How do we estimate fluid needs and when do you recommend water versus sports drink to replenish electrolytes?
We are 50 to 60% water, and we need to make sure that we keep that up for our functions and ﬂuid balance. The problem is the body is really good at regulating hunger and thirst, but there's a lag time between loss of ﬂuid and thirst. So, we may be working out and we may not realize that we're thirsty until it's too late. There are studies on athletes that arrive at their workouts thinking they're hydrated, and they're really not. We don't replace what we should. So most adults need about 12 cups of ﬂuid each day. Some of that comes from our food and some of that comes from food intake. On average, we get 1L (4 cups) water from our food each day depending on what we eat.
- Raw fruits, vegetables=mostly water
- Cooked whole grains/legumes=absorb fluid from cooking
- High fat foods=very little water
We need about 2L (about eight cups) from fluid intake. There's more water needed for larger body size, hard exercise, environmental (warm, dry weather), and if you are sick/lost water via diarrhea/vomiting.
You can estimate your needs by body weight. For every kilogram, need 30-40mL if H2O.
- 110lb person (50kg) = 1.5-2.2 L per day
- 220lbs (100 kg) = 3-4L per day
There are consequences to body water loss:
- .5% body water loss can strain your heart
- 1% reduced aerobic endurance
- 3% reduced muscle endurance
- 4% reduced strength, motor skills, heat cramps
- 5% heat exhaustion, cramping, fatigue, reduced mental capacity
- 6% physical exhaustion, heatstroke, coma
- 10 to 20%, can be very critical and cause death
So it is really important to make sure that we're not losing water more water than we need/are taking in.
Dehydration, as I said earlier, there's a lag. We typically don't notice that we need more water until we've lost 1 to 2% of body water. Symptoms of dehydration include:
- Low blood pressure
- Rapid heart rate
We can't train to become better at being dehydrated. We don't adapt to it, we just have to replace lost ﬂuids. We can train our muscles, we can train everything else, we can't train that and that's really important.
On the other side, we have something called hyponatremia. That's when we take in too much water relative to our sodium losses. There are three ways we can do this:
- Blood volume goes down. For example, you're vomiting and having diarrhea or something is going on where you're losing a lot of blood volume generally and it's messing with the balance of sodium and water where you're having low sodium and too much water (versus dehydration where you're having too much sodium and too little water)
- High blood volume and total water can go way up but sodium isn't rising to the rate the water is.
- Normal blood volume, but you're just drinking too much water, and not taking electrolytes with it can be at risk for this.
Hyponatremia symptoms include:
- GI discomfort
- Swollen hands, feet
- Confusion and/or restlessness
Athletes are at risk when rehydrating without electrolytes. The bottom line is ﬂuid replacement is crucial but don't over drink. If you're a normal person under normal conditions, performing a short bout of exercise, plain water's ﬁne. When you're exercising in a hot, dry climate, exercising for a long time, when you're a pro athlete, and/or when you have more, than two practices per day, at those points you need to replenish using a sports drink.
For more information on hydrations strategies check out the course: Sports Nutrition presented by Carol Mack, PT, DPT, SCS, CSCS, PN-1