Nutrition Research Highlights 4|2012
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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 summarized as “News” items or presented as a “View”, comprising an analysis and expert opinion. Enjoy your reading!
- The health promises of chocolate - too good to be true?
- Breastfeeding linked with small but long term maternal weight loss
- Behind the scenes: Satiation and hunger
On various occasions this summer, the news have reported recent scientific findings suggesting important health benefits of chocolate. In fact, various studies published over the last months propose that chocolate, or more precisely, chocolate compounds called "flavanols", may improve vascular function (1), lower blood pressure (2,3,4,5), increase insulin sensitivity (2,5), improve cognitive function (2), or even reduce the risk of developing cardiovascular disease in general (5,6) or more specifically stroke (7).
How much can we trust these findings? Well, the link to cognitive functions is the result of a single study in a specific setting and is thus to be considered emerging science with the need for confirmation in many more studies. In contrast, the other proposed relationships are results of systematic reviews and meta-analyses, types of scientific evaluations providing pooled evidence from relevant high quality research studies (8), and thus, give confidence in the existence of the proposed benefits for chocolate flavanols. This is also corroborated by a recent favourable scientific opinion of the European Food Safety Authority (EFSA) for a health claim related to cocoa flavanols and maintenance of endothelium-dependent vasodilation, which contributes to an adequate blood flow to body cells and tissues in response to an increase in blood flow, such as after food consumption (9).
However, before staring to indulge in chocolate with official approval it should be stressed that although recent scientific findings are promising this should not lead to people eating masses of chocolate, as this could result in overweight and obesity. Moreover, uncertainty still exists; there are no long-term studies, the many differences in study design, populations, duration etc. complicate an overall conclusion on the evidence, and finally, the beneficial effect may be statistically significant but small in actual health value so that the risk of weight gain could outweigh the benefit.
Nevertheless, there are already the first innovative cocoa products on the market that contain significantly higher contents of flavanols than normal cocoa products, such as for example the "flavanol-rich" cocoa powder or chocolate products approved by EFSA. Those products may deliver sufficient amount of flavanols to guarantee the benefit without delivering also too much fat, sugars and calories.
Last but not least and for those who do not like chocolate: flavanols are not only present in cocoa and chocolate but are also widely present in other plant-derived foods as apples, blueberries, strawberries, peanuts, walnuts, green and black tea, or red wine (10). Thus, these recent research findings on chocolate may actually help to explain part of what is observed and recommended to the public: diets rich in fruits and vegetables promote good health and help preventing the development of chronic age-related diseases. (JW)
Photo: Chocolate bars (wikimedia commons)
The first week of August is not only the beginning of holidays for many in Europe but it is also the World Breastfeeding week (1), launched 20 years ago as part of the World Alliance for Breastfeeding Action. This year's 20th anniversary marks also the 10th anniversary of the Global Strategy for Infant and Young Child Feeding by WHO/UNICEF. WHO recommends a minimum of six months of exclusive breastfeeding for an optimal growth, development and health of the newborn. The exclusive breastfeeding during this period decreases the risk of gastrointestinal infection for the baby and helps the mother with weight loss after birth. However, a recent study (2) revealed that breastfeeding mothers may even benefit from a longer term weight loss. Bobrow et al explored the long-term effects of women's childbearing and breastfeeding patterns on their body mass index (BMI). The study, which was carried out in the UK and included 740.000 postmenopausal women (about a quarter of the total UK women between 50-64 yrs), showed that 6 months of breastfeeding was associated with an average reduction of 1% of their BMI later in life. Despite the limitations of the study and the seemingly small BMI decrease, these results could have significant public health implications since "even a modest 1% reduction in BMI would substantially reduce the number of obesity-related diseases and their costs"(3). In addition, a 1% BMI reduction on a population level has been associated with a 1% reduction in all cause mortality (4). So, albeit small in number, the weight reduction associated with 6 months breastfeeding may turn out to be important later in a mother's life…one more argument to add to the many others that support breastfeeding. (PM)
What determines, in biological terms, whether or not you are hungry? The answer is still a jigsaw but a recent study in mice adds another piece to it (1). We so far knew that after a meal, newly generated glucose from the intestine is released into the bloodstream and that while passing through the portal vein, it is detected by a sensor that transmits a satiety signal to the brain. This response is particularly pronounced if the meal is protein rich, but why is that?
In the study, the authors show that, after eating, the digestion of certain proteins (like casein from milk) generates peptides that can block the so called mu-opoiod receptors*, commanding the brain to drive the production of factors needed for generation of glucose in the intestine. This new glucose can then follow its known path to satiety and suppression of food intake. The complex gut-brain neural circuit that links protein and satiety in mice is illustrated in the Figure. It is another piece to a better understanding of the 'unconscious' biological regulation of food intake and may one day be 'consciously' used to help regulating our eating habits and obesity or metabolic diseases in humans. (SC)
* mu opioid receptors are expressed in both the nervous system and the intestinal tract and are involved in different processes such as analgesia, addiction or GI motility. Blocking or activating these receptors can suppress or increase food intake, respectively.
Image: The modulation of satiety by alimentary proteins (1)
Sports drinks! They are said to improve athletes' physical performance during exercise and accelerate recovery afterwards by enhancing water absorption and replacing electrolytes (mainly sodium) and energy (sugar). It seems to make sense; intense physical activity makes people sweat and this loss of water and minerals, but also the used energy, needs to be replaced for an optimal performance. But what's the scientific evidence supporting the benefits of sports drinks in health and performance? On the occasion of the Olympic Games, a recent series of papers published in the British Medical Journal) have asked just that (1,2,3).
One of the articles (1) concerns hydration in exercise. Timothy Noakes, a professor in exercise physiology and marathon runner, explains that humans have a great capacity to regulate their body temperature, even after prolonged exercise in dry and hot circumstances, loosing a significant amount of water while doing so. Humans are "delayed drinkers", i.e. they do not optimise their hydration status in every moment, but only when they are thirsty. The loss of water from physical activity increases the blood sodium concentration and osmolality*. This change is sensed by the hypothalamus in the brain that triggers other processes resulting in water seeking behaviour. A lasting thirst sensation lowers exercise performance and is regarded as a mechanism to reduce exercise intensity and water loss through sweating and Prof. Noakes argues (1) that thirst only should dictate hydration and there is no need to "stay ahead of thirst".
The recommendations for hydration in sports have changed over the last decades. While in the 70s marathon runners were discouraged to drink because it was thought to slow them down, in 1996 the Position Stand of the American College of Sports Medicine (ACSM) advised athletes to drink as much as tolerable (4). In 2007 this has been revised and the updated Position Stand informs on hydration before, during and after exercise. Pre-hydration is only needed in case a person has suffered substantial fluid deficits. During exercise, the recommendation is to periodically drink, if it is expected that excessive dehydration will occur. Sweating rate is highly dependent on factors such as surrounding conditions (temperature, humidity, wind and sun), type of clothing, intensity and duration of exercise and type of diet but also on age, sex, body weight, genetic factors and training status. This makes it difficult to establish general recommendations. Specifically for marathon runners the ACSM suggests (4) an ad libitum intake between 0.4 - 0.8 L/h, with a higher intake for those with higher body weights, exercising in higher temperatures and/or at higher exercise intensity. After exercise, normal eating and drinking will normally restore the normal hydration status (euhydration), unless excessive dehydration has occurred. These ACSM recommendations are in line with other new/updated fluid replacement position stands published by professional organizations (2), in which a common theme is that the goal of fluid replacement is to avoid excessive dehydration and that drinking in excess of sweating rate should be avoided to prevent hyponatreamia***.
Whether the drinking should come from a sports drink is a matter of debate (2). There are different types of sports drinks with different purposes****. Those in favour of sports drinks claim that the presence of sodium allows for better fluid retention than water and that carbohydrates facilitate water absorption from the small intestine. However, researchers analysing studies provided in support of these claims have concluded that there were important shortcomings in their designs that cast doubt on the validity of their conclusions (3).
It is worth noting that EFSA has already issued positive scientific opinions on two health claims for sports drinks (6). These are detailed in Box 1 and are targeted at "active individuals performing endurance exercise". Though, these opinions are not exempt from controversies (3). We believe that it is particularly important in this case to highlight the target population for which these products are said to be of use. There is a true risk that the claims used will promote sports drinks also among people for whom the evidence does not apply. This is of high relevance in the case of children and adolescents. Sports drinks should by no means be seen by youngsters or their parents as healthy alternatives to soda as they do contain sugar, salt and calories.
The current published research data shows that there is a wide range of individual fluid ingestion by people at all levels of exercise intensity (7). Whether or not following current recommendations, drinking a commercial sports drink or water, or staying ahead of thirst or not, optimal performance for the individual might in the end come down to personal preferences, exercise type or intensity. What has to be kept in mind though is that sports drinks are targeted to adults engaged in sports and not to children or those not actively exercising. (RG)
* osmolality - the concentration of solutes that contributes to a solution's osmotic pressure, i.e. the pressure that needs to be applied to prevent the inward flow of water (because of the higher concentration of solutes)
** Dehydration is defined as more than 2% loss of body mass (or 3% of total body water).
*** hyponatraemia - a disturbance in serum electrolytes in which the sodium levels are lower than normal.
**** Depending the glucose-electrolyte concentration, there are isotonic and slightly hypotonic drinks, intending to enhance water absorption, and hypertonic drinks, intending to supply carbohydrates (energy).
Image: Corbis © Tim Tadder/Corbis
July - August 2012
Nutrition Research Highlights is a bi-monthly publication prepared by the Nutrition Team of the DG-Joint Research Centre, Institute for Health and Consumer Protection. The Nutrition team is comprised of Sandra Caldeira, Raymond Gemen, Petros Maragkoudakis & Jan Wollgast.
The views expressed here do not necessarily reflect the opinion of the European Commission.
© European Union, 2012. Reproduction of articles (excluding photographs) is authorised, except for commercial purposes, provided that the source is mentioned.