Understanding obesity: genes and environment

Caitlin Mouri
23 January 2013

Above: Obese man (©iStockphoto.com/selimaksan)

Did you know? Leptin is a hormone that decreases food intake, increases metabolism, and stimulates physical activity. Leptin is released by fat cells, so it can help compensate for eating too many high-fat foods.One of the major health issues facing humanity today isn't caused by microbes or parasites. Pills and vaccines designed to treat or prevent the condition have yet to achieve any long-term success. And it’s been linked to a host of other health problems, including high blood pressure, diabetes, and cancer. The culprit is obesity, and its causes lie both in our genes and our environment.

At the most basic level, weight gain is the result of an imbalance between energy intake and energy use. We take in energy by consuming food. Energy is used up by our metabolisms and through physical activity. When we consume more energy than we use, it gets turned into fat. Simple, right?

As it turns out, keeping our food intake and energy use balanced is a complicated process. Food intake is controlled by signals sent to and from our brains. Whether we're hungry or full, active or at rest, our bodies are constantly sending messages in the form of nerve signals and hormones. These messages tell us when to seek out more food and when to stay put. When we find something to eat, our brains also tell us if the food is good, and when we've had enough.

Did you know? Fat is one of the three main macronutrients. The other two are carbohydrates and proteins.Our brains have evolved over millions of years to respond differently to fat than to other types of food. Fat leaves a pleasant feeling in our mouths, which makes us want more. And, unlike carbohydrates or proteins, fat is less likely to make us feel full. There's a good reason for this. Fat contains more energy than protein or carbohydrates, and it provides an excellent way of storing extra energy.

This preference for fat has a lot to do with genetics and natural selection. Although too much fat can be a bad thing, fats are an essential part of the human diet. They are a good source of energy, they aid in normal development, and they help with absorbing vitamins and minerals. In times when food was harder to come by, the taste for fatty foods helped humans collect and store as much high-energy nourishment as possible. Individuals who were better at storing fat survived through hard times, and passed their genes on to the next generation.

Did you know? The best way to prevent obesity is to stay active! Take the stairs instead of the elevator, walk to the market instead of driving, or pick up an active hobby that you can enjoy.But in present-day industrial societies, where we can easily satisfy our hunger with french fries and donuts, too much fat puts us at risk for a variety health problems. This is because plentiful high-fat food provides us with way more energy than we actually need. And this is where our environment comes into play. When we rely on cars for transportation and television for leisure, we become less active. And when we don't exercise, our bodies keep our fat safely tucked away for a rainy day. So for those susceptible to weight gain, contemporary life can increase the risk of obesity.

What can be done about this growing problem? In the future, weight-loss programs may be able to use genetic information to create personalized diet and exercise regimes, tailored to each person’s genetic make-up. Indeed, as we learn more about the interaction between our genes and our environment, genomics-based treatments for obesity, as well as other diseases, may become common.

Learn More!

Healthy Living: Obesity (Health Canada)

http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/life-vie/obes-eng.php Obesity in Canada (Public Health Agency of Canada)

http://www.phac-aspc.gc.ca/hp-ps/hl-mvs/oic-oac/index-eng.php Macronutrients: the Importance of Carbohydrates, Protein, and Fat (McKinley Health Center, University of Illinois)

http://www.mckinley.illinois.edu/handouts/macronutrients.htm Tips for Getting Active (National Heart, Lung and Blood Institute)


Other References

World Cancer Research Fund American Institute for Cancer Research. 2007. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. AICR, Washington DC.

http://eprints.ucl.ac.uk/4841/1/4841.pdf World Health Organization. 2000. Obesity: Preventing and Managing the Global Epidemic. Report on a WHO Consultation. Technical Report Series, no. 894. Lenard, NR, Berthoud, HR. 2008. Central and peripheral regulation of food intake and physical activity: Pathways and genes. Obesity. 16:S11-S22.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2687326/ (link to author manuscript) Chung, WK, Leibel, RL. 2008. Considerations regarding the genetics of obesity. Obesity. 16:S33-S39.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2682366/ (link to author manuscript) Ordovas, JM. 2008. Genotype-phenotype associations: Modulation by diet and obesity. Obesity. 16:S40-S46

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2771769/ (link to author manuscript)

Caitlin Mouri

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