What Are The Effects Of Fasting? (Both Good & Bad)

Fasting has recently been thrust into the fitness trend spotlight, but is it an effect way to diet, or just a passing trend? We all remember the Gazelle, the South Beach diet and Tae-Bo, maybe intermittent fasting is just another infomercial that will end soon. Fasting has a large following now, but who knows if it will stand the test of time.

Let’s take a look at the facts, and if intermittent fasting could be an effective way of dieting if you’re trying to lose weight, gain lean muscle or simply maintain your goal weight.

The Different Kinds of Fasting & Their Effects

There are several different types of fasting out there, some more popular than others. Different types of fasting have different effects on the body, and are often implanted for their benefits. Unfortunately, often fasting is employed incorrectly and can have a detrimental effect on the body.

Some of these varieties you’ll probably have come across before, and some may have sparked your interest in the past. Note the differences in these types of fasting and the effects that they have on your body. Whether fasting as a way to lose weight or for religious or medical purposes, knowing the right way to do it will ensure that you stay healthy and avoid the possible downfalls to fasting.

Fasted Cardio

Fasted cardio has been an extremely popular method of burning fat. Fasted cardio is simply when you do your cardio first thing in the morning BEFORE consuming a meal. Breakfast is when you break your fast (the fast while you sleep), so if you do your cardio in the morning before breakfast, you’re technically fasted.

Studies have shown that fasted cardio can burn up to 20% more fat than when cardio is performed after a meal. However, fasted cardio also burns through your amino acids, which can have a negative effect on your muscle mass. If you’re trying to gain muscle, fasted cardio can hurt your gains, and the 20% fat burning increase isn’t really worth the increased amino expenditure.

Intermittent Fasting

Intermittent fasting has recently been thrust into the spotlight as an effective dieting tool. Intermittent fasting, as the name suggests, consists of fasting throughout most of the day, then squeezing your meals for the day within a 6 to 8-hour “feeding” period.

This can definitely have an advantage if you’re trying to lose weight, as being in a fasted state helps your body maintain a fat-burning state. However, as for fasted cardio, this can hurt your muscle gains if you don’t do it correctly.

Trying to pack all of the protein you need to build muscle is going to be counter-productive, as it won’t make up for your lack of protein throughout the day. The body will try to process all of the protein at once, and a good deal of it will be discarded as waste. Your body has a cap on how much protein can be used be the body in a short amount of time, and exceeding this cap with a drastic intake will simply waste all of that protein, which can be an unnecessary drain on your wallet if you’re taking supplements.

If you’re going to give intermittent fasting a try and you’re still trying to build some lean muscle, it would be a good idea to, instead of not eating for 16-18 hours, still spread your protein intake throughout the day and just limit carbs and fats until your “feed” period.

You can do this with low-fat, low-carb protein shakes, or small meals consisting of lean meat. This will keep your body in fat-burning mode, although not as extremely, and your body be able to process and use all of the protein that you need to grow.

Long-Term Fasting

Long-term fasts should only be done for religious or medical reasons. Long-term fasting will result in weight loss, but there is a large amount of negative side effects that go hand-in-hand with long-term fasting.

Muscle spasms, drastically dropped blood pressure, drastically decreased resting heart rate, delirium, muscle loss, low energy and decreased strength are some of the symptoms associated with long-term fasting. If you’re not taking in food, your body will use stored fat and muscle mass as energy, which will decrease the quality of your workouts; and, with nothing to replenish the body after your workout, you’ll be even more depleted.

If you have to fast for a religious or medical reason for over 24 hours, make sure you have a hefty refeed to replenish your body with all of the nutrients that you lost during the fast.


Detoxes, while technically not a “true” fast, are often included in conversations about fasting, and thus deserve an honorable mention. Detoxes are often done by replacing food with juices and shakes, so the body is getting plenty of vitamins in minerals, and usually some carbs, but no fats.

More extreme detoxes can consist of only fruit juice, and exercise should be limited on these diets, as there is little to no protein to use as fuel to rebuild the muscles. Extreme detox diets are usually only 3 or 4 days in length, and should never be subscribed to long-term, as they can starve your body of essential macronutrients.

There are thousands of detox plans online, a simple Google search will have you occupied reading for hours. If you’re interested in giving a juice detox a try, here’s a popular beginner’s plan for you to follow:


Final Thoughts

Depending on what your goals are, fasting can be a useful tool. Whether you’re trying to burn and churn fast with fasted cardio or you’re trying to lean out and still gain a beat of lean muscle with intermittent fasting, make sure you’re getting your getting all of your macronutrients and spreading your protein intake throughout the day.

Transitioning to these diets can be difficult and can create an environment where binge eating is very welcome, but if you stick to your diet, you can see some great results from these types of fasting. Remember, most of the time a diet doesn’t work, it’s not because of the food selection or method, it’s because the diet wasn’t adhered to.

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