New evidence suggests you can reap important health benefits by exercising in a fasted state.
Research published in the August 2019 issue of The Journal of Nutrition found that skipping breakfast before exercise helps curb food intake for the remainder of the day, resulting in an overall energy deficit, in this case averaging 400 calories per day.
Earlier research, published in Y 2015, found that women who skipped breakfast and worked out on an empty stomach had better working memory in the midafternoon and reported less mental fatigue and tension later in the day than those who ate breakfast before exercising.
Fasted exercise has also been shown to be particularly helpful for fat loss, it essentially forces your body to shed fat. The reason for this is because your body’s fat burning processes are controlled by your sympathetic nervous system (SNS), and your SNS is activated by exercise and lack of food.
The combination of fasting and exercising maximizes the impact of cellular factors and catalysts (cyclic AMP and AMP kinases) that force the breakdown of fat and glycogen for energy. A 2012 study confirmed that aerobic training in a fasted state lowered both total body weight and body fat percentage, while exercising in a fed state decreased body weight only.
Exercise and fasting together also yields acute oxidative stress which, paradoxically, benefits your muscle.
A Y 2015 study in the journal Biomolecules explains: “Since the discovery of exercise-induced oxidative stress several decades ago, evidence has accumulated that ROS [reactive oxygen species] produced during exercise also have positive effects by influencing cellular processes that lead to increased expression of antioxidants.
These molecules are particularly elevated in regularly exercising muscle to prevent the negative effects of ROS by neutralizing the free radicals. In addition, ROS also seem to be involved in the exercise-induced adaptation of the muscle phenotype.”
In “The Exercise Mistake Which Makes You Age Faster,“ Ori Hofmekler, fitness expert and author of several books, including “Unlock Your Muscle Gene” and “The 7 Principles of Stress,” addresses this issue as well, explaining that acute states of oxidative stress are:
” … essential for keeping your muscle machinery tuned. Technically, acute oxidative stress makes your muscle increasingly resilient to oxidative stress; it stimulates glutathione and SOD [superoxide dismutase, the first antioxidant mobilized by your cells for defense] production in your mitochondria along with increased muscular capacity to utilize energy, generate force and resist fatigue.
Simply put, exercise and fasting yield acute oxidative stress, which keeps your muscles’ mitochondria, neuro-motors, and fibers intact. Hence, exercise and fasting help counteract all the main determinants of muscle aging.”
Mr. Hofmekler also points out that, combined, exercise and fasting “trigger a mechanism that recycles and rejuvenates your brain and muscle tissues.” The mechanism he refers to is the triggering of genes and growth factors such as brain-derived neurotrophic factor (BDNF) and myogenic regulatory factors (MRFs).
BDNF controls neurogenesis, signaling your brain stem cells to convert into new neurons, while MRFs are instrumental in muscle development and regeneration. In other words, fasted exercise may actually help keep your brain, neuromotors and muscle fibers biologically young.
Most recently, a study published in the October 2019 issue of The Journal of Clinical Endocrinology & Metabolism found that the timing of your meal when exercising impacts “acute metabolic responses to exercise.” In other words, when you eat will impact your body’s responses to your workout, for better or worse.
The study included an acute randomized crossover trial and a six-week randomized training trial involving overweight and/or obese men. In the acute trial, the researchers compared the effects of eating a balanced breakfast before versus after moderate-intensity cycling.
In the training trial, which lasted 6 weeks, they assessed the impact of eating a carbohydrate-rich breakfast either before or after training.
•Exercising before eating a balanced breakfast resulted in higher intramuscular fat utilization in Type 1 and Type 2 muscle fibers. Stored intramuscular fat is thought to play a role in insulin resistance, so this finding suggests fasted exercise improves your insulin sensitivity.
•Exercising before eating a high-carb breakfast resulted in improved glucose sensitivity and lower insulin levels after eating.
•Exercising before breakfast also improved remodeling of skeletal muscle phospholipids and the protein content of the glucose transport protein (GLUT4), which are embedded in your cell membranes and facilitate glucose entry into the cell.
As a principal mediator of glucose uptake by your muscle, GLUT4 helps maintain glucose homeostasis (balance) in your body.
By improving the ability of your muscle to store glucose as glycogen, which is then used to produce energy, GLUT4 helps improve your glucose tolerance and lowers insulin resistance, thus lowering your risk of Type 2 diabetes.
The finding that exercising while fasting has a beneficial impact on GLUT4 is not new.
In a Y 2010 study, those who exercised fasted increased their GLUT4 levels by 28% compared to those who had a carb-rich meal before training, or controls who did not train.
This result was only for the acute impact of fasting exercise. When you exercise fasting, in the long term you also increase autophagy, which facilitates muscle growth. Muscle growth, of course, is enhanced if you are doing resistance training, especially like Blood Flow Resistance Training.
In fact, exercising while fasting for more than 14 to 18 hours likely activates as much autophagy as if you were fasting for 2-3 days. It does this by increasing AMPK, NAD+ and inhibiting mTOR.
Additionally, your muscles are the largest sink for glucose in your body. So, if you have more muscle mass you will be able to easily remove it from your blood and store it in your muscles and, as a result, you will have decreased insulin resistance.
In conclusion, the authors of this October 2019 study noted that “exercise performed before versus after nutrient intake (i.e., in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia.”
Medical News Today quotes co-author Dr. Javier Gonzalez saying their findings “suggest that changing the timing of when you eat in relation to when you exercise can bring about profound and positive changes to your overall health.”
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