Posts Tagged ‘evolution’

It’s 10 O’Clock. Do you Know Where Your Genes Are?

October 5th, 2011

There was a very important story in the New York Times on October 4, 2011 about obesity but you are forgiven if you missed it.  The piece, by Nicholas Wade, tells the story of research on the histories of childbirths on an island in the St. Lawrence River, 50 miles northeast of Quebec. What they found was that the age at which women had her first child fell to 22 years from 26 years from 1799 to 1940. What did you miss? Well, it turns out that the age at which a woman has her first child is a highly heritable trait. And what this finding means is that humans are still evolving.  Statistical tests allowed the researchers to distinguish between the effects of natural selection and changes in cultural practices. Natural Selection Leaves Fresh Footprints on Canadian Island –

(Readers may recall that the above time-frame is not unlike that employed in The Techno-Physio Revolution, which documented the rise in body weight over 350 years.)

 Not only are humans still evolving but that evolution is occurring faster than many assume.  The DNA sequence can only identify large changes sweeping through a population. But phenotypic or bodily data can provide information on more recent changes.  Wade cites a review article of 14 studies. The lead author, Stephen C. Stearns of Yale,  stated, “We had three general aims: first, to correct the still widespread misconception that natural selection is not operating on contemporary humans; second, to make quantitative predictions about future evolutionary change for specific traits with medical significance; and third, to register firmly a point of general cultural interest that follows directly from our first two aims: We are still evolving, and for some traits we can make short-term predictions about our future evolution.” In this study, the authors found that the descendants of women in the Framingham Heart Study, begun in 1948, are predicted to be on average slightly shorter and stouter, to have lower total cholesterol levels and systolic blood pressure, to have their first child earlier and reach menopause later than they would in the absence of evolution. Colloquium papers: Natural selectio… [Proc Natl Acad Sci U S A. 2010] – PubMed – NCBI 

Jeffrey Friedman noted in the essay I quoted yesterday, “natural selection can be observed in a single generation as nature weeds out the maladapted under changing environmental conditions, leaving the more highly adapted individuals to proliferate. Thus, rapid changes in population characteristics are generally the result of a gene/environmental interaction.” 

What does this have to do with obesity? Well, in discussions about the genetic basis of obesity, skeptics often comment is often that increases in the prevalence of obesity (basically in the last 50 years) cannot be the result of genes because the gene pool or natural selection does not change that rapidly. Yet, evidence to the contrary continues to mount. While no one may be sure just how fast the genome is changing, it is probably inaccurate to say that it cannot change quite rapidly. 

Indeed, an examination of 23 studies reporting data from 14 different countries between 1998 and 2008, indicates a high prevalence of overweight and obesity in pre-school children age 2-5 years, in middle and high income countries, among both well-off and low income segments of populations, in both rural and urban areas and among all ethnic and racial groups represented. Global prevalence of overweight and obesity in… [Anthropol Anz. 2011] – PubMed – NCBI

The TechnoPhysio Evolution

June 8th, 2011

Book Review:    The Technophysio Evolution    

The Changing Body, Health, Nutrition, and Human Development in the Western World since 1700

 by Roderick Floud, Robert W. Fogel, Bernard Harris and Sok Chul Hong, (Cambridge Press, 2011)

The authors are distinguished economists (Fogel has a Nobel Prize in Economics). With dizzying detail, it traces the changes in the human body over the last 300 years in Britain, France and the United States. During this period, humans have become much taller and heavier than ever before. The book charts the “technophysio evolution,” a complex interplay between increasing technological changes and improved standards of living, resulting in improved nutrition. The improved nutrition is passed from mother to child to child with improvements in height and weight in successive generations. This is not a straight line but the trends are unmistakable – improved mortality with tall and heavier adults.

The Technophysio Evolution hypothesis has three elements:

  1. The nutritional status of a generation – shown by the size and shape of their bodies – determines how long that generation will live and how much work its members will be able to do.
  2. The work of a generation, measured both in hours, days, and weeks of work and in work intensity, when combined with the available technology, determines the output of that generation in terms of goods and services.
  3. The output of a generation is partly determined by its inheritance from past generations; it also determines its standard of living and its distribution of income and wealth, together with the investment it makes in technology.
  4. The standard of living of a generation determines, through its fertility and distribution of income and wealth, the nutritional status of the next generation.
  5. And so on, ad infinitum.

In other words, increasing body weight is a by-product of advances in wealth and income, producing healthier, i.e. larger children, who, in turn, produce better nourished, i.e., larger,  children.

The “techno” part of this evolution include everything from American colonists moving from a wooden plow to an iron one; improvements in food production and distribution, refrigeration, canning, changes in water, sanitation and public health which reduced mortality from infectious diseases while improving nutrition for more and more people.

The “physio” part incorporates research on the fetal origins of adult disease and will support the attention to epigenetics as an important aspect in the development of obesity. This is not purely genetics or genetic determinism but the process of transition of improvements in nutrition to the health of the mother and her survival as well as to the survival of more children for longer periods of time. Epigenetic changes is coming into focus as a critical stages for the development of obesity and will certainly receive more attention in the future. Epigenetic changes in early life and future risk o… [Int J Obes (Lond). 2010] – PubMed result

Is there an end to the process or is there a natural limit to this growth? Well, we don’t really know but none appears so far. (It seems to me, at least, that evolution has not felt it necessary to provide unlimited height of the species since there does not appear any survival value to being taller. On the other hand, nature has felt that there was a distinct survival value to being able to store energy (read fat) on our bodies and there does not seem to be a particular limit to this.)

by permission, Cambridge University Press


Interestingly, the authors find that, for American white males ages 40-59, the increase in BMI from 1870 to 1980 is less closely related to food consumption than to reduction of contaminated environments and work hours. “Not only have working hours,” they write, “declined substantially throughout the twentieth century, but the type of work became more sedentary, and so required less energy.” However, “The recent large increase of BMI in 1980-2000 (6 percent) is highly connected to increased food intake during the period (22 percent). (At p. 336) Further, they note the average BMI of American white males has increased by 15.7% throughout the 20th Century, half during the last two decades of the twentieth century. “This means that American body size is rapidly moving toward overweight and obesity.This would seem compatible with a new finding from Tim Church and colleagues at the Pennington Biomedical Research Center that in the 1960’s about half of jobs in private industry required at least moderate physical activity. That figure is now less than 20%. Over the last 50 years, occupational daily energy expenditure decreased from by 142 calories in men and a similar amount in women.  Trends over 5 Decades in U.S. Occupation-Related P… [PLoS One. 2011] – PubMed result

What are the policy implications of this Technophysio Evolution?

First, increases in body size are a product of 300 years improvement in technology, productivity and standards of living. This evolution began long before television, fast food, vending machines, sugar-sweetened beverages and other would-be villans in the obesity epidemic.

Second, the very same nutritional improvements which led to larger bodies in Europe and the United States are being actively pursued in undernourished parts of developed nations and throughout the developing world. This indicates greater and greater levels of obesity in the developing world with obesity related diseases.

Third, epigenetics needs to receive more attention as a point of intervention in the development of obesity.

Fourth, simplistic views that blame individuals and proclaim that just cutting back food  or going to the gym will fix the obesity epidemic.  Strategies which just repeat the ELEM mantra (Eat Less Exercise More) have to be questioned if those strategies are likely to affect this profound historical trend.

A few years ago, Gina Kolata, in her book, Rethinking Thin (Farrar,Straus and Giroux, 2007)  discussed the views of some obesity researchers that we are looking at a new stage in the evolution of the species. This tome adds significant evidence that our obesity strategies need to be re-thought to take this 300 year trend into account.

Book Reviews

October 4th, 2009

THE WORLD IS FAT by Barry Popkin (Aver, New York, 2009)

Barry Popkin is a highly respected obesity researcher and professor of Global Nutrition at the University of North Carolina, Chapel Hill. In this book has given us all an insight into his life’s work – understanding the spread of obesity throughout the world.

Popkin’s work is a reader-friendly effort to tackle our persistent, modern problems of obesity: How did we get to this state? What’s the role of the food and beverage industry? What are the influences of evolution and our genes on obesity, as well as food marketing. Specifically, how did the world so quickly change its consumption patterns from long-standing local cuisines to foreign, highly-packaged, highly processed foods. Where other authors have dealt with some of these topics in great detail, Popkin’s humanizes the issues by looking at four typical families in different parts of the world and observe the change in consumption and activity.

His statistics are staggering: the average American drinks sugar-sweetened beverages about 2.5 times a day. More than 450 of a person’s daily calories come from beverages – 40% from soft drinks or fruit juices and 20% from alcohol; a slice of pecan pie, about 500 calories, would take an average adult 2.5 hours of walking or an hour of vigorous aerobics to work off.

Reading Popkin, one wishes for more international studies as countries vary in areas such as TV viewing, food advertisements. He writes, “It isn’t possible to link changes in fast-food intake in these (developing) countries with increases in obesity. However, the shift toward on-the-go eating as opposed to the slower eating of the past is a profound change. The lack of conclusive research on how Western or local fast-food chains are affecting the quantity and quality of food and the overall weight gain is a sharp contrast to the very large number of studies on this topic in the United States.”

The entire world is experiencing what is called “nutritional transition” which involved changes in occupational, lifestyle, transportation as well as nutritional factors. However, there are definite social , cultural, racial and ethnic differences. Disentangling this complex web may well be beyond any one book and it is a shame that international research organizations have not done more to explore these differences. They represent a natural laboratory which is perhaps no longer feasible within the United States because we have so many confounding factors.

This nutritional transition is of nearly unprecedented dimensions, second maybe only to the discovery of cooking or the beginning of agriculture. No wonder Gina Kolata, in her book, Rethinking Thin, The New Science of Weight Loss and the Myths and Realities of Dieting (Farrar, Straus and Giroux, New York, 2007) observed, “Some scientists, including obesity researchers like Jules Hirsch and Jeff Friedman, suggest an intriguing hypothesis. The origin of people’s recent weight gains may have little to do with their current environment or with their willpower or lack of it, or with today’s social customs to snack and eat on the run or with any other popular belief. Instead, they say, we may be a new, heavier human race and our weight may have been set by events that took place very early in life, maybe even prenatally.”

Popkin is active not only in research but in numerous governmental and non-governmental agencies across the globe trying to find strategies to affect global obesity. He offers numerous anecdotes on the efforts of these groups to find solutions. But one comes away with the view of our genetic preferences for sweet and salty foods combining with a vast industrial agricultural process fueled by aggressive and effective marketing creating a tsunami of obesity which is engulfing the world. In the end, one wishes Popkin will go on and explore the development of obesity around the world in even more depth to help us find a way out.

THE EVOLUTION OF OBESITY by Michael. L Power and Jay Schulkin, (Johns Hopkins University Press, Baltimore, 2009)

If Popkin’s book is for the general reader, this tome by Power and Schulkin is for the serious student of evolutionary biology. Popkin gives a chapter to the evolution of the modern diet; these authors give 13. They, senior researchers at the American College of Obstetricians and Gynecologists, take the long view.

Some may wonder why researchers at the home of obstetricians and gynecologists should be addressing obesity. They should not wonder. Body weight is highly regulated to be ‘just right.” Either extreme – underweight or obesity – creates problems for reproduction and survival. As a species, our bodies are interested in surviving to pass on our genes to the next generation and extreme variations in weight impede this genetic imperative.

For those confused about stories on mortality and overweight, the authors clarify that human babies are among the fattest of all mammals and this may have conferred a key support to our survival. Extra fat confers some benefits for mortality but increases other risks. But the authors definitely do not argue that obesity per se was adaptive. They argue, convincingly in my view, that “human obesity is an inappropriate adaptive response to modern living conditions.” And, “Adipose tissue is an endocrine organ whose natural function allows it to greatly increase in size; adipose tissue is meant to be variable. However, the extent of adiposity that is possible in today’s world exceeds the normal adaptive range of endocrine and immune function.”

For those who think that there is a simple answer to obesity …eat less, exercise more…this book will not provide support. The authors note, “Energy intake and energy expenditure are simple concepts in principle but very complex in actual physiology. The simple solution for weight loss, eat fewer calories and expend more, can be very difficult to achieve, for good metabolically adaptive reasons.”

But their main thesis is that fat is important both in our diets and in our bodies which likely arose in order to support the development of larger brains. “This hypothesis, “ they aver, “explains our fat babies, which explains the tendency for women to put on more fat than men do. “

The general reader may find this book too detailed but for the serious student of obesity it is a unique resource of research on every aspect of obesity in both human and animal subjects.

My only problem with the book is that they minimize the chances for drugs to treat obesity given the complexity and redundancy of the biological system to preserve body weight. They note and, given the history of obesity medications it is hard to refute them, that, “ The complexity of an evolved biological system suggests that most simple molecular interventions will have multiple unintended consequences and may trigger compensatory metabolic systems.” Fair enough. But don’t medications for blood pressure control, control of blood glucose or many other drugs have similar complexities to deal with? Why would a drug to decrease excess adiposity seem infeasible when we have several s drugs which increase adiposity? And if bariatric surgery apparently results in long term and significant weight loss without the expected unintended consequences why can’t we find the mechanism and build a drug to do the same thing?

The science is changing so fast in this area that we only hope that this is the first of a series of books allowing us to understand what is happening in our world, and our bodies.

THE END OF OVEREATING by David A. Kessler, MD (Rodale, 2009)

David Kessler’s tenure as the commissioner of the Food and Drug Administration (under Presidents George H.W. Bush and Bill Clinton), where marked by great leadership in the efforts to combat tobacco smoking.

The book should be looked at, as with Caesar’s description of Gaul, as coming in three parts. In the first part, Dr. Kessler explores the evolutionary preference humans have for sweet, fatty and salty foods.

In the second part, he deals with the food industry’s ability to take advantage of these natural likings now part of our brain patterns. The skilled, finely honed marketing machines are derided and blamed for forcing us into what Dr. Kessler calls, “conditioned hypereating” resulting in obesity.

Before you know it, the weight has piled on and your diets have all failed. Just before you throw up your hands in surrender at the nearest Cinnabon, the good Dr. Kessler has a remedy…his trademarked Food Rehab tm diet – the third phase of the book.

On page 207, the good Dr. Kessler states, “The elements of the Food Rehab tm program here have been used and tested in other contexts and still need to be rigorously evaluated for the treatment of “conditioned hypereating. “Nonetheless, I believe they can offer you some help.” The help the Food Rehab tm diet provides is “to change the way you eat.”

Let’s stop here. First, does Dr. Kessler have a reference for ‘tested in other contexts?” Well, no. Even the food companies first test a product in the lab. Shouldn’t a respected physician do the same?

For the statement “change the way you eat,” there is a citation to an abstract by Gary Foster, Ph.D, which states that, “cognitive behavioral therapy achieves about a 10 percent weight loss over twenty to twenty-four weeks with patients regaining one-third of their weight at the one-year mark.” This is left out of the main text. Isn’t this the same failed diets he just decried?

By going down the path of a “new” diet plan, Dr. Kessler has forgone the opportunity to make a real contribution to exert the kind of leadership he showed with smoking for the obesity issue. Many people feel smoking and obesity are parallel conditions and many believe that the tools which were successful in smoking cessation can work in obesity. Others note profound differences between the two problems and doubt that all of the solutions to smoking are likely to work in obesity.

Although he doesn’t know it, Dr. Kessler and I crossed paths on this topic – at least on paper. In 1999, the Internal Revenue Service reversed position and allowed the costs of smoking cessation programs to be deducible as a medical expense. In my position at American Obesity Association, I wrote a letter to the IRS asking that they also reverse their policy on not allowing the costs of weight loss to be deductible which had been issued about the same time as the smoking cessation ruling.

The IRS wrote back and said what evidence they would need to reverse their ruling. But they also said that we could not rely on their smoking cessation ruling because nicotine was addictive and cited an extremely influential study Dr. Kessler had written on the subject. (Kessler, DA, et al, The Legal and Scientific Basis for FDA’s Assertion of Jurisdiction Over Cigarettes and Smokeless Tobacco, JAMA, 1997;277:405-409)

In this paper, Dr. Kessler established that nicotine is a psychoactive (mood-altering) product and that nicotine “plays a role in weight regulation, with substantial evidence demonstrating that cigarette smoking lead to weight loss.” So I told the IRS that, on the basis of this argument, we were not going to argue that eating was addictive, but they could not argue it isn’t. (At the end of the day, we got the IRS to reverse its policy.)

Since then there has been a new research on the brain activity in smoking, obesity and alcohol consumption. Brain serotonin 2A receptor binding: relations to …[Neuroimage. 2009] – PubMed Result. Another study found, in rats, the nicotine exposure prenatally affected endocrine development and led to obesity. Prenatal nicotine exposure alters early pancreatic…[Endocrinology. 2008] – PubMed Result

There are so many questions relating to our understanding of smoking, nicotine addiction and obesity that it is a shame not to have Dr. Kessler’s expertise help lead us out of this quagmire.

CATCHING FIRE: HOW COOKING MADE US HUMAN by Richard Wrangham (Basic Books, New York, 2009)

This brilliant and readable book offers a new hypothesis about evolution of humans and the role of cooking and meal preparation. Wrangham is a professor of biological anthropology and this book shows his facility with the biological evolution of animals in general and primates in particular. More importantly, this book has several important insights into the evolution of obesity.

Briefly, Wrangham argues, pretty successfully in my opinion, that the shift from raw to cooked foods was the key factor in human evolution. Briefly, when early man began using fire, humanity started.

The process he lays out is fascinating. Once Homo Habilis (a chimpanzee like primate) evolved in to Homo Erectus, the species could shrink its digestive system, allowing humans to grow greater brains. Getting the gut to shrink depends on moving from raw food to first pounded meat and then to cooked food which were more pleasurable and digestible. This let early humans to lose tree climbing skills but gain speed in running. Speed in running allowed these first humans to run off predators who quickly overheated because of their body fir. Humans could lose body hair because fire helped them keep warm. Cooking also brought on the division of labor between men and women but promoted male-female bonding, created the household, and even led to the development of nicer people.

There are a couple of interesting aspects of this anthropological view of obesity. Wrangham devotes a fair bit of space to taking on the raw-food advocates. This movement tries to urge people to ‘return’ to the Paleolithic diet which stresses eating raw fruits and vegetables and less grain, beans and potatoes as well are refined or processed foods. Wrangham points out that, in the three studies of raw food consumption, a significant amount of body weight was lost. But there was a price. Constant feeling of hunger was one. The other was such serious energy depletion that fully half of the women in the studies stopped menstruating. Wrangham argues that a primitive society could not have sustained such depletions of energy. Further, he points to studies showing that most animals prefer cooked over raw foods.

Another interesting aspect of the authors work is that soft foods lead to an increase in obesity because fewer calories are burned in the digestive process than is the case with harder foods. (p.77)

He also express support for a more rapid change in evolution than many believe. He notes, “ response to a major change in diet, species tend to exhibit rapid and obvious changes in their anatomy. Animals are superbly adapted to their diets, and over evolutionary time the tight fit between food and anatomy is driven by food rather than by the animal’s characteristics.” (p.89) Later, he cites the Grants studies of finches in the Galapagos to indicate that, if the ecological change is temporary, the changes in the species’ anatomy are also temporary. But if the ecological change is permanent, “the species also changes permanently, and again the transition is fast.” (p.93) (The work of the Grants was brilliantly described in the Pulitzer Prize winning book, “The Beak of the Finch: A Story of Evolution in our Time” by Jonathan Weiner.) He goes on to state, “The adaptive changes brought on by the adoption of cooking would surely have been rapid. “(p.94)

Further, he describes that shrinking the gut increases the size of brain and therefore intelligence. But some animals do not evolve into larger brains. Why? He answers, “Diet provides a major part of the answer…For an inactive person, every fifth meal is eaten solely to power the brain. Literally, our brains use up around 20% of our basal metabolic rate – our energy budget when we are resting – they though they make up only about 2.5 percent of our body weight. “ (p.109)

In his last chapter, Wrangham has some disquieting news for calorie-counters, the foundation of most all weight loss strategies. Wrangham goes through in some detail how Wilbur Olin Atwater came up with the caloric content of protein, fats and carbohydrates and then specific foods. And he documents the refinements in the Atwater system. The formula attributes protein with 4 calories, fats 9 and carbohydrates 4 per gram.

Wrangham spots two problems. First, the Atwater system does not recognize the energy-cost of digestion. Although humans pay less in calories for digestion than other species, it is still significant and can be reduced or increased depending on the food type: protein costs more to digest than carbohydrates and fat has the lowest digestive cost of all. He cites a 1987 study in which people eating a high-fat diet had the same weight gain as others eating almost 5 times the number of calories in carbohydrates. Also, he notes, “ Based on animal studies, we can expect that the costs of digestion are higher for tougher or harder foods than softer foods; for foods with larger rather than smaller particles; for food eaten in single large meals rather then in several small meals; and for food eaten cold rather than hot. Individuals vary too. Lean people tend to have higher costs of digestion than obese people. Whether obesity leads to a low cost of digestion or results from it is unknown. Either way, the variation is important for someone watching his or her weight. For the same number of measured calories, an obese person, having a lower digestive cost, will put on more pounds than a lean person. Life can be unfair.” (p.203) (Thanks doc, we needed that.)

Take away: nutrition scientists know the current calorie information is wrong; but it is too expensive and difficult to fix it. Net for dieters: You’re screwed – even the most rigorous calorie counter is doomed to a high error rate. Wrangham concludes, “The data in standard nutritional tables assume that particle size does not matter and that cooking does nothing to increase the energy value of foods, when abundant evidence shows the opposite to be true…We become fat from eating food that is easy to digest. Calories alone do not tell us what we need to know.”(p.205)

Overall, this is an exciting read. I know of only one other book by anthropologists on obesity (Fat, The Anthropology of an Obsession edited by Don Kulick and Anne Meneley, Jeremy P. Tarcher/Penguin, 2005) . These works show the valuable contributions to obesity we can look forward to from the work of many disciplines.

Genetic Basis of Obesity

September 26th, 2009

Often one hears it stated that obesity is not a genetic disease. If by that the speaker is saying that obesity is probably not due to a single genetic change they are not quite right. There are some rare forms of obesity which are due to a single gene change. Genetic obesity syndromes. [Front Horm Res. 2008] – PubMed Result; Genetic and hereditary aspects of childhood obesit…[Best Pract Res Clin Endocrinol Metab. 2005] – PubMed Result But if they mean a single genetic change cannot account for a worldwide epidemic of obesity occurring over the last 30 years they are probably right. If the speaker means it is unlikely that there will be a treatment for obesity based on gene therapy, they are probably correct. (Although who can predict the future?) However, they miss the point if they do not understand that for millions of years of evolution, the species we call humans have favored genes which maximize its chances for survival and reproduction. So our taste preferences, our physical activity preferences and the like are passed on in the genome and our part of our inheritance. The problem is that for centuries we humans lived in an environment which was totally different than the one we live in now. The disconnect is that our bodies have not yet adapted to this new world where tasty, nutritious food is readily available and where most of us do not have to expend anything other than a minimal effort to obtain it, survive and flourish. Anything policy-makers or parents want to do about obesity must be understood in the context of the powerful force evolution has been in designing how humans acquire, store and use energy from food.

According the CDC:

  1. Biological relatives tend to resemble each other in many ways, including body weight. Individuals with a family history of obesity may be predisposed to gain weight.
  2. Different responses to the food environment are largely due to genetic variation between individuals.
  3. Fat stores are regulated over long periods of time by complex systems that involve input and feedback from fat tissue, the brain and endocrine glands like the pancreas and the thyroid.,
  4. The tendencies to overeat and be sedentary, the diminished ability to use dietary fat as fuel and enlarged, easily stimulated capacity to store body fat are all genetically influenced. The variation in how individuals respond to the food rich environment and the differences in acquiring obesity related comorbid conditions are also genetically determined.

Since 1997, published studies have found that variation in BMI is largely due to heritable genetic differences, with estimates ranging from 55% to 85%. A 2008 study found that 77% of the adiposity in preadolescent children born since the start of the obesity epidemic was due to genetic inheritance compared to 10% for the environment. Evidence for a strong genetic influence on childho…[Am J Clin Nutr. 2008] – PubMed Result

A fast rate of eating appears to be heritable. Eating rate is a heritable phenotype related to we…[Am J Clin Nutr. 2008] – PubMed Result Differences in responding to the obesogenic environment may also be heritable Genetic influence on appetite in children. [Int J Obes (Lond). 2008] – PubMed Result and Appetite is a Heritable Phenotype Associated with …[Ann Behav Med. 2009] – PubMed Result. The FTO gene may be involved. The FTO gene and measured food intake in children. [Int J Obes (Lond). 2009] – PubMed Result and Increasing heritability of BMI and stronger associ…[Obesity (Silver Spring). 2008] – PubMed Result Parental leanness appears to provide strong protection against the development of obesity in children. Development of overweight in children in relation …[Obesity (Silver Spring). 2009] – PubMed Result

There is an interesting scientific debate about what is called the “thrifty gene” hypothesis about how a genetic preference for storing extra energy on our bodies might have developed. Thrifty genes for obesity, an attractive but flawe…[Int J Obes (Lond). 2008] – PubMed Result and The clinical biochemistry of obesity. [Clin Biochem Rev. 2004] – PubMed Result. Some think that childhood obesity is increasing due to ‘associative mating’ by overweight parents who pass on their genetic disposition to obesity to their children. Childhood obesity: are genetic differences involve…[Am J Clin Nutr. 2009] – PubMed Result

The evidence for the genetic basis of obesity, in addition to environmental changes is quite strong. See Implications of gene-behavior interactions: preven…[Obesity (Silver Spring). 2008] – PubMed Result; Genome-wide association scan shows genetic variant…[PLoS Genet. 2007] – PubMed Result and The genetics of obesity. [Metabolism. 1995] – PubMed Result

The environment is thought to be responsible for variations between populations but genetics is responsible for the variations within a given population. Obesity – Missing Heritability and GWAS Utility and Genetic and environmental factors in relative body…[Behav Genet. 1997] – PubMed Result. Genetics may account for many cases of morbid obesityFamilial aggregation of morbid obesity. [Obes Res. 1993] – PubMed Result.

Genetics may play an important role in determining who can benefit from different types of intervention. Implications of gene-behavior interactions: preven…[Obesity (Silver Spring). 2008] – PubMed Result or who is more likely to be affected by obesity Ethnic variability in adiposity and cardiovascular…[Int J Epidemiol. 2009] – PubMed Result. Or experience a comorbid condition like Type 2 diabetes Mechanisms of disease: genetic insights into the e…[Nat Clin Pract Endocrinol Metab. 2008] – PubMed Result

The FTO gene is currently under active research interest for providing a link to how obesity related conditions might arise and how patients can benefit from this knowledge. FTO: the first gene contributing to common forms o…[Obes Rev. 2008] – PubMed Result Genome-wide association scan shows genetic variant…[PLoS Genet. 2007] – PubMed Result

The FTO gene may explain different responses to exercise. FTO Genotype Is Associated With Exercise Training-…[Obesity (Silver Spring). 2009] – PubMed Result .Physical activity and the association of common FT…[Arch Intern Med. 2008] – PubMed Result

A factor in the resistance to describe obesity as a genetic disease may be in the assumption that the human genome does not change rapidly whereas the increase globally in the rates of obesity have occurred in the last 40-50 years. However, evolutionary biologists are debating the speed of genetic change. In “Catching Fire, How Cooking Made us Human” (Basic Books, New York, 2009) Richard Wrangham, the Ruth Moore Professor of Biological Anthropology at Harvard University writes,

A long delay between the adoption of a major new diet and resulting changes in anatomy is also unlikely. Studies of Galapagos finches by Peter and Rosemary Grant showed that during a year when finches experiences an intense food shortage caused by an extended drought, the birds that were best able to eat large and hard seeds – those birds with the largest beaks- survived best. The selection pressure against small-beaked birds was so intense that only 15 percent of birds survived and the species as a whole developed measurably larger beaks within a year. Correlations in beak size between parents and offspring showed that the changes were inherited. Beak size fell again after the food supply returned to normal, but it took about fifteen years for the genetic changes the drought had imposed to reverse. The Grants’ finches show that anatomy can evolve very quickly in response to dietary changes…Other data show that if an ecological change is permanent, the species also changes permanently, and again the transition is fast…The adaptive changes brought on by the adoption of cooking would surely have been rapid. (p. 93-94, emphasis added.) (See Book Reviews)