Optimize Your Hydration: Fluid Intake Volume
Written By: Courteney Benjamin, Head of Product at sum. and Assistant Professor at Samford University, 3/1/2024
Do you work in a field where cognitive performance is important? Are you recreationally active and exercise to optimize your health and longevity? Are you a new mom who is breastfeeding? Do you want to reduce your risk of cardiovascular and renal disease? Are you an elite athlete training for the Olympics? If you answered ‘yes’ to any of these questions (and many more), the first and most meaningful way to optimize your hydration status is really simple. Drink the correct amount of fluid to meet your needs!
Although this idea is extremely simple, determining how much fluid to consume throughout the day and surrounding certain activities that produce a lot of sweat can be complex because our hydration status is constantly changing throughout the day and factors like age, biological sex, exercise intensity, exercise volume, environmental conditions, and other fluid losses (such as through lactating) can change your fluid needs on any given day at various times. For those interested in more specific methods for optimizing their fluid intake volume, be on the lookout for future blogs. For those who are just getting started on their hydration journey, keep reading for simple strategies to determine your daily fluid needs and how sum. can help you meet those needs.
Step 1: Determine general daily fluid needs.
The Institute of Medicine recommends that adult males consume 2.60 L of fluid per day and that adult females consume 1.8 L of fluid per day. If you’re interested in seeing more specific recommendations, this table contains detailed guidelines by age, biological sex, and for pregnant and lactating women. If you currently have no idea about how to start on your hydration journey, aiming for these total daily fluid volumes is a great place to start and will get you closer to maintaining a good hydration status throughout the day.
“If you currently have no idea about how to start on your hydration journey, aiming for these total daily fluid volumes is a great place to start”
Even though these guidelines are a great place to start, individual needs vary and one of the best ways to determine if you are getting the correct fluid intake is by assessing your hydration status. Surprisingly, there is no ‘gold standard’ way to assess hydration status. This means that there is not one blood assessment or urine assessment that can tell you with 100% confidence what your current hydration status is. For this reason, I encourage the majority of people to use a few simple strategies to determine their hydration status.
Urine color- Your goal should be to make your urine color look more like lemonade and less like apple juice. If your urine color (especially first thing in the morning) is on the darker side, you may not have consumed enough fluid the previous day.
Body mass changes- Most daily fluctuations in body mass are due to changes in hydration status. For best results in using this method to determine your hydration status, take your body mass (in the nude!) three days in a row first thing in the morning after urination when you are well hydrated. Average those values. Any future daily body mass losses from that average is most likely related to changes in hydration status. For example, if your average body mass is 130 pounds and you weigh yourself one morning to find the number on the scale is 127.4 lbs, you are probably in a 2% water deficit.
Thirst- Although this one is extremely simple, it is powerful! Research shows that when you feel the sensation of thirst you are already at a 2% fluid deficit. Drink up!
To make your hydration assessment even more powerful, consider combining some of these methods.
The WUT method has become increasingly popular in athletic settings but can be used by anyone. In this method, W=Weight (body mass loss >1-2%), U=Urine color >4, and T=feeling thirsty. Following the Venn Diagram below, you are likely dehydrated if 2/3 criteria are met. You are very likely dehydrated if 3/3 of the criteria are met.[CB1]
Finally, another simple strategy to help determine your hydration status is to use urine color and number of urine voids throughout a 24 hour period. If your urine color is 3 or less on the urine color chart and you pee 7 times or more in a 24 hour period, there is a great chance that you are meeting your fluid intake needs!
To wrap up this section, pick a strategy that is feasible for you and use your hydration assessment method to determine if you should increase or decrease your daily fluid intake.
Step 2: Determine your fluid intake needs during exercise.
Assuming you have done a great job of hydrating throughout the day and are starting your workout hydrated, there are two possible strategies for you to choose from. Dr. Robert Kenefick published a great paper summarizing how to determine which strategy is best for you.
The first is a strategy known as drinking to thirst. This is exactly what it sounds like…drink when you feel thirsty! This strategy only works when you fill your water bottle before your workout and have it readily available to you throughout the session. Now is a good time to remind you that thirst sensation is not the best indicator of your hydration status and when you start to feel thirsty, you are already in a 2% body water deficit (aka behind on fluid intake!). So, consider using this strategy if:
You’re not trying to reach peak performance.
You’re not losing a lot of sweat.
Your exercise session is less than 45-60 minutes.
The second strategy is referred to as programmed drinking. Programmed drinking is a strategy in which an individual has a pre-determined amount of fluid they aim to consume during a given workout. This strategy considers that every individual has unique fluid intake needs because of the wide range of sweat rates seen in individuals on any given day. To use this strategy, you can calculate your sweat rate in a previous workout that is similar in intensity and environmental conditions to the one you are aiming to optimize and use a sweat rate calculator like this one. Once you know your sweat rate, you can aim to consume enough fluid to avoid a 2% body mass loss during the next workout.
Keep in mind that your sweat rate can change on any given day depending on factors like your current hydration status, exercise intensity, environmental conditions, and more so it’s important to calculate your sweat rate often and make adjustments from there. The good news is, after you do this calculation a few times in a few different scenarios, you will quickly start to learn your own individual fluid needs and will get pretty good at knowing how much fluid you need without having to calculate your sweat rate very often. Consider using this strategy if:
You are trying to reach peak performance.
You will lose a large volume of sweat in your workouts.
Your exercise session is greater than 60 minutes.
Regardless of the method you choose, the ultimate goal for any exercise session is not to lose more than 2% of your body mass (especially to maintain aerobic performance) AND to not gain weight during a workout session, which indicates you may be consuming too much fluid.
sum. has you covered because you can easily track and update the size of your beverage from the app depending on your needs that day.
“ the ultimate goal for any exercise session is not to lose more than 2% of your body mass... AND to not gain weight during a workout session”
Step 3: Determine your fluid intake needs after exercise.
Even with the most advanced hydration approaches used during exercise, it is still extremely common for people to lose body mass throughout a workout. This is because it is extremely difficult to replace 100% of the fluid lost in sweat. This means that replacing fluid within two hours of exercise is critical to help you get caught back up on your hydration.
The most updated scientific evidence suggests that individuals should consume 150% of their body mass loss after exercise. To determine this, you simply need to weigh yourself with minimal clothing before and after your workout and replace 150% of that difference. For example, if you weigh 150 pounds before starting your workout and weigh 148 pounds at the end of the workout, you need to replace about 1.36 L (~33 oz) of fluid 2 hours after your workout ends.
Fortunately, sum. makes it extremely convenient and easy for you to get the right amount of fluid to meet your needs. In this scenario, you should select the 32 oz beverage option and try to consume that beverage within about 2 hours.
References
Kenefick, R.W. Drinking Strategies: Planned Drinking Versus Drinking to Thirst. Sports Med 48 (Suppl 1), 31–37 (2018). https://doi.org/10.1007/s40279-017-0844-6
Gandy, J. Water intake: validity of population assessment and recommendations. Eur J Nutr 54 (Suppl 2), 11–16 (2015). https://doi.org/10.1007/s00394-015-0944-8
Armstrong, L. E. (2007). Assessing Hydration Status: The Elusive Gold Standard. Journal of the American College of Nutrition, 26(sup5), 575S-584S. https://doi.org/10.1080/07315724.2007.10719661
Périard JD, Eijsvogels T, Daanen HAM, et al Hydration for the Tokyo Olympics: to thirst or not to thirst? British Journal of Sports Medicine 2021;55:410-411.
Sekiguchi Y, Benjamin CL, Butler CR, et al. Relationships Between WUT (Body Weight, Urine Color, and Thirst Level) Criteria and Urine Indices of Hydration Status. Sports Health. 2022;14(4):566-574. doi:10.1177/19417381211038494
Stand, ACSM Position. "Exercise and fluid replacement." Medicine and science in sports and exercise 39.2 (2009): 377-390.