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)

---

References

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.

https://doi.org/10.1210/jc.2011-2525

3. Berardi, J., PhD, CSCS (2019). Calories in vs. Out? Or hormones? The debate is finally

over. Here’s who won. [Photograph]. Precision Nutrition.

https://www.precisionnutrition.com/calories-in-calories-out