March 2016

Suggested Citation: Garko, M.G. (2016, March). The obesity epidemic in America – Part III: The immediate cause. Retrieved (insert month, day year), from

The Obesity Epidemic in America – Part III: The Immediate Cause

 Michael G. Garko, Ph.D.
Nationally Syndicated Host & Producer– Let’s Talk Nutrition


“Everyone and everything has been blamed for its cause: school meals, processed food, fast food, beverages, fat, sugar, working parent, you name it” (Ayoob, 2010). Of course, what is being referred to in the quote is the overweight and obesity epidemic in America.

In an effort to identify the causes of the epidemic, simplistic explanations have been proposed. For example, one popular argument is that those suffering from being overweight or obese are unwilling to assume personal responsibility for their health and wellbeing as reflected in their failure to practice self-control. Another is that overweight and obese people lack the will power to change their diet and lifestyle so they can lose the excess weight and keep it off.

Such shame and blame explanations do little to understand the nature of the problem, identify its causes or create effective solutions to resolve it. The truth be told, there is no simplistic answer as to why humans become overweight or obese, generally, or why the United States is caught in the clutches of an overweight and obesity epidemic, specifically.

In a word, the etiology of the excess weight problem in the United States is complex and not reducible to a single factor. Rather, it is a multidimensional problem with a host of interdependently connected factors. The following factors are cited in the literature as being implicated in one way or another in causing the seemingly unrelenting rise of overweight and obesity in America: Evolution (e.g., human physiology designed to conserve and store weight/body fat), defective genes, familial obesity, medical conditions (e.g., Cushing’s Syndrome, Polycystic Ovary Syndrome, underactive thyroid and hormone imbalance), gender, race, insomnia, stress,  socio-economic status, sedentary lifestyle, overeating, lack of will power or self-control, technological advances promoting a sedentary lifestyle, agriculture, societal influences, psychosocial reasons and over abundance of processed foods, among others (e.g., see National Heart Lung and Blood Institute, 2010). Thus, it can be seen how complicated the nature of the problem is.

Given its complexity, it would be beyond the scope of this article to examine myriad of factors contributing to overweight and obesity in America. Hence, the March, 2016, issues of Health & Wellness Monthly focuses more narrowly on the most immediate, underlying cause of overweight and obesity (which is a net energy/caloric imbalance), notwithstanding the nutritional, genetic, physiological, behavioral, psycho-social and cultural-societal reasons why a net energy/caloric imbalance is created in the first place and leads to humans becoming overweight or obese. The article is an update of a piece published December, 2010, in Health and Wellbeing Monthly. Overweight and obesity will be defined. Since they are important to understanding overweight and obesity, the concepts of energy and calories will be discussed. Also, the relationship among food, calories, energy and weight gain will be explained. Finally, particular attention will be given to overeating and a sedentary lifestyle, two major factors contributing to an energy imbalance resulting in either overweight or obesity.

Overweight and Obesity Defined

The term “overweight” refers to an excessive amount of body weight, which can be constituted of muscle tissue, bone, adipose or fat tissue and water, while the term “obesity” refers to an excessive amount of adipose or fat tissue (see National Institute of Diabetes and Digestive and Kidney Diseases, 2010).



The human body is a virtual energy machine. Above all of the other functions it must perform, the first priority of the human body is to satisfy its need for energy. Every cell of every type of tissue, organ and system of the body requires an ongoing supply of energy to function. Without a sufficient amount of energy the overall biological, physiological and psychological structure and function of the body would become compromised, susceptibility to disease would be increased and the ability of the body to heal and repair itself would become impaired. As it will be seen, while it is essential for existence, having too much energy can be harmful to health.

Energy Defined

Technically, energy is the capacity to do work. Work is achieved when there is a release of energy resulting in movement and change (e.g., a change in the amount and type of energy). In physiological terms, work can include anything involved in or implicated with the movement of molecules to muscles. Consequently, humans evolved with a number of physiological processes to carry out different types of work including (1) initiating various chemical reactions resulting in increases and decreases in energy (i.e., metabolic processes), (2) growing and reproducing through the acquisition and processing of nutrients (i.e., generative processes), (3) responding to internal and external changes (i.e., responsive processes) and (4) coordinating/sequencing and regulating of all metabolic functions/chemical reactions through specific pathways by the use of enzymes (i.e., control processes) (see Enger, et al., 2005). All of these and other specific related types of work occurring within the human body require the intake, transformation and expenditure of energy.

Potential  and Kinetic Energy

Generally speaking, there are two major types of energy, potential energy and kinetic energy. Potential energy is stored energy. As it turns out, the human body possesses a unique evolutionary capacity to store large amounts of energy, especially in the form of adipose tissue or fat. An overabundance of stored energy is directly related to the conditions of overweight and obesity.

Kinetic energy is potential energy which has been released, thereby, causing things to be put into motion. In short, when potential energy is released it is transformed into kinetic energy. A sprinter ready to run a 100 yard dash possesses the potential energy required to complete the run. The conversion of the sprinter’s potential energy into kinetic energy occurs during the actual running of the 100 yards.

Transformation of Energy

It is important to understand that energy is not created. The law of conservation of energy, also known as the first law of thermodynamics, states that energy cannot be created or destroyed but can only be transformed or converted from one form to another. For example, in order to engage in any sort of physical activity of any kind, whether running a marathon, walking down the street, mowing the lawn or weight-training at the gym, there is a conversion of potential chemical energy stored in the body into mechanical energy resulting in movement of the body through the contraction of muscles. The transformation of energy also applies to the different types of physical and chemical (i.e., physiological processes) the body must carry out.

Six Forms of Energy

There are six specific forms of energy all of which can be in either a potential or kinetic state and all of which are interchangeable with one another according to the laws of thermodynamics: 1. chemical, 2. mechanical, 3. heat, 4. electrical, 5. light, and 6. nuclear. Humans are in one way or another implicated with all of these forms of energy. However, the chemical, mechanical, heat and electrical forms of energy are of special importance in physical activity. For example, during physical activity chemical energy is converted into mechanical, electrical and heat energy to allow for muscle contraction and movement of the body, electrical nerve impulses to stimulate muscle contraction and warming of muscles for ease of movement, respectively.

Relationship Among Food, Calories, Energy and Weight Gain

The energy humans require to engage in work of any kind is derived from three major types of foods called macronutrients. They are carbohydrates, fats and proteins. Chemical energy is contained within the chemical bonds of these macronutrients. The amount of chemical energy contained in carbohydrates, fat and protein is measured in terms of calories.

Definition of a Calorie

In scientific terms, a calorie (more accurately a kilocalorie or kcal) is the amount of heat required to increase the temperature of one liter of water one degree Fahrenheit or stated in another way to increase the temperature of one kilogram of water by one degree Celsius. This definition of a calorie represents a way to measure energy derived from food. In that regard, acalorie is a unit of heat reflecting the energy value of food.

Amount of Energy Contained in Macronutrients

Generally speaking, one gram of carbohydrate and one gram of protein each are equal to four calories each, while one gram of gram of fat equals nine calories. The calories contained in these macronutrients serve as potential energy for the body to engage in physiological work of one sort or another.

Macronutrient Forms of Energy Storage

Through the process of digestion, carbohydrates, fats and proteins are broken down into molecules the body can use and store as energy. Carbohydrates are broken down and stored as serum glucose, liver glycogen and muscle glycogen. Fat is broken down and stored as serum-free fatty acids, serum triglycerides, muscle triglycerides and adipose tissue triglycerides. Protein is broken down and stored as muscle protein.

Adenosine Triphosphate – The Energy Currency of the Body

An important principle of energy is that cells neither acquire nor are able to use the energy directly from food for their continuous, immediate and long-term energy needs. Instead, the chemical energy in food needs to be transformed into a form the body can use for its immediate purposes. Through a complex series of chemical reactions (a topic too broad to consider here) the energy-containing chemical bonds found in carbohydrates, protein and fat are broken and energy is released, converted, transported to and stored in the cells of the body.

All the different forms of energy extracted from carbohydrates, protein and fat and then stored in the body serve to replenish adenosine triphosphate (ATP). ATP is a complex, energy-rich molecule. It is the primary energy currency used to satisfy the body’s continuous and immediate need for energy to carry-out all of its physiological functions. Only a relatively small amount of ATP is stored in the tissues of the body. At any one time, the amount of available or stored ATP in the body is approximately 85 grams or three ounces. This amount of ATP would be only enough energy to fuel running full-out for a few seconds (Katch & McArdle, 1993). Therefore, ATP must be continuously synthesized/made to allow the body to function physiologically. When carbohydrates, fat and protein are consumed, all the potential energy contained within these macronutrients is utilized for the purpose of re-synthesizing ATP.

Why Calories Count

Make no mistake about it, calories can add up unsuspectingly fast. Calories count because all other factors contributing to weight gain being equal (e.g., type-quality of food, amount of physical activity, stress levels, thyroid function, genetics, hormones, etc.), the chronic consumption of surplus calories is at the center of putting on unwanted, excess pounds and becoming overweight or obese. While this may seem like an obvious observation to some, what is not so obvious to many is how calories are related to food, energy and weight gain and the principle of balancing calories.


Given that macronutrients contain energy and all of the body’s biochemical and physiological functions require energy, it is useful to think of energy in the form of calories as being a common denominator in the immediate cause of overweight and obesity.

Immediate Cause of Overweight and Obesity

At its most fundamental bio-physiological level, the immediate cause of overweight and obesity is an imbalance between the amount of calories consumed from food and drink with the number of calories expended or otherwise burned as body fuel. That being said, there is a constellation of nutritional, genetic, physiological, behavioral, psycho-social and cultural-societal reasons why the imbalance occurs leading to humans becoming overweight or obese.

Principle of Balancing Calories-In and Calories-Out

At the end of the nutritional day, preventing overweight or obesity becomes balancing the number of calories consumed each day with the number of calories expended either through physical activity and the various energy-requiring physiological processes and functions of the body. The following graphic provided by the Centers for Disease Control and Prevention (2010) is useful in explaining the principle of balancing calories:



If you are… Your caloric balance status is…
Maintaining your weight in balance.” You are eating roughly the same number of calories that your body is using. Your weight will remain stable.
Gaining weight in caloric excess.” You are eating more calories than your body is using. You will store these extra calories as fat and you’ll gainweight.
Losing weight in caloric deficit.” You are eating fewer calories than you are using. Your body is pulling from its fat storage cells for energy, so your weight is decreasing.





Fat Myth

A common myth is that only eating fat will make a person fat.Excess calories can come from an overconsumption of carbohydrates, fats or protein and will be stored as fat tissue, no matter their macronutrient origin. It is also worth mentioning that one pound of body fat is equivalent to 3500 calories. If you were interested in losing one pound of fat in a week, then you would have to burn 3500 calories more than what you typically consume in seven days. In other words, you would need to have a calorie deficit of 3500 calories. The calorie deficit can be created in just three ways: 1. Decrease daily food intake, 2. Increase daily physical activity or 3. Practice a combination of both.

Sedentary Lifestyle and Consumption of Excess Calories

Among all of the factors helping to create the immediate imbalance between the number of calories consumed with the number of calories expended, a sedentary lifestyle and the intake of excess calories account for most of the variance in the imbalance, and, thus, are major factors in causing overweight and obesity. In a real and practical sense, nutrition and physical activity possess a synergistic impact on preventing excess calories and creating deficit calories, thereby, bringing about and sustaining a balance between consumed calories and expended calories.


Whether or not people become overweight or obese distills down to one fundamental, principle. That is, if more calories are consumed than are expended/burned, then the excess calories will be stored as excess adipose or fat tissue, a necessary condition for obesity. Hence, the most immediate cause of the overweight and obesity epidemic in America is an imbalance between the consumption versus the expenditure of calories, notwithstanding the nutritional, genetic, physiological, behavioral, psycho-social, and cultural-societal factors implicated with creating the calorie imbalance.

In the final analysis, there are three important principles related to the balancing of calories and whether weight will remain stable, be gained, or lost. First, if the amount of calories consumed equals the amount of energy expended by the body, then weight will remain stable. Second, if more calories are consumed than the amount of energy expended, then weight will be gained, with the excess energy being converted into and stored as adipose tissue or fat. Third, if fewer calories are consumed than expended, then weight will be lost in that the body will begin to use its fat stores to obtain the extra energy it needs to function and maintain itself.

Proper nutrition and physical activity are among the most important factors in preventing the immediate cause of overweight and obesity. Together, they are foundational to good health and wellbeing, generally, and preventing overweight and obesity, specifically. If these were the only two factors causing the obesity epidemic in America, then the solution to the problem would be easier to design and carry out. However, nutrition and physical activity become intertwined with various other genetic, physiological, behavioral, psycho-social and cultural-societal factors, making difficult for overweight and obese individuals to lose weight and keep it off and for others not to become overweight or obese. Thus, creating effective and workable solutions to the problem is not limited to single factor explanations or quick-fix protocols. In the upcoming issue of Health and Wellbeing Monthly, proposed interventions to address the obesity epidemic will be addressed and evaluated.

Beyond all of the public health policies, theories and interventions to curb one of the serious health threats to American adults and children in the 21st century, the battle against overweight and obesity in the United States begins on an individual level. Adults and children need to be educated about basic principles of nutrition and the immediate cause of how people become overweight or obese. Knowing how humans gain excess weight at the most fundamental bio-physiological level, serves as a modest but yet significant step in the effort to confront the overweight and obesity epidemic in America. In that regard, it is hoped this article makes a contribution to informing health consumers about the most immediate cause of overweight and obesity.


Ayoob, K.T. (2010). Stop the blame and start the action: Preventing generation z from becoming xxl. Childhood Obesity, 6 (4), 164.

Centers For Disease Control and Prevention (n.d.). Balancing calories. Retrieved September 25, 2010, from

Enger, E.D., Ross, F.C. & Bailey, D.B. (2005). Concepts in biology (11th ed.). Boston: McGraw Hill.

Katch, F.I. & McArdle, W.D. (1993). Introduction to Nutrition, exercise, and health. (4th ed.). Philadelphia: Lea & Febiger.

National Heart Lung and Blood Institute (n.d.). Overweight and obesity. Retrieved November 11, 2010, from

National Institute of Diabetes and Digestive and Kidney Diseases (2010). Overweight and obesity statistics. Retrieved September 25, 2010, from

Suggested Citation: Garko, M.G. (2016, March). The obesity epidemic in America – Part III: The immediate cause. Retrieved (insert month, day year), from