Causes of Obesity

excercise scriptTheories for the causes of this epidemic are multiple and complex, and influence is as much by culture and bias, as hard science.  These range from those who claim that obesity is a result of simple gluttony and laziness to those who claim a genetic or even an infectious cause. The truth is that multiple behavioral, environmental, genetic and metabolic factors combined produce a propensity toward becoming overweight.

A brief description of each of these follows:

Genetic Factors

There is no question that genetics play a large role in the tendency to gain weight.  For example:

  • The bodyweight of adopted children shows little correlation with that of the adoptive parents who raised and taught them how to eat.  However, their weight does have an 80% correlation with the genetic parents, whom they have never met.
  • Identical twins with the same genes show a much stronger similarity in bodyweight than fraternal twins who have different genes.
  • Certain people groups, such as the Pima Indians tribe in Arizona, have a very high incidence of severe obesity.  The National Institutes of Health has been studying this particular group for many years and have formulated what is called the Pima Paradox.
  • There are two groups of Pima Indians: one living in Arizona and the other in Sierra Madre, Mexico.   The Mexican Pima have low rates of obesity, while those in Arizona suffer from obesity rates among the highest in North America.  Both consume similar amounts of calories, however while the Mexican Pima practice a traditional lifestyle consisting of a low-fat diet and 23 hours of physical labor per week, the Arizona Pima live like most other modern Americans, consuming diets consisting of approximately 40% fat and engaging in only about two hours of activity per week.  The leading theory is that after many generations of living in the desert, the most successful Pima were those who were able to store as much fat as possible, thus providing a survival advantage in times of famine and drought.  However, these fat-storing genes are now working against them, thus the Pima Paradox.  The Pima Indians apparently have a genetic predisposition to gaining weight and when confronted with a typical modern American lifestyle, it is nearly impossible for the Arizona Pima to maintain a healthy weight.  However,  a genetic predisposition certainly does not completely explain the prevalence of obesity in America, and other factors are certainly quite apparent.  Most profoundly the environment which modern American culture has created has led to profoundly unhealthy lifestyle habits, as is explained further below.


In addition to what is genetic propensity, the environment in which we live and the choices we make are linked to our weight.  Our environment is linked to (although does not need to dictate) behavior.  To understand its influence on the obesity epidemic, one must compare today’s American lifestyle with that of long ago.  At the turn of the century, 80% of Americans lived on farms and consumed a diet of fresh vegetables, meat and dairy.  Daily life consisted of primarily physical labor and meals were prepared and consumed at home.  Obesity rates at that time were approximately 10% nationwide and further, the United States ranked #1 in the world in life expectancy.

In the last 100 years a dramatic shift has occurred, such that the typical American lifestyle consists of little activity, coupled with a dramatic increase in the consumption of processed, poorly nutritious, calorically dense foods.

We have become the wealthiest and most prosperous nation on Earth; ironically we now rank 24th (last among industrialized nations) in life expectancy.  Many experts believe this can be traced directly to our habits, especially our diet.  In fact, many of us are so consumed in it that we don’t even realize the problem has become.  Many experts hold that our bad habits are literally killing us.


Listed below are several facts which illustrate this point.

  • fast_food_killsOnly 19% of American adults engage in a high level of physical activity, and only 12% exercise regularly.  In fact, 60% of Americans get little or no exercise and 70% are not regularly active during their leisure time.  Notably, the Department of Health and Human Services recommends approximately 150 minutes of moderately intense aerobic physical activity weekly.  Very few Americans accomplish this.
  • Over 70% of the foods produced in the United States is now refined or processed.
  • Americans eat an average of 90-100 (25 ounces) grams of meat daily, when we only need 25-50 grams (4 ounces).
  • fast food warningIn 2005, Americans spent $140 billion in fast food.  This is compared to $6 billion in 1970.  In fact, the average American eats over 50% of their meals at fast food restaurants.  Even more impressive, McDonald’s services over 25% of the U.S. population daily.  Indeed, studies have found an association between the expansion of the fast food industry and America’s increasing BMI.
  • There are 85,000 fast food restaurants in the United States and fast food currently accounts for 12% of the American diet.
  • The average American consumes around 3,700 calories a day, with the recommended daily allowance of 2,000 – 2,200.  Notably, there is approximately 3,500 calories in a single pound of fat.
  • fast-food-statsAmericans consume 3-4 times the amount of added sugar recommended by the FDA.  In fact, high fructose corn syrup, the primary additive in sweetened drinks has increased 1000% since its introduction in 1967 and now adds, on the average, more than 300 calories per day to the American diet.
  • A recent study from the Journal of Food Consumption and Analysis revealed that three food groups, sweets, desserts and soft drinks, account for approximately 25% of all calories consumed by Americans.  Salty snacks and fruit flavored drinks make another 5%, bringing the total energy contributed by nutrient poor foods to at least 30% of caloric intake.
  • Another study of 4,760 adults in 1999 revealed that the top five food items consumed were soft drinks, pastries, hamburgers, pizza and potato chips.  In contrast, such healthy foods as vegetables and fruit make up only 10% of the calorie intake in the U.S. diet.

Given these statistics, it is really no wonder there is an obesity epidemic in our country. In fact, one would wonder why the problem isn't even worse than it really is. 


It used to be thought that weight gain or loss was simply a function of “calories in” versus “calories out”.  While that basic concept remains to be true (and is paramount to the success of weight loss surgery), it is much more complex than simple arithmetic.

Obesity researchers now refer to the “set point” theory of body weight.  This is the idea that there is a sort of thermostat in the brain which makes one resistant to weight change.  If one tries to override that set point, the body responds by lowering metabolism and becoming and becoming more “efficient”.  Therefore, weight loss slows and once efforts to restrict calories are stopped, the weight comes back.  This helps explain why medical weight loss (or dieting) routinely produces approximately 10% excess weight loss, plateaus, and then ultimately fails.  Weight regain is experienced in 95-100% of individuals. 

There is only one known way to offset this normal physiological process and that is by revving up the metabolism on a daily basis with consistent, vigorous exercise (see Medical Weight Loss – Exercise).

Lessons Learned

  1. Understand obesity is a chronic disease process that while manageable will never be cured.  This will be a daily battle for the remainder of your life.
  2. Understand that in order to lose weight and keep it off, it will require a radical and permanent change in behavior and environment.
  3. Understand that you will need to make specific and focused efforts to raise your metabolism on a daily basis in order to lose weight and keep it off.  In other words, you need to exercise regularly and daily – no excuses if you want to guarantee success.