Causes of the Obesity Epidemic in the United States; A Post by Joseph Dixon, April 12, 2014

After teaching/directing Obesity: Biology, Behavior, and Management for two semesters, I have attained an appreciation of the complexity of obesity and its causes and its effects on individuals and the population in general. Having taught Nutrition and Health for close to 25 years, I had a basic understanding of obesity, but I never went into a deep analysis of it. Quite honestly, it bored me. But after hearing all of the amazing and interesting lecturers we have had in class this semester, and the lecturers from last spring, too, I have become immensely interested in this field of nutrition. So much so that I started this blog on the topic! And after all of the lectures, and the discussions among the students and the guest lecturers, I have to start summing up what I think we learned this semester and what are the causes of the obesity epidemic in the United States. First and foremost, I think all of the students in the class would say that the causes of obesity are complex and many layered. I think it is helpful to break up the causes into age groups, as each age group has its own special circumstances and therefore, its own reasons for obesity in that particular group. The age groups for which the data are reported are:
Early childhood, 0 to 5 years old
Late childhood, 6 to 11 years old
Adolescents, 12 to 19 years old
Young adulthood, 20 to 39 years old
Full Adulthood, 40 to 59 years old

The slide below shows the increase in obesity in children and adolescents from 1963 to 2008. In the period from 1964 through about 1974, the baseline for obesity was about 4% of all children. Even during non-obesogenic times there were obese children. However, the obesity rate in 2 to 5 year old children steadily climbed until about 2005, when the obesity rate was about 12 %. Note that in 2003 (the golden star) the obesity rate in 28,353 children in the Mass WIC program was 17.1%, indicating that the obesity rate at lower economic levels is even higher than for the national rate (Gorman). The rate of obesity in 6 to 11 year old children also steadily climbed from 1974 to about 2005, when the rate was about 18%. The rate in 12-19 year old adolescents was very close to the rate observed in 6 to 11 year old children. These results very strongly relate that most obesity in childhood occurs by the age of 5 years old, and that the remaining increase occurs primarily in the 6 to 11 year old age period. Therefore, these are the periods that we need to be especially concerned about. It is still important to be concerned about the 12-19 year old group because these adolescents are susceptible to developing eating disorders.

Pic 1 Trends in Childhood Obesity

Before we go much further, let’s discuss the “Standard Model” for the rise in Obesity in the United Sates, because some parts of it relate to the increased obesity in children.  I call it the “Standard Model” because I do not think there is an official name for it, but I do believe most nutritionists I know consider most aspects of the “Standard Model” to be correct.

The “Standard Model” for the increase in obesity in the US- 5 major reasons for the obesity epidemic:

1.Due to the Green revolution in the US, the per capita availability of kcal is now about 3000 kcal per person per day, so companies have come up with innovative ways to sell these kcal in thousands of new products.

2.Therefore, there has been an expansion of high kcal product lines of every kind, as outlined by Michael Moss (See earlier blog post). These products populate the new generation of mega supermarkets. Also there has been a proliferation of major chain fast food restaurants, and “Mom and Pop” fast food restaurants that sell foods such as “Chinese take out,” fried chicken, and “Tex-Mex,” such that 50% of all food is eaten out of the home (See slide below). And don’t forget the modern shopping mall with its food court!

3. The explosion of income inequality in the US has forced people at the lower incomes levels to buy very cheap, calorie dense processed foods and snack foods, rather than more expensive healthy foods (See blog post on the SNAP program).

4. The explosion in the number of TV channels (now over 500 in some areas), and the introduction of the internet and computer games, have led, altogether, to much less physical activity in children and adults. In fact, James Levine of the Mayo Clinic, has observed that people who are obese stand or move 2 hr less per day than lean people.

5. And finally, there is one reason (and this does not pertain to childhood obesity) that is rarely mentioned: the increase in per capita alcohol consumption, where alcohol intake has doubled in the US from 1988 to 2002 (See slide below). This increase is most likely due to the increase in the popularity of the NFL, of sports in general, and the sheer increase in the number of beer commercials. After all, ESPN was launched in September 1979 and has steadily increased in popularity. Other sports only networks have come on board in the past twenty years. The increased popularity of sports, and possibly the increased stress of everyday life, may have influenced the intake of alcohol by Americans.  After all, this is another complex societal issue!

There are several other reasons (termed metabolic) that will be addressed later in this post.

The slide below indicates where Americans are eating their food.

Pic 2 Food Expenditures away from home

Pic 3  Consumption of foods

One can read through the above reasons and understand how they could easily affect obesity in children. For example, young children in low and middle income homes may be “parked” in front of the TV for a good part of the day. While they are watching TV, they are given high calorie snack foods to eat in order to placate them. And then for dinner, a cheap high calorie meal is purchased from a fast food restaurant. Such a scenario could certainly explain the large increase in obesity in young children that we have observed.

Another reason for obesity that isn’t on the above list and that applies specifically to infants and very young children is that, now that we have been in the obesity epidemic for at least 20 – 25 years, obese mothers are now giving birth to very large babies that have a high probability of growing up obese. In fact, the article by Gorman’s group (see below) indicated that the strongest association with obesity observed in the 28,000 children (2 to 5 years old) in the MA WIC program was the birth weight of the infant.

Metallinos-Katsaras E, Must A, Gorman K.   A longitudinal study of food insecurity on obesity in preschool children.
J Acad Nutr Diet. 2012 Dec;112(12):1949-58.

(You will need to obtain the full article through Rutgers Libraries)

Adult Obesity.  The data below are the most up-to-date data on the rates of adult obesity in America.

Pic 4 Table of Adult Obesity

The Table below (Extracted from the tables above and others in the article) shows the obesity rates in adults for 2011-2012. The rates for the groups specified were:

Adolescents, 12 to 19 years old                     20.5 %

Young adulthood, 20 to 39 years old            30.3 %

Full Adulthood, 40 to 59 years old                39.5 %

Obesity in young adulthood. The 2011-2012 data show a large increase in obesity in going from adolescents (20.5%) to young adulthood (30.3% obesity). This increase is somewhat understandable considering the transition to a more complex life as young adults enter the workforce and start families. Both of these life events present with large increases in time commitments, and therefore, the time available to prepare healthy foods in the home decreases, and the time that can be committed to exercise also decreases. When you add in the fact that a large percentage of jobs involve sedentary circumstances because of the need to sit at computers for long periods of time, the amount of total exercise is decreased even further.   The long work hours common to many entry level jobs means that less time is available to prepare healthy foods and therefore, the reliance on prepared foods and take out food transforms the diet to one containing a large percentage of high fat, high carbohydrate, calorie dense meals.

Obesity in full adulthood. There is a further increase in obesity from young adulthood (30.3% obesity) to full adulthood, 40 to 59 years old (39.5 % obesity).   It is not hard to imagine that many in this group have been obese for some time and have not exercised sufficiently for many years. Starting at the age of 45 years old, there is a decrease in total energy expenditure (See Slide below) that is usually linked to a decrease in basal metabolism but also may be due to a lower basic activity level. In general, adults in this group start to lose lean muscle mass that contributes both to basal metabolic rate and the amount of energy expended with movement.

Certainly in full adulthood, the end result of being obese, having a lower activity level for many years, and having a decline in total energy expenditure, is an increase in the progression of obesity, and simultaneously, these factors make attempts to lose weight in full adulthood extremely difficult, if not impossible.

Pic 5 Total Energy Expenditure

What about other hypotheses for the increase in obesity in the US over the past 40 years?

There are certainly some metabolic scenarios that could influence the increase in obesity in certain individuals. Whatever the metabolic situation that is being evoked, one cannot imagine that this metabolic condition arose since the year 1969, or increased since 1969, when the rise in obesity started to increase in the United States.

Some researchers and journalists have hypothesized that a change in the macronutrient composition of the American diet, starting approximately in the 1960s, may be behind the steady increase in obesity in the US.   The changes in macronutrient content of the diet are depicted below.  The increase in the carbohydrate content of the diet led to the increased consumption of glucose and other monosaccharides that may have stimulated insulin secretion from the pancreas.

Pic 6  Macronutrients over time

In the slide depiction below, according to this scenario, higher insulin levels lead to a situation where more energy is stored in adipose, and thus there is a siphoning of energy nutrients to storage in the adipose, leading to either 1) less energy for basal metabolism and movement, or 2) an increase in hunger that increases total energy consumption in order to compensate for the energy that was siphoned by the adipose. Certainly it is possible that high insulin levels may stimulate the storage of energy in adipose when there is a concomitant lower release of fatty acids from adipose during the course of the day. This would increase the intake of calories to replace what was stored, and as days go by, more and more fat would accumulate in adipose.

However, it is difficult to envision that this metabolic mechanism is involved in the development of obesity in early childhood, 0 to 5 years old, or even in the development of obesity in late childhood, 6 to 11 years old, or in adolescents, 12 to 19 years old.

Pic 7 Metabolic Cuase

Increased adipocyte number hypothesis. One metabolic situation that has been discussed for over 60 years is often evoked to explain why, after becoming obese, it is so difficult to lose weight. This hypothesis is called the “set point” hypothesis, and it posits that once a certain level of obesity is achieved, the body comes to a new set point and “wishes” to maintain this new level of energy.

This hypothesis was updated when it was discovered that early obesity leads to increased numbers of adipocytes (fat cells) in the body, and that later in life, these adipocytes are programmed to become full of fat in order to maintain an energy store in case of times of deprivation. Therefore, the “set point” hypothesis posits that the drives to eat are enhanced until all the fat cells are filled. Some aspects of the “set point” hypothesis have been verified using many techniques, and it is probably true to state that most adipose researchers consider the “set point” theory to be operating under certain circumstances.


Considering all that was discussed above concerning the increas in obesity, we can develop a few leading reasons why the US population has become much more obese in the past 40 years. Therefore, some suggestions on how to combat obesity can be made.

Early childhood is where the obesity epidemic starts. Certainly, obese children make up a population that will become much more obese in the years ahead. Therefore, everything that will prevent childhood obesity should be attempted in order to stop obesity where it begins. Many of the ideas on how to do this have been presented throughout this blog.  The class is now in the process of developing additional strategies!

Next, actions must be taken to attack the development of obesity in late childhood, 6 to 11 years old, and in adolescents, 12 to 19 years old. If we can stop obesity in these groups, we may have a chance to prevent obesity in most Americans above the age of 20.  But if we do not stop the development of obesity in children and adolescents, we will have no chance to stop the overall obesity epidemic in the United States.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: