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Genetics and Weight Loss

When we look at people who are overweight today, they tend to have immediate families that are overweight. However, all of their great-great-grandparents were almost certainly of normal weight. If their ancestors could be lean with identical genetic material, the cause of their weight gain must be in their current environment. It must be something to which only certain people are susceptible, just as some of us can have a fatal allergic reaction to a small amount of peanuts.¹ Genes protect some of us, but not most of us, from being affected.

While genes are a major enabler of weight gain, genetic change cannot be the cause. Up until the beginning of the twentieth century, less than 1% of Americans were severely overweight. Today that number is closer to 34%. There is no theory which suggests how the human genome could evolve rapidly enough to account for such a major change in the population. Furthermore, for evolution to be a cause of the increase, being overweight would need to give some type of evolutionary advantage. In fact, this is not the case. Being overweight is associated with health problems including decreased fertility.²

The Real Role of Genetics in Weight Gain

Human genetics cannot explain the over 3,000% increase in the number of Americans who have become severely overweight since the beginning of the twentieth century, but they may be able to explain why scientists have had such a hard time identifying the real culprit. To study what causes weight gain, scientists want to look at the actions of a group of people over time, see who gained weight, and figure out what they did differently from those who did not gain weight. But what if some people in our group are not going to gain much weight no matter what they do because of a genetic variation they have? To complicate matters, what if that genetic variation occurs at different rates in different countries?

The genetic disparity in the way various groups react to specific factors in their diet takes away one of the most useful tools researchers have. The Western diet is associated with weight gain wherever it becomes more prevalent. When immigrants from low weight countries move to the U.S., those who keep their traditional diets remain lean, while many of those who adopt the American diet gain weight.

The components of the Western diet include refined grains, sugars, red meat, vegetable oils, dairy products, coffee, and soft drinks. Since scientists know that this diet is associated with weight gain, one of the first things they try to do when studying the obesity level of a country’s population is to examine its consumption of each of these parts of the diet, in order to try to figure out which cause weight gain. However, this approach does not work. For each of these components, there are countries where consumption is very high but people are very thin. The same is true of different groups within the United States. We all know people who “can’t get fat.” This observation has scientific backing. Estimates for the importance of genetics in predicting obesity in the United States have ranged as high as 85%.

Because we are in only the very early stage of understanding the effects of our genetic variations, scientists are unable to genetically screen out from their studies the people who cannot easily become overweight. If we could do such screening, it would be relatively easy to look at the differences in diet between lean people and those who have become overweight, without the confusion caused by any genetic factors that keep people thin despite their diet.

Studies of identical twins can eliminate genetics as a factor in obesity, but they have been performed to only a small degree. It is not easy to follow large numbers of twins for a long enough period of time to be able to see differences in their diets and diet outcomes. It is easier to try to understand the mechanism causing genetically predisposed people to become overweight. For the data we have, comparisons are going to help us only when we look at the same country over time.³

In addition to confounding scientists, the idea that genes, by themselves, cause weight gain has done a lot of damage to individuals. If you think your weight problems are genetic, that is akin to saying that they are beyond your control, and it can stop you from believing that it is in your power to find a solution. Even if you are overweight, barring a rare genetic disease that you would probably be aware you had, all of your ancestors were extremely lean until about a hundred years ago. There is a set of circumstances that will make you thin as well.

Over the last 150 years, there have been enormous changes in our environment. A large number of us have become overweight in response to these changes, but many of us have genes that have protected us from gaining weight. Since people have never before lived in a period in which large numbers have gained weight, these genes must have developed for another reason, and they must have some other function. After all, we can’t develop a new gene and spread it to a large part of the human race in a hundred years, so any such gene which exists would have to also perform another function. Scientists have not yet established with certainty what the function is, but we will see a possible explanation later.

Ethnicity and Weight Gain

One identifiable genetic trait that corresponds to our ability to gain weight is ethnicity. After adjusting for income level, education, and diet, there are still variations among ethnic groups in the United States that can be explained only by genetic differences.⁴

Comparing residents of Japan and Japanese Americans allows us to observe this relationship. According to the 2008 Central Intelligence Agency World Factbook, Japan’s populace has the longest life expectancy of any major country. Only Andorra, with a population of 70,000, has a slightly higher life expectancy. Japanese born today are expected to live 82 years, compared to 78 years for people born in the United States today. In addition, the Japanese have the lowest rate of people in the developed world who are severely overweight, at about 3% in 2005, according to the Organization for Economic Cooperation and Development Factbook. This was over 90% less than in the United States in the same year.

One explanation for this could be that genetics are largely or entirely responsible. The Japanese and American populations are ethnically different, and all of the East Asian countries have lower rates of obesity than ethnically European countries. There is an easy way to test if this is true, and that is to look at Japanese immigrants to the United States. What we find is that as Japanese immigrants adopt the American diet, they tend to gain weight. In fact, even in Japan, people are gaining weight as Western food becomes more prevalent. However, the Japanese in Japan and Japanese immigrants in the United States remain thinner than many other ethnic groups.⁵

This tells us that, even if genes are partially responsible, there is something in the American diet which is not so prevalent in the Japanese diet which causes weight gain in people who have that genetic predisposition. If we can identify this substance and remove it, we should be able to eliminate the modern problem of obesity. Since obesity has been linked to an assortment of chronic health problems, we may even start to live as long as the Japanese.

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Citations:

¹Powell, Alvin. "Obesity runs in families - and friends, too." Harvard University Gazette. 4/04/2009 http://www.news.harvard.edu/gazette/2007/03.08/09-obesity.html.

² Lucas, Michael. "Obesity may decrease men’s fertility, a new study suggests." HeatlhHype.com. 4/04/2009 http://www.healthhype.com/obesity-may-decrease-men%E2%80%99s-fertility-a-new-study-suggests.html.

³ Yang, Wenjie . "Genetic Epidemiology of Obesity." Epidemiologic Reviews. 4/04/2009 http://epirev.oxfordjournals.org/cgi/content/abstract/29/1/49.

⁴ Fernández, José R. "Using Genetic Admixture to Study the Biology of Obesity Traits and to Map Genes in Admixed Populations." Nutrition Reviews. 4/03/2009 http://www3.interscience.wiley.com/journal/120843214/abstract?CRETRY=1&SRETRY=0.

⁵ Kovacs, Jenny. "Diets of the World: The Japanese Diet." WebMD. 4/04/2009 http://www.webmd.com/diet/features/diets-of-world-japanese-diet.

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