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    Default Should I Do Cardio Fasted?

    The Lowdown on Fasted Cardio

    Great for Fat loss or Not?

    Team MD
    One of the most popular bodybuilding strategies for accelerating fat loss is to perform aerobic exercise after an overnight fast. The strategy is based on acute research showing that low glycogen levels cause your body to shift substrate utilization away from carbs, thereby allowing greater mobilization of stored fat for energy.
    Indeed, some studies have shown that consumption of carbohydrates prior to engaging in aerobic exercise reduces entry of long-chain fatty acids into the mitochondria, thus inhibiting fat oxidation.1,6,9,5 Here’s the kicker, though: results are specific to low-intensity cardio. While fat breakdown is accelerated during fasted high-intensity cardio, the amount of available fatty acids exceeds the body’s ability to use them for fuel.3,7 Hence, the common practice of performing HIIT while fasted is actually counterproductive from a fat-burning standpoint.
    While acute research would seem to suggest a potential benefit to performing fasted cardio— at least at lower intensities— there’s one not-so-little problem when attempting to extrapolate results into practice: namely, the amount of fat burned during exercise does not necessarily reflect actual fat loss. Understand that the human body continually adjusts its use of substrate in accordance with a multitude of factors that can change from moment to moment.14
    Take home point: Fat burning must be evaluated over the course of days— not on an hourly basis— to truly understand its effect on body composition.5

    The Study
    Recently, my lab sought to determine whether fasted cardio actually promoted differences in fat loss over time. Twenty recreationally trained college-aged women were randomly assigned to either a fasted training (FASTED) group that performed exercise after an overnight fast or a non-fasted training (FED) group that consumed a meal prior to exercise. On training days, the morning meals were consumed in the form of a shake that provided 40 grams of carbs and 20 grams of protein. These meals were ingested under the supervision of the research team to ensure that subjects adhered to either the FASTED or FED conditions.
    The training protocol consisted of one-hour sessions of supervised steady-state treadmill exercise performed at 70 percent of maximal heart rate— an intensity that equated to a fast walk/jog. The low-intensity nature of the protocol ensured that any fat-burning advantages associated with fasted cardio would translate into greater improvements in body composition. Training was carried out three days per week for four weeks.
    To help control food intake and thus optimize fat loss, subjects were given customized meal plans designed to create a 500-calorie deficit. The meal plans provided a balance of carbs (~45%), protein (~30%) and fats (25%), and allowed ample ability for the subjects to choose their preferred foods. Subjects recorded their daily food consumption in an online journal for continual monitoring of nutritional intake. Nutritional counseling was provided throughout the study period to enhance dietary adherence.
    The results were somewhat surprising: Although both groups lost a significant amount of weight and body fat, no differences were noted between conditions in any body composition measure. Adherence to the program was excellent, with average attendance equating to more than 95 percent of total sessions.

    The Thermic Effect of Exercise, and Fat Stores
    The discrepancies between acute and long-term findings can be explained by the fact that consuming a meal before exercise increases a phenomenon termed the thermic effect of exercise (TEE). The influence of performing cardio in the fed state on TEE was demonstrated in a crossover study by Paoli et al,12 where subjects participated in two separate treatment conditions: On one occasion the subjects performed a bout of moderate-intensity cardio after eating; in the other they performed the same exercise protocol after an overnight fast. Meals were individually prepared by the researchers so the total quantity of food and macronutrient ratio did not differ between conditions. Results showed a greater utilization of fat as a fuel source following exercise in the fed condition, with differences remaining significant 24 hours post-workout. Similar results have been reported by other researchers,2,4,11 although a recent study contradicts these findings.10
    The take home point here is that acute studies do not distinguish between subcutaneous fat and IMTG, and thus the net effect of increasing fat utilization during training becomes increasingly less relevant with long-term aerobic adherence.

    Study Limitations
    So does this mean that there is no benefit to performing fasted cardio? Not necessarily.
    A couple of study limitations need to be taken into account when attempting to draw evidence-based conclusions. For one, the study was of relatively short duration, spanning only four weeks. While this period of time was sufficient to achieve significant fat loss, it remains possible that very slight differences between conditions might take longer to manifest.
    Moreover, the findings are specific to young, recreationally trained women and cannot necessarily be generalized to hard-training physique athletes. It has been postulated that the true benefit of fasted cardio is specific to those with low levels of body fat (e.g., pre-contest bodybuilders) who are trying to lose that last pound or two of stubborn fat. Whether this outcome plays out in practice is yet to be determined.

    The Bottom Line
    It appears clear that if there are in fact any benefits from fasted cardio, they would be minor at best. Although it remains possible that lean bodybuilers might see small but potentially meaningful benefits on fat loss from performing exercise prior to a morning meal, the strategy just as easily could have a negative impact on fat burning via a reduced TEE. When considering all the evidence, the best advice here would be to experiment with both strategies and try to objectively determine what works best for you as an individual.
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    my 2 cents.. cortisol levels are at their highest in the morning. With that being said I don't think high intensity cardio should be done at that time.
     

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    I do 20 to 30 min in the morning. Just steady cardio nothing crazy and it seems to work for me.
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    Quote Originally Posted by chihuahua View Post
    my 2 cents.. cortisol levels are at their highest in the morning. With that being said I don't think high intensity cardio should be done at that time.
    Dbol + Caffeine + Vit C and you are safe
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    If I'm cutting I do my cardio in early morning no food just a 0 calorie free e-drink and my thermos.This works well for me esp if I add in arimidex that helps shed water .The am cardio helps me more than anything else except diet to get the abs to make a guest appearance.
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    I never do a truely fasted cardio. I get my best results from 5-10g of BCAA and adding a small amount of custom carbs like HCBD (5g).
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    Quote Originally Posted by drtbear1967 View Post
    I do 20 to 30 min in the morning. Just steady cardio nothing crazy and it seems to work for me.
    ^^This^^ Steady is the key.
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    Starvation cardio works for me. 22-25mins on the treadmill walking at 2.8mph at a 12degree incline.
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    Quote Originally Posted by LeatherHead View Post
    Starvation cardio works for me. 22-25mins on the treadmill walking at 2.8mph at a 12degree incline.
    Same here but I make sure I'm on something anti-catabolic and drink bcaa's before and during. Zero calories.
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