If you’re a regular at the gym or do any research into the best time for cardio and weight training, you’ve probably come across the debate about working out in a fasted state versus a fed state.
The premise behind doing fasted cardio is that it maximizes fat burning. When you have nothing in your stomach, your body has nothing immediate to grab energy from.
Because of this, it’s going to burn through stored glucose (glycogen in the liver and the muscles) and then tap into your body fat.
This is a large reason some choose to take a fat burner on non-workout days, as doing so can allow you to stay on track with your fat loss results even on the days you don't train.
And while this seems logical, it’s not as simple as just burning through all of your stored glycogen in a 15-minute intense cardio session…
It’s more complicated than that, but you get the idea.
The idea behind why people tell you that you should take fat burners on an empty stomach is similar. When your body doesn’t have a bunch of food to sort through when it’s trying to absorb something, it’s a lot more efficient.
Key Takeaways
- “Empty stomach” dosing can speed stimulant onset but may increase jitters, nausea, and GI discomfort.
- Taking with a light snack can smooth absorption and tolerance with minimal impact on fat-loss goals.
- Caffeine sensitivity, product formula, and time of day matter—test timing and start with lower doses.
- Fat burners work best alongside calorie control, protein, sleep, and resistance training.
Remember that fat burners aren’t the be-all for fat loss—they are kind of like a crutch to a good idea.
You can’t fully rely on them to get the job done, but when you lean on them a bit to give you a hand, they can be a great addition to help you achieve your goals.
They do so in 3 ways 1:
- Trigger thermogenesis by increasing your body’s temperature to boost caloric expenditure
- Regulate appetite and help curb cravings by controlling hunger hormones and insulin
- Increase fat oxidation during exercise while preserving lean body mass
The problem with most conventional fat burners, however, is that they’re loaded with a bunch of synthetic ingredients and stimulants, so it’s hard to find one that does what you’re looking for without compromising your long-term health.
But it’s important to remember that they’re not all designed this way, so always follow the instructions on the label.
As a general rule, though, taking a fat burner on an empty stomach is ideal.
Here’s why:
If taken before breakfast, your fat burner will be more effective
There’s a simple reason behind this that aligns with the role of boosting your metabolic rate to increase calorie expenditure.
Your metabolism functions on a similar path to how you do. Straight out of bed, chances are you won’t be bright-eyed and bushy-tailed. You’re going to be a bit groggy, probably a little slow, and maybe even a little moody.
Your metabolism is the same.
At 6 am right when your alarm goes off, your metabolism won’t be screaming in your ear to get up and sure isn’t going to be firing at the same rate as it is at 2 pm or even noon.
Your metabolism works on a cycle that follows closely to your sleep-wake cycle.
It’s been shown that during normal sleep, your metabolic rate drops by approximately 15% and reaches its lowest point in the morning, assuming you’re on a regular sleep schedule/circadian pattern 2.
So, when you pop that fat burner first thing in the morning, you’re giving your metabolism a little kick in the pants to get it to where it should be.
At the same time, you’ll boost your body temperature faster; your core body temperature is at its lowest during sleep and gradually increases after waking.
You won’t get any nasty side effects
Ever noticed that some supplements say “take with food” but others don’t?
That’s because some can produce some unpleasant side effects when taken on an empty stomach, while others are better absorbed in the presence of certain compounds, like carbohydrates or fat.
Take B vitamins, for example. Take those on an empty stomach and chances are you’re going to feel nauseous.
Taken with glucose, peak HMB concentrations were delayed, and it decreased absorption; studies suggest that glucose may increase HMB excretion or delay gastric emptying, hence muting the effect 3.
Forskolin also has good bioavailability, with absorption rates being measured potentially around 100% 4.
Both compounds have shown no adverse effects taken orally 5, 6.
References
- AE Jeukendrup, R Randell. Fat burners: nutrition supplements that increase fat metabolism. Obesity Reviews. 2011 Oct; 12(10): 841-851.
- S Sharma, M Kavuru. Sleep and metabolism: an overview. Int J Endocrinol. 2010 Aug.
- JM Wilson, PJ Fitschen, B Campbell, et al. International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB). J Int Soc Sports Nutr. 2013;1 0(1): 6.
- B Salehi, M Staniak, K Czopek, A Stepien, K Dua, R Wadhwa, DK Chellappan, O Sytar, et al. The therapeutic potential of the labdane diterpenoid forskolin. Applied Sciences. 2019 Oct; 9(19).
- Memorial Sloan Kettering Cancer Center. Forskolin. Updated April 14, 2020.
- JG Wilson, JM Wilson, AH Manninen. Effects of beta-hydroxy-beta-methylbutyrate (HMB) on exercise performance and body composition across varying levels of age, sex, and training experience: A review. Nutr Metab (Lond). 2008; 5:1.
- JM Wilson, PJ Fitschen, B Campbell, JG Wilson, N Zanchi, L Taylor, C Wilborn, DS Kalman, JR Stout, JR Hoffman, TN Ziegenfuss, HL Lopez, RB Kreider, AE Smith-Ryan, J Antonio. International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB). J Int Soc Sports Nutr. 2013 Feb 2; 10(1): 6.
- G Tinsley, AH Givan, AJ Graybeal, MI Villarreal, AG Cross. β-Hydroxy β-methylbutyrate free acid alters cortisol responses, but not myofibrillar proteolysis, during a 24-h fast. Br J Nutr. 2018 Mar; 119(5): 517-526.
- V Fattori, MS Hohmann, AC Rossaneis, FA Pinho-Ribeiro, WA Verri. Capsaicin: Current Understanding of Its Mechanisms and Therapy of Pain and Other Pre-Clinical and Clinical Uses. Molecules. 2016; 21(7): 844.
- J Zheng, S Zheng, Q Feng, Q Zhang, X Xiao. Dietary capsaicin and its anti-obesity potency: from mechanism to clinical implications. Biosci Rep. 2017; 37(3).
