, when diets contained more animal fat, 50% or more were found to be net base-producing.

Conclusions  The investigators found that animal food consumption in traditional hunter-gatherer societies varied widely and contributed up to 95% of the diet in the Arctic, but only 10–15% in other locations. In their accompanying editorial, Eaton and colleagues remind us that, although genetic evolution during the last few millennia has continued, basic chemical and physiologic processes have been preserved. To better address today’s serious health issues, they urge health promotion researchers to consider an intellectual paradigm shift that encompasses paleoanthropologic and evolutionary insights.
   Reference  Ströhle A, Hahn A, Sebastian A. Estimation of the diet-dependent net acid load in 220 worldwide historically studied hunter-gatherer societies. American Journal of Clinical Nutrition 2010;91:406–12.
Eaton SB, Konner MJ, Cordain L. Diet-dependent acid load, Paleolithic nutrition, and evolutionary health promotion. American Journal of Clinical Nutrition 2010;91:295–7.

For More Information  For the complete article, please go to the following URL: http://www.ajcn.org/cgi/content/full/91/2/406
To contact the corresponding author, Anthony Sebastian, please send an e-mail to anthony_sebastian{at}msn.com.
For the complete editorial, please go to the following URL: http://www.ajcn.org/cgi/content/full/91/2/295
To contact the corresponding author, S Boyd Eaton, please send an e-mail to sboydeaton{at}comcast.net.

Researchers Use Free-Access Vending Machines to Monitor Calorie Intake

Background  There is universal agreement that excessive calorie intake has contributed to the modern obesity epidemic, although scientists continue to grapple with being able to accurately measure how many calories a person eats. This is due to a variety of methodologic factors, including the inability of people to remember what and how much they have eaten and the fact that having to write down what we eat can cause us to change what we eat. As a partial solution, some investigators have developed laboratory methods designed to assess energy intake under controlled conditions, and although these methods do not replicate what “free-living” individuals consume, they are thought to be useful tools in assessing the effect of behavioral and pharmaceutical interventions on eating behaviors. Nothing is known, however, about the reproducibility of data collected using these methods. To study this, a group of international researchers tested whether data collected using a computerized vending machine system to dispense self-selected foods upon demand was consistent over time. Their findings are published in the February 2010 issue of The American Journal of Clinical Nutrition.

Study Design  This study investigated eating habits of 12 individuals (mean age: 36 y) who were studied at least twice while being supervised in a controlled metabolic ward. In general, subjects were healthy but overweight or obese. At the beginning of the study, participants completed a questionnaire identifying foods that they particularly liked and disliked. Using this information, the researchers stocked a refrigerated vending machine to which the subjects had free access for 3 d. Daily energy, protein, fat, and carbohydrate intakes were calculated from the actual weights of food consumed, and measures of reproducibility were determined by comparing data collected during one 3-d visit to those collected at repeat 3-d visits.

Results  Although there was variability in intake among subjects, mean energy intake greatly exceeded what would be recommended for these subjects: 5974 and 4067 kcal/d for men and women, respectively. However, individuals tended to consume similar amounts on repeated visits, which suggests a relatively high level of reproducibility for this method of assessing caloric intake. Similar results were found for protein, carbohydrate, and fat intake.

Conclusions  This study found high within-person reproducibility of ad libitum energy intake over a 3-d period with use of a computerized vending machine system. Although the authors admit that the method does not provide an assessment of the usual intake of free-living subjects, they propose that it is useful for the assessment of intake in subjects confined to a controlled environment. Of note, however, is the extremely high mean energy intakes reported for these subjects. This finding brings into question whether having access to the vending machine may have resulted in uncharacteristic overconsumption for this group of subjects. In future studies, researchers may want to include testing the motivation to eat to better understand the reasons for overconsumption.
   Reference  Venti CA, Votruba SB, Franks PW, Krakoff J, Salbe AD. Reproducibility of ad libitum energy intake with the use of a computerized vending machine system. American Journal of Clinical Nutrition 2010;91:343–8.

For More Information  For the complete article, please go to the following URL: http://www.ajcn.org/cgi/content/full/91/2/343
To contact the corresponding author, Arline Salbe, please send an e-mail to arline.salbe{at}kronosinstitute.org.

Salt versus Salted Foods: Differential Relations with Cardiovascular Disease and Cancer?

Background  The American Cancer Society has identified high consumption of processed meats as a risk factor for colorectal cancer, and high intake of salt and/or highly salted, preserved foods is related to greater risk of stomach cancer. Elevated salt intake (from seasonings or processed, preserved foods) is also associated with increased risk of cardiovascular disease. Why these relations exist is not known, partly because it is difficult to tease apart the independent effects of salt itself compared with the foods in which it is present. Understanding whether it is the sodium itself or the food vehicle in which it is found that influences chronic disease is important because this knowledge may help experts develop more accurate and effective messages concerning their prevention and treatment. In a large-scale clinical trial, the Japan Public Health Center–based Prospective Study Group examined the statistical associations between salt or salty food intake and risk of cancer and cardiovascular disease in a large group of Japanese men and women. You can read about their findings in the February 2010 issue of The American Journal of Clinical Nutrition.

Study Design  Study participants (n = 77,500; mean age: ~57 y) were recruited from 9 public health center areas between 1995 and 1998 and followed for 7–10 y. Subjects were excluded if they had a history of cancer or cardiovascular disease. At enrollment, each participant completed a food-frequency questionnaire that quantified usual consumption of 138 foods and beverages, with a special emphasis on commonly consumed Japanese products (eg, soy sauce, miso soup, pickled vegetables). Associations between incident cases of cancer or cardiovascular disease and sodium or salted foods was then determined mathematically.

Results   Overall, dietary sodium contribution was greatest from cooking or table salt (38.8%) followed by miso soup (18.8%), pickled vegetables (11.1%), dried and salted fish (3.4%), and salted fish roe (0.7%). Median sodium intake was ~4900 mg/d, a value substantially higher than the National Academy’s adequate intake level of 1500 mg/d. Although the researchers found no independent relation between table salt consumption and cancer, higher intake of salted fish roe was significantly associated with higher risk of total cancer as well as cancers of the gastrointestinal tract; similar relations were found for dried and salted fish. Conversely, whereas there was an independent positive relation between total sodium or table salt consumption and risk of cardiovascular disease, there were no unhealthful associations between salted foods and cardiovascular disease. In fact, higher intake of dried and salted fish was related to lower risk of cardiovascular disease.

Conclusions  These results provide powerful, albeit observational, evidence that high sodium consumption is related to elevated risk of cardiovascular disease but not cancer. In contrast, higher intake of salted fish roe is associated with elevated risk of cancer but not cardiovascular disease; dried and salted fish may actually reduce risk of cardiovascular disease.

For More Information  For the complete article, please go to the following URL: http://www.ajcn.org/cgi/content/full/91/2/456
To contact the corresponding author, Manami Inoue, please send an e-mail to amnminoue{at}ncc.go.jp.