Thursday, September 2, 2010

Obesity, Diabetes and Exercise

In the US there is the ongoing search for the genes which cause obesity and diabetes. As we have demonstrated obesity leads to Type 2 Diabetes and obesity is merely a mass balance problem; Input-Output=Net Accumulation.

Now in the Mumbai press they state that exercise can overcome genes! Wow, I hope this gets over here. They state:

Obesity researchers have rubbished the excuse that we are "slaves" to our genes. They found that by exercising people could slough off 40 percent of the extra weight that "fat genes" laid on them.

Although some have a tendency to be overweight, scientists at a Medical Research Council unit in Cambridge discovered that an active lifestyle could counter a person's genetic inheritance, reports The Telegraph.

The original article in the journal PLOS states:

We have previously shown that multiple genetic loci identified by genome-wide association studies (GWAS) increase the susceptibility to obesity in a cumulative manner. It is, however, not known whether and to what extent this genetic susceptibility may be attenuated by a physically active lifestyle. We aimed to assess the influence of a physically active lifestyle on the genetic predisposition to obesity in a large population-based study.

Our study shows that living a physically active lifestyle is associated with a 40% reduction in the genetic predisposition to common obesity, as estimated by the number of risk alleles carried for any of the 12 recently GWAS-identified loci.

The findings of this study indicate that the genetic predisposition to obesity can be reduced by approximately 40% by having a physically active lifestyle. The findings of this study suggest that, while the whole population benefits from increased physical activity levels, individuals who are genetically predisposed to obesity would benefit more than genetically protected individuals. Furthermore, these findings challenge the deterministic view of the genetic predisposition to obesity that is often held by the public, as they show that even the most genetically predisposed individuals will benefit from adopting a healthy lifestyle. The results are limited by participants self-reporting their physical activity levels, which is less accurate than objective measures of physical activity.

Now if we add calorie restrictions and target BMI less than 22.5 we get the ideal result, no Type 2 Diabetes, unless of course they patient has totally destroyed their pancreas.

There also was a recent posting on VOX looking at the explosion of obesity in 18 years olds in the past century.

The VOX authors state:

It seems we are but helpless bystanders to the obesity pandemic sweeping the globe. More than a third of US adults, about 70 million persons, are obese. Yet before we can come up with appropriate measures to counter this disturbing trend, we need to know more about its development.

The official view propagated by the Centre for Disease Control is that in the US the epidemic appeared rather suddenly in the 1980s . We believe this view is misleading. All the studies underpinning the official view refer to period effects – that is, they are based on data that are averaged across the population for particular years. They do not look at birth-cohort effects – that is, the evolution of weight among people of the same birth year.

We all know that weight changes over time, as do other variables, such as wages. Suppose you are earning $20 per hour today, but we do not know when you reached that wage. Similarly, when someone’s weight is measured we do not know when she reached that weight. Hence, the official estimates based on such measurements do not lead to convincing trends. This has prompted us to estimate the trends by birth cohorts in our recent research . The advantage of this approach is that birth cohorts experienced similar social, economic, and technological changes that would have affected their weight. Similarly with wages – your wage today depends on what schools you attended from the very beginning.

The authors conclude:

The lifestyle changes of the 20th century affected the four groups under study somewhat differently. Identifying the deep causes of the long-run trends is outside of the scope of this study, but the “creeping” nature of the epidemic, as well as its persistence, does suggest that its roots are embedded deep in the social fabric and are nourished by a network of disparate slowly changing sources as the 20th-century US population responded to a vast array of irresistible and impersonal socio-economic and technological forces.

The most obviously persistent among these were:

  • the major labour-saving technological changes of the 20th century,
  • the industrial processing of food and with it the spread of fast-food eateries (To illustrate the spread of fast food culture, consider that White Castle, the first drive-in restaurant, was founded in 1921. McDonald started operation in the late 1940s, Kentucky Fried Chicken in 1952, Burger King in 1954, Pizza Hut in 1958, Taco Bell in 1962, and Subway in 1962.),
  • the associated culture of consumption,
  • the rise of an automobile-based way of life,
  • the introduction of radio and television broadcasting,
  • the increasing participation of women in the work force, and
  • the IT revolution.

It is not at all clear that the authors have demonstrated any basis for their claims, even in the detailed paper (an NBER working paper). The true fact is the mass balance equation. Missing from the above is the school bus and the school lunch and breakfast programs. We drive our children from and to everything and then we also feed them nutritionist based government funded and mandate useless calories. Go to any school lunchroom and you see where it begins. The Burger King issue is a canard. Before Burger King there were hamburger stands, malt shops, drug store counters, lots of places. I would always get a sugar fix on my paper route at a small deli some halfway through my route. I could afford a stop once a week but that was with an up hill 12 mile paper route, after walking from and to school a mile each way.

The solution is simple, get rid of school lunches and school breakfasts ... low BMI is a lot better than high BMI.