Nutrition Research Highlights 6|2013
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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!
Social environments can shape our eating behaviour – who is present during the eating occasion may impact on what and how much we eat. Early observations in the 1990s found that people eating in social settings ate substantially more than when eating alone, and that the bigger the party, the more one would eat (1)! It is thought that because meals consumed during social occasions tend to take longer and the atmosphere is relaxing, individuals become less restrictive when it comes to food (2).
However, research shows that we are also influenced by what and how much others eat. A recent review has examined how we mirror the eating behaviour of others and how perceived eating norms* related to food choice and intake can affect what we eat (2). Experiments revealed that eating in the presence of someone who had been instructed to have high snack intake led study participants to consume more snacks, too. In the reversed condition, i.e. where participants ate in the company of low snack consumers, their own snack intake was also low.
Two main theories exist to explain what drives us to copy other people's eating behaviours. First, an individual considers the amount consumed by their company to be appropriate quantity at the occasion, and eating more than others would be seen as greedy. This holds especially if the company are slim or of similar body size as the individual. Secondly, people eat the same amount as others in order to be liked or to gain social acceptance, particularly when eating with new friends and acquaintances (2).
Perceived eating norms also play an important role in modifying food choice and consumption. People look outwards to the behaviour of others and change their behavioural intentions accordingly to conform to what is considered to be the norm, especially the norm of their peers (2). For example, a study on the habitual intake of sugar-sweetened beverages (SSB) in teenagers found that, if participants believed their friends drank large quantities of SSB, the likelihood of drinking a lot of SSB themselves also increased (3). On the other hand, if people believe their peers are eating a healthy diet, their own intention to eat a better diet also increases (2).
Because perceived norms can work in favour of healthy eating, it is possible to influence people's perception on healthy and unhealthy diets by changing the norm (see our previous story on nudging). Scientists are now thinking of ways to provide more positive eating norm messages to get populations to eat more healthily and be more physically active.
So how about doing some scientific investigation yourself? When having a meal with others, have a look around you. Are you being influenced by what and how much others are eating? How about acting as a role model for a day by having some healthier options and seeing if others will follow! (TNM)
* Perceived eating norms: refers to an individual's beliefs about how others around them behave, which in turn, influences how they choose to behave when it comes to making food choices and the amount of food eaten (2).
As nutrients enter our mouth and digestive system, they prompt a myriad of reactions – some define the taste of foods, others prepare the body for digestion and others still will eventually signal satiation. How does the brain sense it is time to end the meal and put the fork down?
This question has been the focus of much attention as it is now believed that overeating is associated with a defect in this sensing mechanism and the communication between the gut and the brain (also known as the gut-brain axis). In particular, high-fat foods activate a food reward mechanism in the brain involving dopamine, an important molecule that regulates pleasure. Paradoxically, prolonged high-fat intake is associated with dopamine deficiency and one can imagine that this dopamine deficiency entices overeating in an attempt to restore the pleasure gained from food intake.
A recent study (1) has brought more evidence to support this line of thought and also identified an additional messenger in gut-brain communication. Experiments in mice show that a lipid satiety messenger called oleoyl-ethanolamine (OEA) links excessive fat intake to dopamine deficiency. As expected, mice fed a high-fat diet did not respond with dopamine release in the brain and this deficiency was paralleled by low levels of OEA. Moreover, injecting OEA in mice altered their eating behaviours. Those mice previously on high-fat diets began eating low fat foods and restored dopamine signalling suggesting that OEA enhanced the reward value (pleasure) of low-fat foods. Whether the same messenger will have similar effects in humans remains to be seen. But the potential of OEA to curb overeating and promote lower fat intake while apparently keeping the reward value of foods deserves further investigation! (SC)
In May 2013, after more than a decade's worth of study, the American Psychological Association published the 5th edition of its Diagnostic and Statistical Manual of Mental Disorders (DSM-5). For the first time in the history of the DSM, binge eating disorder (BED) is officially recognised as a mental disorder. The DSM-5 defines BED "… as recurring episodes of eating significantly more food in a short period of time than most people would eat under similar circumstances, with episodes marked by feelings of lack of control" (1). In addition to BED, obesity was considered for inclusion in DSM-5 as a mental disorder, the underlying idea being that overeating and obesity are the result of an addiction* to food.
Eventually, obesity was not included as a mental disorder, but the discussion about food addiction** is far from resolved. Proponents say it shares sufficient neurobiological parallels with drug addiction and it helps to explain at least in part the obesity epidemic happening around the globe (2). In their view, formal recognition of food addiction as a condition would open new treatment avenues and help relieve those affected from the stigma of gluttony.
The faction arguing against the concept's usefulness, in turn, considers the scientific evidence for food addiction too preliminary (3). Despite the neurobiological similarities to drug dependence, food addiction is seen as devoid of clinical utility (with respect to diagnosis and treatment). Instead, terms such as "hedonic eating" are used to describe (over)eating in the absence of hunger. The hedonic qualities of a food or meal comprise everything to do with palatability, or in other words, how much we like that food/meal.
Considering that obesity affects an ever-growing number of people, understanding the public's perspective seems highly appropriate. Results from a recent online survey among 215 US and 264 Australian citizens (4) give a first idea of how people perceive the concept of food addiction and food taxation as a policy option for its control. The majority of respondents (72%) believed food addiction causes obesity. Likewise, 86% of the participants thought that certain foods are addictive. At the same time, 32% indicated "personal choice" as the primary cause of obesity as compared to 23% for "environment", 15% for "biology", and 12% for "genetics"; 18% indicated some other cause or combination of factors. The survey further revealed that half of the respondents considered the individual responsible for becoming obese, and three-quarters saw the individual as in charge of losing weight. So, despite viewing food addiction as a likely reason for overeating and weight gain, people first and foremost look to themselves as the agent of change. Furthermore, 57% disagreed that a tax on certain foods – as a measure outside one's own control – would lower obesity rates while 49% doubted the benefits of such a tax to society. However, more population-based surveys and research is needed before any conclusion can be drawn.
Obviously, establishing food addiction and obesity as mental disorders would have a tremendous impact on the practice of treating eating behaviours linked to excess weight gain. Public health policy makers would do well to endorse a likely increase in the medicalisation of obesity only if the scientific evidence is clearly supportive. Moreover, they need to factor in potential responses by individuals as well as society before implementing specific policy. Until then, behavioural therapy in most cases appears to be the reasonable approach where primary prevention has failed. (SSgB)
* According to the American Society of Addiction Medicine, "[a]ddiction is a primary, chronic disease of brain reward, motivation, memory and related circuitry. Dysfunction in these circuits leads to characteristic biological, psychological, social and spiritual manifestations. This is reflected in an individual pathologically pursuing reward and/or relief by substance use and other behaviors."
** A universal definition of food addiction does not exist, but the online Psychology Dictionary briefly describes it as an "eating disturbance where a person is preoccupied with weight, body image and food."
1. http://www.dsm5.org/Documents/Eating%20Disorders%20Fact%20Sheet.pdf (accessed 5 December 2013)
Sugar-sweetened beverages (SSBs) often attract public and scientific interest because of their potential contribution to obesity and related conditions (1), and we have dealt with this issue in a previous issue of our newsletter. In this article instead we focus on the growing interest in the health benefits associated with increased water intake, which include weight control, dental health, improved motor skills or brain hydration (2-4). Regarding the latter, scientists have looked into the effects of dehydration on brain function in UK adolescents (3). They showed that while the brain appears to be able to compensate for water restriction, at least in the short term, some researchers claim that school performance could be compromised (5). On these grounds, we have decided to address the important issue of adequate hydration* and the development of healthy drinking habits in children.
Hydration in children – recommendations vs intakes
The human body is comprised of between 45-75% water (60% on average). Water is vital for maintaining good health as it is the main component of body fluids, e.g. blood, saliva and urine. It furthermore supports the regulation of body temperature and offers the basis for all chemical reactions (6, 7). Three major states of hydration can be distinguished: 1) optimal hydration, when all bodily needs for water are met; 2) hypo-hydration, when water balance is insufficient for all body functions to run smoothly; and 3) hyper-hydration, in which over-consumption of water, under certain circumstances, can lead to water intoxication (6, 7).
We can absorb water virtually from all foods. Drinking water and other beverages such as juices or fizzy drinks contributes an average of 80% to our daily consumption whereas solid foods contribute the remaining 20%. In 2010, the European Food Safety Authority (EFSA) (6) issued a scientific opinion on Adequate Intakes* of water. Values are available for specific age groups by gender and physiological state (pregnancy and lactation). It should be noted that individual water requirements are also influenced by physical activity, environmental temperature, dietary factors and some pathophysiological states such as diabetes mellitus and kidney disease (6, 7). The EFSA reference values for total water intake from all sources, including solid foods, range from 1.3 l/day for boys and girls aged 2–3 years old to 2.5 l/day for adolescent (14+ years) and adult males (6).
Studies reporting water intakes of European children and adolescents are scarce (8-10). A pan-European study of adolescents aged 12.5 to 17.5 years showed that while water accounted for the majority of fluid consumed, approximately 65% of male and female adolescents had total water intakes below the levels recommended by EFSA (8, 9). Remarkably, around 12% of adolescents stated that they did not drink plain water at any time during the reporting period. Along the same lines, 15-year trends in water intake in German children and adolescents showed low total water intakes, especially of tap water (10).
It must be stressed that data on beverage intake often are difficult to compare due to differences in assessment methodology and in the categorisation of beverages and liquid products between studies (6). The issue is further complicated by the fact that underreporting of true intakes can undermine substantially the validity of results obtained.
Since water does not contain energy, increased consumption may limit excess weight gain (4). Furthermore, promoting water consumption could serve as a means to support the development of healthy lifestyle habits among youth (11). Stahl and colleagues (12) observed that optimally hydrated children had a better dietary profile than hypo-hydrated children as they consumed significantly less energy-dense foods. The importance of developing healthy hydration practices often is overlooked or lacks emphasis in public health initiatives (2). Critics suggest this may be an opportunity missed thus far to establish and maintain a healthy habit throughout life.
The school environment and new opportunities
Children spend a lot of their time in school or in child care, which makes these settings ideal for interventions that encourage development of healthy behaviours, including good drinking habits, among both children and parents. Water consumption or promotion of healthy drinking behaviour, however, requires an additional step to the usual health promotion and educational intervention models. This step is related to making water constantly available and easily accessible to children during school times; it also requires that water promotion be dealt with and considered by public health professionals and not only as the by-product of other health promotion activities.
Interventions to influence drinking habits, e.g. placement of water coolers in secondary schools, seem feasible (13). Muckelbauer and colleagues (4) suggested that a combined educational and environmental intervention promoting water consumption is effective in preventing overweight in school children, including those from materially deprived urban areas. These findings are based on a randomised trial of 32 elementary schools in socially deprived areas of two German cities where water fountains were installed and teachers gave four classroom lessons to promote water consumption in the intervention schools. At the end of the study, the intervention group showed a one glass per day higher water consumption and markedly less new cases of overweight compared with the control group (4).
To conclude, while there is a wide range of beverage categories to satisfy different tastes and needs, children and adolescents often do not consume enough water. Instead they opt for SSBs and other beverages. Early education of children and their families on how to drink in a healthy way, and provision of easily accessible, safe and palatable drinking water would help reduce and ideally prevent obesity. (TM)
* Adequate Intake (AI): The recommended average daily intake level based on observed or experimentally determined estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate. The AI is used when a Recommended Daily Allowance cannot be determined (14).
November - December 2013
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. Sandra Caldeira, Anastasia Livaniou, Tsz Ning Mak, Theodora Mouratidou, Carlos Martin Saborido, Stefan Storcksdieck genannt Bonsmann and Jan Wollgast contributed to this issue.
The views expressed here do not necessarily reflect the opinion of the European Commission.