Je hebt natuurlijk wel gedeeltelijk gelijk.
Er zijn voorstanders en tegenstanders van activiteit op nuchtere maag. Ik heb er ooit mijn voordeel mee gedaan, maar een andere manier had wellicht net zo goed kunnen werken.
Onderstaand artikel van Jerry Brainum vond ik in mijn archief wat jouw mening onderschrijft.
A commonly used technique by bodybuilders seeking to lose excess body fat prior to a contest involves doing aerobic exercise while in a fasted state. The usual practice is to do the aerobics first thing in the morning, prior to eating or drinking anything. The rationale behind this is that when you first awaken, both your stored glycogen and insulin levels are low due to a lack of food intake over an 8-hour (or however long you slept) time period. Glycogen is basically stored complex carbohydrates, and are the primary fuel for anaerobic exercise, such as typical weight-training sessions. Glycogen, however, is also involved in the initial stages of aerobics. In fact, during the first 30 minutes of aerobics, the usual fuel mixture being utilized is a 50/50 ratio of stored glycogen in muscle, along with circulating blood glucose. Fat doesn't even kick in until around the 30 minute mark, and the use of fat as a primary fuel increases with the duration of the exercise. By the 90-minute mark, fat is now the primary fuel, as much of the stored muscle glycogen and blood glucose levels have significantly declined by that point.
With fasted aerobics, the idea is that you will be able to tap into fat stores much faster than usual, since the primary blockers of fat use, insulin and carbs as glycogen, are low. This makes sense from a physiological point of view, since it's true that when you awaken, your stored glycogen levels are rather low, having been used during the hours you have slept. And because you haven't consumed any food, your insulin levels are also at a low point. This is important, since when insulin levels in the blood are high, fat mobilization is blunted significantly. This is one reason why you wouldn't want to consume carbs during your workout if your goals are to lose body fat. But would eating carbs before the workout adversely affect fat usage? The answer will soon be apparent.
There is some evidence that doing aerobics or"cardio" in a fasted state does indeed promote changes in the body that favor fat usage as a fuel source during exercise. For example, one 6-week study of fasting cardio showed a greater increase in intramuscular fatty acid binding protein and uncoupling protein-3 when doing the exercise fasted compared to doing it after eating a meal. The fatty acid binding protein is used to transport fat into the mitochondria of cells, where the oxidation or "burning" of fat actually occurs. Having this increase in intramuscular fat stores would suggest that those fat stores are more easily used during exercise. Indeed, having larger intramuscular fat stores is considered desirable for athletes and those who exercise regularly. In those who are sedentary, the same intramuscular fat stores are considered unhealthy and are associated with insulin resistance and diabetes onset. The uncoupling protein-3 is a thermogenic protein that converts fat into heat. Thyroid hormones promote the use of fat as a fuel by stimulating the activity of uncoupling proteins, especially in the cell mitochondria, which as noted, is the site of fat oxidation in the body. Other studies have shown that fasted cardio promotes improvements in glucose tolerance and insulin sensitivity, as well as boosting the activity of enzymes related to the breakdown of body fat.
As such, there is a good theoretical basis for the notion that fasted cardio does boost fat oxidation compared to doing the same aerobics after a meal. But in reality, the research on this is paradoxical, with some studies showing a definite beneficial effect, and other studies showing not differences between doing aerobics in either a fed or fasting condition. A new study that featured non-obese young women sought to answer the question of whether doing aerobic exercise in a fasted state leads to a greater loss of body fat compared to doing them after a meal. The study stands out from that of previous studies because it was the first that examined the effects of fasted versus fed aerobics on subjects who were on a lower total caloric intake.
The study
The study consisted of 20 healthy young women, with an average age of 22. These women all did some form of aerobic exercise several times a week, and a few were even off-season track and field athletes. None were obese, and none of them lifted weights. But for the purposes of this study--to examine the effects of fed versus fasted aerobics--they couldn't be considered untrained because of their regular participation in both aerobic exercise and track events.
The training consisted of an hour of steady-state aerobics three days a week on a treadmill. For the first five minutes of exercise, the women did a warm-up consisting of exercise at a rate of 50% of maximal heart rate, which is low intensity. For the following 50 minutes, they raised the intensity of the exercise to 70% of maximal heart rate (based on age), then finished with another 5-minute low intensity cool-down. They trained mainly at the 70% rate because prior studies have shown that this is about the rate at which the highest use of fat occurs during exercise. The higher the intensity of the exercise, as measured by heart rate, the greater the use of circulating carbs (glycogen and glucose) as fuel for the exercise. High intensity interval exercise, for example, uses mainly carbs to fuel the exercise, but the exhaustion of carbs during that type of exercise leads to greater fat usage in the hours following the exercise.
Women who did the exercise while fed ingested a meal replacement shake immediately prior to the exercise, while those in the fasted group got the same shake immediately after the exercise.
The primary result of the study was that both groups lost weight and fat, but neither group showed any more significant loss compared to the other. The primary result of the study was that both groups lost weight and fat, but neither group showed any more significant loss compared to the other. In short, in this study, doing fasted aerobics provided zero advantages for promoting a greater loss of body fat. While this study used a steady-state type of aerobics in which the heart rate is raised to a certain point and maintained for the duration of the exercise, another study showed the same results when interval aerobic exercise was done under either fasted or fed conditions.
Why would doing aerobics in a fasted state not produce better results than doing the same exercise following a meal? After all, all the requirements for burning more fat, such as lower insulin levels, lower glycogen and so on exist mainly in the fasted state. But not considered is the thermogenic effect of food. When you consume a meal prior to exercise, the meal contributes a small thermogenic effect; that is, it promotes the conversion of some of the calories consumed in the meal into heat, also known as a futile energy cycle, since calories are bring used without any work being performed. When you do the exercise after the meal, the exercise extends and adds to the meal's thermogenic effect. So the net effect is a greater use of calories to the extent that even if the fasted cardio did promote a faster use of fat as a fuel source, the effect of the meal and the exercise lead to the same results.
There are other aspects to consider when contemplating doing fasted aerobics. For one, when you first awaken in the morning, your cortisol levels are at the highest level of the day. Cortisol is an adrenal steroid hormone that is a major arbiter of muscle catabolism through working with another protein, myostatin. Under some circumstances, it's possible that you will tap into not only fat, but also muscle when doing fasted aerobics. Some studies have found that exercise under fasted conditions causes the loss of about 14 grams of protein per hour, and this protein comes from muscle.
Admittedly, any muscle you lose would be minuscule unless you did hours of extended fasted aerobics, but why chance the loss of any muscle at all when it's clear that fasted aerobics offers no real fat-loss benefits compared to doing fed aerobics? Admittedly, any muscle you lose would be minuscule unless you did hours of extended fasted aerobics, but why chance the loss of any muscle at all when it's clear that fasted aerobics offers no real fat-loss benefits compared to doing fed aerobics?
Interestingly, the authors of this study say that the results are more specific to lean young, active women, since these were the study subjects. They note that the "applicability of the present study's results to [contest preparation] remains open to question." However, based on previous studies that have also compared the effects of fasted versus fed aerobics, and not found any superior results in terms of fat loss with fasted aerobics, I'd say it's fair to say that doing fasted aerobics doesn't offer any additional benefits in this regard to competitive bodybuilders or fitness competitors, either.
References
Schoenfeld, B, et al. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nut 2014.
Info waarnaar je vroeg mbt vetverbruik heb ik zo niet bij de hand, maar zal je vast zelf kunnen terugvinden
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