Should You Eat Breakfast Before You Exercise?

Should You Eat Breakfast Before You Exercise? by Dr. Joseph Mercola for Mercola

If you’re in the habit of eating breakfast before exercising in the morning, you may want to reconsider the order in which you start your day as there are significant benefits to exercising in a fasted state.

A common belief is that you need to eat breakfast to optimize exercise performance. While there’s evidence to support this stance,1 other evidence suggests you can reap important health benefits by exercising in a fasted state.

Fasted Exercise Curbs Food Intake and Improves Cognition

Research2,3 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,4 published in 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 (in this case a cereal-based meal) before exercising.

Fasted Exercise Boosts Fat Loss

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 study5 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.

Fasted Exercise Rejuvenates Your Muscles

Exercise and fasting together also yields acute oxidative stress which, paradoxically, benefits your muscle. A 2015 study6 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,7 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.”

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 neurotropic factor (BDNF) and myogenic regulatory factors (MRFs).

BDNF controls neurogenesis, signaling your brain stem cells to convert into new neurons,8 while MRFs are instrumental in muscle development and regeneration.9 In other words, fasted exercise may actually help keep your brain, neuromotors and muscle fibers biologically young.

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