Autophagy is the body’s way of cleaning out damaged cells and toxins. Some researchers believe that fasting and restricting calories can induce autophagy. Intermittent fasting has become a popular diet trend, with advocates claiming it can lead to weight loss, improve metabolism, and extend lifespan. But how long do you need to fast to activate autophagy? Here’s what the research says about whether 20 hours of fasting is enough.
What is Autophagy?
Autophagy is a natural process in the body that disassembles unnecessary or dysfunctional cells. It allows the orderly degradation and recycling of cellular components. There are three main types of autophagy:
- Macroautophagy – old or damaged organelles, proteins, or pathogens are captured in autophagosomes (membranes) and broken down by lysosomes.
- Microautophagy – cellular components are directly taken in by lysosomes.
- Chaperone-mediated autophagy – proteins with a specific signal sequence are recognized by chaperone proteins and transported directly to lysosomes.
This cellular “housekeeping” process is going on at low levels constantly, getting rid of old cell components to regenerate newer, healthier ones. But the level of autophagy can be upregulated by cellular stressors like starvation, growth factor depletion,high temperature, hypoxia, and oxidative stress.
Autophagy provides fuel for energy and building blocks for renewed cell growth. It also removes damaged proteins and organelles that could lead to disease. This is why autophagy is generally thought of as a beneficial and pro-survival process.
Autophagy and Fasting
Fasting has been shown to be one of the most effective ways to induce autophagy. When nutrients are scarce, autophagy ramps up recycling efforts to supply the body with energy from stored proteins and fats.
Research suggests that fasting for periods longer than 24 hours can significantly increase markers of autophagy and autophagy gene expression in humans and animals. Significant autophagy signaling has been observed in humans after a 48-hour fast.
Benefits of Fasting-Induced Autophagy
There are several hypothesized benefits of upregulating autophagy through fasting:
- Supports cellular renewal – The recycling process of autophagy provides raw materials for cellular rejuvenation.
- Clears damaged proteins/organelles – Autophagy removes dysfunctional cell components that could accumulate and cause disease.
- Fights infections – Autophagy can eliminate intracellular pathogens like viruses and bacteria.
- Reduces inflammation – Autophagy modulates inflammatory signaling pathways.
- Prevents aging – Autophagy counteracts the aging process by recycling old cellular components.
Some of these benefits have been demonstrated in animal and human trials of fasting and calorie restriction diets. More research is still needed to verify the mechanisms and effects of fasting-induced autophagy.
How Long to Fast for Autophagy
Most of the current research indicates that the process of autophagy starts ramping up between 12-24 hours of fasting. Autophagy signaling and activity continue to increase past 24 hours, until nutrients are introduced again.
Here is a summary of the evidence on fasting duration and autophagy:
- In mice, autophagy markers increased by 300-900% after 24-48 hours of fasting.
- In human trials, autophagy marker LC3B-II increased significantly after 24 and 48 hours of fasting.
- Mice starved for 48 hours showed a 55-85% increase in autophagy activity compared to fed mice.
- Mice fasted for 72 hours showed 150% increase in liver autophagy compared to 24 hour fasted mice.
Based on the research, it appears that at least 24-48 hours of fasting is required to significantly activate autophagy in humans. Shorter fasts under 24 hours generate more modest increases in autophagic activity.
20 Hours Fasting and Autophagy
There is limited evidence specifically on a 20 hour fasting period and autophagy. One study in mice found that 20 hours of fasting increased some autophagy markers but not others compared to fed mice.
Overall the research suggests:
- 20 hours of fasting may induce a low to moderate level of autophagy.
- 20 hours fasting does not maximize autophagy – longer durations like 24-48 hours have a bigger impact.
- 20 hours is enough fasting to see some upregulation of autophagy, but extending to 24+ hours provides more significant benefits.
Other Ways to Induce Autophagy
Fasting is one of the most potent triggers of autophagy, but other interventions can also activate the process:
Calorie Restriction
Cutting calorie intake by 30-40% has been shown to induce autophagy, even without full fasting. This level of calorie restriction requires strict dietary changes.
Exercise
Both endurance and resistance exercise can activate autophagy in skeletal and cardiac muscle. The impact depends on exercise intensity and duration.
Ketogenic Diet
Ketogenic diets are very low carb, which mimics fasting metabolism. Following a ketogenic diet for 3-5 days has been shown to increase autophagy.
Intermittent Fasting
Intermittent fasting cycles between fasting and feeding. Many protocols involve 16-20 hour fasts, which research suggests is enough to see some autophagy activation.
Pharmaceuticals
Some compounds like spermidine, rapamycin, metformin and lithium may enhance autophagy. But these drugs can have side effects and are not yet approved for this purpose.
Autophagy and Disease
Impaired autophagy regulation is implicated in many diseases:
Neurodegenerative Diseases
Autophagy dysfunction is linked to buildup of abnormal proteins seen in Alzheimer’s, Parkinson’s, and Huntington’s disease.
Cancer
Too much and too little autophagy can promote or suppress tumor growth. The role of autophagy in cancer is complex.
Infection
Autophagy fights viruses, bacteria and other pathogens. Defects in autophagy genes increase susceptibility to certain infections.
Metabolic Syndrome
Impaired autophagy is associated with insulin resistance, high blood sugar, and abnormal lipid metabolism.
Heart Disease
Insufficient autophagy allows protein buildup in heart muscle cells, contributing to cardiovascular disease.
While the links between autophagy and disease are not fully characterized, there are opportunities to modulate autophagy to help prevent and manage certain conditions.
Conclusion
Research shows that fasting for 20 hours may induce a low to moderate level of autophagy. However, studies indicate that extending fasting to 24 hours or longer provides more potent activation of autophagy.
Other lifestyle interventions like calorie restriction, exercise, and ketogenic diets can also upregulate autophagy without prolonged fasting. Considering potential health benefits and risks, 20 hours of fasting could have positive effects, but longer fasts seem to maximize autophagic activity.
More human clinical trials are still needed to establish optimal fasting protocols for autophagy induction. But the current evidence suggests that the longer the fast, the more profound the autophagic response.