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Why Exercise Takes Away Appetite
Why Exercise Takes Away Appetite
Have you ever wondered why after a hard workout you seem to have lost your appetite? Maybe you don’t realize you’ve skipped your lunch until dinner time. Researchers at Wilfrid Laurier University in the Energy Metabolism Research Laboratory (EMRL) are interested in determining why this effect occurs.
It is well documented that in the hours following moderate-intensity exercise (such as light jogging or biking) our perceptions of hunger and fullness can be altered, leading to a reduced appetite. These changes in perceived appetite appear to be related to changes in different gastrointestinal hormones. These hormones when secreted in the body either stimulate or suppress our appetite. Ghrelin is a well-established appetite-stimulating hormone, and GLP-1 and PYY which are appetite-inhibiting hormones, are examples of these hormones. In the hours following moderate-intensity exercise ghrelin is reduced and GLP-1 and PYY are increased which can contribute to a feeling of fullness or reduced appetite. Research from the EMRL has previously explored how exercise intensity affects this response and found that high-intensity exercise (such as a hard 30-minute run or repeated 30-second running sprints) suppressed appetite and reduced ghrelin when compared to lower-intensity exercise. Research from other laboratories worldwide has found that higher-intensity exercise results in greater suppression of appetite and reductions in ghrelin.
While a host of research has explored how exercise affects our appetite and gastrointestinal hormones, there is little work exploring why these changes occur. We have proposed different mechanisms for why exercise may alter our appetite and hormones; however, there is still very little research exploring these mechanisms. The EMRL team is focused on investigating the different mechanisms responsible for exercise-induced appetite suppression. One way our team is investigating how exercise suppresses appetite is by producing a molecule called lactate. Lactate is produced when our body uses glucose to produce energy. The body produces more lactate when you undergo more intense exercise such as hard running or sprinting on a bike. Research from the EMRL has highlighted a relationship between lactate and appetite suppression.
My research builds on this by exploring how lactate suppresses appetite. At the beginning of my Ph.D., I led a project which hypothesized potential mechanisms for how lactate suppresses appetite. We hypothesized three mechanisms including:
1) lactate inhibits the release of ghrelin;
2) lactate activates appetite-suppressing signals in the brain; and
3) lactate blocks ghrelin’s actions in the brain.
My PhD research explores whether these changes occur following exercise or lactate ingestion. My first study is exploring how lactate affects appetite-suppressing signals in humans following exercise, however, this study is limited to what we are able to measure in humans. We have almost finished data collection for this study and will be finished in early 2023.
My second study is exploring how lactate affects appetite-suppressing signals in the brain in mice following exercise which will allow us a more comprehensive examination of how lactate affects these appetite pathways. This study is also close to completion and will be finished in 2023.
My final study will look at how ingesting a lactate solution affects appetite-signaling pathways in the brain in humans. We will begin this study in 2023. Following my PhD work, more research will be required to see if the short-term effects of lactate generation (during exercise) or ingestion on appetite would have long-term effects like weight loss.
About Seth
Seth McCarthy is an exercise physiologist and nutrition researcher who is pursuing a PhD in Kinesiology and Physical Education at Wilfrid Laurier University. A specialist in appetite regulation and how it is affected by exercise, Seth has over five years of experience working in the Energy Metabolism Research Laboratory supervised by Dr. Tom Hazell. While Seth’s work is mainly focused on improving our understanding of exercise-induced appetite suppression in hopes of using exercise to suppress appetite and lead to weight loss, he has also studied how exercise affects post-exercise metabolism and blood pressure, as well as how different types of exercise training can improve fitness in adults.
Seth received his Bachelor of Human Kinetics from the University of Windsor in 2018 and his Master of Kinesiology from Wilfrid Laurier University in 2020. He currently holds the Alexander Graham Bell Canada Graduate Scholarship at the Doctoral level from the Natural Sciences and Engineering Research Council of Canada and has previously held the Canadian Institute of Health Research Canada Graduate Scholarship at the Masters level as well as Ontario Graduate Scholarships at the Masters and Doctoral level.
In addition to Seth’s research ventures, he has worked as a contract teaching faculty member in the Department of Kinesiology and Physical Education at Wilfrid Laurier University teaching Exercise Nutrition to 3rd and 4th-year undergraduate students, as well as speaking to different audiences about exercise and nutrition.