Some trends are questionable. This one can kill you. Let’s talk about why depriving your body of water is never a good idea.
TL;DR: Dry fasting (no food or water for extended periods) is being promoted online for “accelerated autophagy” and rapid weight loss. This is genuinely dangerous. Dehydration can cause kidney damage, seizures, and death. The autophagy benefits people are chasing don’t require dehydration. There is no safe way to do extended dry fasting.
- Dry fasting means zero water, sometimes for 24 to 72+ hours
- Proponents claim it accelerates cellular cleanup (autophagy)
- Your kidneys can be damaged within 24 to 48 hours without water
- Autophagy is triggered by calorie restriction, NOT dehydration
- This is one trend I’m not going to “both sides.” It’s simply dangerous.
I Don’t Usually Use the Word “Dangerous”
If you’ve read my other posts about diet trends, you know I try to be balanced. Oatzempic? Probably won’t hurt you, just won’t work. Berberine? Some modest benefits, not what TikTok claims. Apple cider vinegar? Minor effects, overhyped.
I approach most trends with curiosity and nuance. I explain what’s real, what’s exaggerated, and let you make informed decisions.
This post is different.
Dry fasting is not a trend I can discuss with academic detachment. It’s not something where I say “the evidence is mixed” or “it might work for some people.” This practice can cause permanent organ damage. It can kill you.
I need you to understand that before we go any further.
What Is Dry Fasting?
Dry fasting means abstaining from both food AND water for an extended period. No liquids at all. Not water, not tea, not broth. Nothing.
There are variations:
Soft dry fasting: No drinking water, but you might shower, brush your teeth, or have other external contact with water.
Hard dry fasting: No water contact whatsoever. No showering, no brushing teeth, no washing hands. The idea is that your body might absorb water through the skin (it doesn’t absorb significant amounts, but that’s the belief).
Intermittent dry fasting: Shorter periods without water, like 16 to 20 hours, sometimes done daily.
Extended dry fasting: Going 24, 48, 72 hours or longer without any water intake. Some extreme practitioners claim to go 5 to 7 days or more.
The practice has roots in religious fasting (Ramadan, for example, involves daytime dry fasting), but the current social media trend takes it to dangerous extremes in pursuit of weight loss and “autophagy.”
The Autophagy Argument
Here’s the pitch you’ll see online:
“Autophagy is your body’s cellular cleanup system. It breaks down damaged cells and recycles them. Fasting triggers autophagy. But dry fasting triggers it FASTER because your body is under more stress. You get 3x the benefits in less time.”
This argument is seductive because it contains a kernel of truth wrapped in dangerous nonsense.
The true part: Autophagy is real. It’s a legitimate biological process where cells break down and recycle damaged components. It does increase during periods of caloric restriction. Research on autophagy won the Nobel Prize in Medicine in 2016. It’s not pseudoscience.
The dangerous nonsense: The claim that dehydration accelerates autophagy in a beneficial way. The claim that stressing your body with water deprivation produces better results. The claim that this is safe or healthy.
Let me be very clear: autophagy is triggered by energy restriction (not eating), not by dehydration (not drinking). Your cells don’t clean themselves better because you’re dehydrated. They start to die.
What Actually Happens When You Stop Drinking Water
Your body is approximately 60% water. Every single biological process depends on adequate hydration. Here’s what happens when you cut off the supply:
Hours 0 to 12: Your body starts conserving water. Urine becomes more concentrated. You might feel thirsty but otherwise okay.
Hours 12 to 24: Thirst intensifies. Your mouth and lips become dry. Headaches often begin. Cognitive function starts to decline. You may feel dizzy or lightheaded.
Hours 24 to 48: This is where things get serious. Your kidneys are working overtime to conserve water, concentrating waste products that should be diluted and flushed out. Blood pressure can drop. Heart rate may increase. You might experience muscle cramps, confusion, or irritability.
Hours 48 to 72: Kidney function becomes compromised. Electrolyte imbalances can cause cardiac arrhythmias. Severe confusion or delirium may occur. Blood becomes thicker, increasing clot risk. Fainting is common.
Beyond 72 hours: Organ failure becomes a real possibility. Kidneys can be permanently damaged. Seizures can occur. Without intervention, death follows.
The exact timeline varies based on factors like temperature, activity level, body size, and baseline health. But make no mistake: the human body cannot survive more than a few days without water. There is no adaptation, no “metabolic switching,” no cellular magic that changes this fundamental biological reality.
The Kidney Problem
I want to focus on kidneys specifically because the damage here can be permanent.
Your kidneys filter about 120 to 150 quarts of blood every day, producing 1 to 2 quarts of urine. They remove waste products, balance electrolytes, and regulate blood pressure. They need water to do this.
When you’re dehydrated:
Waste products concentrate. Substances that should be diluted and excreted instead build up. This includes urea, creatinine, and other metabolic byproducts.
Blood flow to kidneys decreases. Your body prioritizes the brain and heart, reducing circulation to other organs.
Acute kidney injury can occur. This is exactly what it sounds like: your kidneys stop working properly due to the insult of dehydration.
Kidney stones become more likely. Concentrated urine allows minerals to crystallize and form stones.
Existing kidney problems worsen dramatically. If you have any underlying kidney issues (and many people do without knowing), dry fasting can push you into acute kidney failure.
Some kidney damage from dehydration is reversible if caught early. Some isn’t. I’ve seen patients who caused permanent harm to their kidneys through extreme fasting practices. They didn’t think it would happen to them.
“But I Felt Amazing During My Dry Fast”
This is something I hear, and I need to address it directly.
Some people who dry fast report feeling euphoric, clear-headed, even spiritual. They interpret these feelings as evidence that the practice is beneficial.
Here’s what’s actually happening:
Ketosis. When you don’t eat, your body switches to burning fat for fuel and produces ketones. Some people experience a sense of mental clarity from ketosis. This happens with regular fasting too. You don’t need to avoid water.
Stress hormones. Dehydration is a physiological stressor. Your body releases cortisol and adrenaline. These hormones can create feelings of alertness and energy, similar to a “fight or flight” response. This isn’t wellness. This is your body panicking.
Mild delirium. As dehydration progresses, cognitive changes occur. Some people experience these early changes as pleasant or mystical before they become obviously problematic.
Endorphins. Physical stress can trigger endorphin release. This is the same phenomenon that causes “runner’s high” or why some people feel good after intense physical challenges. It doesn’t mean the activity is healthy.
The dangerous part is that feeling good during dry fasting doesn’t mean you’re not causing harm. Organ damage can occur silently. Kidneys don’t have pain receptors. You might feel fine while they’re being damaged.
The Religious Fasting Comparison
Some dry fasting advocates point to religious practices as evidence of safety. “Muslims fast during Ramadan without water, and they’re fine.”
This comparison misses crucial differences:
Duration. Ramadan fasting is from dawn to sunset, roughly 12 to 16 hours depending on location and season. Practitioners break their fast every evening with food AND water. This is not the same as 48 or 72+ hour dry fasts.
Hydration before and after. During Ramadan, people hydrate thoroughly before dawn and after sunset. They’re not chronically dehydrated.
Exemptions. Islamic law specifically exempts people who are ill, pregnant, breastfeeding, traveling, or for whom fasting would be harmful. The religious tradition recognizes that fasting isn’t safe for everyone.
Community and monitoring. Religious fasting typically happens within a community context with shared meals and social support. It’s not done in isolation by people chasing Instagram aesthetics.
I respect religious fasting traditions. They’re not what the extreme dry fasting community is promoting.
The Weight Loss Illusion
Yes, you will lose weight if you stop eating and drinking. Some of it rapidly.
Here’s what you’re actually losing:
Water weight. A huge portion of initial weight loss from dry fasting is simply dehydration. You haven’t lost fat. You’ve lost water. The moment you rehydrate, that weight returns.
Glycogen and associated water. When you deplete glycogen stores, you release the water bound to glycogen. Again, this comes back when you eat normally.
Some muscle. Extended fasting without adequate protein breaks down muscle tissue. This actually slows your metabolism long-term.
Some fat. Yes, some fat loss occurs. But this happens with regular fasting too. The dehydration component doesn’t accelerate fat loss. It just makes the scale drop faster in a misleading way.
The “dramatic results” people post are largely water loss. The before and after photos showing 10 pounds lost in 3 days? That’s not fat. That’s dehydration. And it’s not sustainable or healthy.
Who Is Promoting This?
I want to address the ecosystem that pushes dry fasting, because understanding the incentives helps you evaluate the claims.
Fasting coaches and course sellers. People who have built businesses around extreme fasting practices. They sell programs, consultations, and community memberships. Their income depends on you believing this works.
Biohacking influencers. Content creators who differentiate themselves by promoting increasingly extreme practices. Moderate advice doesn’t generate clicks. Extreme advice does.
Wellness retreat operators. Some facilities offer supervised dry fasting experiences. They have financial incentives to present the practice as safe and beneficial.
Supplement companies. Brands that sell electrolyte products, “breaking fast” supplements, and related items benefit from fasting culture generally.
Notice who isn’t promoting extended dry fasting: mainstream medical organizations, nephrologists, emergency physicians, or any credentialed health professionals who would be liable for the consequences.
What the Evidence Actually Shows
Proponents of dry fasting often claim there’s research supporting it. Let’s look at what actually exists:
Animal studies on water restriction: Yes, some exist. They generally show stress responses and survival adaptations, not health benefits. Animals that survive water restriction aren’t thriving; they’re coping.
Studies on Ramadan fasting: These show that intermittent dry fasting (12 to 16 hours) is generally safe for healthy adults. They don’t support extended dry fasting.
Autophagy research: The Nobel Prize-winning work on autophagy involved caloric restriction in yeast and mice, not dehydration. The research does not support the claim that dry fasting enhances autophagy beyond what regular fasting achieves.
Clinical studies on extended dry fasting: There essentially aren’t any, because no ethics board would approve a study that deliberately dehydrates human subjects for 48 to 72+ hours. That should tell you something.
The absence of evidence isn’t always evidence of absence. But in this case, the reason there’s no evidence is that researchers consider the practice too dangerous to study.
What I Want You to Do Instead
If you’re interested in the legitimate benefits of fasting, there are safer ways:
Intermittent fasting with water. Time-restricted eating (like 16:8) has actual research support and doesn’t require dehydration. Drink water freely.
Extended water fasting with supervision. If you want to try a longer fast (24 to 72 hours) for autophagy or metabolic benefits, do it with full hydration and ideally with medical supervision. Electrolytes matter.
Caloric restriction without dehydration. The autophagy benefits come from not eating, not from not drinking. You can achieve the cellular cleanup without risking your kidneys.
Work with professionals. If you have significant weight to lose or metabolic health goals, work with doctors, dietitians, or bariatric specialists who can guide you safely.
The benefits people chase through dry fasting can be achieved through safer methods. There’s no unique advantage to dehydration. There’s only additional risk.
When to Go to the Emergency Room
If you or someone you know has been dry fasting and experiences any of the following, seek medical attention immediately:
- Confusion or disorientation
- Rapid heartbeat or palpitations
- Severe dizziness or fainting
- Inability to urinate or very dark urine
- Muscle cramps or spasms
- Seizures
- Chest pain
These are signs of serious dehydration or electrolyte imbalance. They require medical intervention, not “pushing through.”
Key Takeaways
- Dry fasting (no food or water) is genuinely dangerous, not just another questionable trend
- Autophagy is triggered by caloric restriction, NOT dehydration
- Kidney damage can occur within 24 to 48 hours without water
- The “amazing” feelings during dry fasting are stress responses, not wellness
- Weight loss from dry fasting is mostly water loss that returns immediately
- There are no benefits to dry fasting that can’t be achieved more safely with regular fasting
A Final Word
I write about diet trends because I believe in informed decision-making. I usually present evidence, acknowledge nuance, and let you decide what’s right for you.
This is different. There is no nuance here. Dry fasting is dangerous. The potential harms are severe and sometimes irreversible. The supposed benefits are achievable through safer means.
Please don’t do this to your body. And if someone you care about is considering it, please share this with them.
