How To Interpret Studies On Screen Time And Eating Behaviour
Much of the research on the contribution of screen time, sedentariness, food consumption and other factors comes from cross-sectional or longitudinal studies, where researchers essentially describe correlations and statistical “effect sizes”. To be at all meaningful, analyses in such studies need to be adjusted for known (or at least likely) confounders (or at least the confounders that happen to available). No matter how you turn and wind the data, such studies by definition cannot prove causality or (even less likely) predict the outcome of actual intervention studies. Nevertheless, such studies can be helpful in generating hypotheses. Thus, for example, I read with interest the recent paper by Lei Shang and colleagues from the University of Laval, Quebec, Canada, published in Preventive Medicine Reports. The researchers looked at cross-sectional data on 630 Canadian children aged 8-10 years with at least one obese biological parent. While the overall median daily screen time was about 2.2 hours, longer screen time was associated with higher intake of energy (74 kcal) and lower intake of vegetables & fruit (- 0.3 serving/1000 kcal). This unhealthy “effect” of screen time on diet appeared even stronger among children with overweight. Thus, there is no doubt that the study shows that, “Screen time is associated with less desirable food choices, particularly in overweight children.” The question of course remains whether or not this relationship is actual causal or in other words, does watching more television lead to an unhealthier diet (I am guessing no one assumes that eating an unhealthier diet leads to more TV watching). Unfortunately, this is not a question that can be answered by this type of research. Nor, is this type of research likely to predict whether or not reducing screen time will get the kids to eat better. Indeed, it doesn’t take a lot of imagination to come up with other explanations for these findings that would not require any assumption of a causal link between eating behaviours and television watching. For one, TV watching could simply be a surrogate measure for parenting style – perhaps parents that let their kids watch a lot of TV are also less concerned about the food they eat. And, for all we know, reducing TV time may (e.g. by cutting the kids off from TV – or cutting the parents off from a convenient babysitter) in the end make the kids eating behaviours even worse. Who knows – that’s… Read More »
Skinny Kids Eat More Candy
A common assumption is that kids with obesity consume more high-caloric foods – which of course includes confectionary items like chocolate and non-chocolate sweets. Now, a study by Constantin Gasser and colleagues from Melbourne, Australia, in a paper published in the American Journal of Clinical Nutrition, present a systematic review and meta-analysis of confectionary consumption and overweight in kids. The researchers identified 19 studies fort their systematic review, 11 of which (∼177,260 participants) were included in the meta-analysis. Overall, odds of excess weight of kids in the highest category of sweets consumption was about 20% less than in the reference category. This inverse association was true for both chocolate and nonchocolate confectioneries. Furthermore, in the longitudinal studies and the randomised controlled trial included in the review, no associations were observed between confectionery consumption and overweight, obesity, or obesity-related outcomes. Thus, based on data from well over 175,000 kids, there appears to be no relationship between sweets consumption and excess weight – if anything, the relationship is the opposite of what one may expect. As so often, when data don’t fit the “accepted” hypothesis, the authors are also quick to point out that these findings could well be explained by reverse causality (overweight kids avoiding sweets) or underreporting by heavier kids (a polite way of saying that heavier kids may be less honest about their candy consumption). On the other hand, it may also well be that regular (non-restrictive) sweet consumption actually does in fact make kids less vulnerable to overeating, simply by ruining their appetite (just as grandma always warned you it would – as in, “No sweets before supper!”). Overall, the findings remind me of a previous study that failed to find any association between sugary pop consumption and body weight in Ontario and PEI kids (if anything skinny kids in PEI drank more pop than those with excess weight). Whatever the true answer may be, these findings certainly do not support the notion that sweet or chocolate consumption is a key factor in childhood obesity. @DrSharma Edmonton, AB
Reducing Infant Food Reinforcement Through Music
Even infants know to pick one reward over the other – but obviously, as in adults, the one they pick depends on the choices available to them. Given the highly rewarding nature of food, picking a favourite food over. almost anything else appears the natural choice. Thus food reinforcement is generally established at an early age and tends to continue throughout life. One hypothesis is that the development of obesity is due to a lack of access to pleasurable alternatives in one’s environment, thereby increasing the reinforcing value of eating Now, Kai Ling Kong and colleagues, in a paper published in OBESITY, test the hypothesis that conditioning infants as young as 9-16 months to an cognitively stimulating alternative reinforcer may reduce the appeal of food as the default goto reward. The researchers studied 27 infants, who were found to have rather high food reinforcing ratios at baseline, half of who were randomised to 6 weeks of a program that provided them with a rich variety of music and playful activities, which encouraged infants and parents to participate at their own level in singing, moving, listening, or exploring musical instruments. Participating parents and infants attended weekly, 45-min classes as a group for 6 weeks and parents were encouraged to listen and sing together with their infants at home during everyday home activities such as bath time, meal time, and bed time using the CD and instructional song book provided by the program. The remaining infants in the active control group consisted of weekly, 45-min play dates held during the same 6 weeks as the music group and were provided with a variety of age appropriate toys (no musical toys) and books for participating parents and infants to play with and enjoy during everyday home activities such as bath time, meal time, and bed time using the toy provided by the program. The reinforcing value of food and music was assessed using a computerized task by having infants press a mouse button to earn rewards (either food or 10 secs of a song) both before and after the interventions. The song used for both pre- and post-intervention assessments was not used in the 6-week music program to avoid familiarity and biases. While the researchers found a significant decrease in the food reinforcing ratio (a measure of food preference) for the infants in the music group, the food reinforcing ratio in the control group actually increased. As the authors note, “Our findings provide initial evidence that alternatives to food may be cultivated at a young age to alter… Read More »
Diet-Induced Obesity Is Transmitted Through The Germline
To anyone following the “biological” literature on obesity, it should be pretty evident by now that environmental factors can epigenetically modify genes in ways that allow “information” on environmental exposures in parents to be directly transmitted to their offspring. Now a paper by Peter Huypens and colleagues from the Helmholtz Zentrum München, Germany, published in Nature Genetics, shows that both maternal and paternal exposure to weight gain induced by a high-fat diet in mice can substantially increase the risk for obesity in their offspring. The key novelty in this study was the fact that the researchers isolated egg and sperm from both male and female mice that had been exposed to high-fat diets (or not) and used these germ cells in various combinations using in-vitro fertilization to create the offspring that were then implanted into surrogate female mice. In all cases, risk for obesity as well as signs of insulin resistant tracked with both the male and female exposures, pretty much confirming that diets eaten by mothers and fathers can directly influence “genetic” risk for obesity in the next generation. If transferable to humans (and there is little reason to doubt that this is the case), these findings suggest that a large proportion of the “heritability” of obesity is due to epigenetic modification that transfers risk from one generation to the next. This means that efforts to prevent childhood obesity need to focus on the parents rather than the kids – kids born to mothers and fathers who have obesity are already born with a substantial higher risk than those born to lean mothers and fathers. Perhaps our best chances of tackling obesity in the next generation of kids is to focus efforts on younger adults of child-bearing age. @DrSharma Edmonton, AB
How Much Of The Confusion In Childhood Obesity Studies Is Simply Regression To The Mean?
When it comes to childhood obesity interventions, there is much confusion as to what works and what doesn’t. Thus, for every study showing that a given “intervention” (e.g. school intervention programs, exercise programs, removing vending machines, etc. ) changes weight measures, there is at least another study showing that it doesn’t. Although this problem is by no means specific to research in childhood obesity, for reasons stated below, research in this area appear to be particularly prone to this problem. Now, a paper by Cockrell Skinner Asheley and colleagues, published in Childhood Obesity, suggests that much of this confusion may simply be due to the statistical phenomenon of “regression to the mean” (RTM). As readers may be well aware, regression to the mean refers to the well-described phenomenon that “outliers” (up or down) tend to “regress” towards the mean on repeated measures. Or as the authors explain, “Today, RTM is often conceptualized primarily in the context of measurement error or repeated measures. Blood pressure provides a reasonable example. If one measure of blood pressure is obtained and is either much higher or lower than the mean, a second measure will likely be closer to the mean. If conceptualized as measurement error, then an average of multiple measures is often used to reduce measurement error, thereby also reducing regression to the mean.” Repeated measures however do not solve the problem when the measured values actually do change over time (as in a child’s body weight). As the authors note, “However, this does not address changes in the true value of the variable over time, which are not due to measurement error. Whenever two variables are not perfectly correlated (such as blood pressure at two time points), there will always be RTM when measured in terms of standardized variables. This occurs regardless of measurement error, the order of measurement, and whether the two variables are repeated measures of the same construct. Additionally, as noted by Barnette et al., regression to the mean can occur in nonnormal distributions and those that are not continuous. For example, RTM can occur in binary data and cause subjects to change categories without a change in their actual status.” While this issue tends to affect all types of research, which is why every experiment would ideally have rigorous controls and the most robust research methods generally use some form of randomisation, this is particularly difficult in studies in childhood obesity.… Read More »
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