Your Fueling and Hydration Questions—Answered!


Last month I asked readers of the morning shakeout to submit their fueling and hydration questions for the experts at Precision Fuel & Hydration to answer and boy did they deliver! Below you’ll find questions and detailed answers from PF&H’s experts about navigating the contradicting views and latest trends in fueling and hydration advice, changing your fueling strategy based on how much you sweat, adjusting your fueling and hydration strategies for different seasons, how to determine your carbohydrate needs, pulling yourself out of a bonk, the importance of fat for runners, fueling for recovery, and much more. One lucky winner—Randy S.—was chosen to win a $100 PF&H gift card.

(And if you’re interested in trying Precision Fuel & Hydration products for yourself, check out this link and save 15% off your first order.)

Chris M. asked: “With such changing science in fueling and hydration, and so much information on the internet, how’s an amateur athlete supposed to sort through and choose the right fuel for their distance/event/time of year, without spending a bazillion dollars trying different things and reading/watching millions of hours watching different things?!”

Emily from PF&H answered: “Navigating the contradicting views and latest trends in fueling and hydration advice is no easy feat for athletes of all levels! The key is to try to avoid the latest hype and focus on the basic needs of an endurance athlete. When you boil sports nutrition down to the fundamentals, there are 3 acute costs of taking part in endurance exercise:

1. Calories burned (mainly in the form of carbohydrate)

2. Fluid lost as sweat (water)

3. Sodium lost in sweat

Of course, the wider topic of good nutritional practices for athletes is significantly more complex than the turnover of these 3 elements. But for us, the trio (which we refer to as ‘the 3 levers’) sit head and shoulders above the others in the hierarchy of importance during endurance exercise. 

These are the acute costs of taking part in endurance exercise, so replacing a reasonable proportion of them in relation to your rate and magnitude of loss during exercise should cover the bases in terms of what your body needs to perform at your best.

Although the latest fads may make headlines and can sometimes contribute marginal gains, to save time (and money), your primary focus should be on taking in the correct quantities of carbohydrate, fluid and sodium to meet your individual needs in certain environments. 

Our free Fuel & Hydration Planner can help you determine your specific needs. Another important consideration to help know what you should be taking in is to better understand and collect data on your losses. To do this, finding out your sweat sodium losses and compiling data on your sweat rate in different conditions is helpful. Once you know your losses and the numbers you’re aiming to hit, the strategy will then require trialing in training to refine the plan and train your gut to tolerate your targets.”

Amanda H. asked: “Should I change my fueling strategy based on how heavily I sweat? How do I adjust based on exertion and temperature?”

Emily from PF&H answered: “As everyone sweats differently, both in terms of volume and how salty their sweat is, you certainly do need to personalize your approach to hydration. How much and what you drink will indeed also need adjusting based on the intensity at which you;re exercising and the conditions in which you’re exerting yourself in.

Warmer conditions and/or higher intensity output will increase your sweat losses and therefore how much you need to drink to stay on top of those losses. So, it’s helpful to measure your sweat rate in a range of temperatures and intensities, including some which simulate your predicted race conditions. 

Here’s a detailed explanation of how to conduct this data collection (weighing yourself pre/post sessions) and, based on these results, you can learn how much more total fluid you lose on average and increase your intake targets accordingly to limit performance impacting levels of dehydration.

Your carbohydrate targets will also vary based on the intensity and duration of your effort, but not directly as a result of the temperature. What the weather may impact are the logistics of hitting your numbers and the format of the carbohydrate you consume. 

When preparing for hot races, it may help to decouple your hydration and fueling strategies. This means getting in your electrolytes through fluid, but more of your carbs from gels and chews. If you’re drinking more fluid because it’s hotter, but most of your fluid is carb-rich energy drink, it’ll be easy to overdo the latter and run into GI distress. Equally, if all of your carbs are in your bottles but it’s colder than anticipated and you don’t drink as much, you risk undergoing it.”

Stuart F. asked: “How should I adjust my hydration and fueling for a race in early summer, when most of my training will be in winter and spring?” 

Emily from PF&H answered: “As I mentioned when answering Amanda in the last question, warmer conditions will, of course, increase your sweat losses and therefore how much you need to drink. Measuring your sweat rate in race conditions (potentially simulating these indoors if you’re not lucky enough to be doing any heat training or a camp) will help you home in on your fluid needs on race day. 

Practicing using the fueling products you plan to use on the big day in race conditions (and for as close to race duration as you get in training) to make sure you can tolerate them is also likely to be beneficial.”

David G. asked: “After years of half marathons and shorter races, I’m now training for my first marathon. (Aiming for 3:15:00). I find that I can easily go for 17 miles with nothing more than a single 15g “superstarch energy” pouch and no hydration, at least during the cool/cold months. Can I get away with this, or should I force myself to carry water and practice dosing it even if I don’t feel like I need it?”

Emily from PF&H answered: “Whilst many of us can run for that distance without anything, you’ll come very close to completely depleting your energy stores by the end of your race, and you’ll likely be nearing the point at which dehydration starts to hinder your performance as well (especially if you’re racing in hotter/more humid conditions than you train in).  

Fueling and hydrating won’t give you superpowers, but if you want to perform at your best in both your longer training sessions and on race day, it’s worth experimenting with upping your carb and fluid intake a bit. Aiming to get in ~60 grams of simple carbs per hour will help maintain your energy levels, allowing you to train and race harder for longer and preventing you from ‘hitting the wall’. 

Your fluid and sodium intake during a marathon will have less influence on your performance than your carb consumption. Depending on your sweat rate and how salty your sweat is, our Fuel & Hydration Planner would recommend drinking ~10-15oz (~300-450ml) of fluid per hour with a tolerance of +-5oz (150ml) an hour. Adding some sodium into any fluids you take on board will help you absorb that water as well as boost carbohydrate absorption into your bloodstream. That’s likely to prove beneficial to your performance but, as the tolerance suggests, don’t be overly concerned about hitting those numbers dead on if your instincts tell you to drink a little less. You definitely shouldn’t force fluids down. 

Another tactic to consider is ‘pre-loading’, i.e. proactively making sure you start optimally hydrated. Drinking a strong electrolyte drink before a big training session or race can significantly improve your performance.” 

Jason C. asked: “Fueling during a half or full marathon, how do I determine grams of carbs per hour? I’ve heard 60-90 is standard. But now I’m hearing 120g could be the right number.”

Emily from PF&H answered: “The amount of carb per hour you should be aiming for depends on both the intensity and duration of your session or race.

For efforts lasting between 1-2 hours, it can be beneficial to consume ~30-60 grams of simple carbs per hour. This equates to about 16-32oz (500ml-1l) of a ‘standard’ isotonic energy drink, or about 1-3 standard energy gels or chews per hour.

The harder the work and longer the duration within this bracket, the more appropriate it is to push the intake up towards ~60 grams per hour. This is especially true for athletes who are super fit and therefore able to sustain extremely high level workloads.

Certainly beyond two hours, research generally points towards a solid dose-response relationship with higher carb intakes usually eliciting better performance outcomes.

Athletes significantly passing the 2-hour mark can benefit from higher intakes of 60 to 90 grams of carbohydrate per hour, as long as the amount consumed doesn’t cause stomach problems. 

The higher the amount of carbohydrate you’re aiming to ingest, the more crucial practicing this and ‘training your gut’ becomes. An hourly intake of ~90 grams per hour (ie. 3 x PF 30 Gels or 1 x PF 90 Gel) is not something all athletes can achieve immediately and it can take a bit of time to build up to this rate of consumption, especially if you’ve been prone to suffering from GI issues in the past.

We’re increasingly seeing elite athletes reach the higher end of these recommendations and sometimes push over 100 grams, even 120 grams per hour. However this isn’t necessarily right for everyone and takes a lot of gut training. You can read more on what the evidence says about consuming more than 90g of carb per hour here.

The free Fuel & Hydration Planner is a useful place to start if you’re trying to dial in on how much you need for your next race.”

Robert P. asked: “Assuming that you aren’t eating so much that it is causing you GI distress, is more calories per hour always better than fewer, or is there a point of diminishing returns? I try to shoot for 400 cals/hour (100g/h) on my trail races (typically ranging from 6-12 hours) and it seems to work for me, but I’m curious what determines the upper limit of how much energy to consume (if not GI distress).”

Emily from PF&H answered: “The biggest limiting factor on how much you can consume is the rate of absorption of the carbohydrates by your gut. In theory “the more the better” to help you run further for faster, but there is only so much your gut can transport into the bloodstream to use at any given time. 

Not too long ago in the sports science research world, 60g/h was thought to be the limit, but with the addition of fructose at a 2:1 glucose:fructose ratio, 90g/h became the new scientific upper boundary.

It’s widely accepted that you can train your gut to adapt and absorb more carbohydrate, and more evidence has emerged showing up to 120g/h can be achieved and, as I said in the previous answer, we’re seeing more and more athletes reaching the top end of, and exceeding, the recommendations. 

If you consume more carb than your gut can tolerate and absorb, this will sit in the gut and can cause GI discomfort. And, just because you can tolerate more it doesn’t necessarily mean that is best in all situations. The highest intake levels suit very high intensity, long duration activity – if you’re undertaking exercise for shorter durations and/or at lower relative intensities, then this may not be needed.”

Frank asked: “For short runs of <1 hour you don’t really need to take gels. But then above that you should. Do you include the first hour when calculating what you need? IE, say you’re aiming for 90g/hr and do a 1h30 run, do you go for 135g? Or do you ignore the first hour and just have 45g?”

Emily from PF&H answered: “You’re absolutely right that consuming carbohydrate during runs under 60 minutes is not a necessity, as your body’s carbohydrate fuel stores (glycogen) can last up to ~90 minutes.

Once your effort duration pushes past this point, fueling plays an important role in maintaining performance. But, this doesn’t mean waiting until your stores are depleted to start fueling. Instead, taking a proactive approach by consuming carbohydrates earlier and consistently from around 20 minutes in will help you reach your target. 

So, when calculating your per hour intake, be sure to include the first hour in the numbers. So, in your example you’d indeed aim for 135g overall. (But, as per my previous answer, it’s unlikely that you’d want/need 135g of carb during a 1.5 hour run…).

How you try to hit your numbers is down to a mixture of personal preference, race logistics and gut tolerance. This is demonstrated in our case study database with a variety of race day strategies.” 

Laura asked: How many chews are equal to one packet of gel?

Emily from PF&H answered: “1 PF 30 Chew packet contains 30g of carb (served as 2 15g chews), which is the same as 1 PF 30 Gel (or 1 PF 30 Caffeine Gel, which also contains 100mg of caffeine).

Our fueling range was designed to make hitting your numbers as easy as possible by highlighting the amount of carb in each product smack bang on the packaging and in its name. (The hydration range works the same way, with the milligrams of sodium per litre (32oz) on the packaging / in the name).” 

Randy S. asked: “I’m an ultrarunner and I’m curious about strategies for pulling myself out of a bonk or how to adjust nutrition if I feel like I’ve fallen behind during a race? Is it best to knock back 2-3 gels at once or just shorten the duration between gels or some other strategy? Thanks!”

Emily from PF&H answered: “It can take days to recover completely from a major ‘bonk’, but if you do feel yourself falling behind, then there are a few adjustments you can make in an effort to turn things around…

— As you said, consuming some simple carbs (e.g. gels or chews) to increase your blood glucose levels is the main thing you can do. It’ll take ~15-20 minutes to process a gel though, so don’t expect an instant energy boost. Consuming 2-3 gels in a few minutes is tough on the stomach and can lead to GI discomfort, so instead increasing the quantity in smaller, more frequent doses is likely the best approach

— Stay hydrated – ensure you’re keeping adequately hydrated by consuming both fluid and sodium to replace a big enough proportion of your sweat losses. Dehydration impacts absorption of fuel in the gut, so appropriately hydrating is crucial to getting necessary carbs on board

— Slow down – slowing your pace to conserve energy is important if you’re starting to feel depleted. Continue to move, but with a lower intensity while you refuel and hydrate, until you start feeling better again

As the saying goes, “an ounce of prevention is worth a pound of cure”, so ideally you’d be fueling sufficiently to meet energy demands by starting exercise with topped up glycogen stores and taking in carbohydrate during exercise to prevent depletion.”

Marc M. asked: “How do I know if I am taking too much salt during a long race (12+h) in total? Is there a “too much“, if I stick to my usual regimen (e.g. 1xPH1000/hour), pee normally, feel good etc?”

Emily from PF&H answered: “This is a question we get asked a lot at PF&H. Although the short answer is ‘yes’, it’s theoretically possible to OD on sodium (as it is with nearly all nutrients), it’s not quite as simple as that…

Overdoing your sodium intake to the extent that it’s detrimental or dangerous just through drinking a sports drink is highly unlikely. That’s as long as you apply some basic common sense and take the time to understand your body’s needs. 

Severe hypernatremia (high blood sodium levels) due to acute sodium ingestion can only normally occur in the body when salt is either consumed in very large quantities without water, or when it’s taken in a solution that is significantly saltier than blood. Documented occurrences of this happening are extremely rare in adults, and this is because people just don’t tend to voluntarily ingest massive amounts of salt or super salty liquids as it’s rather unpalatable and goes against all our natural instincts to do so.

In the short term, if you take in a bit of extra fluid and sodium than you need, one of the first things your kidneys do is excrete most of the excess intake through urine. The kidneys are highly sensitive to the total amount of salt and fluid in the body and can dial up and down the amount of fluid you pee out, as well as the concentration of sodium in that pee. This is primarily how things are kept balanced in the face of a bit of excess intake.

Of course, this is to prevent sodium overload happening in the first place and that’s where understanding your losses and planning appropriately for the conditions comes in. Ultimately, you’re aiming to find a ‘sweet spot’ of sodium replacement that meets your individual needs based on how much sweating you’re doing and how much sodium you lose in your sweat. When you get this right you’re more likely to feel good (as it sounds like your current strategy is allowing Marc) and be able to perform at your best because your body will have a much easier time maintaining homeostasis.

If you want to read a bit more into this subject area (and have a spare ~9 minutes), it’s worth checking out a blog our founder Andy wrote as he answered the question of ‘can you overdose on sports drink?’.” 

Marie B. asked: “How do can we calculate our fueling needs for AFTER the long run. If for instance you run 18/20-miles on a Saturday morning, how do you know what (and how much) to drink for optimal recovery the rest of Saturday + the next day? Thanks!”

Emily from PF&H answered: “There are many things that contribute to a proper recovery but it’s really important that you replenish your glycogen (the storage form of carbohydrate in your body) levels and are adequately rehydrated before you go again.

The first four hours after your run are the most important from a refueling point of view, as your body is primed to take up glucose in this timeframe. Absorption is faster at first (30-60 minutes) and then slows down as more time passes. So, the recommendation we see in the literature is to consume 1.2 grams of carbohydrate per kilogram of bodyweight each hour for those first four hours. 

For the rest of the day and the day after, you can resume your typical day-to-day carbohydrate strategy, focusing more on daily totals and overall intake. Eating enough the following day, even if it’s a rest day, is crucial for recovery, as is getting ample protein for muscle repair and combating muscle protein breakdown. 

From a rehydration perspective, this will largely be based on how much fluid loss you accumulated. To fully rehydrate, it’s helpful to consume ~150% of your losses, as you won’t absorb and retain everything you ingest (some excreted in urine, for instance) and your sweat may not immediately stop at the end of your run. Let’s say you lose about a kilo of bodyweight after your run – you’d want to drink ~1.5 litres of fluid in the first 2-3 hours to appropriately rehydrate. Just be sure to add electrolytes to this fluid, in order to replace your sodium losses and stay away from the dreaded hyponatremia.”

JP asked: “PF&H seem to have pre- and in-workout nailed. Any plans for future products in the recovery space? Along the same lines, how come none of PF&H’s products contain any forms of protein? Thanks!”  

Emily from PF&H answered: “As I covered when answering the last question above, a proper recovery from endurance exercise relies on a number of other things and you’re right in thinking protein is important, as it helps repair your muscles and combat muscle protein breakdown. Our products don’t contain protein but, of course, we still think protein is important part of both your day-to-day diet and post-exercise routine! For most individuals, optimal protein intake in the recovery period is agreed to be between ~0.25-0.3 g/kg bodyweight, with the upper end being more appropriate if you’re looking to increase muscle mass. 

Never say never but, for now, we don’t have plans to add protein to our line up, we’re happy helping athletes nail their carb, fluid and sodium intakes!

Rehydrating after a big session is a crucial part of a proper recovery and many athletes use our PH 1500 in cases where a proactive approach is needed, such as when you’re training more than once a day, or competing in a multi-stage race.

And, whilst we don’t have a fueling product specifically aimed at recovery, replenishing your carbohydrate stores after significant efforts is also really important. As mentioned earlier, you should aim to replace 1.2 g/kg each hour for the first 4 hours after a workout to aid your recovery and the article I’ve linked to there has some practical advice for how to achieve that.”

Kristen K. asked: “How does creatine help a runner? (For context: I can’t lose weight, is it the creatine? Or is it the timing of my meals).”

Emily from PF&H answered… “Creatine can help regenerate more ATP (energy) in your body, which is useful when you’re burning through it and need a quick turnaround. While creatine exists in food, taking creatine daily as a supplement can increase the amount you have available on board to engage in this process. 

As a runner, creatine can support you when you need short bursts of power or sprints, or when you’re at the end of a long race and have to battle it out in a finish-line push. Though it’s a “marginal gain”, it’s a well-researched supplement with additional benefits outside of sport even.

Since creatine pulls water into your muscle cells, you might notice a small amount of water retention, especially if you do a loading week where you take a higher dose of creatine to reap its benefits sooner. But, this is transient and small (~1-2 kg) plus often not even noticeable if you forego the loading week. Bottom line, creatine won’t be the limiting factor in weight loss. (And neither will meal timing 😉).”

Kristen K. asked: “What are the benefits of fat for runners?” (For context, my meal delivery plan has high unsaturated fat.)

Fat is one of the three macronutrients – protein, carbohydrate and fat – and they are all valuable for athletes. One’s not “better” than the other, they just provide different services to the body. 

Consuming enough dietary fat helps you absorb fat-soluble vitamins (A, D, E, K), regulate hormones, maintain body temperature and can be an energy source for light to moderate / long duration exercise. Under consuming dietary fat can lead to deficiencies of key vitamins and/or nutrients, contribute to low energy availability and menstrual dysfunction in females / decreased testosterone in males, all of which could negatively impact athletic performance. 

Your meal delivery plan is spot on being high in unsaturated fat instead of saturated fat, as the latter is one we see correlated with negative cardiovascular outcomes. 

But, monounsaturated (olives, olive oil, avocado, nuts) and polyunsaturated (nuts, seeds, fish) fats are excellent ways to get your dietary fat intake. Particularly, Omega-3 and omega-6 are called essential fatty acids, as you can only get them through foods vs. synthesising them in the body.

While fat is an important macronutrient, it doesn’t mean it can or should completely replace carbs when it comes to your fuelling strategy. Fueling hard endurance efforts with adequate carbohydrate is still the best nutritional approach to maximising endurance performance that we currently have at our disposal. With that being said, some selective and intelligent use of periods of low carbohydrate availability may be useful in training to drive enhanced adaptations and to make the most of fat burning abilities where they could offer an advantage.”

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