Quick answer: Autophagy is the process cells use to break down and recycle damaged parts. Fasting is one of the best-known triggers: when nutrients are low, the energy sensor AMPK switches on and the growth pathway mTOR switches off, signaling cells to clean house. Much of the research is in animals and cells, but supporting autophagy through time-restricted eating, exercise and sleep is a reasonable healthy-aging strategy for many people.
Key takeaways
Cells rely on autophagy to clear out worn components and reuse their building blocks.
Fasting is a well-known trigger, because low nutrients switch on AMPK and switch off mTOR, signaling cells to clean house.
Much of the research is in animals and cells, so time-restricted eating, exercise and sleep are reasonable and gentle ways to support it.
What is autophagy?
The word means “self-eating.” Cells wrap damaged proteins and worn-out parts, including mitochondria, in small sacs and break them down into reusable building blocks.
How fasting turns on autophagy
With the energy shift, when food intake drops, the body moves from burning glucose to burning fat. AMPK activation follows, as this energy sensor starts recycling pathways (see what is AMPK?). With mTOR inhibition, less incoming nutrition quiets this growth signal, which allows autophagy, and FOXO factors are proteins that switch on genes involved in cell maintenance.
Possible benefits (mostly from research models)
Possible benefits, mostly from research models, include clearing damaged proteins and organelles, lower inflammation and oxidative stress, and support for immune defense. Fasting may also help protect brain cells and support healthier aging.
Other ways to support autophagy
Time-restricted eating, such as an overnight fast of 12 to 14 hours, regular exercise, and quality sleep all support autophagy. You can find more strategies in autophagy without starving yourself.
Who should be cautious
Fasting is not appropriate for people who are pregnant or breastfeeding, have a history of eating disorders, are underweight, or take insulin or other glucose-lowering medications without supervision. Talk with your provider first.
Autophagy and healthy aging
Autophagy declines with age. When it slows, damaged proteins build up (loss of proteostasis), worn-out mitochondria linger and nutrient-sensing pathways stay stuck in “grow” mode. Supporting this cleanup process is one of the core ideas behind healthy aging. Related: hormesis.
What the research shows
The link between fasting and autophagy is strong in animal studies but still thin in humans. These are the most relevant human studies.
Autophagy markers in people (Jamshed 2019, randomized crossover study). 11 adults with overweight ate between 8 a.m. and 2 p.m. for 4 days and between 8 a.m. and 8 p.m. for 4 days. The early window lowered average 24-hour glucose by 4 mg/dL and, in morning blood samples, raised ketones and the activity of the autophagy-related gene LC3A and the gene SIRT1. A key limitation is that gene activity in blood cells is only an indirect sign of autophagy; the study did not measure autophagy in tissues, and it lasted only 4 days in 11 people.
Two low-calorie days a week (Harvie 2011, randomized trial). 107 premenopausal women with overweight or obesity followed either a 5:2-style plan (about 650 kcal a day on 2 days a week) or a daily 25% calorie cut for 6 months. Weight loss was similar (6.4 kg vs. 5.6 kg), and both groups saw comparable drops in high-sensitivity CRP, LDL cholesterol, triglycerides and blood pressure. Fasting insulin and insulin resistance fell slightly more with the 5:2 approach. A limitation is that only women were studied, for 6 months.
Alternate-day fasting vs. daily calorie cutting (Trepanowski 2017, randomized trial). Researchers in Chicago assigned 100 adults with obesity to alternate-day fasting (25% of energy needs on fast days and 125% on feast days), daily calorie restriction (75% of needs every day) or no change for one year. Weight loss was the same in both diet groups at 6 months (6.8% each) and similar at 12 months (6.0% vs. 5.3%). Dropout was highest with alternate-day fasting (38%, vs. 29% with daily restriction), and LDL cholesterol was 11.5 mg/dL higher in the fasting group by month 12. A limitation is that 86 of the 100 participants were women, so the results may not apply equally to men.
Strength of the evidence: Human evidence for fasting-driven autophagy is early and indirect; the better-proven effects of fasting are modest weight and metabolic changes similar to daily calorie restriction.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you want to try fasting safely, or if you take diabetes or blood pressure medication and want to fast. The same is true if you have a history of disordered eating and want guidance, or if you want a personalized healthy-aging plan.
See a medical provider promptly if you feel faint, confused or very weak while fasting, or if you take insulin and your blood sugar drops.
Curious whether fasting fits your health goals?
A free 15-minute consultation with Dr. Kneessi. No cost, no obligation. In-office in Odenton, MD or by telehealth.
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Is a daily fasting window safe for me, given my blood sugar and medications?
Would a fasting window be safe for me, given my health history?
How long a daily fast would be reasonable for me to start with?
Which signs would tell me fasting is not agreeing with me?
Frequently asked questions
How long do you need to fast for autophagy?
There is no proven human threshold. Animal studies suggest longer fasts increase autophagy, but even overnight fasting and exercise may help.
Does coffee break a fast?
Plain black coffee has very few calories and is generally considered fine during a fast.
Can I trigger autophagy without fasting?
Exercise and sleep also support autophagy.
Is intermittent fasting safe for everyone?
No. It is not recommended in pregnancy, for people with eating disorders, or without supervision if you take glucose-lowering medication.
Sources
- Mizushima N, Komatsu M. Autophagy: renovation of cells and tissues. Cell 2011. PMID: 22078875. https://pubmed.ncbi.nlm.nih.gov/22078875/
- Kim J, et al. AMPK and mTOR regulate autophagy through direct phosphorylation of Ulk1. Nat Cell Biol 2011. PMID: 21258367. https://pmc.ncbi.nlm.nih.gov/articles/PMC3987946/
- Alirezaei M, et al. Short-term fasting induces profound neuronal autophagy. Autophagy 2010. PMID: 20534972. https://pmc.ncbi.nlm.nih.gov/articles/PMC3106288/
- He C, et al. Exercise-induced BCL2-regulated autophagy is required for muscle glucose homeostasis. Nature 2012. PMID: 22258505. https://pmc.ncbi.nlm.nih.gov/articles/PMC3518436/
- Rubinsztein DC, Mariño G, Kroemer G. Autophagy and aging. Cell 2011. PMID: 21884931. https://pubmed.ncbi.nlm.nih.gov/21884931/
- National Institute on Aging: Research on Intermittent Fasting Shows Health Benefits
- Harvard T.H. Chan School of Public Health: Intermittent Fasting
- Jamshed H, et al. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients 2019. PMID: 31151228. https://pubmed.ncbi.nlm.nih.gov/31151228/
- Harvie MN, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond) 2011. PMID: 20921964. https://pubmed.ncbi.nlm.nih.gov/20921964/
- Trepanowski JF, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Intern Med 2017. PMID: 28459931. https://pubmed.ncbi.nlm.nih.gov/28459931/
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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