new article- fasted cardio is out.....YES!

[terraj]

A new article on fasted cardio appearing in the Strength and Conditioning Journal by Brad Schoenfeld, MSc, CSCS

Sorry I have no refs.


Does Cardio After an Overnight Fast Maximise Fat Loss?

A common fat burning strategy employed by bodybuilders, athletes, and fitness enthusiasts is to perform cardiovascular exercise early in the morning on an empty stomach. This strategy was popularized by Bill Phillips in his book, ‘‘Body for Life’’ (23). According to Phillips, performing 20 minutes of intense aerobic exercise after an overnight fast has greater effects on fat loss than performing an entire hour of cardio in the postprandial state. The rationale for the theory is that low glycogen levels cause your body to shift energy utilization away from carbohydrates, thereby allowing greater mobilization of stored fat for fuel. However, although the prospect of reducing the body fat by training in a fasted state may sound enticing, science does not support its efficacy.

First and foremost, it is shortsighted to look solely at how much fat is burned during an exercise session. The human body is very dynamic and continually adjusts its use of fat for fuel. Substrate utilization is governed by a host of factors (i.e., hormonal secretions, enzyme activity, transcription factors, etc), and these factors can change by the moment (27). Thus, fat burning must be considered over the course of days—not on an hour-to-hour basis—to get a meaningful perspective on its impact on body composition (13). As a general rule, if you burn more carbohydrate during a workout, you inevitably burn more fat in the post- exercise period and vice versa.
It should be noted that high-intensity interval training (HIIT) has proven to be a superior method for maximizing fat loss compared with a moderate- intensity steady-state training (10,26,29). Interestingly, studies show that blood flow to adipose tissue diminishes at higher levels of intensity (24). This is believed to entrap free fatty acids within fat cells, impeding their ability to be oxidized while training. Yet, despite lower fat oxidation rates during exercise, fat loss is nevertheless greater over time in those who engage in HIIT versus training in the ‘‘fat burning zone’’ (29), providing further evidence that 24-hour energy balance is the most important determinant in reducing body fat.

The concept of performing cardiovascular exercise on an empty stomach to enhance fat loss is flawed even when examining its impact on the amount of fat burned in the exercise session alone. True, multiple studies show that consumption of carbohydrate before low- intensity aerobic exercise (up to approximately 60% V_o2max) in untrained subjects reduces the entry of long-chain fatty acids in the mitochondria, thereby blunting fat oxidation (1,14,18,28). This is attributed to an insulin -mediated attenuation of adipose tissue lipolysis, an increased glycolytic flux, and a decreased expression of genes involved in fatty acid transport and oxidation (3,6,15). However, both training status and aerobic exercise intensity have been shown to mitigate the effects of a pre-exercise meal on fat oxidation (4,5,24). Recent research has shed light on the complexities of the subject.

Horowitz et al. (14) studied the fat burning response of 6 moderately trained individuals in a fed versus fasted state to different training intensities. Subjects cycled for 2 hours at varying intensities on 4 separate occasions. During 2 of the trials, they consumed a high-glycemic carbohydrate meal at 30, 60, and 90 minutes of training, once at a low intensity (25% peak oxygen consumption) and once at a moderate intensity (68% peak oxygen consumption). During the other 2 trials, subjects were kept fasted for 12–14 hours before exercise and for the duration of training. Results in the low-intensity trials showed that although lipolysis was suppressed by 22% in the fed state compared with the fasted state, fat oxidation remained similar between groups until 80–90 minutes of cycling. Only after this point was a greater fat oxidation rate observed in fasted subjects. Conversely, during moderate-intensity cycling, fat oxidation was not different between trials at any time—this is despite a 20–25% reduction in lipolysis and plasma Free fatty acid concentration.

More recently, Febbraio et al. (9) evaluated the effect of pre-exercise and during exercise carbohydrate consumption on fat oxidation. Using a crossover design, 7 endurance- trained subjects cycled for 120 minutes at approximately 63% of peak power output, followed by a ‘‘performance cycle’’ where subjects expended 7 kJ/(kg body weight) by pedaling as fast as possible. Trials were conducted on 4 separate occasions, with subjects given (a) a placebo before and during training, (b) a placebo 30 minutes before training and then a carbohydrate beverage every 15 minutes throughout exercise, (c) a carbohydrate beverage 30 minutes before training and then a placebo during exercise, or (d) a carbohydrate beverage both before and every 15 minutes during exercise. The study was carried out in a double- blind fashion with trials performed in random order. Consistent with previous research, results showed no evidence of impaired fat oxidation associated with consumption of carbohydrate either before or during exercise.

Taken together, these studies show that during moderate-to-high intensity cardiovascular exercise in a fasted state—and for endurance-trained individuals regardless of training intensity— significantly more fat is broken down than that the body can use for fuel. Free fatty acids that are not oxidized ultimately become re-esterified in adipose tissue, nullifying any lipolytic benefits afforded by pre-exercise fasting.

It should also be noted that consumption of food before training increases the thermic effect of exercise. Lee et al. (19) compared the lipolytic effects of an exercise bout in either a fasted state or after consumption of a glucose/milk (GM) beverage. In a crossover design, 4 experimental conditions were studied: low-intensity long duration exercise with GM, low-intensity long duration exercise without GM, high- intensity short duration exercise with GM, and high-intensity short duration exercise without GM. Subjects were 10 male college students who performed all 4 exercise bouts in random order on the same day. Results showed that ingestion of the GM beverage resulted in a significantly greater excess postexercise oxygen consumption compared with exercise performed in a fasted state in both high- and low- intensity bouts. Other studies have produced similar findings, indicating a clear thermogenic advantage associated with pre-exercise food intake (7,11).

The location of adipose tissue mobilized during training must also be taken into account here. During low-to- moderate intensity training performed at a steady state, the contribution of fat as a fuel source equates to approxi- mately 40–60% of total energy expen- diture (30). However, in untrained subjects, only about 50–70% of this fat is derived from plasma Free fatty acids; the balance comes from intra- muscular triglycerides (IMTG) (30).
IMTG are stored as lipid droplets in the sarcoplasm near the mitochondria (2), with the potential to provide approximately two-thirds the available energy of muscle glycogen (32). Similar to muscle glycogen, IMTG can only be oxidized locally within the muscle. It is estimated that IMTG stores are approximately 3 times greater in type I versus type II muscle fibers (8,21,31), and lipolysis of these stores are max- imally stimulated when exercising at 65%V_o2max(24).

The body increases IMTG stores with consistent endurance training, which results in a greater IMTG utilization for more experienced trainees (12,16,22,31). It is estimated that nonplasma fatty acid utilization during endurance exercise is approximately twice that for trained versus untrained individuals (24,32). Hurley et al. (17) reported that the contribution of IMTG stores in trained individuals equated to approximately 80% of the total body fat utilization during 120 minutes of moderate- intensity endurance training.
The important point here is that IMTG stores have no bearing on health and/or appearance; it is the subcutaneous fat stored in adipose tissue that influences body composition. Consequently, the actual fat burning effects of any fitness strategy intended to increase fat oxida- tion must be taken in the context of the specific adipose deposits providing energy during exercise.

Another factor that must be considered when training in a fasted state is its impact on proteolysis. Lemon and Mullin (20) found that nitrogen losses were more than doubled when training while glycogen depleted compared with glycogen loaded. This resulted in a protein loss estimated at 10.4% of the total caloric cost of exercise after 1hourofcyclingat61%V_o2max.This would suggest that performing cardio- vascular exercise while fasting might not be advisable for those seeking to maximize muscle mass.

Finally, the effect of fasting on energy levels during exercise ultimately has an effect on fat burning. Training early in the morning on an empty stomach makes it very difficult for an individual to train at even a moderate level of intensity. Attempting to engage in a HIIT style routine in a hypoglycemic state almost certainly will impair performance (33). Studies show that a pre-exercise meal allows an individual to train more intensely compared with exercise while fasting (25). The net result is that a greater number of calories are burned both during and after physicalactivity,heightening fat loss.

In conclusion, the literature does not support the efficacy of training early in the morning on an empty stomach as a tactic to reduce body fat. At best, the net effect on fat loss associated with such an approach will be no better than training after meal consumption, and quite possibly, it would produce inferior results. Moreover, given that training with depleted glycogen levels has been shown to increase proteolysis, the strategy has potential detrimental effects for those concerned with muscle strength and hypertrophy.

[baseline_9]

I hate to disapoint you but....

This debate has been going on for over a decade

You can ready studys that support both sides of the argument

You could find another study next week that supports fasted cardio


I will say however that i do not think fasted cardio is a must do thing

I dont think it matters when u do ur cardio, as long as u do it

I think that most people do the AM fasted cardio because its easy to set ur alarm 60 mins early....

Atleast thats why i do it in the morning, not because i think im getting any added benefit from the fact that im glycogen depleted

[baseline_9]

I will also say that there are more studys nowadays against fasted cardio

[EASTCOASTKID]

Listen to your body not research. People get paid to write these articles.
My stats teacher always said I can make AIDS look positive if I want too....

FOOD FOR THOUGHT! and my 2 cents

[Sgt. Hartman]

Interesting article but I agree with the above posts. I just spent 10 minutes searching for studies on fasted cardio and found an equal amount of studies supporting each side.

IMO the biggest determining factor is genetics and BF % which it seems this study did not really account for.

In actuality, the type or time of cardio that is most beneficial is individual specific, and can only be learned through experience ie. trial and error.

This is what Lyle McDonald says about it:



This is probably one of the most commonly asked questions which is why it’s worth addressing. It’s worth keeping in mind that this idea usually comes out of the bodybuilding subculture, usually contest bodybuilders who, assuming their diet is working properly, are getting towards the low-end of body fat levels. And the short-answer to your question is that the body fat of the person is going to be the main determinant of whether doing cardio fasted in the morning is important or not.

To understand that, I need to cover a bit of background physiology, I’d mention that this is discussed in much more detail in both my Ultimate Diet 2.0 and The Stubborn Fat Solution for anybody who is truly interested in the topic. But simply, there are three primary steps involved in ‘losing’ fat, they are:

Mobilization
Transport
Oxidation (burning)

Mobilization refers to actually getting stored fat (specifically fatty acids) out of the fat cell; this process is under the primary control of insulin and the catecholamines although hormones such as growth hormone , cortisol and others play secondary or tertiary roles. Transport refers to the actual transport of fatty acids (bound to albumin) within the bloodstream; this step can be an issue when folks are dealing with stubborn body fat (such as lower ab/low back fat in men and hip/thigh fat in women); blood flow is impaired in those areas. Finally is oxidation which is the actual burning of fatty acids within tissues such as skeletal muscle, liver and heart.

Now, in lean individuals (where lean is around 12-15% body fat for men and about 19-22% for women), fat mobilization becomes a problem; blood flow is often an issue as well. As folks get leaner, the body undergoes a series of adaptations that occur to make getting fat out of the fat cells more difficult. For the most part, oxidation isn’t so much of a problem although there are strategies (such as skeletal muscle glycogen depletion) that can enhance the process; read my Ultimate Diet 2.0 for more details.

At the other extreme, that is in the very obese (here I’m talking about perhaps 35%+ body fat for men and 40%+ for women), the reverse problem is present. There are tons of fatty acids floating around in the bloodstream, but for a variety of reasons, oxidation has become impaired. To fully discuss this issue (along with approaches of fixing it) would require a full article an I won’t say much more about this group here.

And between those two extremes (so from about 15-35% body fat in men and ~20-40% body fat in women), there are really no issues. Mobilization is usually not a problem since the body hasn’t started to fight back, transport isn’t an issue since stubborn fat isn’t being targeted, and oxidation is rarely a problem since the defects which show up at the extremes of obesity generally aren’t present.

And that provides the answer:
For the lean trying to get very lean (15% body fat or less for men, 22% or less for women), various strategies, including fasted cardio are probably going to be required to offset the mobization and blood flow defects. That’s why that specific group found decades ago that fasted morning cardio worked best. And why I wrote The Stubborn Fat Solution since it deals with how to overcome all of the problems.

But for folks who aren’t that lean yet, the folks in the middle range of body fat levels, it really doesn’t matter. The best time to do cardio will be whenever it will most consistently get done. If that’s first thing in the morning, fantastic. If not, also fantastic. It’s more important in this situation that it gets done than when it gets done.

Again, for the extremely obese, different strategies entirely are required but, again that would take a full article to address so I won’t talk about it here.

[Dukkit]

Next there will be a study saying WHY SEX IS BAD.

And I just couldnt handle that.

lol

[terraj]

I hate to disapoint you but....

This debate has been going on for over a decade

You can ready studys that support both sides of the argument

You could find another study next week that supports fasted cardio


I will say however that i do not think fasted cardio is a must do thing

I dont think it matters when u do ur cardio, as long as u do it

I think that most people do the AM fasted cardio because its easy to set ur alarm 60 mins early....

Atleast thats why i do it in the morning, not because i think im getting any added benefit from the fact that im glycogen depleted

IMO physical exertion on an empty gut is muscle wasting, but that is my thought process.

Anyway I thought it was an interesting read and this is a forum for such topics...

Here is another one Myths Under The Microscope Part 2: False Hopes for Fasted Cardio

By Alan Aragon © 2006





False Hopes

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 [1]. 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.

Let The Research Speak

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 [2]. More recently, De Glisezinski’s team observed similar results in trained men at 50% VO2 max [3]. 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 [4].

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 [5]. Wallis’ team saw suppressed fat oxidation in moderately trained men & women when glucose was ingested during exercise [6].

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 [7,8]. 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) [9]. 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 [10]. 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. 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 metabolic 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.





References

1.
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.
2. Ahlborg, G., and P. Felig. Influence of glucose ingestion on fuel-hormone response during prolonged exercise. J. Appl. Physiol. 1976;41:683-688.
3. 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.
4. Coyle EF, et al. Fatty acid oxidation is directly regulated by carbohydrate metabolism during exercise. Am J Physiol. 1997 Aug;273(2 Pt 1):E268-75.
5. Civitarese AE, et al. Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes. Am J Physiol Endocrinol Metab. 2005 Dec;289(6):E1023-9.
6. Wallis GA, et al. Metabolic response to carbohydrate ingestion during exercise in males and females. Am J Physiol Endocrinol Metab. 2006 Apr;290(4):E708-15.
7. Coyle, et al. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J. Appl. Physiol. 1986;6:165-172.
8. Coyle, et al.. Carbohydrates during prolonged strenuous exercise can delay fatigue. J. Appl. Physiol. 59: 429-433, 1983.
9. Horowitz JF, et al. Substrate metabolism when subjects are fed carbohydrate during exercise. Am J Physiol. 1999 May;276(5 Pt 1):E828-35.
10. Febbraio MA, et al. Effects of carbohydrate ingestion before and during exercise on glucose kinetics and exercise performance. J Appl Physiol. 2000 Dec;89(6):2220-6.

[gbrice75]

Great articles, very interesting indeed. Great timing as well; i'm about 3 weeks away from a schedule change that will have me doing am fasted cardio and weight training in the early evening, thereby allowing me to truly focus carbs around my workout window.... time to make a decision on whether that will be optimal for me or not.

[Damienm05]

I dunno, I've seen too much literature supporting fasted cardio since joining this board to dismiss it based on this article (although, it's a good read and makes some sense).

I will say that, as I've said in other threads, catabolism via cardio is so stupidly overblown unless you're already at a very low body fat percentage or are carrying an amount of LBM well beyond genetic potential - it's only in these situations wherein fat becomes a last resource for fuel and muscle is preferred. I'm not talking about intense conditioning here, just sustaining 60-70% of max HR PWO/AM-fasted. I'm not speaking from speculation but my own experiences with cardio on a varying schedule and those of clients I've trained and people I've advised.

Now, in the same vein, I haven't noticed a difference in fat burning results based on when I do my cardio either but I think the fact that I do it consistently and in conjunction with a pretty good diet would make any increased results based on time of day too trivial to recognize.