Water is a vital nutrient that our bodies need to function properly, but it contains no calories. This may seem counterintuitive – after all, water is necessary for survival, so shouldn’t it provide us with energy in the form of calories? The reason behind this lies in what calories are and what role they serve in our diet.
What are calories?
Calories are a unit of measurement for energy, specifically the energy we get from food. When we eat foods that contain carbohydrates, proteins, and fats, our bodies break these macronutrients down through digestion and absorb their energy in the form of calories. This energy is then used to fuel our cells and bodily functions. So for a substance to contain calories, it must provide usable energy that our bodies can extract and utilize.
Water contains no macronutrients
Water is a micronutrient that contains no carbohydrates, proteins, or fats. Since water lacks these macronutrients, our bodies cannot break it down to extract energy from it. This means water passes through our system without delivering any calories to our cells. While water is essential for many vital bodily functions and processes, it does not provide fuel for energy, motion, growth, or heat production in the way food does. That’s why we can drink large quantities of water without gaining weight or feeling full the way we would if we ate calorie-containing foods.
The roles of water in the body
So if water doesn’t provide calories, what does it do? Here are some of the key roles water plays:
- Transports nutrients and waste – Water moves nutrients through the bloodstream and lymph system to the cells. It also transports waste from the cells to the kidneys and digestive tract for removal.
- Temperature regulation – Water helps regulate body temperature through perspiration and respiration.
- Digestion and absorption – Water facilitates digestion by helping break down food and allowing the body to absorb nutrients.
- Cushions joints – Water in cartilage and spinal discs acts as a shock absorber.
- Lubrication – Water moistens mucous membranes and lubricates joints.
While these functions are critical, they do not involve providing usable calories for energy. That is why water can facilitate so many life-sustaining processes without containing any calories.
How the body obtains energy from foods and beverages
To understand why water lacks calories, it helps to know how the body extracts energy from other foods and drinks.
When we consume carbohydrates, proteins, and fats, enzymes and acids in our digestive system break these macronutrients down into simple sugars (glucose), amino acids, and fatty acids. These digested components are then absorbed into the bloodstream through the small intestine. Once in the bloodstream, they travel to cells throughout the body.
The cells contain mitochondria – small structures that convert the sugars, amino acids, and fatty acids into ATP (adenosine triphosphate). This ATP is the energy source that powers most cellular functions. Therefore, the calories obtained from carbohydrates, proteins, and fats ultimately get turned into cellular energy.
Water plays an important role in this process by dissolving nutrients and transporting them through the body. But because water lacks macronutrients itself, it cannot be broken down to produce ATP energy. So it passes through the system without delivering calories.
Water’s contributions to energy balance
Although water does not contain calories, it does contribute to our overall energy balance in indirect ways:
- Digestion and metabolism – Water enhances digestion and allows efficient metabolism of foods into energy.
- Thermogenesis – Drinking cold water can cause a slight temporary increase in metabolic rate as the body warms the water to body temperature.
- Fullness – Water fills the stomach, which can mitigate overeating and excessive calorie intake.
- Alertness – Being well-hydrated prevents fatigue and improves mental acuity and work performance, which helps maintain an active lifestyle.
So while the calories in food and beverages power our bodies directly, water plays a supporting role by enabling us to digest, absorb, transport, and utilize those calories most effectively. Staying well-hydrated optimizes this process.
The hydration needs of different people
Water requirements can vary based on factors like age, gender, activity levels, and climate:
| Group | Total Daily Water Needs* |
|---|---|
| Infants (0-6 months) | 600-900 ml |
| Infants (7-12 months) | 800-1200 ml |
| Children (1-3 years) | 1300 ml |
| Children (4-8 years) | 1600 ml |
| Boys (9-13 years) | 2100-3200 ml |
| Girls (9-13 years) | 2100 ml |
| Boys (14-18 years) | 3400-4500 ml |
| Girls (14-18 years) | 2100 ml |
| Adult males | 3700 ml |
| Adult females | 2700 ml |
| Pregnant women | +300 ml/day |
| Breastfeeding women | +600-900 ml/day |
*Including water obtained from food and beverages – not just drinking water.
Factors like sweating, diarrhea, vomiting, and medications can also influence water needs. Doctors may recommend increased fluid intake for some medical conditions.
Recommendations for water intake
Here are some general recommendations for getting adequate hydration through water and other beverages:
- Drink 6-8 glasses of fluid per day (8 oz per glass). About 20-30% of daily fluid intake comes from food.
- Drink more water before, during, and after physical activity.
- Drink extra water in hot climates or at high altitudes.
- Thirst is an early indicator of under-hydration – drink fluids soon after feeling thirsty.
- Avoid waiting until thirst becomes extreme before drinking.
- Moderate dehydration can occur even with mild thirst. Dark yellow urine indicates the need for more fluid intake.
- Focus on water, but variety is important too. Herbal tea, milk, and fruits and veggies containing water all contribute.
- Beverages containing caffeine and alcohol tend to have a diuretic effect, so moderation is key.
Signs and symptoms of dehydration
Since water is so critical for health, insufficient intake can cause dehydration. Mild to moderate dehydration can occur even before feelings of extreme thirst set in. Here are some signs and symptoms:
- Thirst
- Fatigue
- Dry mouth
- Muscle weakness or cramps
- Dizziness
- Headache
- Reduced urination and dark yellow urine
- Rapid heart rate
- Fever
- Confusion
Severe dehydration requires urgent medical treatment to prevent serious complications. Left untreated, extreme fluid loss can be life-threatening.
Can drinking extra water lead to more calories burned?
Sometimes claims are made that drinking extra water throughout the day can significantly increase the number of calories burned. Is this true?
While water does contribute indirectly to energy expenditure through its roles in digestion, absorption, transport, and preventing fatigue, the direct calorie-burning effects are more modest. Here’s a look at what the science says:
- Drinking an extra 1 liter (34 oz) of water per day only burns about an extra 23 calories.
- One study found a temporary metabolic boost of 24-30 calories over 1-1.5 hours after drinking 17-18 oz of water.
- Another study showed a 30% increase in metabolic rate, but only for about 10 minutes after drinking 20-24 oz of water.
- The body quickly regulates itself back to normal after a brief energy surge from drinking water.
- Long-term studies show no significant extra calorie expenditure from increased water consumption.
So while staying well-hydrated provides many health benefits, the calorie-burning effects directly attributable to water are small and transient. For weight management, focusing on nutrition and exercise is far more impactful than drinking extra water alone.
Water myths and misconceptions
There are many myths surrounding water and hydration. Here’s a look at some common misconceptions:
Myth: Everyone needs 8 glasses of water per day
This popular advice lacks solid scientific basis. Water needs vary based on factors like age, gender, activity level, and climate. The 8 x 8 rule may over-estimate or under-estimate needs for many people.
Myth: Only plain water hydrates the body
While water is ideal, other beverages like milk and juice also contribute to hydration. Even caffeinated drinks can contribute to fluid needs, though moderation is key.
Myth: Dehydration is obvious
Thirst isn’t always a reliable early indicator of fluid needs. Mild dehydration can manifest through fatigue, headaches, and reduced cognitive performance before thirst becomes extreme or noticeable.
Myth: Sports drinks are best for re-hydrating
Water is an efficient re-hydrator for most people engaging in less than 60-90 minutes of strenuous activity. Sports drinks provide extra carbs and electrolytes, but are not essential for shorter, lighter workouts.
Myth: Coffee and tea dehydrate the body
Caffeine has mild diuretic effects, but coffee and tea still contribute to fluid intake. Moderation is important since very high caffeine intake can increase urination.
Key takeaways
To summarize the key points:
- Water contains no carbohydrates, proteins, or fats, so the body cannot extract calories from it.
- Calories in food come from macronutrients that are broken down and converted to cellular energy.
- Water supports digestion, nutrient absorption, temperature regulation, joint cushioning, and other functions.
- Water needs vary based on factors like age, gender, activity, and climate.
- Dehydration can occur before extreme thirst sets in.
- Drinking extra water produces a minor, temporary calorie burn rather than major increases in energy expenditure.
- Hydration myths oversimplify recommendations for meeting fluid needs.
The bottom line
Water is a crucial nutrient, but it lacks macronutrients that could be metabolized into calories. So drinking plain water provides hydration without adding dietary energy. While some sources claim dramatically increased calorie burning from extra water consumption, the direct effects are minor and temporary. For weight management and energy levels, a balanced diet and active lifestyle play a far greater role than fluid intake alone. Water supports health in many ways, but the number of calories in water remains zero.
