The Oversimplification of Obesity
Obesity is the result of more calories in than calories being expended, right? Sure. That cannot
be disputed, but this may be an oversimplification of the process. It is similar to the notion that
economic success is solely attributed to hard work and the individual’s efforts. The answer is
“yes, but...” with many caveats. The result of obesity stems from multifaceted issues that
contain nuance and intricacies of energy balance, metabolic adaptations, potential genetic
differences, and the role of adipose tissue in obesity.
Energy homeostasis is typically referred to by the simplified equation of “calories in = calories
out” (CICO). A calorie is a unit of energy commonly used in the context of nutrition and
metabolism. When an individual eats the same amount of energy that is expended, the equation
balances out and achieves homeostasis, resulting in weight maintenance. When an individual
eats more energy (calories) than is expended this will result in weight gain. The opposite is true
for weight loss. On the topic of obesity, it becomes an issue when the energy in becomes
excessive and consistent because the surplus is stored as adipose tissue.
With a prolonged positive energy balance the body will undergo various metabolic changes that
promote further energy conservation and storage. These adaptations include a decrease in
RMR (resting metabolic rate – energy expended at rest), reduced NEAT (non-exercise activity
thermogenesis), and alterations in hormonal regulation of appetite and satiety.
Adipose tissue, also known as body fat, is found in various regions of the body; Subcutaneous
(under the skin) and visceral (around the organs). Adipose tissue plays several important roles.
Until recently adipose tissue was thought of as only a storage for energy but these cells do
more. They provide insulation and protection of vital organs, are an active endocrine organ, and
act as a hormone storage site. In obesity, adipose tissue undergoes hypertrophy (increase in
cell size) and hyperplasia (increase in number of cells). This triggers secretion of a hormone
called adipokines and with obesity becomes dysregulated, leading to chronic low-grade
inflammation, insulin resistance, and further dysfunction of metabolic pathways. (1)
Two major players in the game of energy homeostasis are leptin and ghrelin. Leptin is a
hormone produced in adipose tissue and regulates appetite by signaling to the brain that an
individual is full and cues satiety when appropriate. Ghrelin, known as the hunger hormone (can
be remembered as the ghrrrelin stomach growl), is produced in the stomach and with the
release increases the desire for food and intake. An individual with obesity may have a
disrupted balance of these two hormones and others, which disrupts the balance of hunger and
satiety leading to overeating and continued weight gain. (2)
Another factor in the progress of obesity is the interplay between the individual and their
environment. Genetic predisposition does not solely cause obesity, but certain genetic variations
can influence a person’s susceptibility to excess energy intake; A sedentary lifestyle, multiple
socioeconomic factors, and an obesogenic environment can help facilitate steady weight gain
through a person’s life.
Calories in, calories out holds up... but as described above, it is an oversimplification. The true
scale to represent homeostasis may look more like the one below. A healthcare professional
must be able to understand the multifaceted nature of the condition and develop appropriate
interventions taking all into account.
(3) (Calories in vs. Out? Or hormones? The debate is finally over. Here’s who won., 2019)
1. Choe, S. S., Huh, J. Y., Hwang, I. J., Kim, J. I., & Kim, J. B. (2016). Adipose Tissue
Remodeling: Its Role in Energy Metabolism and Metabolic Disorders. Frontiers in
endocrinology, 7, 30. https://doi.org/10.3389/fendo.2016.00030
2. Guyenet, S. J., & Schwartz, M. W. (2012). Clinical review: Regulation of food intake,
energy balance, and body fat mass: implications for the pathogenesis and treatment of
obesity. The Journal of clinical endocrinology and metabolism, 97(3), 745–755.
3. Berardi, J., PhD, CSCS (2019). Calories in vs. Out? Or hormones? The debate is finally
over. Here’s who won. [Photograph]. Precision Nutrition.