Exercise on an EMPTY Stomach
Updated: Aug 16
I'll keep this week post brief. As we discuss in the podcast episode this is a very individual topic that comes down to numerous individual factors. If you do need more guidance please leave a comment on the post or directly contact us through the contact form. If you'd prefer to listen to our thoughts then the full episode is just down below. Before we get into the rest of the post I was to make clear that by empty stomach we mean food. You should remain as hydrated as possible and ensure sufficient fluid intake around physical activity.
Can you exercise on an empty stomach?
You can, however, this relies on numerous factors. You may wake in the morning and want to get some exercise in before work. You know from previous that if you eat now you'll have to wait a couple of hours before exercise otherwise you'll feel sick. What do you do? This is where it becomes very individual. What training are you going to do? Is this something you do regularly? (body has adapted) When was the last time you ate? Religious reasons? As I said numerous factors. There's probably more.
Our advice in this scenario
If you're doing something relatively "light" ie easy jog, low volume weight training basically anything not too arduous on the body then you should be alright. If however, you're doing something like a marathon or high-intensity interval training then it's advised to get on some food not only from a safety standpoint but performance as well. Even with light work, I'd be inclined to eat something like a banana but that's me personally because as I said numerous individual factors.
Speaking of performance
Now, this is where it gets more clear cut. There are probably cases where individuals have adapted to training in a fasted state and then there's the whole intermitted fasting thing (discussed in podcast) which could mean potential for training in a fasted state so overtime they could have adapted. Looking at data and my own personal experience eating prior to exercise is crucial for performance output.
The effects of nutrition on exercise metabolism and performance remain an important topic among sports scientists, clinical, and athletic populations. Recently, fasted exercise has garnered interest as a beneficial stimulus which induces superior metabolic adaptations to fed exercise in key peripheral tissues. Conversely, pre-exercise feeding augments exercise performance compared with fasting conditions. Given these seemingly divergent effects on performance and metabolism, an appraisal of the literature is warranted. This review determined the effects of fasting vs pre-exercise feeding on continuous aerobic and anaerobic or intermittent exercise performance, and post-exercise metabolic adaptations. A search was performed using the MEDLINE and PubMed search engines. The literature search identified 46 studies meeting the relevant inclusion criteria. The Delphi list was used to assess study quality. A meta-analysis and meta-regression were performed where appropriate. Findings indicated that pre-exercise feeding enhanced prolonged (P = .012), but not shorter duration aerobic exercise performance (P = .687). Fasted exercise increased post-exercise circulating FFAs (P = .023) compared to fed exercise. It is evidenced that pre-exercise feeding blunted signaling in skeletal muscle and adipose tissue implicated in regulating components of metabolism, including mitochondrial adaptation and substrate utilization. This review's findings support the hypothesis that the fasted and fed conditions can divergently influence exercise metabolism and performance. Pre-exercise feeding bolsters prolonged aerobic performance, while seminal evidence highlights potential beneficial metabolic adaptations that fasted exercise may induce in peripheral tissues. However, further research is required to fully elucidate the acute and chronic physiological adaptations to fasted vs fed exercise.
Aird TP, Davies RW, Carson BP. Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis. Scand J Med Sci Sports. 2018;28(5):1476-1493. doi:10.1111/sms.13054
Lots of word salad going on there. It does, however, support what I said earlier about long runs/training sessions. "Pre-exercise feeding bolsters prolonged aerobic performance" because as we know the bodies primary energy source is glucose so once this is depleted it's safe to say our level of performance will decrease. This is why you see long-distance athletes having a little gel sachet on the move to top up glucose levels. This again is individual as if you are not exercising for "performance" then it's really not as relevant.
Does it aid in weight loss?
A claim that gets thrown around is that by exercising on an empty stomach your body has to turn to fat for energy. This is true and some do actually train the body to be able to efficiently use fat as an energy source, more so that if they are doing a long arduous event that once glucose is depleted the performance levels don't drop drastically. This, however, has nothing to do with fat loss. It's clear why it's misinterpreted as such "using fat for energy". If you're in a calorie surplus and smashing loads of fasted exercise you are still going to gain weight. Energy balance is what's crucial for weight loss. I'd personally argue that by eating before/during you are more likely to increase performance output, therefore, increase calories burned.
Excess Postexercise Oxygen Consumption (EPOC)
Or commonly known as the "afterburn" effect where the body burns extra calories after certain activities. On an article, I read that was against training on an empty stomach one of the points made was the increase in EPOC when exercising in a fed state over a fasted state. Here is the conclusion of the study that was referenced (GM = glucose in milk)
Conclusion: These results suggest that preexercise intake of GM increases EPOC above that observed in the fasting condition, and high intensity short duration exercise increases fat oxidation during recovery period more than low intensity long duration exercise.
Lee YS, Ha MS, Lee YJ. The effects of various intensities and durations of exercise with and without glucose in milk ingestion on postexercise oxygen consumption. J Sports Med Phys Fitness. 1999;39(4):341-347.
Now what was difficult to tell was how significant this EPOC effect actually was. Something we said in the podcast was that perhaps by getting on glucose before the session you are actually increasing performance, therefore, burning extra calories due to higher output. So if weight loss was the goal and you saw this you'd be inclined to eat beforehand however if the effect is very limited then by eating before you are perhaps adding more energy to your daily total for very little extra benefit. Let's look at some more data on the extent of EPOC.
Let's look at cardio:
Although exercise intensity has been identified as a major determinant of the excess postexercise oxygen consumption (EPOC), no studies have compared the EPOC after submaximal continuous running and supramaximal interval running. Eight male middle-distance runners [age = 2.1 +/- 3.1 (SD) yr; mass = 67.8 +/- 5.1 kg; maximal oxygen consumption (VO2max) = 69.2 +/- 4.0 ml.kg-1.min-1] therefore completed two equated treatments of treadmill running (continuous running: 30 min at 70% VO2max; interval running: 20 x 1-min intervals at 105% VO2max with intervening 2-min rest periods) and a control session (no exercise) in a counter-balanced research design. The 9-h EPOC values were 6.9 +/- 3.8 and 15.0 +/- 3.3 liters (t-test:P = 0.001) for the submaximal and supramaximal treatments, respectively. These values represent 7.1 and 13.8% of the net total oxygen cost of both treatments. Notwithstanding the higher EPOC for supramaximal interval running compared with submaximal continuous running, the major contribution of both to weight loss is therefore via the energy expended during the actual exercise.
Laforgia J, Withers RT, Shipp NJ, Gore CJ. Comparison of energy expenditure elevations after submaximal and supramaximal running. J Appl Physiol (1985). 1997;82(2):661-666. doi:10.1152/jappl.19188.8.131.521
"The major contribution of both to weight loss is therefore via the energy expended during the actual exercise." Is a crucial takeaway point. Essentially saying that EPOC was pretty insignificant.
Let's look at resistance exercise:
The literature regarding caloric cost of EPOC after RE is widely variable. Some research suggests that the EPOC after RE lasts 36 h (25), and others showed a return to resting values in under 20 min (14,16,17). In our current study, the EPOC was measured to be a total of 7.4 kcal, and the metabolic rate (V˙O2) returned to baseline levels within 20 min postexercise. In addition, no significant difference was found between a 30-min postexercise caloric cost and a 30-min resting caloric expenditure. The postexercise caloric cost was measured to be 48.9 kcal, whereas resting was 41.5 kcal. On the basis of these results, the effect of EPOC with regard to caloric expenditure was deemed negligible. This is beneficial to note because of the potential for caloric cost from an initial lift carrying over to the next. On the basis of the current results and other literature (14,16,17), the EPOC between RE in succession would most likely be minimal.
APA LYTLE, JASON ROBERT1; KRAVITS, DANIELLE M.1; MARTIN, STEVEN E.1; GREEN, JOHN S.1; CROUSE, STEPHEN F.1; LAMBERT, BRAD S.2 Predicting Energy Expenditure of an Acute Resistance Exercise Bout in Men and Women, Medicine & Science in Sports & Exercise: July 2019 - Volume 51 - Issue 7 - p 1532-1537
Once again this suggests that EPOC does of course exist but to a "negligible" amount. I thought it was important to discuss this as if you are in a situation where you need to train fasted/empty stomach and you came across articles claiming EPOC is increased by eating before exercise you may force yourself to eat when in reality you'd rather not. So from the data, it's clear that EPOC is insignificant and that the major contributor to weight loss is the calorie expended during the exercise. Once again I'd say that eating beforehand will increase performance so in turn should increase calories expended during activity.
We go into a lot more detail on the podcast episode which can be found at the top of this article but I believe this post gets the core message out there. However, as I also said it comes down to numerous individual factors so it's hard to give "one size fits all" advice. If you do need any more guidance then please get in touch and we will help the best way we can.
Final Points. Yes, you can exercise on an empty stomach but take note of some of the key points I've made. Especially if the exercise is deemed quite arduous I'd always recommend taking some food on board but then the body can adapt. I mean yeah there are so many factors so It's hard to say any of this with pure conviction! Do you partake in intermittent fasting and train or perhaps wake up on an empty stomach and hit the gym? I'd love to know how you find it. Leave a comment or drop us an email! Back next week with more health and fitness related information to wrap your brains around! Speak soon.