How Does Dehydration Affect Body Composition?

Shannon Miller

March 3, 2022

We are made of up to 60% water. You read that correctly: close to two-thirds of our body is comprised of H2O. It’s no surprise that water is one of the most important compounds in the body, with essential functions that keep us alive and healthy. When it comes to body composition, water is essential to lean muscle mass development and can have an effect on body composition data if the body is over- or under-hydrated. Read on to learn more about the importance of hydration and how it can contribute to body composition goals.

Why does the body need water?

Water is the foundation of many critical functions in the body. Water molecules help with waste removal, temperature regulation, transport of carbohydrates and protein in the bloodstream, joint lubrication, and shock absorption for the brain and spinal cord. It is also the main building block of many types of cells in the body. Without enough water, symptoms such as headaches, dry mouth and dizziness may arise. Inside the body, dehydrated cells send a message to the brain to release vasopressin, which can elevate blood pressure. Experts agree that consuming one-half your body weight in ounces of water per day can provide adequate hydration. That means for a 150-pound person, 75 ounces of water per day is required.

Want to build muscle? Drink more water.

Muscle tissue is comprised of around 80% water. According to cell studies, without enough water to transport to muscle cells, protein synthesis (growth) decreases and protein catabolism (breakdown) increases. Although further human research may be needed, this could mean that consistent dehydration hinders muscle growth, and as a result, affects the proportion of lean muscle mass in the body. Research also suggests dehydration is linked to a lower ability to generate upper and lower body strength. A higher proportion of lean muscle mass in the body in relation to fat mass may increase resting metabolic rate and overall health.

How are body composition and dehydration linked?

A hydrated body can more easily perform cellular functions essential to health. When it comes to body composition changes (fat mass loss, lean muscle gain, for instance) water intake has a profound effect. Increasing water intake along with a healthy diet is linked to greater fat loss (up to a 44% increase!). It’s easy to see how dehydration can be a detriment to body composition goals that include fat mass loss. When the body is dehydrated, exercise performance can be hindered and risk of injury may increase. Chronic dehydration may mean your intentions at the gym to build muscle or burn fat could be affected negatively, thus could possibly stunt progress towards your goals.

Can hydration affect DEXA scan data?

While a DEXA scan cannot indicate levels of hydration, if you are severely under-hydrated or over-hydrated, data may not represent your body composition accurately. However, we say “severely” because it would take an enormous amount of water consumed before a DEXA scan to shift a reading by just 1% (we do not recommend drinking a large amount of water before any test, but a few chugs from a water bottle is just fine!). Why would a shift in data happen if the body increased in water content? A DEXA scan compares fat mass to lean mass. Lean mass measurement combines all non-fat matter like blood and interstitial fluids (aka: water). Therefore, extreme water consumption before a scan would increase the proportion of lean tissue when compared to fat mass. This would overestimate true lean mass percentage and underestimate body fat percentage. Conversely, if the body was severely dehydrated, a scan may overestimate body fat percentage. Luckily, DEXA scan technology is not as sensitive to hydration levels like other methods of body composition analysis technologies such as bioelectrical impedance.

It’s very clear that hydration is important to health, but it can be a missing link to progress when it comes to body composition goals. Make a habit out to drink plenty of water each day, and increase water consumption during and after strenuous workouts – your muscles depend on it!

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