Nutrition Research Highlights 1|2011
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This newsletter is published by the Nutrition & Health Group of the JRC’s Institute for Health and Consumer Protection. Regularly surveying the top nutrition and medical journals, we select the most recent news on nutrition research, relevant to current societal debates or policies. These are then summarised as “News” items or presented as a “View”, comprising an analysis and expert opinion. Enjoy your reading!
When we eat a particular food, we generally feel less desire to eat it again, due to the effects of habituation, i.e. a decrease in our responsiveness to that food and in our willingness to consume it again. Interestingly, a recent publication demonstrated that habituation also occurs when we merely imagine that we are eating a food! Morewedge et al. (1) performed different combinations of experiments in which participants first imagined eating chocolate and cheese before actually eating it. According to the study, people who repeatedly imagined eating a food many times (33x), consumed less quantity of it afterwards, when compared to people that only imagined eating the foods three times, imagined eating a different food or did not imagine anything. The decrease in real food consumption due to prior imagined food consumption is due to a diminished desire to eat the food, and not due to a decreased liking of the food. Such findings may have important implications in the field of nutritional research, for example in developing more effective nutritional interventions by reducing the desire to eat "unhealthy" or "fat" foods. Could they have an effect at your dinner table too? (PM)
Photo: Oscar Brunet - Copyright © Fotolia.com
It is well established that obesity, as defined by a body mass index (BMI)* above 30, is associated with an increased risk of death from stroke, heart disease and certain cancers. However, a recent study (1) compiling previously published data and including a staggering 1.46 million white adults, confirmed that overweight (BMI 25.0 - 29.9) and obesity (BMI>30) are also associated with increased all-cause mortality and not just with mortality attributed to strokes, heart disease and cancers. The subjects analysed were non-smokers with no cancer or heart disease diagnosis. Importantly, a BMI range of 20.0-24.9 was associated with the lowest all-cause mortality. The study also reports that 11% and 17% of non-Hispanic U.S. white men and women respectively had a BMI>35 in 2008. The authors note that the results of this study are most relevant to people of Caucasian origin living in affluent countries but similar analyses are underway in other populations. (PM)
A recent study on the evidence supporting exclusive breastfeeding for the first 6 months of a baby's life has caused quite a stir. Fewtrell et al. (1) discuss on potential risks of iron deficiency anaemia, food allergies and coeliac disease in babies that are only exposed to solid foods after the age of 6 months. Current World Health Organisation (WHO) recommendations (2, 3) state that babies should be exclusively breastfed up to this age.The stir caused appears to be unjustified though. The utmost importance of mother's milk is not questioned by this study. The discussion revolves around when to optimally introduce solid foods (i.e. weaning) while maintaining breastfeeding. The answer is not straightforward; all experts agree on the need for additional large randomized trials to clearly define all the health benefits and/or possible limitations of exclusive breastfeeding for six months. WHO bases its recommendations in the observations "that babies who are exclusively breastfed for six months experience less morbidity from gastrointestinal infection" as well as on advantages for the mother, e.g. faster weight loss. The European Food Safety Authority (EFSA) has also issued a Scientific Opinion (4) on this matter and concluded that "the introduction of complementary food into the diet of healthy infants in the EU between the age of 4 and 6 months is safe and does not pose a risk for adverse health effects". However, we should note that EFSA refers to EU born babies, where morbidity and mortality from infections is lower than in other parts of the world. Overall, despite the turmoil, the message is still clear: worldwide women should try to adhere to a 6 months exclusive breastfeeding, keeping of course in mind that the mother-baby pair should be followed and managed individually to identify any potential issues such as the ones discussed by Fewtrell et al. (SC)
Photo: Oscar Brunet - Copyright © Fotolia.com
We all know that "we are what we eat" but honey bees know it better. Think of the queen bee and the bee workers; they are identical genetically speaking but they do not have much more than that in common. Bee workers are small, sterile and strive to feed and care for the hive throughout their short existence.
Queens are large, can live for years and lay thousands of eggs a day. So, what makes a queen bee? The answer lies in what they eat: Royal jelly! Both queen and workers larvae feed on royal jelly early in development but workers soon switch to pollen and nectar while queens continue to feed on jelly into adulthood. This high royal jelly intake is thought to orchestrate a series of hormonal and metabolic networks that will shape the queen bee. But other cues
seem to be crucial in the making of a queen bee...
Epigenetics (from the greek epi=above or over), is a big word that refers to "all the weird and wonderful things that can’t be explained by genetics" (as simply put by Prof. Denise Barlow). Textbooks say that it is the study of heritable changes in genome function that occur without a change in DNA sequence. An example, particularly relevant here, is a small chemical modification of the DNA, called methylation, that can affect the expression of genes and the diversity and abundance of particular proteins resulting in very different outcomes (phenotypes) for a cell or organism.
Indeed, DNA methylation is a crucial determinant of the fate of larval development and adult behavior in the honey bee Apis mellifera (1, 2). How or whether royal jelly will directly affect DNA methylation is not yet clear. A recent study by Lyko et al (2) has shown that DNA methylation patterns (epigenome) of the brains of queens and workers are different. Likewise, others are now moving beyond genomic analyses and exploring differences in human epigenomes, in an attempt to link these differences to disease or particular phenotypes. Feinberg and colleagues looked at the global DNA methylation from 74 subjects (3). They found several variable regions between individuals and interestingly could significantly correlate four of those with body mass index (BMI). How these changes in methylation in specific DNA sequences arise is not clear and they are likely the result of exposure to many nutritional and environmental factors.
There is a myriad of external factors that can affect DNA methylation and research is ongoing to understand which nutritional factors can affect an individual's epigenetic status and its consequences. Some of the best studied examples involve exposure to bioactive food compounds including folate (a water soluble form of vitamin B) or polyphenols (present in green tea or soya) which can modify DNA methylation and are associated with altered risk of particular types of cancers or heart disease..
Exposure to epigenetic modifiers can occur at any time and its consequences may be long-lasting. Individuals who suffered early prenatal malnutrition (their pregnant mothers were exposed to famine during the Dutch Hunger Winter in 1944-45) had, 60 years later, less DNA methylation of a particular gene compared with their unexposed, same-sex siblings (4). The Dutch Hunger Winter Study also revealed that babies whose mothers were exposed to the famine during early gestation had normal birth weights but they grew up to have higher rates of obesity than those born before and after the war (5). Can a father's diet also contribute to their children development in ways that are independent of genetic factors? Animal studies indicate so. When Ng et al (6) fed male rats a high-fat diet, the animals naturally displayed increased adiposity, glucose intolerance and insulin resistance. Their daughters had normal body weight and fat, but surprisingly they developed a condition similar to diabetes in adulthood. Another study (7) found that the offspring of male mice fed a low-protein diet exhibited changes at the level of DNA methylation in the liver and also that the expression of many hepatic genes were altered. A likely explanation is that the father's diet causes epigenetic alterations, such as DNA methylation to the father's sperm that will in turn be transmitted to their offspring through the germ line.
The challenge in the field is now to firmly prove that nutritional factors can cause epigenetic changes that alter disease susceptibility. The fact that epigenetic alterations can have such important, long-lasting and possibly even trans-generational consequences should be considered when assessing food safety and nutrition quality. (SC)
Photo: M. Dykstra - Copyright © Fotolia.com
Nutrition Research Highlights is a bi-monthly publication prepared by the Nutrition & Health Group of the DG-Joint Research Centre, Institute for Health and Consumer Protection. The Nutrition team is comprised of Sandra Caldeira, Petros Maragkoudakis & Jan Wollgast.
The views expressed here do not necessarily reflect the opinion of the European Commission.
© European Union, 2011. Reproduction of articles (excluding photographs) is authorised, except for commercial purposes, provided that the source is mentioned.
ISSN:1831-9459 (printed version), 1831-9467(online version)