💦 Drink more water for metabolic health and weight loss?!

🚰 Can drinking more water help us lose weight and improve metabolism?

Water makes up about 60 percent of our bodies, and getting in enough clean water is of profound importance to every aspect of health. Water is the medium of our entire cellular biology, and therefore our lives! But did you know that adequate hydration also may be key to optimizing metabolic health and healthy weight, specifically?

According to Dr. Richard Johnson, professor of medicine at the University of Colorado and author of the incredible book Nature Wants Us to Be Fat, even mild dehydration stimulates the development of obesity. He also states in his book that “people with obesity are ten times as likely to be dehydrated as their leaner counterparts.” (!!)

Why might this be? Interestingly, making new fat tissue in the body is a way for humans to store more water—called “metabolic water”—which can then be released into the body in times of water scarcity.

🐫 Think about camels: they can survive in the desert with low water supply in part because they store water in the fat cells of their fatty humps for times of drought!

How dehydration leads to obesity is one of the most fascinating stories in all of medicine. Dehydration activates a process in the brain called the “polyol pathway,” which stimulates the body to manufacture fructose. The fructose our bodies produce does two things:

1. It stimulates a hormone called vasopressin, which tells our kidneys to retain water.

2. It causes us to “print fat”—literally manufacturing more fat and filling our cells with it—by disrupting mitochondrial function.

📚️ What does the research say about hydration, weight and metabolic health?

The data shows that water is far more than just a thirst-quencher—it's a powerful metabolic tool. And a cheap and simple one, at that! (Isn’t it funny how some of the most basic things, like sunlight, deep breaths, walking, lifting heavy things, sleeping, and water can profoundly impact our metabolic health?!). Emerging research shows that increasing daily water intake can support measurable fat loss, increase metabolic rate, and even reduce the risk of childhood obesity. And what's especially compelling? These effects are often independent of diet, exercise, or caloric restriction, suggesting that water alone can be a quiet driver of weight regulation.

🤓 Study #1: Higher water intake may support weight loss

In this weight loss trial, 173 overweight women (aged 25–50) who drank <1 liter of water daily at baseline were followed for 12 months to assess the effects of increasing water intake on weight loss. Women who increased water intake to ≥1 liter/day lost an average of 2.3 kg (5 lbs) more than those who did not, independent of diet, physical activity, and caloric intake. This research showed that absolute and relative increases in drinking water were associated with significant loss of body weight and fat over time, independent of covariates.

🤓 Study #2: Dehydration puts us at risk for type 2 diabetes

This review article looked at many studies and found strong evidence that there is a relationship between type 2 diabetes development and low water intake. Specifically, they found:

• Not drinking enough water might raise your risk of type 2 diabetes, though scientists are still figuring out exactly how.

• When you're dehydrated, your body makes more vasopressin, a hormone that raises blood sugar and signals the liver to make even more.

• People with type 2 diabetes often have higher vasopressin levels, suggesting low water intake could be a factor.

• Dehydration can also raise aldosterone, another hormone that may make it harder for insulin to work properly.

• Long-term low hydration can affect cells and may lead to insulin resistance, a key part of type 2 diabetes.

There are several other studies with similar findings:

• Low Water Intake and Risk for New-Onset Hyperglycemia: In a 9-year study of 3,615 middle-aged adults with normal fasting glucose, those who reported drinking more than half a liter of water per day had a significantly lower risk of developing high blood sugar compared to those drinking less than 0.5 liters daily, suggesting an inverse and independent association between water intake and hyperglycemia risk.

• Higher plain water intake is associated with lower type 2 diabetes risk: a cross-sectional study in humans: In this study, “plain water intake had a significant negative correlation with T2D risk score.”

• Reduced water intake deteriorates glucose regulation in patients with type 2 diabetes: In this study, “3 days of low total water intake in people with T2DM acutely impairs blood glucose response during an oral glucose tolerance test.”

• Water intake and risk of type 2 diabetes: A systematic review and meta-analysis of observational studies: In this study, the “intake of water was correlated with reduced risk of type 2 diabetes in women and men. These results support the current recommendations of water intake as an inseparable part of a diet with the lowest risk of diabetes mellitus.”

• Effects of hydration on plasma copeptin, glycemia and gluco-regulatory hormones: a water intervention in humans: In this study of 39 healthy individuals, both an acute (downing 1 liter of water) and a week long intervention (1 week of 3 extra liters of water day) of increasing water intake significantly reduced plasma copeptin levels, which is a surrogate marker for vasopressin—a hormone involved in water balance and which predicts diabetes development and metabolic syndrome. With extra hydration, there was also a drop in fasting glucagon, a hormone that raises blood glucose by stimulating liver glucose production; this suggests hydration may support metabolic health by modulating vasopressin and glucagon pathways.

🤓 Study #3: Multiple mechanisms by which water intake supports weight loss

In this 8-week study, 50 overweight girls (BMI 25–29.9) were instructed to drink an additional 1.5 liters of water daily (500 ml before each main meal) above their usual intake. Researchers measured changes in body weight, BMI, and body composition and found statistically significant reductions: on average weight decreased from 65.86 to 64.42 kg (-3.2 pounds) and BMI from 26.70 to 26.12. These results support the role of water-induced thermogenesis in promoting modest but significant weight and fat loss. While it was a small study without a control group, the paper suggests 3 ways that drinking water might elicit this type of weight loss:

1. 🥵 Triggers a thermogenic “heat” response: Drinking water may activate the sympathetic nervous system, which is the “fight or flight” arm of the nervous system. This leads to a temporary increase in heart rate, blood pressure, and metabolic rate, a process known as water-induced thermogenesis. Think of it like flipping on the furnace—your body burns more energy to process the sudden fluid intake, possibly due to signals from osmoreceptors that detect changes in the blood's fluid balance. The paper references a 2003 study that showed that drinking 500 mL of water increases metabolic rate in men and women by 30%, and this is observed within 10 minutes after drinking water!

2. 🔥 Helps burn fat: Water is essential for metabolizing stored fat, and even mild dehydration can slow down fat-burning and overall metabolism.

3. 📉 Reduces hunger: Drinking water before meals can naturally suppress appetite, making it easier to eat less without feeling deprived.

🤓 Study #4: Water fountains in schools prevent development of overweight

In this randomized controlled trial of 32 elementary schools, researchers installed water fountains and delivered four classroom lessons promoting water consumption in the intervention group. After one school year, children in the intervention group drank more water (1.1 more glasses, on average, per day) and had a 31% lower risk of becoming overweight compared to the control group. What this means is that while the baseline overweight rate was 23.4% in the intervention group (the group that got the water fountains), this did not change throughout the year (this intervention group ended the year with 23.5% of kids overweight). In contrast, in the control group that didn’t get the water fountains, overweight rates went from 25.9% to 27.9%, up almost 2%. Therefore, the increased water intake was associated with much lower chances of developing overweight throughout the school year.

🔬 What’s happening at the level of the cell?

This review looked at what is actually happening in a fat cell when we get dehydrated. When a fat cell (adipocyte) is well-hydrated (euhydrated), it keeps a healthy balance: it makes fat (called triglycerides) from sugar and fatty acids when needed, and breaks down that fat when the body needs energy (lipolysis). Any extra glycerol (a building block of fat) gets sent out of the cell. The fatty acids are either burned for energy or sent elsewhere.

But when the fat cell starts to get dehydrated, things change: The cell begins making and storing more fat, and it becomes less able to burn fat for energy. Instead of using fatty acids as fuel, it holds onto them.

To make even more fat, the cell increases a special channel (called aquaporin 9) that pulls in extra glycerol, which is the backbone of triglycerides, a storage form of fat Meanwhile, insulin pushes more glucose (sugar) into the cell, which also gets turned into fat.

Bottom line: A dehydrated fat cell becomes a fat-storing machine and struggles to burn fat properly!

🤔 What should we be drinking: water, or something else?

So, given that the many studies listed above used plain water as the hydration source, is it the best beverage for optimal hydration? While water is foundational, SO important, and widely accessible, there are other beverages that also may be helpful in retaining fluids—especially in physically demanding or high-heat conditions. Let’s explore how hydration status is measured and how other drinks stack up against water.

How is “hydration” status measured in research studies?

Hydration is measured in a variety of ways, including:

• 🩸 Blood markers such as serum osmolality and sodium concentration assess fluid balance and solute concentration in the bloodstream.

• 🚽 Urine markers like urine specific gravity and osmolality indicate how concentrated the urine is, helping to detect dehydration.

• 🧍 Body weight changes over short periods (e.g., before and after exercise) reveal acute fluid loss; advanced methods like bioelectrical impedance analysis (BIA) and salivary osmolality provide additional hydration insights in clinical or research settings. BIA estimates total body water (TBW) and fluid compartments (intracellular vs. extracellular).

And don’t forget the simplest marker: urine color! A practical, though less precise, indicator. Pale yellow = better hydrated; dark yellow or amber = dehydration.

Then there is the Beverage Hydration Index (BHI). The BHI measures how effectively a specific drink is retained in the body compared to plain water, which has a BHI of 1.0. Beverages like oral rehydration solutions, milk, and electrolyte drinks often have higher BHI values—typically ranging from 1.2 to 1.6—indicating better hydration and fluid retention.

In a 3-week trial among Guatemalan sugarcane farmers laboring in extreme heat, researchers tested the effects of increasing electrolyte beverage intake on hydration, muscle damage, and kidney function. The intervention drink was a WHO-style oral rehydration solution (ORS) containing 2.6 g sodium chloride, 2 g potassium chloride, 13.5 g glucose, and 40 kcal per liter, provided at escalating doses: 2.5 L per day in Week 1, 5 L per day in Week 2, and 10 L per day in Week 3. Results showed that higher electrolyte intake was associated with lower levels of muscle breakdown (creatine kinase), stable kidney function, and better overall hydration, supporting the use of electrolyte-enhanced fluids to protect worker health in hot, physically demanding environments.

Additionally, a study on the Beverage Hydration Index ranked drinks for their level of hydration. In the study, seventy-two healthy, physically active men aged 18–35 participated in a randomized, controlled hydration study conducted across three university laboratories. After an overnight fast and standardized water intake, each participant consumed 1 liter of still water or a test beverage, and hydration status was assessed through cumulative urine output over several hours, serum and urine osmolality, and urinary sodium and potassium concentrations to calculate the Beverage Hydration Index (BHI) for each drink.

The findings showed that compared to plain water, oral rehydration solution (a version of electrolyte water with a small amount of glucose), orange juice, and milk were above-average hydration beverages. The water content of the drinks used in this study varied from 100% to 88%, so the actual amount of water ingested varied between drinks. After correction for this, orange juice was no longer significantly different than water. Oral rehydration solutions seem to hydrate more effectively than plain water because they contain sodium (± other electrolytes) and small amount of glucose, which help pull water into cells via specialized transporters, restoring cellular fluid balance.

This study is nicely summarized in this article.

💧 Bottom line: Hydration isn’t a wellness extra—it’s a key metabolic strategy

• Dehydration flips the fat switch. When your cells sense water scarcity, they go into storage mode: making and holding onto fat to stockpile “metabolic water.”

• Water helps burn fat. It boosts thermogenesis, supports fat metabolism, and suppresses appetite—benefits shown even without diet or exercise changes.

• Hydration is protection. Clean, electrolyte-rich water supports mitochondrial function, kidney health, and efficient cellular energy.

• Tap water isn’t always safe. Check yours—arsenic, PFAS, and other toxins are common. A solid filter is essential.

• Electrolytes improve hydration. Oral rehydration solutions (electrolyte drink with small amount of glucose) and milk seem to retain fluid better than water alone.

Writing this newsletter makes me feel so inspired to make it a habit to drink more water. I know I don’t drink enough unless I’m actively thinking about it. But like with all things, there is a limit… you don’t want to drink so much that you throw off your biology — this can be dangerous. So don’t go overboard! A good rule of thumb: if your urine isn’t a very light yellow throughout the day… drink more water!

⚠️ Clean water note

The Environmental Working Group (EWG) has a tapwater database where you can search the purity of your water based on zip code. In my community, the water contained 820 times the amount of arsenic recommended as safe. 🤦‍♀️ You can use their Water Filter Guide to match your zip code’s water quality with the right filter. This showed me that reverse osmosis filtration (over a charcoal filter) was the best option for subpar LA water.

I HIGHLY recommend investing in a high quality water filter to ensure you are getting a consistent supply of clean water, every single day. You want your water filter to do more than just make the water taste better: you want it to remove disease causing substances like heavy metals (like lead and arsenic), industrial chemicals (like PFAS), pesticides, pharmaceuticals, and chlorine, fluoride, chromium-6, and more. I prefer an undersink reverse osmosis filter with a spigot, which makes it easy to use clean water for cooking and drinking throughout the day; you generally have to change the filters out once per year. There are decent countertop and pitcher versions available too, which are less expensive, and you can read more about the different types of filter technology and find a list of tested examples on the EWG website.

With good energy 💓

Dr. Casey

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