Can exercise help reduce appetite and cravings?

It’s that time of year when we all set lofty goals for the year ahead. This year will be different, right? This year you’ll tackle that big project, lose that weight, go to the gym, spend more time with those you love, save more for your retirement, and learn a new word every day. 2022 is your year! For tips on creating SMART goals, be sure to check out THIS article. While my capacity to improve your 401(k), your vocabulary, or your personal relationships is quite limited, I’d like to offer some advice that will help you maintain that goal of improving your metabolic health for years to come, specifically when it comes to controlling your hunger.

We know that metabolic health, including insulin sensitivity, can be improved with diet. Popular ways of achieving improved metabolic health include carbohydrate restriction and/or periods of fasting. However, one of the biggest challenges faced by those who adhere to these practices is dealing with feelings of hunger and a drive to eat. With some understanding of why we feel hunger and some strategies to control it, you’ll be better prepared to tackle your metabolic resolutions. While we’re here, it would be a great disservice to talk about hunger without educating you on the medical term for “stomach growling”- that awkward thing that happens right in the middle of a meeting before lunch and everyone around you hears it. The term physicians use to describe a tummy rumble is “borborygmus” (bor-buh-RIG-mis). Try saying that five times in a row without smiling. ☺

Feelings of hunger and satiety (the sensation of not being hungry) are largely regulated by hormones.[1] Ghrelin is one well-known hormone that tells your body it’s hungry. Other hormones (for example: GLP-1, Leptin, PP, and PYY) tell your body it’s full and reduce hunger.[2] It has been found that exercise increases circulating levels of satiety hormones,[3,4] which increases feelings of satisfaction and decrease food-seeking behaviors.[5] In addition to these hormones, exercise helps improve glucose uptake and utilization in the cells throughout the body which can cause you to be less hungry as well.[6,7] Is this true for you? I know it is for me because I rarely feel like eating right after a workout.

To understand the impact of exercise on hunger further, my team recently ran a study where we asked participants to fast for 36 hours on two separate occasions. During one of the fasts, we asked participants to just live their lives normally but to avoid exercise, yard work, or anything else that might get their heart pumping faster. For the other fast, we started their 36 hours with a steady jog on the treadmill for close to an hour and then asked them to continue to fast like before (without any other exercise). We took blood samples every 12 hours to test their hunger hormone levels, and we found that ghrelin (the hormone that tells you you’re hungry) was significantly lower for up to 24 hours if they exercised at the beginning of their fast. Other hormones that signal satiety (like GLP-1 and PP) were higher in the exercise condition. So, in theory, exercise should help you get through a fast or a rough patch in your day and keep you on track by making you less hungry, right? Well, how did people actually feel?

To assess this, we took things one step further and asked participants to rate their hunger, thirst, and stomach discomfort on a scale of 0-10 several times throughout each fast. Thirst stayed low throughout the fasts because we asked everyone to drink plenty of water. It was no surprise that hunger and stomach discomfort increased steadily over the 36-hour fast regardless of whether they started their fast with exercise or not. 36 hours is a long time to go without food, so you’re going to be hungry. In fact, we didn’t see any real difference in hunger and stomach discomfort ratings between the two fasting conditions which tells us two things.

1. Objective markers of hunger and satiety (the hormone levels) do not necessarily correlate to subjective ratings of the same feelings. This may be because we’ve trained our bodies to want food on a regular schedule and when that schedule isn’t met, our bodies recognize the change, and they react with some borborygmus (remember your fancy new word?) and accompanying hunger. The psychological responses to hunger can be very strong, even if you aren’t all that hungry.
2. While we didn’t see a decrease in hunger and stomach discomfort when we added exercise, we also didn’t see it increase. This means we can get a greater metabolic benefit by adding exercise to our fast (i.e.- building ketones and depleting glucose stores faster) without feeling extra hunger from it.

With these findings in mind, you may consider exercising at a time of day when you start to feel some of those hunger pains. Doing so may help you stay on track with your goals a little longer. Just like most things, our bodies are very adaptable and can usually adjust to things if we train them. Hunger is no exception. Sometimes all you need is to drink some more water, quietly tell your body and mind that you’re doing ok, give yourself a positive affirmation, and move on. As you find strategies to train your hunger, you’ll find that you can curb your cravings more than you think. Stick with your goals, create healthy habits, mix in some science-backed strategies and you’ll be on your way! Here’s to a successful 2022!

References

1. Blundell J, de Graaf C, Hulshof T, et al. Appetite control: methodological aspects of the evaluation of foods. Obes Rev. 2010;11(3):251-270.
2. Buchwald H, Dorman RB, Rasmus NF, Michalek VN, Landvik NM, Ikramuddin S. Effects on GLP-1, PYY, and leptin by direct stimulation of terminal ileum and cecum in humans: implications for ileal transposition. Surg Obes Relat Dis. 2014;10(5):780-786.
3. King NA, Caudwell PP, Hopkins M, Stubbs JR, Naslund E, Blundell JE. Dual-process action of exercise on appetite control: increase in orexigenic drive but improvement in meal-induced satiety. The American journal of clinical nutrition. 2009;90(4):921-927.
4. Blundell JE, Gibbons C, Caudwell P, Finlayson G, Hopkins M. Appetite control and energy balance: impact of exercise. Obes Rev. 2015;16 Suppl 1:67-76.
5. Hopkins M, King NA, Blundell JE. Acute and long-term effects of exercise on appetite control: is there any benefit for weight control? Curr Opin Clin Nutr Metab Care. 2010;13(6):635-640.
6. Flores-Opazo M, McGee SL, Hargreaves M. Exercise and GLUT4. Exerc Sport Sci Rev. 2020;48(3):110-118.
7. de Graaf C, Blom WA, Smeets PA, Stafleu A, Hendriks HF. Biomarkers of satiation and satiety. The American journal of clinical nutrition. 2004;79(6):946-961.