How Water Intake Affects Body Composition

One of the most commonly overlooked pieces of the body composition puzzle is water intake. I have had several clients who had weeks where they nailed macros, workouts, and sleep but their water intake is non-existent. They feel like shit and did not make any progress. The following week, we get water intake back on point, and viola, they feel better, look better, and are back to progressing. Water contributes to innumerable physiological functions from body temperature regulation, to energy production, to nutrient transportation. We also know water plays a huge role in body composition. Rather than overlooking water, let’s look at the mechanism to understand how your water intake, or lack thereof, may be affecting your progress and long term health.

Dehydration and Water Weight

Our bodies are badass. They are constantly adapting to keep us alive through various homeostatic feedback loops. When something is off in our bodies, our bodies go to work adjusting to that stimulus. When our water intake is not sufficient, the main adaptations occur from increased levels of the body’s chief fluid regulating hormone angiotensin II (AngII). AngII acts on two transmembrane receptors that stimulate increased thirst. In most animals, this causes them to actively seek water. Research has shown even when humans are thirsty, we won’t drink water because we don’t like the taste, we don’t want to pee so much (I’m not making this up), or we just don’t know the benefits of drinking water (1). Adaptations also include an increased appetite for sodium which binds to water to help hold on to whatever water the body does receive. Lastly, there is a release of antidiuretic hormone (ADH) which leads to water conservation by the kidneys.

These all occur to regulate plasma volume back to normal levels and help the body hold onto whatever water is there. These things are all helpful so we don’t die when we have days when we forget to drink water (guilty). However, this is also going to cause an increase in “water weight”. The linear mind may think less water in, less body weight. However, as we’ve seen the adaptations that occur when hypohydration invalidates this thought.

The body is going to hold on to whatever water it can until it is sufficiently hydrated and can start allowing water to leave the body.

Furthermore, it is worth mentioning chronic hypohydration and the resulting chronically elevated levels of AngII can impact much more than weight. Elevated AngII levels are related to several conditions including long term weight gain, obesity, diabetes, Alzheimer’s, and cancer. So yeah, you’re going to hold some water, but you could be putting yourself at even greater risk.

Water Intake and Body Composition

On the flip side, sufficient water intake has been associated with improved body composition. In a two-year cross-sectional study at CEU San Pablo University in Madrid, Spain, researchers analyzed the correlation between body anthropometrics and hydration status and water intake (2). The study took place with 358 healthy volunteers: 121 males and 237 females, aged 20-22 years old. The participants completed a Hydration Status Questionnaire and International Physical Activity Questionnaire to estimate water intake, hydration status, and exercise-related water loss. The researchers estimated how much water participants lost when using the bathroom. They manually took body measurements such as weight, height, and waist circumference, calculated BMI, and used bioelectrical impedance analysis to estimate total body water, body fat percentage, lean body mass, and dry lean body mass. After normalizing data for body weight, water intake was inversely correlated with body weight, BMI, waist circumference, body fat percentage, and positively correlated with total body water (2).

While mechanisms for this are still up for debate, there are strong hypotheses worth discussing.  First, studies have shown those who increase their water intake before a meal experienced decreased caloric intake during the said meal. Second, studies in humans and rodents have shown increased water intake to lead to increased fat lipolysis (fat breakdown). They may be due to increased cell volume which may result in increased insulin sensitivity and increased metabolic function.


While it is not breaking news that you should drink water, these studies do help enlighten why it is important for body composition and long term health. Many of the traditional suggestions for water intake still apply:

-For active individuals, aim to drink your body weight in ounces of water per day.

-Drinking water before meals may help decrease caloric intake at that meal and improve digestion.

-Listen to your body. After hard workouts or sodium-rich meals, you may need more water (even if it means you pee a little more often).

In addition to this, there are some less scientific and more anecdotal tips that have worked well for my clients and me:

-Instead of thinking of it as a hindrance, be grateful you get to drink all the water you want. A large portion of the world is not so lucky.

-Get a water bottle that makes drinking water more enjoyable. My favorites are by Contigo. That straw is a game-changer.

-Get a water bottle that helps you track your intake. There are high tech ones like Hidrate Spark (which I have and enjoy) or just basic ones that have measurements on them.

-Get a big water bottle, sometimes just the act of not having to fill up your water is helpful. One of my clients swears by this one.

-Try water flavoring like mio.

-Throw in the occasional unsweetened carbonated beverage or two, I find AHA to be the most flavorful.

Water intake is non-negotiable if you want to achieve your physique goals. Instead of treating it as a secondary nuisance, treat it like the critical piece of the puzzle that it is. Further, be grateful you get to drink as much water as you do and get creative with ways to make drinking water less boring and more enjoyable.


1. Thornton, S. (2016). Increased hydration can be associated with weight loss. Frontiers

In Nutrition, 3.

2. García, A., Moráis-Moreno, C., Samaniego-Vaesken, M., Partearroyo, A., &

Varela-Moreiras, T. (2019). Influence of water intake and balance on body

composition in healthy young adults from Spain. Nutrients, 11(8), 1923.

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