When you fast you force your body to start looking elsewhere for fat and to begin becoming more efficient in its use of the energy you do have present. This can result in some health benefits such as improved mitochondrial function and weight loss. However at the same time it also means that your body will be without many important nutrients for at least a short amount of time and this can cause some damage. The effects on the metabolism are uncertain and it could have either positive or adverse effects on weight loss in the long term.
If you are going to fast then it is advisable to keep it under 48 hours at all times. At the same time you should make sure to use juice fasting, water fasting or an isotonic drink to maintain hydration. Fasting on a weekly basis is not highly recommended and particularly as a bodybuilding practice, though fasting occasionally in a safe manner might help to improve energy efficiency and protein synthesis. If you are on any course of medication, have heart problems, are pregnant or breastfeeding then you should not consider fasting until you are healthy again.
First, let’s define fasting as not consuming calories for more than 24 hours (vs time restricted eating, where you eat during a limited window within a 24 hour period).
Fasting can help you lose weight in two ways:
- When you fast, you’re likely consuming less calories, which can help you to lose body fat
- When you fast, studies have shown that you might be losing hard-earned muscle at a rate of .25 – 1lb per day!
People also report feeling much better when fasting, ridding themselves of hunger and cravings, sleeping better and having improved mental clarity. These benefits are likely from the increase of ketones in the body.
Time restricted eating, on the other hand, might help you with #1 (eating fewer calories) without causing lean tissue loss.
Last, a well formulated ketogenic diet could help you with weight loss AND feeling the benefits of fasting without restricting food quantities.