Burn off significantly more body fat exercising before meals, rather than after them.
The Best Time to Exercise for Weight Loss
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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
What is the optimal exercise timing for weight loss? Is it better to exercise in the morning or the evening? Before breakfast or after breakfast? There was a Nobel Prize-winning exercise physiologist who said he always ran a mile every morning before breakfast. Was he right? Let’s find out.
More than a dozen experiments have been published comparing the amount of fat burned in a fasted versus fed state, and every single one found more fat was burned on an empty stomach. On average, a single bout of low-to-moderate intensity activity before a meal burned off three grams more fat than the same amount of exercise after a meal. That’s about three-quarters of a pat of butter’s worth of fat––enough to improve insulin sensitivity. The same amount of exercise, but more fat loss, all because of timing.
Now, just because you burn more fat while you’re exercising doesn’t necessarily mean you end up with less fat at the end of the day. Maybe your body offsets the extra fat loss that occurs during exercise with a little extra fat storage when you finally do eat, balancing it out. Researchers in Japan set out to investigate the possibility that your body makes up for it later by measuring 24-hour fat balance after 100 minutes of running, either before breakfast or after lunch. On the exercise-after-lunch day, they burned a total of 608 calories of fat over the course of that day. In contrast, on the exercise-before-breakfast days, in the same 24-hour period they burned through nearly 90 percent more, 1,142 calories of straight fat. So, the next day, they woke up with about a quarter-cup of fat less after the same amount of exercise. That’s remarkable!
What about just something like walking? Sixty minutes before breakfast, after lunch, or after dinner. Over the 24 hours they exercised in the evening, 432 calories were burned off. On the afternoon exercise day, they burned off 446 calories of fat. They also had a control day with no exercise at all, and on that day, they burned through 456 fat calories. That’s disappointing—it’s like they never walked at all. But the same amount of exercise before breakfast resulted in 717 calories of fat loss. Over the course of a day, timing matters, so much so that when it comes to an hour of walking, exercise increases 24-hour fat burning only when it is performed before breakfast. Here’s the fat balance graph with no exercise. You can see the fat storage bump up at breakfast, lunch, and supper, before slowly coming back down overnight. Exercise in the afternoon or evening, and end up with more fat than not exercising at all, but exercise in the morning and at least your fat balance comes back to baseline.
All such similar studies on both men and women show we burn through more fat on the days we exercise before, rather than after eating. After reading the chronobiology chapter in How Not to Diet, though, or watching my chronobiology videos, an alternative explanation may spring to mind. Maybe it’s just a morning thing. Maybe it has nothing to do with meals, and your circadian rhythm is just dictating the difference? No. Exercising in the morning after breakfast appears no better than exercising in the evening after dinner, and exercising before breakfast works better than immediately after breakfast––both still in the morning. It really does seem to be a pre- versus post-meal effect. But why?
Carbohydrate is the preferred fuel of the body. When you eat sugars or starches, they get broken down and converted into blood sugar. After a meal, blood sugars rise and your muscles are quick to snatch it up for fuel without having to rely much on your energy stores. If you instead take a siesta, and your muscles have no immediate need for energy, the excess blood sugar from a meal can be stored in our muscles in the form of glycogen for later use. Glycogen is just a bunch of blood sugar molecules strung together into a mass of branches that can be broken off and used for quick bursts of energy any time we need them.
If you exercise after a meal, your muscles can siphon off some of the extra blood sugar floating around for energy. Before a meal, your muscles have to instead resort to dipping into your energy stores and end up burning mostly a combination of glycogen and fat. That explains why you burn more fat during fasted exercise, but what about all the extra fat burned throughout the rest of the day?
Glycogen is more than a store. Glycogen isn’t just an energy reserve, but acts as a sensor capable of activating metabolic pathways. Exercising before breakfast can exhaust as much as 18 percent of your glycogen stores, and that depletion can act as a powerful rallying cry to your fatty tissues to start pulling more of their own weight by breaking down more fat. The lower glycogen stores fall, the greater the sustained 24-hour fat loss.
How long do you have to go without food in order to trigger this effect? Six hours may be sufficient; so, it doesn’t have to be before breakfast. If you timed it right, you could exercise before a late lunch, or if you have an early enough lunch, maybe before dinner when you get home from work. If exercise in a fasted state isn’t possible, does it matter what you eat? Insulin release after a meal appears to play a critical role in suppressing fat breakdown, explaining why lower glycemic foods—in this case, muesli versus cornflakes—can have less of an effect. Lentils were identified as a promising option for maintaining athletic endurance (which can take a hit on an empty stomach) while maintaining more of the fat dissolution. Lentils are said to be “unlikely to be consumed by the general population…due to low palatability.” They obviously haven’t tried my mom’s lentil soup.
It’s worth mentioning that although there’s increased 24-hour fat burning exercising in a fasted state, the only way to see if this facilitates weight loss over time is to put it to the test, which we’ll explore next.
Please consider volunteering to help out on the site.
- Haxhi J, Scotto di Palumbo A, Sacchetti M. Exercising for metabolic control: is timing important?. Ann Nutr Metab. 2013;62(1):14-25.
- Betts JA, Chowdhury EA, Gonzalez JT, Richardson JD, Tsintzas K, Thompson D. Is breakfast the most important meal of the day?. Proc Nutr Soc. 2016;75(4):464-74.
- Vieira AF, Costa RR, Macedo RC, Coconcelli L, Kruel LF. Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis. Br J Nutr. 2016;116(7):1153-64.
- Venables MC, Jeukendrup AE. Endurance training and obesity: effect on substrate metabolism and insulin sensitivity. Med Sci Sports Exerc. 2008;40(3):495-502.
- Iwayama K, Kawabuchi R, Park I, et al. Transient energy deficit induced by exercise increases 24-h fat oxidation in young trained men. J Appl Physiol (1985). 2015;118(1):80-5.
- Iwayama K, Kurihara R, Nabekura Y, et al. Exercise increases 24-h fat oxidation only when it is performed before breakfast. EBioMedicine. 2015;2(12):2003-2009.
- Iwayama K, Kawabuchi R, Nabekura Y, et al. Exercise before breakfast increases 24-h fat oxidation in female subjects. PLoS One. 2017;12(7):e0180472.
- Kim HK, Ando K, Tabata H, et al. Effects of Different Intensities of Endurance Exercise in Morning and Evening on the Lipid Metabolism Response. J Sports Sci Med. 2016;15(3):467-76.
- Farah NM, Gill JM. Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men. Br J Nutr. 2013;109(12):2297-307.
- Philp A, Hargreaves M, Baar K. More than a store: regulatory roles for glycogen in skeletal muscle adaptation to exercise. Am J Physiol Endocrinol Metab. 2012;302(11):E1343-51.
- Montain SJ, Hopper MK, Coggan AR, Coyle EF. Exercise metabolism at different time intervals after a meal. J Appl Physiol (1985). 1991;70(2):882-8.
- Stevenson EJ, Astbury NM, Simpson EJ, Taylor MA, Macdonald IA. Fat oxidation during exercise and satiety during recovery are increased following a low-glycemic index breakfast in sedentary women. J Nutr. 2009;139(5):890-7.
- Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise. Am J Physiol. 1997;273(4):E768-75.
- Thomas DE, Brotherhood JR, Brand JC. Carbohydrate feeding before exercise: effect of glycemic index. Int J Sports Med. 1991;12(2):180-6.
- Gonzalez JT, Stevenson EJ. New perspectives on nutritional interventions to augment lipid utilisation during exercise. Br J Nutr. 2012;107(3):339-49.
- Schoenfeld BJ, Aragon AA, Wilborn CD, Krieger JW, Sonmez GT. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 2014;11(1):54.
Motion graphics by Avo Media
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
What is the optimal exercise timing for weight loss? Is it better to exercise in the morning or the evening? Before breakfast or after breakfast? There was a Nobel Prize-winning exercise physiologist who said he always ran a mile every morning before breakfast. Was he right? Let’s find out.
More than a dozen experiments have been published comparing the amount of fat burned in a fasted versus fed state, and every single one found more fat was burned on an empty stomach. On average, a single bout of low-to-moderate intensity activity before a meal burned off three grams more fat than the same amount of exercise after a meal. That’s about three-quarters of a pat of butter’s worth of fat––enough to improve insulin sensitivity. The same amount of exercise, but more fat loss, all because of timing.
Now, just because you burn more fat while you’re exercising doesn’t necessarily mean you end up with less fat at the end of the day. Maybe your body offsets the extra fat loss that occurs during exercise with a little extra fat storage when you finally do eat, balancing it out. Researchers in Japan set out to investigate the possibility that your body makes up for it later by measuring 24-hour fat balance after 100 minutes of running, either before breakfast or after lunch. On the exercise-after-lunch day, they burned a total of 608 calories of fat over the course of that day. In contrast, on the exercise-before-breakfast days, in the same 24-hour period they burned through nearly 90 percent more, 1,142 calories of straight fat. So, the next day, they woke up with about a quarter-cup of fat less after the same amount of exercise. That’s remarkable!
What about just something like walking? Sixty minutes before breakfast, after lunch, or after dinner. Over the 24 hours they exercised in the evening, 432 calories were burned off. On the afternoon exercise day, they burned off 446 calories of fat. They also had a control day with no exercise at all, and on that day, they burned through 456 fat calories. That’s disappointing—it’s like they never walked at all. But the same amount of exercise before breakfast resulted in 717 calories of fat loss. Over the course of a day, timing matters, so much so that when it comes to an hour of walking, exercise increases 24-hour fat burning only when it is performed before breakfast. Here’s the fat balance graph with no exercise. You can see the fat storage bump up at breakfast, lunch, and supper, before slowly coming back down overnight. Exercise in the afternoon or evening, and end up with more fat than not exercising at all, but exercise in the morning and at least your fat balance comes back to baseline.
All such similar studies on both men and women show we burn through more fat on the days we exercise before, rather than after eating. After reading the chronobiology chapter in How Not to Diet, though, or watching my chronobiology videos, an alternative explanation may spring to mind. Maybe it’s just a morning thing. Maybe it has nothing to do with meals, and your circadian rhythm is just dictating the difference? No. Exercising in the morning after breakfast appears no better than exercising in the evening after dinner, and exercising before breakfast works better than immediately after breakfast––both still in the morning. It really does seem to be a pre- versus post-meal effect. But why?
Carbohydrate is the preferred fuel of the body. When you eat sugars or starches, they get broken down and converted into blood sugar. After a meal, blood sugars rise and your muscles are quick to snatch it up for fuel without having to rely much on your energy stores. If you instead take a siesta, and your muscles have no immediate need for energy, the excess blood sugar from a meal can be stored in our muscles in the form of glycogen for later use. Glycogen is just a bunch of blood sugar molecules strung together into a mass of branches that can be broken off and used for quick bursts of energy any time we need them.
If you exercise after a meal, your muscles can siphon off some of the extra blood sugar floating around for energy. Before a meal, your muscles have to instead resort to dipping into your energy stores and end up burning mostly a combination of glycogen and fat. That explains why you burn more fat during fasted exercise, but what about all the extra fat burned throughout the rest of the day?
Glycogen is more than a store. Glycogen isn’t just an energy reserve, but acts as a sensor capable of activating metabolic pathways. Exercising before breakfast can exhaust as much as 18 percent of your glycogen stores, and that depletion can act as a powerful rallying cry to your fatty tissues to start pulling more of their own weight by breaking down more fat. The lower glycogen stores fall, the greater the sustained 24-hour fat loss.
How long do you have to go without food in order to trigger this effect? Six hours may be sufficient; so, it doesn’t have to be before breakfast. If you timed it right, you could exercise before a late lunch, or if you have an early enough lunch, maybe before dinner when you get home from work. If exercise in a fasted state isn’t possible, does it matter what you eat? Insulin release after a meal appears to play a critical role in suppressing fat breakdown, explaining why lower glycemic foods—in this case, muesli versus cornflakes—can have less of an effect. Lentils were identified as a promising option for maintaining athletic endurance (which can take a hit on an empty stomach) while maintaining more of the fat dissolution. Lentils are said to be “unlikely to be consumed by the general population…due to low palatability.” They obviously haven’t tried my mom’s lentil soup.
It’s worth mentioning that although there’s increased 24-hour fat burning exercising in a fasted state, the only way to see if this facilitates weight loss over time is to put it to the test, which we’ll explore next.
Please consider volunteering to help out on the site.
- Haxhi J, Scotto di Palumbo A, Sacchetti M. Exercising for metabolic control: is timing important?. Ann Nutr Metab. 2013;62(1):14-25.
- Betts JA, Chowdhury EA, Gonzalez JT, Richardson JD, Tsintzas K, Thompson D. Is breakfast the most important meal of the day?. Proc Nutr Soc. 2016;75(4):464-74.
- Vieira AF, Costa RR, Macedo RC, Coconcelli L, Kruel LF. Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis. Br J Nutr. 2016;116(7):1153-64.
- Venables MC, Jeukendrup AE. Endurance training and obesity: effect on substrate metabolism and insulin sensitivity. Med Sci Sports Exerc. 2008;40(3):495-502.
- Iwayama K, Kawabuchi R, Park I, et al. Transient energy deficit induced by exercise increases 24-h fat oxidation in young trained men. J Appl Physiol (1985). 2015;118(1):80-5.
- Iwayama K, Kurihara R, Nabekura Y, et al. Exercise increases 24-h fat oxidation only when it is performed before breakfast. EBioMedicine. 2015;2(12):2003-2009.
- Iwayama K, Kawabuchi R, Nabekura Y, et al. Exercise before breakfast increases 24-h fat oxidation in female subjects. PLoS One. 2017;12(7):e0180472.
- Kim HK, Ando K, Tabata H, et al. Effects of Different Intensities of Endurance Exercise in Morning and Evening on the Lipid Metabolism Response. J Sports Sci Med. 2016;15(3):467-76.
- Farah NM, Gill JM. Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men. Br J Nutr. 2013;109(12):2297-307.
- Philp A, Hargreaves M, Baar K. More than a store: regulatory roles for glycogen in skeletal muscle adaptation to exercise. Am J Physiol Endocrinol Metab. 2012;302(11):E1343-51.
- Montain SJ, Hopper MK, Coggan AR, Coyle EF. Exercise metabolism at different time intervals after a meal. J Appl Physiol (1985). 1991;70(2):882-8.
- Stevenson EJ, Astbury NM, Simpson EJ, Taylor MA, Macdonald IA. Fat oxidation during exercise and satiety during recovery are increased following a low-glycemic index breakfast in sedentary women. J Nutr. 2009;139(5):890-7.
- Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise. Am J Physiol. 1997;273(4):E768-75.
- Thomas DE, Brotherhood JR, Brand JC. Carbohydrate feeding before exercise: effect of glycemic index. Int J Sports Med. 1991;12(2):180-6.
- Gonzalez JT, Stevenson EJ. New perspectives on nutritional interventions to augment lipid utilisation during exercise. Br J Nutr. 2012;107(3):339-49.
- Schoenfeld BJ, Aragon AA, Wilborn CD, Krieger JW, Sonmez GT. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 2014;11(1):54.
Motion graphics by Avo Media
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Title
The Best Time to Exercise for Weight Loss
LicenseCreative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Content URLDoctor's Note
Why not just fast longer for weight loss? See my video Is Fasting Beneficial for Weight Loss?.
One popular workout I looked into specifically was swimming. See Is Swimming Good for Weight Loss?
Stay tuned for Better to Exercise Before or After Meals for Weight Loss and Blood Sugar Control?, coming up next.
For more weight-loss tips, check out How Not to Diet from your local public library.
This is the start of a new volume of videos, which includes a series on the best time to exercise and another on yoga, how to get a good night’s sleep, and more. Each video in this new volume will be released online over the next few months—available for free, of course—but if you don’t want to wait, you can stream all of them right now.
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