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  • Fasting before aerobic training leads to reductions in both body weight and body fat, while eating before a workout decreases only body weight
  • When you exercise while fasting, it essentially forces your body to shed fat, as 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
  • Exercise and fasting also yield acute oxidative stress, which may actually benefit your muscle
  • A post-recovery meal of fast-assimilating protein such as high-quality whey protein, eaten within 30 minutes of your workout, is very important when you exercise while fasting; this will essentially “rescue” your muscle tissue out of a catabolic state and supply it with the proper nutrients to stimulate repair and rejuvenation

What Will Cause You to Lose More Fat -- Exercising Fasted or Non-Fasted?

March 16, 2012 | 177,593 views

By Dr. Mercola

Periodic fasting may offer multiple health benefits, as long as it's done properly.

Many equate fasting with not eating for long periods … but beneficial fasting is not about starving yourself.

After all, you're fasting almost every day insofar as your first morning meal is 'breaking the fast' (breakfast) from the time of your last meal the day before.

Giving your digestive system a rest allows vital energy resources to be directed toward bodily healing, repair, detoxification and maintenance.

Fasting periodically, such as eating very lightly for two days each week, has been found to trigger a variety of beneficial hormonal and metabolic changes that may help prevent age-related brain shrinkage, heart disease, diabetes, and possibly even cancer. 

And now new research suggests fasting before exercise may help you to achieve your desired results faster …

Fasting Before Exercise Helps You Burn More Fat

If you're already devoting the time to working out, you're probably interested in making the most of that time and getting in the most possible benefit in the shortest amount of time.

One way to boost your return on your exercise "investment" may be to do your workout while fasting.

A recent study sought to evaluate the effects of aerobic training in a fasted versus a fed state.

Specifically, 19 men were placed in one of two groups -- one that practiced aerobic training after fasting for Ramadan (which requires fasting from dawn to sunset for one month), and one that did the training after eating.


The fasting group experienced reductions in both body weight and body fat, the latter of which remained unchanged in the fed group.

The researchers concluded:



Why Fasting Might Take Your Exercise Program to the Next Level

Simply put, exercise and fasting yield acute oxidative stress, which actually benefits your muscle. According to fitness expert Ori Hofmekler, acute oxidative stress is:




The combined effect of both intermittent fasting and short intense exercise may go way beyond helping you to burn more fat and lose weight; it may help you to:

Boost cognitive function Boost testosterone Prevent depression


As Ori explains:


Tips for Fasting and Exercising Safely: A Post-Workout Recovery Meal is Crucial

Exercise and fasting help counteract all the main determinants of muscle aging, while boosting fat-burning compared to working out after eating. However, fasting incorrectly can cause more harm than good. To start, you need to make sure that you're not fasting to an unhealthy extreme. In other words, fasting does not mean that you starve yourself for days. Instead, intermittent fasting involves either fasting completely or simply minimizing your food intake during the day to small servings of light, low-glycemic, mostly raw foods such as fruits, vegetables, whey protein or lightly poached eggs every 4-6 hours.

You then do your workout while fasting (30 minutes after your latest snack) followed by a very important recovery meal (whey protein) and then you eat your main meal at night. It's very important that you eat an appropriate recovery meal after your workout session, as this will prevent brain and muscle damage from occurring. Ori explains:




So it's crucial that you eat within 30 minutes after your workout, and your meal must include fast-assimilating protein. Whey protein is an ideal option here. Then, as mentioned, you will eat your main meal of the day at night, so your "fasting" time consists only of the daytime hours, either fasting completely or eating light, mostly raw foods every 4-6 hours.

Additionally, if you don't have enough energy or don't feel good then it is likely time to shift your experiment and reduce the hours of fasting. This process should make you feel better and if it doesn't then it is best to reevaluate.

If Fasting is Too Extreme, Try Exercising Before Breakfast

You can get many of the same benefits of fasting and exercise by exercising first thing in the morning, when your stomach is empty. This is because eating a full meal, particularly carbohydrates, before your workout will inhibit your sympathetic nervous system and reduce the fat burning effect of your exercise. Instead, eating lots of carbs activates your parasympathetic nervous system, (which promotes energy storage—the complete opposite of what you're aiming for).

As mentioned earlier, training on an empty stomach will effectively force your body to burn fat, while also offering additional benefits. For instance, in one study those who fasted before exercise had increased levels of a certain muscle protein that plays a pivotal role in insulin sensitivity. As I've explained in numerous articles, insulin resistance is the root cause of most chronic disease, making maintaining proper insulin regulation a primary factor of good health.

Always Listen to Your Body When it Comes to Eating and Exercise

The majority of the "fuel" used during most exercise is not actually coming from the food you have just eaten. If you're working out at a moderate to high intensity you're using glycogen and fat that is stored in your muscles, liver, and fat cells. Typically, your body has enough of that stored fuel to last for one to two hours of intense work, or three to four hours at moderate intensity.

Therefore, if you are consuming a high-quality diet, eating every three to four hours, your body probably does not need anything to eat before you begin your workout. Still, some people do have a hard time exercising without eating something first.

Typically these people are more sensitive to changes in their blood sugar levels, which can decline during the first 15-25 minutes of their workout. It is this decline in blood sugar that causes dizziness, faintness, nausea or lightheadedness. This is especially true if you exercise first thing in the morning. Of course, a number of individual factors can also play a role in whether it's appropriate to exercise while intermittent fasting, such as your age, when you last ate, whether or not you're pregnant, taking medications, your medical history, level of fitness, and the type of workout you engage in.

I believe the best approach is to use some common sense and listen to your body, and if you feel weak or nauseous while exercising on an empty stomach, you may want to eat a small meal, such as a high-quality whey protein shake, before your workout.

Ideally you will want to shift your body so it is using fat to fuel the bulk of your energy and shift it away from using sugar that most people are using. It may take a few weeks to shift your body into fat-burning mode and your food choices will be crucial. Rather than consuming 50% carbohydrate you can cut that down by 20-25% and replace that with healthy fats, like coconut oil, egg yolks, butter, avocados, and nuts.

A study published in the journal Medicine and Science in Sports & Exercise, demonstrated that consuming whey protein (20g protein / serving) 30 minutes before resistance training boosts your body's metabolism for as much as 24 hours after your workout.i It appears as though the amino acids found in high-quality whey protein activate certain cellular mechanisms (mTORC-1), which in turn promote muscle protein synthesis, boost thyroid, and also protect against declining testosterone levels after exercise.

In practical terms, consuming 20 grams of whey protein before exercise and another serving afterward will most likely yield the double benefit of increasing both fat burning and muscle build-up at the same time. Again, not everyone will need to eat something prior to exercise, but if you do, a high-quality whey protein is one of your best bets. It'll curb your hunger while still optimizing fat burning.