Nutrition myths by Alan Aragon


Purple Belt
Mar 20, 2008
Reaction score
Myths Under The Microscope: The Low Intensity Fat Burning Zone & Fasted Cardio

By Alan Aragon


Why do natural bodybuilding contests for the most part look like swim meets minus the pool?

The obvious answer is the relative absence of anabolic and androgenic drugs that enable

The bandwagon is lead by blind horses

Many trainees pigeonhole weight training as an activity exclusively for building muscle, and cardio exclusively for burning fat. On the contrary, weight training can yield very similar results to cardio of similar intensity when 24-hr energy expenditure and macronutrient oxidation is measured [14]. The obvious advantage of weight training is the higher potential for lean mass and strength gains. In the bodybuilding context, cardio should be viewed as merely an adjunctive training mode to further energy expenditure and cross-complement the adaptations specific to weight training. As far as cardio being absolutely necessary for cardiovascular health, well, that depends upon the overall volume and magnitude of your weight training - another topic for another time.

Chaos theory strikes again

On the surface, it seems logical to separate carbs from cardio if you want a maximal degree of fat oxidation to occur during training. But, there’s the underlying mistake - focusing on stored fuel usage during training instead of focusing on optimally partitioning exogenous fuel for maximal lipolytic effect around the clock. Put another way, it’s a better objective to coincide your carb intake with your day’s thermic peaks, where insulin sensitivity & lean tissue reception to carbs is highest. For some reason, this logic is not easily accepted, nor understood. As we know, human physiology doesn’t always cooperate with logic or popular opinion, so let’s scrutinize the science behind the claims.


Carbohydrate ingestion during low-intensity exercise reduces fat oxidation

As far as 3 decades back, Ahlborg’s team observed that carb ingestion during low-intensity exercise (25-45% VO2 max) reduced fat oxidation compared to fasted levels [15]. More recently, De Glisezinski’s team observed similar results in trained men at 50% VO2 max [16]. Efforts to determine the mechanism behind this phenomenon have been made. Coyle’s team observed that at 50% VO2 max, carbohydrate availability can directly regulate fat oxidation by coordinating hyperinsulinemia to inhibit long-chain fatty acid transport into mitochondria [17].

Carbohydrate’s effect on fat oxidation during moderate-intensity exercise depends on conditioning level

Civitarese’s team found glucose ingestion during exercise to blunt lipolysis via decreasing the gene expression involved in fat oxidation in untrained men [18]. Wallis’ team saw suppressed fat oxidation in moderately trained men & women when glucose was ingested during exercise [19].

In contrast to the above trials on beginning and intermediate trainees, Coyle’s team repeatedly showed that carb ingestion during moderate-intensity (65-75% VO2 max) does not reduce fat oxidation during the first 120 min of exercise in trained men [20,21]. Interestingly, the intensity margin proximal to where fat oxidation is highest was unaffected by carb ingestion, and remained so for the first 2 hours of exercise.

Horowitz’ team examined the effect of a during-training solution of high-glycemic carbs on moderately trained men undergoing either low intensity exercise (25% VO2 max) or high-moderate intensity (68% VO2 max) [22]. Similar results to Coyle’s work were seen. Subjects completed a 2-hr cycling bout, and ingested the carb solution at 30, 60, and 90 minutes in. In the low-intensity treatment, fat oxidation was not reduced below fasted-state control group’s levels until 80-90 min of exercise. In the 68% group, no difference in fat oxidation was seen whether subjects were fasted or fed throughout the trial.

Further supporting the evidence in favor of fed cardio in trained men, Febbraio’s team investigated the effects of carb ingestion pre & during training in easily one of the best-designed trials on this topic [23]. Subjects exercised for 2 hrs at an intensity level of 63% VO2 max, which is now known as the point of maximal fat oxidation during exercise [1]. Result? Pre & during-training carbs increased performance - and there was no difference in total fat oxidation between the fasted and fed subjects. Despite the elevated insulin levels in the carb-fueled groups, there was no difference in fat availability or fat utilization.

Summing up the research findings

• At low intensities (25-50% VO2 max), carbs during exercise reduce fat oxidation compared to fasted trainees.
• At moderate intensities (63-68% VO2 max) carbs during exercise may reduce fat oxidation in untrained subjects, but do not reduce fat oxidation in trained subjects for at least the first 80-120 minutes of exercise.
• Carbohydrate during exercise spares liver glycogen, which is among the most critical factors for anticatabolism during hypocaloric & other conditions of ****bolic stress. This protective hepatic effect is absent in fasted cardio.
• At the established intensity level of peak fat oxidation (~63% VO2 max), carbohydrate increases performance without any suppression of fat oxidation in trained subjects.

Not an "Either-Or" Issue

The current facts have been presented in parts 1 & 2, and the bases for conclusion should be self-evident. Let me clarify that HIIT and linear high-intensity cardio are not the best and only ways to go. Many folks have perfectly legitimate orthopedic, cardiac, and even psychological reasons to avoid them. Not only that, I sincerely believe that both low and high-intensity cardio have unique benefits unto themselves. Optimally, both types should be done, since each has specifically different effects. Saying that one is bottom-line superior to the other for improvement in body composition is as false as blanketly saying 5 reps per set is superior to 15. On the contrary, there is well-established benefit in periodizing training variables, including intensity of cardio.

Too Much of the Same?

I've heard it mentioned that high-intensity cardio shouldn’t be done concurrently with high-intensity weight training due to excessive stress on the central nervous system. Perfect excuse. My primary response is, there's no solid proof of that danger. Certainly there's no evidence of it in my observations as a professional in the field, working with bodybuilders, and all types of other competitive athletes such as gymnasts, sprinters, boxers, etc (you know, athletes whose incredible physiques have nothing to do with weights + high intensity cardio). It's true that some folks regard a precociously low carb intake as a legit reason to keep intensity low. However, if your nutritional program doesn't adequately support productive training, then you've designed it ass-backwards, painting yourself into a corner of compromised adaptation.

The Options

Options can be broken down in the following ways: If you're pressed for time, and you can do HIIT without any delayed onset muscle soreness overlap (by virtue of doing a low frequency of HIIT), and you can tolerate it joint-wise & heart-wise, and you hate spending time doing cardio to begin with, then do HIIT. On the other hand, if you have the time to allot for low-intensity steady state (LISS), and you do a particularly high volume & magnitude of resistance training which raises potential recovery conflicts posed by a high frequency of HIIT, then do LISS. If you're somewhere in between the aforementioned 2 camps and you don't have a specific preference or tolerance limit, do both types on either a cyclical, rotational, or even combined basis. Also, it can't be overstated that unless you undergo a very gradual progression towards the the musculoskeletal tolerance for something like sprinting, you can get hurt pretty bad & there goes your productive training for several weeks.

Fasted = Suboptimal

Fasted cardio is not optimal for reasons spanning beyond its questionable track record in research. There’s unavoidable positive ****bolic synergy in fed (read: properly fueled) training, regardless of sport. This effect increases with intensity of training; even in untrained subjects, whatever fat oxidation is suppressed during training is compensated for in the recovery period by multiple mechanisms, many of which are not yet identified.

Athletes are known for their gravitation towards self-sacrifice, but some rely on hearsay, while others rely on science. Did you know that way back in the 60's, it wasn’t uncommon for coaches to tell athletes in various sports to avoid drinking water before and during training? No comment needed. Good thing researchers questioned it, and enough data surfaced to validate claims of the skeptics. Sometimes counterproductive dogma indeed dies, thank goodness. However, the myths addressed here are admittedly more subtle than the water example. Even on suboptimal protocols, athletes all over the world still inch along, although not at optimal rates, and not necessarily to optimal levels.


I see the bottom line like this.. Do the type you have a personal preference for, and also respect your physical limits. HIIT is quicker but riskier. LISS is safer but takes twice as long to accomplish the same thing. Again, do what you prefer & can tolerate, but do NOT make the mistake of assuming that LISS burns more fat. That's misunderstanding the physiology of the matter.

I'll end off by challenging you to diligently review the facts before blindly latching onto the myths.


1. Achten J, Jeukendrup AE. Relation between plasma lactate concentration and fat oxidation rates over a wide range of exercise intensities. Int J Sports Med. 2004 Jan;25(1):32-7.
2. Thompson DL, et al. Substrate use during and following moderate- and low-intensity exercise: implications for weight control. Eur J Appl Physiol Occup Physiol. 1998 Jun;78(1):43-9.
3. Phelain JF, et al. Postexercise energy expenditure and substrate oxidation in young women resulting from exercise bouts of different intensity.J Am Coll Nutr. 1997 Apr;16(2):140-6.
4. Lee YS. Et al. 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 Dec;39(4):341-7.
5. Melanson EL, et al. Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation. J Appl Physiol. 2002 Mar;92(3):1045-52.
6. Saris WH, Schrauwen P. Substrate oxidation differences between high- and low-intensity exercise are compensated over 24 hours in obese men.
7. Grediagin A, et al. Exercise intensity does not effect body composition change in untrained, moderately overfat women. J Am Diet Assoc. 1995 Jun;95(6):661-5.
8. Mougios V, et al. Does the intensity of an exercise programme modulate body composition changes? Int J Sports Med. 2006 Mar;27(3):178-81.
9. Okura T, et al. Effects of exercise intensity on physical fitness and risk factors for coronary heart disease. Obes Res. 2003 Sep;11(9):1131-9.
10. Tremblay, et al. Impact of exercise intensity on body fatness and skeletal muscle ****bolism. ****bolism. 1994 Jul;43(7):814-8.
11. Yoshioka M, et al. Impact of high-intensity exercise on energy expenditure, lipid oxidation and body fatness. Int J Obes Relat ****b Disord. 2001 Mar;25(3):332-9.
12. Broeder CE, et al. The effects of either high-intensity resistance or endurance training on resting ****bolic rate. Am J Clin Nutr. 1992 Apr;55(4):802-10.
13. Gutin B, et al. Effects of exercise intensity on cardiovascular fitness, total body composition, and visceral adiposity of obese adolescents. Am J Clin Nutr. 2002 May;75(5):818-26.
14. Melanson EL, et al. Resistance and aerobic exercise have similar effects on 24-h nutrient oxidation.. Med Sci Sports Exerc. 2002 Nov;34(11):1793-800.
15. Ahlborg, G., and P. Felig. Influence of glucose ingestion on fuel-hormone response during prolonged exercise. J. Appl. Physiol. 1976;41:683-688.
16. De Glisezinski I, et al. Effect of carbohydrate ingestion on adipose tissue lipolysis during long-lasting exercise in trained men. J Appl Physiol. 1998 May;84(5):1627-32.
17. Coyle EF, et al. Fatty acid oxidation is directly regulated by carbohydrate ****bolism during exercise. Am J Physiol. 1997 Aug;273(2 Pt 1):E268-75.
18. Civitarese AE, et al. Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes. Am J Physiol Endocrinol ****b. 2005 Dec;289(6):E1023-9.
19. Wallis GA, et al. ****bolic response to carbohydrate ingestion during exercise in males and females. Am J Physiol Endocrinol ****b. 2006 Apr;290(4):E708-15.
20. Coyle, et al. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J. Appl. Physiol. 1986;6:165-172.
21. Coyle, et al.. Carbohydrates during prolonged strenuous exercise can delay fatigue. J. Appl. Physiol. 59: 429-433, 1983.
22. Horowitz JF, et al. Substrate ****bolism when subjects are fed carbohydrate during exercise. Am J Physiol. 1999 May;276(5 Pt 1):E828-35.
23. Febbraio MA, et al. Effects of carbohydrate ingestion before and during exercise on glucose kinetics and exercise performance. J Appl Physiol. 2000

Read the red folks:)
Interesting stuff, but not exactly revolutionary.
someone translate into three sentences or so. i got kicked in the head and i am a little dumber
No, read it and educate yourself.

While I agree with the sentiment, better for people to know than not to know.

Easy summary: Fasted cardio is dumb and ineffective, UNLESS you're out of shape and quite overweight, and doing low intensity cardio for long periods of time. If you're even close to being an athlete, get your carbs in pre- and post-workout.

A lot of people on this forum might want to take this to heart, I constantly see people bad-mouthing pre and during workout carbs, and suggesting that we all just drink water.
A lot of people on this forum might want to take this to heart, I constantly see people bad-mouthing pre and during workout carbs, and suggesting that we all just drink water.

After reading that one thread on the subject, I decided to drop the water and take a carb+protein drink.
someone translate into three sentences or so. i got kicked in the head and i am a little dumber

Didn't read it all, but it seems like the main point was:

"Although you burn fat more exclusively at low intensity exercises, high-intensity exercises are more beneficial for you in the long run."


"Although some people rely on cardio for fat loss, weight training has similar effects and can be beneficial for fat loss as well"