Now a study by Silje Steinbeckk and colleagues from Norway, published in JAMA Pediatrics, suggests that while genetic factors are important, these may not act through an effect on appetite or eating behaviour.
The longitudinal study was conducted in a representative birth cohort at the Trondheim Early Secure Study, enrolled at age 4 years during 2007 to 2008, with follow-ups at ages 6 and 8 years. Analyses included 652 children with genotype, adiposity, and appetite data.
While there was clear effect of genetic risk (measured as a composite score of 32 genetic variants) on increase in body weight and fat mass), there was no clear relationship to appetite traits measured at age 6 years with the Children’s Eating Behavior Questionnaire.
Thus, the authors conclude that while genetic risk for obesity is associated with accelerated childhood weight gain, appetite traits may not be the most promising target for preventing excessive weight gain.
So if not through appetite, how do these genes increase the risk for weight gain. Obviously there are a number of possibilities ranging from subtle effects on energy metabolism, adipocyte differentiation or other factors that may not directly be related to eating behaviour.
Another possibility may well be that the instrument used to assess appetite traits may simply not be sensitive and reliable enough to capture subtle changes in ingestive behaviour.
Thus, while there is no doubt that genetic risk may well be a key determinant of childhood obesity, exactly how this effect is mediated remains unclear.
Thus, a study by Miram Salama and colleagues from Laval University, QC, published in Physiology and Behavior, shows that mental work may very much influence food preferences and satiety.
Using a cross-over design, 35 healthy young adults were randomly assigned the one of the two following conditions: mental work (reading a document and writing a summary of 350 words with the use of a computer) or control (rest in seated position).
After 45 mins of each condition, participant were offered a standardized ad libitum buffet-type meal. Appetite sensations (desire to eat, feeling of hunger, fullness level and estimated amount of food that can be consumed) were measured using a visual analogue scale (VAS).
While women not only had a higher caloric intake after the mental work (by about 100 extra Cal), men reduced their caloric intake (by about 200Cal).
While women selectively increased their preference for carbs, men reduced their intakes of dessert.
In both men and women, participants with the highest waist circumference also had the lowest satiety efficiency in response to mental work.
These results suggest that mental work can change energy intake and preferences in both men and women, albeit in different directions.
Why this would be is anyone’s guess – it is also not clear exactly how this mechanism works. One speculation would be that there are differences in how men and women respond to mental stress – but that is certainly work for a future study.
This, according to a study by Ruth Brown and colleagues from Toronto’s York University, published in Medicine and Science in Sports and Exercise.
The study included 58 adult men and women of either normal weight (NW) or overweight (OW), who reported either attempting (WL) or not attempting weight loss (noWL)
Following 25 mins of exercise on a treadmill at either a moderate (60% HRmax) or a vigorous intensity (75% HRmax), participants were asked to estimated the number of calories they expended through exercise and create a meal that they believed to be calorically equivalent to the amount of calories they had just burnt.
Both the moderate and intense exercise groups were on average spectacularly wrong in their estimates.
In contrast, the active weight loss (WL) groups appeared to do far better at estimating energy consumption than the non-WL groups.
As an example, following vigorous exercise, the OW-noWL overestimated energy expenditure by 72%, and overestimated the calories in their food by 37%.
Although the WL groups did better, all groups showed a wide range of over and underestimation (-280 kcal to +702 kcal).
These findings show that while most people tend to over or underestimate caloric expenditure with exercise, overweight adults who are not attempting weight loss may be even more off the mark than others.
The most obvious solution would be to use some kind of monitor that does a better job of predicting calories consumed that just guessing.
That is of course, if overcompensating is not your goal (as in people who actually gain weight when they begin exercising).
For those interested in staying in energy balance, perhaps simply stepping on the scale regularly during the week should be enough.
For those interested in losing weight, they may need to be reminded that exercise (alone) is actually a pretty inefficient way to lose weight, so the calories burnt during exercise probably don’t matter all that much for weight management (despite all other benefits of exercise – its the calories you eat or drink that count).
Now Suzanne Higgs and Jason Thomas from the University of Birmingham, UK, in a paper published in Current Opinion in Behavioral Science review the role of social norms in eating behaviours and discuss how these norms could potentially be targeted to improve eating behaviours.
“We eat differently when we are with other people compared with when we eat alone. Our dietary choices also tend to converge with those of our close social connections. One reason for this is that conforming to the behaviour of others is adaptive and we find it rewarding. Norms of appropriate eating are set by the behaviour of other people, but also shared cultural expectations and environmental cues. We are more likely to follow an eating norm if it is perceived to be relevant based on social comparison. Relevant norms are set by similar others and those with whom we identify… Norm matching involves processes such as synchronisation of eating actions, consumption monitoring and altered food preferences.”
“Social norms may have had a role to play in recent rises in obesity by reinforcing new behaviour patterns associated with overeating and weight gain. For example, increases in average portion size may have created new consumption norms that are diffused through social networks. It might also be that the social context of eating has changed recently in ways that favour overconsumption. For example, more people eating away from home in fast food restaurants with others might be associated with social facilitation of eating.”
If, how and to what extent, eating culture can be changed at a population level through public health and policy interventions will certainly remain the subject of further study.
Now a study by Robert Eckel and colleagues, published in Current Biology, illustrates how sleep deprivation and timing of meals can markedly alter insulin sensitivity.
Studies were conducted in 16 healthy young adults (8w) with normal BMI. Following a week of 9-hr-per-night sleep schedules, subjects were studied in a crossover counterbalanced design with 9-hr-per-night adequate sleep (9-hr) and 5-hr-per-night short sleep duration (5-hr) conditions lasting 5 days each, to simulate a 5-day work week. Sleep was restricted by delaying bedtime and advancing wake time by 2 hr each.
Energy balanced diets continued during baseline, whereas food intake was ad libitum during scheduled wakefulness of 5- and 9-hr conditions.
Overall, the simulated 5-day work week of 5-hr-per-night sleep together with an ad libitum diet resulted in a 20% decrease in oral and intravenous insulin sensitivity, which was compensated for by increased insulin secretion..
These changes persisted for up to 5 days after restoring 9-hr sleep opportunities.
The authors also showed that shifting circadian rhythm resulted in morning wakefulness and eating during the biological night, a factor that may promote weight gain over time.