Biology in the News Explained

Obesity: Are genes or lifestyle more important?

Either the media or the public (seems to be a bit of a chicken and egg question) seems to want every problem to be defined in black and white terms. If you are Josephine Public, this makes sense because we all would love easy answers to the vexing problems that confront society, even as we know deep down that there usually aren’t any. The media aggravates this problem with their desperation to oversimplify stories for fro yo-easy consumption, and yet to create controversy at the same time. It accomplishes both to declare emphatically that if you have a nagging weight problem, it is not your fault, it is all in the genes, while other media outlets exhort us to eat less and exercise more, so we can enjoy thin, fulfilling lives.

There are a few reasons why the genetics of obesity are newsworthy. First, many people believe the obese among us have suffered enough, both from their condition, and from the finger wagging of the thin, and all the chastising is not helping people regain a healthier weight. Second, plenty of research papers do show unequivocally that there is indeed a strong genetic component to weight set point in people. This is nothing new, it has been documented in research journals since the 1980′s at least (e.g. Stunkard et al., 1986, in which body mass indices (BMI) of adopted children were compared to those of biological vs. adoptive parents; and Stunkard et al., 1990, in which BMI of identical and fraternal twin sets reared together vs. apart were measured). Third, we live in a time of increasingly rapid advances in biological knowledge, especially in genetics, which has led the media to promote the romantic notion that all problems can be traced to genetics solved by genetic tinkering. With the massive failures in gene therapy of the 1990s all but forgotten, one of the biggest political footballs has become the assumed silver bullet of stem cell research.

There is no reason not to conduct any sort of genetic research; it will always provide information. However, geneticists are reductionists and, because of what they do, overly enamored of the “nature” side of the nature/nurture debate. Our recent breakthroughs in genetics, coupled with the politically rightward trajectory of the western world, has recently given “nature” hugely disproportionate emphasis. These cultural and political swings occur back and forth over time. But just as the political moderates are drowned out by the extremists on both sides, so are those of us pointing out that nearly all traits observed in biological organisms, including humans, are a result of the interaction of genetics with environment – the nature/nurture dichotomy is a myth.

The message is so at odds with the popular conception of weight loss — the mantra that all a person has to do is eat less and exercise more — that Dr. Jeffrey Friedman, an obesity researcher at the Rockefeller University, tried to come up with an analogy that would convey what science has found about the powerful biological controls over body weight…Those who doubt the power of basic drives… might note that although one can hold one’s breath, this conscious act is soon overcome by the compulsion to breathe…

Such dramatic statements certainly make for good copy. But what the story’s author, and perhaps interviewees failed to mention is the recent increase in average weight and obesity in both western and developing countries that has been well documented (as reported by the multinational Organisation for Economic Cooperation and Development):

…obesity rates have increased in recent decades in all OECD countries for which trend data is available. There remain however notable differences in obesity rates across countries. In the United States, the obesity rate among adults (30.6% in 2002) is the highest in OECD countries, followed by Mexico (24.2% in 2000) and the United Kingdom (23% in 2003). Obesity rates in Continental European countries are lower, but are also rising.

Are those with a genetic disposition for getting fat reproducing at a higher rate around the world than those who are thin? It is unlikely. And why are there lower obesity rates in other western nations and developing countries? There are several major correlates of obesity rates over time and space: fast food, television, and cars (Cheng, 2005), which tend to go together. But it is possible that car ownership alone is enough to cause the weight effect (Bell et al., 2002, from their abstract):

Our main outcome measure was current obesity status and the odds of becoming obese over an 8-year period. In 1997, 84% of adults did not own motorized transportation. However, the odds of being obese were 80% higher (p<0.05) for men and women in households who owned a motorized vehicle compared with those who did not own a vehicle. Fourteen percent of households acquired a motorized vehicle between 1989 and 1997. Compared with those whose vehicle ownership did not change, men who acquired a vehicle experienced a 1.8-kg greater weight gain (p<0.05) and had 2 to 1 odds of becoming obese.

Meanwhile, in European countries, not only do fewer people own cars than in the U.S., but people generally have a different relationship with food there too, tending much more to buy locally, non-mass produced food. The U.S.’s penchant for pursuing the efficiency of mass production may be brilliant in many contexts, but the industrialization of farms and food production is a disaster for human health. Forgetting the reliance on low-nutrition packaged food (no matter how much the label screams “healthy!” at you), we also have a system that, thanks to the U.S.D.A.’s grading system, which ignores nutrition and taste in favor of appearance, makes even “fresh” food unpalatable. It is no wonder that most Americans prefer Big Macs to string beans.

The genes/environment interaction is well known for many species of organisms, and can be referred to as “phenotypic plasticity.” For example, there is a species of caterpillar whose appearance depends on when it is born, either spring or summer. All caterpillars feed on oak trees, but in the spring they looks like oak flowers, while in the summer they resemble oak twigs. The difference is striking. There are no genetic differences between the two types – their form depends completely on diet, i.e. whether it consists of flowers or leaves (Greene, 1996). Similarly, there could be two people who both have the genetic disposition to be fat. One that lives a “western” lifestyle revolving around fast food, television, and automobiles, is likely to be fat. The other, living as a subsistence farmer in a town with no electricity and only bicycles and feet for transportation, is not as likely to be fat. Those without the genetic disposition for putting on fat would be thin under either condition.

The obsessive focus by some scientists and journalists on genetics, and by others on environment, is blinding us to the importance of the interaction of the two. Those in the media emphasizing exercise are well-intentioned, but misguided. Human bodies predisposed to putting on a lot of weight are probably not going to be much affected by an hour of “cardio” three or four times a week. We have to take a step back and imagine what it is our bodies are designed to do. In a non-technological world, our bodies are designed to walk – a lot. Some mammals are selected for lying around most of the time, with short bursts of speed and strength occurring at occasional intervals (e.g. lions and other large predators). Other migratory mammals, such as grazers, can keep up a moderate pace for a long time, but must spend a lot of their time eating because they eat a low-energy food.

What humans appear to be designed for is walking and running over long times and distances. There are legends of American Indian lacrosse games on miles-long fields lasting for days, and there was a time when native Mexicans were known for their extraordinary running ability (Dyreson, 2004). Some African hunters follow their game long distances for days. More examples can be found. But because humans are designed for locomotion by foot, “exercise” needs to be better defined. Getting your heart rate up once in awhile, with the great majority of the time being spent at rest, is simply not what humans are designed to do, and thus our bodies will not be in the proper balance of nutrient use vs. storage. Obesity research makes it clear that it doesn’t necessarily matter how many calories you burn while you are exercising. Weight is much more complex than “calories in, calories out.” A common big difference between those who are thin and those who are fat is that for the thin people, walking is incorporated to a much larger degree into their daily life.

What can someone living a western lifestyle do? I am not a dietitian or a doctor, but the research suggests that if you are someone who has a tendency to be overweight, whose diets work for a while but never for good, who has tried working out at the gym to no avail, the only way to lose weight over the long term is to make sweeping lifestyle changes, that include a lot of walking every day, in addition to periodically more strenuous exercise. I am not someone who is naturally thin. A post-pregnancy regimen that got me back into shape quickly was at least 4-5 miles of walking per day, usually weight(=baby)-bearing, plus more strenuous workouts 4-5 days a week (if I reduced that to just 3 days a week, it kept me in a holding pattern, but I didn’t make any progress on my conditioning).

Maybe you can’t walk to work from your house, but maybe you could find a place to park two miles away. But maybe your commute’s too long already, though, to add an hour and a half to it. Maybe you are spending so much time away from home, or it takes so much extra effort to find real food, that it seems unthinkable to prepare anything but pre-packaged foods. Unfortunately we have developed our way into a lifestyle corner that is not amenable to staying within the normal parameters for being human.

The media, government, and non-governmental organizations can talk about genes and diet and exercise until they are blue in the face. As long as we continue to build exurban communities with zoning that requires complete dependency on cars to do the briefest errand, often to the fast-food place which is much closer and more accessible than a local farmer’s market, a lot of people will continue to be fat. But despite the realities of modern U.S. life, if we do not find a way to change the policies that lead to these destructive lifestyles, we are dooming many of ourselves, and our children, to a lifetime struggle with health. Instead of living our lives, many more of us will be dealing with constant health problems, which all of us will pay for, one way or another. Fortunately in the U.S., it is truly possible to effect substantive change at the lowest local level. If we do not, Dr. Friedman, we only have ourselves to blame, genes be damned.

References

Bell, A.C., Ge, K., Popkin, B.M. (2002). The road to obesity or the path to prevention: motorized transportation and obesity in China. Obesity Research 10, 277–283.

Cheng, T.O. (2005) Fast food, automobiles, television and obesity epidemic in Chinese children. International Journal of Cardiology, 98, 173-174.

Dyreson, M. (2004) The foot runners conquer Mexico and Texas: Endurance racing, indigenismo, and nationalism. Journal of Sport History, 31, 1-31.

Greene, E. (1996) Effect of light quality and larval diet on morph induction in the polymorphic caterpillar Nemoria arizonaria (Lepidoptera: Geometridae). Biological Journal of the Linnean Society, 58, 277-285.

Stunkard, A.J., Harris, J.R., Pedersen, N.L. & McClearn, G.E. (1990) The body-mass index of twins who have been reared apart. New England Journal of Medicine, 322, 1483-1487.

Stunkard, A.J., Sorensen, T.I.A., Hanis, C., Teasdale, T.W., Chakraborty, R., Schull, W.J. & Schulsinger, F. (1986) An adoption study of human obesity. New England Journal of Medicine, 314, 193-198.

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