Nutrition Research Highlights 2|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!
- Mediterranean Diet vs. Metabolic Syndrome: 1-0
- Obesity on the rise across continents (and species!)
- A lifetime of Omega-3 deficiency
Mediterranean Diet vs. Metabolic Syndrome: 1-0
The Mediterranean Diet (*) has long been considered as a dietary habit with protective effects against cardiovascular diseases and was recognised last year as an Intangible Cultural Heritage of Humanity by UNESCO. A recent study by Kastorini et al. (1) analysed 50 research articles, including more than 500.000 subjects, and concluded that this diet is effective against the metabolic syndrome (**) in general as well as each of its individual components, such as waist circumference, cholesterol levels, blood lipids, blood pressure and glucose metabolism. The authors suggest that their results are of importance from a public health point of view and present the Mediterranean Diet as a cost-effective, healthy and "delicious" way to fight the growing metabolic syndrome epidemic. (PM)
* Characterised by high consumption of monounsaturated fatty acids from olives & olive oil, daily consumption of fruits, vegetables, whole grain cereals, low-fat dairy products; weekly consumption of fish, poultry, tree nuts, and legumes; low consumption of red meat, and moderate daily consumption of alcohol.
** The term Metabolic Syndrome refers to a combination of medical conditions that are associated with increased risk of cardiovascular disease and diabetes
Obesity, once an epidemic (a localised disease outbreak), currently a pandemic (a larger or global outbreak), and potentially becoming endemic (disease constantly present) is one of the biggest public health concerns. An article published in The Lancet (1) by Finucane, Stevens and colleagues has estimated the national, regional and worldwide changes in Body Mass Index (BMI) (*), based on data collected from community and national health examination surveys including 9.1 million people from 1980 to 2008. The authors analysed the trends in mean BMI for 199 countries and territories and estimated that in 2008, an alarming 1.46 billion adults worldwide were overweight, of which one-third (0.5 billion) were obese. Curiously, obesity is also on the rise in animals. We may have occasionally come across a fat cat or dog, but Klimentidis et al. (2) systematically examined more than 20,000 animals from eight species living with or around humans in industrialised societies and found that in all cases their body weight has been increasing in the last decades. This includes experimental animals (rodents and primates) in research colonies, domestic animals (dogs and cats) and even feral rats living in cities, suggesting other, as-of-yet unidentified factors that may contribute to obesity. (PM)
A lifetime of Omega-3 deficiency
Omega-3 (n-3) and Omega-6 (n-6) are polyunsaturated fatty acids (PUFAs) present in foods. Both are essential (i.e. must be consumed via diet) but despite their chemical similarity their effects on human metabolism are distinct. Much attention has been given to their ratio in the diet; for example, epidemiological studies have linked high n-6/n-3 ratios to cardiovascular or neuropsychiatric diseases. A recent study (1) modeled a lifetime of n-3 deficiency in mice (from gestation onwards). The mice had indeed less n-3 in the brain and this was related to specific molecular alterations. Importantly, they also showed behavioural changes; mice deprived of n-3 were more anxious and displayed depression-like behaviours. By showing such behaviour in mice and understanding the effects of the lack of n-3 in the molecular functions of their brains, these findings strengthen the proposed link between low levels of n-3 and mood disorders. (SC)
Photo: © gandolf - Fotolia.com
A letter recently published in Nature Medicine (1) concluded that "activation of brown adipose tissue might be a therapeutic approach to reduce elevated triglyceride concentration and combat obesity in humans". But what is brown adipose tissue and what implications does it have in obesity?
The adipose tissue (i.e. fat) is composed of white adipose tissue (WAT) and brown adipose tissue (BAT). WAT is the main energy storage depot of the body, i.e. excess food intake can accumulate in WAT in the form of lipids, leading to overweight or obesity. BAT on the other hand, "burns" lipids to generate body heat and thus spends the energy stored in WAT. BAT adipose cells are considerably different from WAT, one of the main differences being that BAT cells contain larger and more numerous mitochondria (organelles that produce energy within cells), resulting in the characteristic brown colour due to the iron contained in the mitochondria (2). Until recently, BAT in humans was believed to exist only in infants, serving as a protection mechanism against hypothermia, as infants lack the shivering reflex, i.e. the involuntary shaking of the muscles around vital organs to increase temperature (thermogenesis). This led to the belief that the adult human does not possess this BAT-associated, "fat burn", temperature generating mechanism and consequently BAT activation as a therapeutic approach to obesity had generally been discarded (3).
However, recent research has changed this view. Positron emission tomography (PET), a technique used to diagnose tumours, identifies areas in the body with increased uptake of glucose, indicating an abnormally rapid division and growth of cells.
PET can also detect non-tumour related activities in organs of the body that have high energy expenditure such as the brain, heart or active muscles. In the mid-nineties, clinicians employing PET observed that many patients displayed a symmetrical high glucose uptake in the neck and shoulder area (see photo *). This was not related to tumours and was originally explained as muscle activity due to the anxiety of the patient during PET. As computer tomography (CT) was coupled with PET, it became clear that the areas of symmetrical high glucose uptake were not muscle, but a tissue with the characteristics of adipose (3).
It is now established that BAT can be present and functional in adults (4, 5), and further research has made researchers re-evaluate its importance in human metabolism. An important human BAT characteristic is that it is activated by exposure to a mild cold environment or during winter, but not at higher temperatures (6, 7). In addition, the presence of active BAT seems to be positively correlated with lower BMI and inversely correlated with higher age and BMI values (4, 6, 7). Researchers in the field argue that from an evolutionary perspective, BAT was present in early humans (just like extensive body hair) but likely declined as man was able to find increasingly efficient protection from cold (8, 9). Saverio Cinti (**) goes one step further, stating that the indoor temperatures two centuries ago were significantly less than today, and suggests that "reduced energy dispersion, due to diminished energy expenditure for heat generation, could thus be considered as one of the mechanisms favouring the current diabesity (obesity & type-2 diabetes) pandemic" (9). In other words, increased indoor heating would prevent you from "burning" energy to produce body heat and could hence contribute to obesity. Another important finding is that BAT like fat cells can exist interspersed in the WAT of rodents and humans. It has been suggested that WAT can be converted to BAT in rodents, cold exposure being one of the triggers (8, 10). If this is further confirmed, a possible plasticity of the adipose tissue in humans could serve as a powerful target for a therapeutic approach against obesity.
While research on the role of BAT in obesity is blooming and filled with more questions than answers, the findings so far could lead to new and original ways to fight obesity. One is likely many years away; new drug targets may arise from studying the molecular mechanisms underlying the generation or activation of BAT in adulthood. The other one however, if confirmed, would be in everyone's reach; simple, cheap and environmentally friendly – just turn down the heating. (PM)
* Upper chest and neck PET imaging under cold (top) or warm (bottom) conditions. Red colour indicates high glucose uptake corresponding to active BAT. Photo: © 2009 Massachusetts Medical Society. N Engl J Med 2009;360:1518-25
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)