Nutrition Research Highlights 3|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!
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- Tell me your grades! And your BMI*?
- Digesting dietary choline & science news
- Flavour learning: sour and bitter can taste good!
Unhealthy diets are a preventable risk factor for most non communicable diseases (cardiovascular diseases, cancer, diabetes) and hence they are obvious targets for various intervention strategies. Malaysia just introduced new measures to curb the problem such as banning 'unhealthy' foods and beverages from school canteens. One measure that is causing much debate is listing the student's BMI in their end of term school reports. The idea is to alert parents to their children's weight and health. Various US states have also implemented this, but never without controversy. Many argue that a child's weight should not be discussed in school. But would there be such strong opposition if the report was on blood pressure levels instead? Why is any measure of weight such a sensitive issue? Whether the measure is effective remains to be seen but the furore around it served to bring the child obesity topic to the table once more. Let us know how you feel (JRC-Nutrition@ec.europa.eu) about this measure or others that you would like to see implemented against obesity (SC).
* BMI: Body weight (Kg) divided by the square of height (m)
An interesting link between high-fat consumption and the generation of metabolites that promote the build-up of arterial plaques, an early phase of atherosclerosis, has been discovered recently (1). The interesting aspect of the new link is that the metabolites are generated from various forms of choline present in high-fat foods through a chain of events that involve not only the liver but also intestinal bacteria. 'Digesting' these results is not straight forward: should we avoid choline-rich foods? Choline is an essential nutrient, i.e. despite the body's ability to synthesize some itself, we still have to ingest it. Choline deficiency occasionally occurs, e.g. in postmenopausal women, when the body's own choline production is reduced, and can cause severe organ dysfunction as well as disturbance of amino acid metabolism leading to accumulation of the amino acid homocysteine, which in turn has been linked to increased risk of cardiovascular disease and of neural tube defects (e.g., "spina bifida") in newborns (2). Thus, any recommendation to reduce choline intake levels could result in undesired health outcomes. In fact, the study itself only alerts to a possible risk of excess intake of dietary choline from high-fat foods of animal origin (beef & chicken liver, egg yolk, pork, shrimp, bacon, milk and dairy products). Thus, this study adds on existing dietary guidelines to reduce animal fats and alerts to possible risk of excess choline intake from supplements or extreme diets (low carbohydrate-high protein/fat). With a varied (even vegetarian) diet there are plenty of opportunities to get our regular choline without using supplements. In fact, choline is also found in plant products including soybeans, wheat, spinach, cauliflower, cabbage, brussels sprouts and others (3). And finally, startling news from scientific research should be digested separately from our meals without putting in question all current dietary guidelines (JW).
As the twig is bent, so grows the tree…This saying will likely have an equivalent in many other languages; it means that an influence in a child will persist throughout adulthood. A recent series of articles (1, 2) describe how babies learn to accept the sour and bitter taste of a particular protein hydrolysate formula (PHF) if they are exposed to it before they are 4 months old. From then on, children will reject this food (see photo). The authors believe that the principles revealed in these rigorous studies with infant formulas can be applied to the breastfeeding situation and can be useful in familiarizing infants with flavours that their mothers consume and transmit to breast milk, for example bitter-tasting but quite healthy vegetables! (SC)
Photo: Babies' (7.5 months old) facial responses as they consume PHF. Babies were fed for 7 months cow milk formula (A) or PHF (B). Copyright © 2011 American Society for Nutrition - Reproduced from Am J Clin Nutr 2011 93:1019-1024.
Bacteria, Microbes, Bugs… Call them what you like, these simple life forms are still very much in the centre of our attention, even after ~4000-5000 yrs of documented human history. From the great plague epidemics in antiquity and middle ages to the modern, more "modest" meningitis, cholera or food poisoning outbreaks (as the current Escherichia coli outbreak), it would seem that bacteria have done their best to maintain a negative publicity. What might not be widely known however is the important positive role of microbes. Cheese and yoghurt (mentioned by Homer and Pliny thousands of years ago), are examples of a wide range of foods that owe their existence to benign bacteria such as Lactobacillus.
A fact that not many may be aware of is that we are actually hosting many bacteria in our bodies. In fact, there are 10 times more bacteria in our bodies than our own cells! Most are in the gut and make up our intestinal flora, which breaks down otherwise indigestible diet ingredients in our intestine (1).
The Russian Ilya Metchnikoff (Noble Prize in Medicine, 1908) was the first to suggest the link between the gut flora and health and to introduce the concept of beneficial gut bacteria, that later evolved into the concept of probiotics* by Dr. Minoru Shirota in Japan in the 1930's.
The current research on the role of gut bacteria in health and disease is exciting and ongoing. A few years ago a Nature article (2) observed that the composition of the microbial gut flora, mainly comprising of the bacterial groups Bacteroidetes & Firmicutes, is different in obese and lean people. Specifically, obese people appear to have a decreased proportion of Bacteroidetes, which is then increased as the same people loose weight. The authors further suggest that this obesity-associated change in microbial gut flora may present a target for therapeutic approaches of obesity. On the other hand, a later study (3) with more participants reached the opposite conclusion i.e. that in overweight and obese people the proportion of Bacteriodetes was increased. These are just two of various studies on the topic and since no definite answer exists, the debate continues.
Various mechanisms have been proposed to explain the link between gut microflora and obesity. Firmicutes and Bacteriodetes for example are able to use compounds for their energy needs that are non-digestible by our intestinal system. As these bacteria break down indigestible substances, they produce compounds such as short chain fatty acids (SCFAs) that are readily digestible by our intestine. Thus, as the intestinal flora converts indigestible compounds into digestible ones, our organism can accumulate more energy. Others suggest that gut bacteria may, under certain conditions, contribute to intestinal inflammation. Long-term, low-grade intestinal inflammation is a characteristic of obesity and so gut bacteria may be implicated in its development (4). Various other factors, that can cause changes in the gut microflora, have also been hypothesised to contribute to obesity, but it remains difficult to determine them with certainty.
The complexity of the gut microflora is immense but a recent study (5) has gone a step further in understanding it. The authors analysed the microbial and genetic composition of 39 samples of gut microflora from individuals in different countries. Despite their complexity, the samples could be categorised in three groups, referred to as enterotypes. These enterotypes were not continent- or nation-specific and did not correlate with individual characteristics such as the nutritional habits of their hosts. However, when the authors looked specifically at particular functional properties of the three enterotypes, they did find associations between them and properties of their human hosts. As acknowledged by the authors, the study has its limitations, but nevertheless it anticipates a new field of research into "human and animal symbiotic properties" that may "lead to the discovery of those microbial properties that are correlated with the health status of individuals".
Our millennia old symbiotic relationship with gut flora bacteria continues to fascinate microbiologists and public alike. The recent findings generate many questions, which, if answered, may truly revolutionize the way we understand human health in general. In the meantime, let's just relax this summer and enjoy fruits mixed with a pH 4.6, 108 cfu/g milk co-culture of Lactobacillus bulgaricus and Streptococcus thermophilus, commonly known as "yoghurt" (PM).
Photo: (left to right): Food (Streptococcus thermophilus & Lactobacillus bulgaricus) and gut (Bifidobacterium longum) bacteria.
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 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)