A weighty matter

I think we all recognise that over the past few decades, the average person has become a more sedentary creature. It's nice then to get some data to back it up.

Researchers have looked at US data on occupations and physical activity and shown that, since the 1960's, the estimated mean daily energy expenditure due to the job we do has dropped by more than 100 kcal.

While this is US data, it should inform the obesity debate in this part of the world. A recent report from the European Commission found that 23% of Irish adults are considered obese. While an OECD report in 2010 found that Ireland was the second most overweight country in Europe.

The researchers used data from the US Bureau of Labor Statistics and from the US National Health and Nutrition Examination Surveys.

The findings suggest that this significant reduction in calories expended daily accounts for a "significant portion of the increase in mean US body weights for women and men".

Figure 1. Service, goods producing and agriculture jobs in US from 1960 to 2008.

The proportion of Americans in 'service' jobs as opposed to manufacturing, construction and agricultural jobs has increased hugely since 1960. (Fig 1)

As you might expect, the amount of physical activity involved in something like financial services or teaching is much less than that required for agricultural or construction (the most energy intensive) jobs (Fig 2). Hence, the fall in average daily energy expenditure.

Figure 2. Estimated median and range of physical activity intensity (METs) as well as the estimated caloric expenditure of each occupation.

Employment is, of course, not the only factor involved here. For example, the authors note that since 1960, the amount of energy spent on housework has 'greatly decreased' for women and slightly increased for men.

Diet and exercise probably remain the two most important factors which we can influence but it is interesting to see that the job we do also influences our likelihood to be overweight.

Things like how we travel to work, whether we use stairs or not were not considered in the study and it is unlikely to be as clearcut as we might like to think.

The results come as Safefood Ireland launch a two-year Stop the Spread campaign to encourage Irish people to measure their real waist size.

Safe Food say that only 38% of adults believe they are overweight. In fact, 66% of the public are overweight. The other 285 just don't know it or are in denial!


Reference: 
Church TS, Thomas DM, Tudor-Locke C, Katzmarzyk PT, Earnest CP, et al. (2011) Trends over 5 Decades in U.S. Occupation-Related Physical Activity and Their Associations with Obesity. PLoS ONE 6(5): e19657. doi:10.1371/journal.pone.0019657

Sleep, Diet and Life Expectancy

Sleep seems to be on the mind of lots of scientists over the last few days with a number of intriguing sets of results being published.

According to a study published on Tuesday in PLoS Biology, when flies are starved they are able to stay awake for long periods of time without feeling the downsides of going without a nap.

The experiment was conducted by starving some flies while allowing others to feed normally and then providing a physical jolt to prevent them from nodding off. The starved flies were less susceptible to the effects of sleep deprivation such as cognitive impairment.

The scientists also made use of mutant fruit flies which lack the 'canonical clock gene cycle'. Such flies normally die within 10 hours of being deprived of sleep, but when starved they lasted nearly three times as long.

The authors believe that two genes recently shown to control the response to starvation in fruit flies brummer (bmm) and Lipid storage droplet 2 (Lsd2) also have a role to play in sleep regulation.

"brummer mutants, which are fat, show exaggerated response to sleep loss. In contrast, mutants for Lipid storage droplet 2 are lean and are able to stay awake without becoming sleepy or showing signs of cognitive impairment" the authors write.

"Given that metabolic pathways are highly conserved between mammals and flies, it will be interesting to determine whether lipid [fat] metabolism also plays a similar role in mammals".

Meanwhile, a recent study reported in the September 1st issue of Sleep found that men with serious sleep problems had much higher mortality rates.

The study of 1,742 men and women, who were randomly sampled in Pennsylvania and studied for 14 and 10 years respectively found that the overall mortality rate was 21% for men and 5% for women.

'in men who experienced insomnia, that mortality rate was significantly increased' However, in men who experienced insomnia (who slept for less than 6 hours a night), that mortality rate was significantly increased. In women, on the other hand, mortality was not found to be associated with insomnia and disrupted sleep.

Of the men who were studied, 51% of insomniacs died during the study period, compared to just 9% of normal sleepers.

“Insomnia has potentially very severe side effects,” said study co-author  Edward Bixler. “It needs to be treated, and more effort needs to be put into sorting out better treatments.”

More evidence of sleepless nights being bad for your health came from a report also published on Wednesday (Sept. 1st) in which US researchers found that teenagers who sleep for less than 8 hours a night during Monday to Friday eat more snacks and fatty foods then those who get a solid eight hours.

The study analysed 240 teenagers and asked them to wear wrist monitors that measured sleep duration. During the study period, researchers discussed eating habits with the participants twice a day to monitor their food intake.

'teens who did not sleep well consumed 2.2% more calories from fat' The results, also published in the September issue of Sleep, showed that teens who did not sleep well consumed 2.2% more calories from fat compared to those who slept for eight hours. Girls were more prone to this than boys; consuming 3.3.% more calories from fat compared to 0.9% in boys.

Teenagers who slept for eight hours or more a day during the working week consumed 1,723 calories per day, with 1,968 calories being consumed by those who  slept for less than eight hours.

The authors of this study have suggested that sleep may be the "missing link" in the fight against obesity, which up to now has focused on diet and exercise.

From this handful of recent studies it seems that diet and sleep are certainly closely linked and that more research is required to find out exactly the nature of that link.

One thing is for sure, if the results of the the mortality study is anything to go by, the outcome of cutting back on sleep time (either by choice or not) can be serious effects on your health and life expectancy.

References:
Thimgan MS, Suzuki Y, Seugnet L, Gottschalk L, & Shaw PJ (2010). The perilipin homologue, lipid storage droplet 2, regulates sleep homeostasis and prevents learning impairments following sleep loss. PLoS biology, 8 (8) PMID: 20824166


Vgontzas AN; Liao D; Pejovic S; Calhoun S; Karataraki M; Basta M; Fernández-Mendoza J; Bixler EO (2010). Insomnia with short sleep duration and mortality: the Penn State Cohort SLEEP, 33 (9), 1159-1164


Weiss A; Xu F; Storfer-Isser A; Thomas A; Ievers-Landis CE; Redline S (2010). The association of sleep duration with adolescents’ fat and carbohydrate consumption SLEEP, 33 (9), 1201-1209

Man does not live on bread alone...

Examination of paintings of the Last Supper have shown that portion size has increased dramatically over the years.



"If art imitates life and if food portions have been generally increasing with time, we might expect this trend to be reflected in paintings that depict food" according to Brian and Craig Wansink, the former a economist and the later a theologian.


Writing in the International Journal of Obesity, the academics compared the "food-to-head ratio" in 52 of the best known depictions of the Last Supper. In 18% of the paintings, the attendees were depicting as enjoying fish as their main dish. Lamb (14%) and pork (7%) were also recorded with 46% of the paintings having no discernable main dish.


The authors showed a significant positive relationship between the relative size of that main dish and the passage of time from 1000 BC - 2000 BC. This means that as time progressed, portion size got larger.


"The last thousand years have witnessed dramatic increases in the production, availability, safety, abundance and affordability of food. We think that as art imitates life, these changes have been reflected in paintings of history's most famous dinner", said co-author Brian Wansink.