There is a fasting craze lately that is continuing to swell largely because so many seem to be deriving benefits from it. While it may not be a priority for most healthy adults, it can be a life-changer for those with below par health as well as a source of health optimization for those already in good health.
The term “Intermittent Fasting” (IF) is used (incorrectly) to broadly describe many different methods of fasting with many different and varied benefits depending upon the method. There are endless ways to fast, but, in short, here are the most typical:
- Restricted Calorie Fasts in which for any number of days one will eat significantly fewer calories than one expends. This is different than simply being on a calorie restricted diet. The calorie restriction is more extreme and unsustainable in the long-term. An example would be Valter Longo, PhD’s ProLon eating program for 5 days, typically done from every month to once per year depending upon one’s health and goals. Dr. Longo refers to this as a “Fasting Mimicking Diet”.
- Time Restricted Eating in which one will daily eat only within a limited number of hours during the 24-hour period. An example would be one that restricts eating for 16 hours with a window of unrestricted eating for 8 hours daily (typically referred to as a 16:8 intermittent fast). There are 12:12’s and 18:6’s etc.
- Water-only fasts. These are, as the name implies, what most would think of as a true fast in which no calories are consumed for a number of consecutive days, or, one day per week or month.
Again, within (and perhaps beyond) these are endless permutations, all with the idea that the period of caloric restriction will help in some way. Well, what are those ways?
Studies bear out that, contrary to popular belief, some form of fasting, but typically Time Restricted Eating, leads to fat loss in those who are overweight, and, does so better than caloric restriction (the standard of just eating fewer calories daily) over the long term in regards to fat lost and period over which it stays off (at least 2 years).
Reduced Fasting Blood Glucose
This has been shown multiple times in studies and therefore considered one of the best ways (pharmacologically or not) to control or reverse diabetes, Type 2.
Activation of AMPK helps control blood glucose and upregulate autophagy.
By upregulating autophagy, the body rids itself of misfolded proteins, senescent cells, and other non- or dysfunctional cells while providing fuel (recycling) for other healthy cells.
The effect IGF-1 has upon aging is still very controversial. We know that it tends to improve both cognitive and physical function while helping to build muscle and lose fat. While IGF-1 does not cause cancer (if that were the case, then all of us would be at increased risk of developing cancer while young and enjoying the benefits of elevated IGF-1) anymore than gasoline starts a fire, IGF-1 can speed the growth of pre-existing cancers. So reduced IGF-1 could be considered good for those in middle-age who have a higher risk of cancer, and there is proof that reducing IGF-1 helps eliminate cancer, especially with chemotherapy and immunotherapy.
Reduced Activation Of mTOR (“Mammalian Target Of Rapamycin”)
Similarly to IGF-1, there is controversy here as well regarding risk versus benefit and at what stage in life one is. It is argued that higher mTOR early and late in life is likely most beneficial, but during the “middle years”, it is better to slow growth.
Depending upon the length and type of fast, most who fast state that after a period of time that varies by individual, they feel sharper mentally and more energetic. And for those worried about muscle loss, it turns out that as long as one exercises the muscles during a fast there should be little, if any, muscle loss.
The only real restrictions to fasting are somewhat obvious:
- Do not fast while pregnant.
- Do not fast if malnourished, underweight, or anorexic.
- Do not fast without supervision by a doctor if you are taking any medication for hypertension, diabetes, cancer, or any pathology especially of the liver or kidneys.
- Use caution when fasting if over the age of (roughly) 65 years old.
In addition, some find it easier to gradually shift to a fasted state. Eg, before a water-only fast, it may be easier to reduce caloric intake for a few days prior to beginning the fast, and/or consider moving toward, if not into, ketosis (via a ketogenic diet, eg) days or weeks prior to beginning the water-only fast. Most also do better if when breaking the fast they do so gradually. It is important to know that even after the fast is complete, the benefits accrued remain for days, weeks or months following, and, of course, arguably “permanently” in terms of the autophagy that occurs.