Why Is It So Hard to Lose Fat? Because It Has to Get Out through Your Nose! A Lab Based Activity on Oxygen Consumption, Metabolic Equations, and the Futility of Exercise‐Only Weight Loss Plans
Authors: Merritt Edward K 
Published: June 2021

Daily physical activity and exercise programs are often thought to be an effective method for overweight individuals to quickly lose substantial fat mass. However, few people have realistic expectations for the amount of exercise‐induced fat loss that can be achieved for the average person. Even fewer understand the biochemistry that occurs in the body when fat is “lost” and where the lost mass has gone. Understanding that fat is “burned” with the help of inhaled oxygen, and most of the mass lost must be exhaled from the body as carbon dioxide might help people have more realistic expectations for weight loss. Therefore, the purpose of this study was to design a lab‐based activity that provided students with a basic understanding of metabolic biochemistry and engaged them with collection of their own data to determine a realistic time scale for exercise‐induced fat loss.

Prior to the lab component a brief presentation is given and questions are asked (e.g. “When you lose weight, where does it go? Literally, where is the mass you lost?”) to help students understand the chemistry of the breakdown of fat stores with inhaled oxygen and subsequent carbon dioxide exhalation. Students are tasked with completing 10 minutes worth of exercise, walking or running, on a measured track and at a pace he/she could maintain for one hour. Each student records the distance and time. The relationship of walking and running to physics concepts of work and energy are presented with the concept of “calorie burn” and relationship to oxygen consumption. Metabolic equations that allow calculation of oxygen consumption based on speed of walking or running are introduced. Students calculate the oxygen consumed and calories burned during his/her exercise. Finally, the amount of energy (i.e. calories) in one pound of fat is discussed, and students calculate how long he/she would have had to exercise at the pace walked or run to burn 10 pounds of fat. For a person of average size and fitness, 60+ hours of exercise (1 hour per day, 5 days per week, for 12 weeks) is necessary to burn 10 pounds of fat. A subsequent lab activity using a metabolic cart reinforces these concepts and proves the validity of the calculations used in this activity.

This activity has been done with 2 exercise physiology classes (n = 32) with pre‐ and post‐activity follow up questions. Prior to the lab, nearly all students believe exercise is an effective method for most people to lose substantial weight (29/32). Very few students know that fat lost is converted to carbon dioxide and water (2/32). Immediately upon completing the lesson, discovering how long it would take to lose 10 pounds of fat with exercise alone, students are astonished, engaged, and excited to ask follow‐up questions. Long‐term follow‐up indicates the activity was memorable. On end of semester evaluations, a majority of students indicate this was the most memorable laboratory activity (18/32) and the concepts learned in this specific lab were the concepts they were most likely to tell someone about outside of class (19/32). Nearly all students were able to answer the question “Where does fat go when it is ‘lost’?” (30/32) and know that substantial weight loss through exercise alone will take months of dedicated, daily exercise (26/32).

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.