Preface: Outside of basic, most important recovery considerations like sleep, sufficient protein, stress management, plant intake and the overall healthfulness of the diet, there are a few main points to address when it comes to fuelling best exercise specific to nutrition.
The 3 checkboxes include.
1. Hydration.
2. Caffeine.
3. Carbohydrate availability with gastrointestinal stress in mind.
There is quite a large caveat to everything here, but fortunately it only applies to a very small percentage of the population, and of that population it applies rarely. If you’re a very high-level endurance athlete, currently in an acute phase of training (not competition) where you’re seeking training adaptations (not best possible performance) then the below still applies, but there are nuances that aren’t covered that are relevant to you and you only. For everyone else who isn’t the aforementioned, the below is all you really need to know.
Below covers the whys, when it's relevant, and practical hows of the above three points.
1. Hydration
Preface: Hydration does not have to come from drinking water exclusively. This is why the term ‘fluid’ is used below.
Seemingly a no brainer this is one big one that often gets overlooked and forgotten that can notably improve your work capacity and performance. Being in a state of poor hydration has been shown to impair sports performance significantly, and even pose risk of severe illness and death [1].
When it comes to hydration the goal is... hydration not hypo or hyperhydration. Yes, overhydration is something to be aware of. There are many proposed ways to control hydration, but the way that works just fine in almost all instances is “listening to your body”... A terrible phrase used by complete nutrition morons very often, yes, but relevant in this situation. Simply drinking to thirst and being aware of “how you feel” (another equally moronic phase) with an awareness of internal and external cues like urine color, is very often sufficient provided you’re able to stay vigilant ' and ‘on top of hydrated' [2].
Having it in the back of your mind is a good idea, especially around exercise because dehydration can really creep up on you. Furthermore, ensuring you start exercising well-hydrated is paramount and deserves extra emphasis, so do your best to avoid feeling like you should be better hydrated prior to an exercise bout. Consider factors like climate, intensity and exercise duration alongside your internal and exercise thirst cues.
Sometimes more quantitative means of hydration intake are a good idea. Dosing 5-10mL per kilogram of body weight 1-2 hours prior to activity is a reasonable start [3]. Applying habitual intake ranges can be a good idea but, of course heavily limited by climate, activity levels, mass of the human and more.
Rates at which we excrete fluid from our body can be measured and calculated as ‘sweat rates’. The use of sweat rates as a guide to fluid intakes has many flaws [2], it's a little inconvenient, invasive at times and full of variables so it should be used to just get a ‘rough idea', of sufficient fluid intakes. Basically determining sweat rates involves measuring body weight, urine output, fluid intake and sometimes more invasive things before and after a bout of exercise. Again many variables can cause issues with reliability, relevance is low and it’s need is rare so I'll leave sweat rates at that.
Hydration & having carbs in fluid while you exercise.
Hydration gets a little more complicated when whatever you drink during exercise also aims to fuel via 'during exercise carbohydrates' (more on this below). What I mean by this is drinking something with carbs(or 'sugar') in it while you train. Chunking a random scoop of a 'carb powder' like maltodextrin into a shaker with water to a ratio that looks ‘about right’ might be a sub-par idea. The issue is, a carbohydrate concentration that is too great can worsen hydration status and impair nutrient/fuel absorption, both of which impair performance. If the concentration is too great, the body will draw fluid into the gut to dilute it. [5]
This is easily solved with a carbohydrate concentration of 6-8%. Isotonic sports drinks do this really well, that's why they're a ‘sports drink’ and that's why they work, despite what your high school rugby coach said about sports drinks being 'bad'. If the drink has between 6-8g of carbohydrates per 100ml of fluid you're good to go. If you're going to mix it yourself, measure it, don't guess it!
2. Caffeine
Caffeine is one of the few supplements that really works [6]… like actually does something helpful. During training your habitual intake is likely just fine and it’s a good idea to save ‘the big dog dose’ for when you really need it like in competition or really hard phases of training. Many may not be aware (including high-level athletes) that the real world amounts of caffeine needed to sit within the ergogenic dose ranges, which basically means the range of caffeine intake prior to exercise that notably improves sports performance are massive! This dose is between 3-6mg per kilogram of body weight [6]. For a 75kg athlete achieving the ergogenic dose of caffeine would require between ~3.5-5.5 regular back coffee or ~2.5-3.5 full-size Monster energy drinks. Again, habitual intake or the intake you 'feel to be sufficient' will do fine during training phases, but if you really want a caffeine kick up the ass, the ergogenic caffeine range 60 minutes or less prior to starting an exercise bout will achieve this effect.
3. Carbohydrate availability with gastrointestinal stress in mind.
This is a big one and by far the most nuanced component of fuelling exercise & sport, so it will need to be further broken down into smaller sections.
The body has three fuel sources available, protein, carbs and fats. But fuelling isn't the primary function of all three and in an exercise setting one of them heavily fuels the work while the others don’t contribute much at all.
Protein serves primarily as a building block, or 'bricks within the structure of the human', but thanks to some complex metabolic stuff, protein can be converted into fuel for ATP regeneration (the fundamental energy currency) when really needed. So now that we know protein isn't really a source of fuel, that leaves carbs and fats.
Fats are a few things including a fuel source, and a pretty often used one. But fats don't really fuel exercise... The role of fats in the context of fuel is primarily centred around everyday existence. Fats are utilised within the mitochondria of the cell, through the citric acid cycle (also known as the Kreb cycle), but as mentioned they're almost always not the predominant fuel of hard exercise/activity, especially anaerobic (without air (very intense work)) activity because they can’t be oxidised (used) fast enough to regenerate ATP at a sufficient rate, to fuel really hard activity. [9,10]. It’s undeniable that higher carbohydrate diets promote best performance [11]
So if you're planning on doing exercise, glucose (carbohydrates) is your friend. (Thanks for that one Charles P). The idea of eating fats prior to activity to fuel exercise is almost always a fallacy (unless you’re that high level endurance athlete in training blocks I mentioned before) unless the body has no glucose available (due to prolonged carbohydrate restriction and glycogen depletion (glycogen = the bodies 'storage tanks' of carbs)). The body will always preferentially use glucose when exercise gets hard, provided it is available, and for good reason.
So in short, if planned exercise is going to be hard and you want to perform your best, you want glucose to be available when you need it. [7]
So what does glucose availability really mean?
Carbohydrate availability doesn't always absolutely mean you 'need' to eat carbs or 'sugar' (fundamentally the same thing once it’s floating in the blood) prior to exercise and very often doing so will make very little. Pre-exercise carbs go from 'not really needed', to 'why not do it’, to 'an absolute need to perform optimally' depending on the type, duration, and intensity of exercise.
What glucose availability simply means is whether the body has glucose available at it's disposal when it's required, which means keeping 'the glucose storage tanks' away from empty. When I say storage tanks, as mentioned before I'm referring to glycogen which is present in the liver and muscle. Some extra glucose is also present and available in the bloodstream, more so after carbohydrate ingestion [9,10]. If there are carbohydrates in these ‘tanks’ the body has fuel to use. The problem is, glycogen runs empty if you don't top up what you previously used. The more activity you do the emptier it gets and the more you need to keep it topped.
So now that you’re aware that you need to eat carbs to fuel best exercise performance, the question now becomes a case of dose, type, and timing of carbohydrate. Unfortunately it’s not a matter of covering one at a time, in the aforementioned order. While there is a hierarchy starting at dose, all three factors heavily integrate and influence one another, so I’ll do my best to break it down.
Let's start with the thing that matters to all who do exercise... the dose.
The dose
As mentioned the dose of carbohydrates needed to continually fuel exercise comes down to the demands for it within the umbrella of situational Calorie ceilings. Carbohydrate needs are not simply a factor of matching intake with use because we need to consider Calories and of course where they’re coming from. While you can manipulate Calories through protein and fats, as they probably should stay fixed throughout various total Calorie intake fluctuations, for the purpose of this article we’ll assume both protein and fats are sufficient and not beyond. If a Calorie deficit is present because you're in a dedicated fat loss phase, your carbohydrate dose will likely fall slightly short of ‘optimal sports performance requirements’ in order to create that deficit of energy required for fat loss to happen. If gaining weight is the goal, a surplus of Calories and carbohydrates relative to usage applies.
Carbohydrates are not essential to survival and baseline human function, which means protein and fats need to be covered first. But who wants to 'function at baseline', especially if you’re into sport and exercise? Once sufficient protein and fats are present within the diet to ensure optimal function and health, the rest of your ' Calorie budget' can and should be dedicated to carbs if you want to best fuel exercise. So just to be clear, total carbohydrate dose is limited by how many Calories you have to work with only after protein and fat needs are dealt with. Most of the time, dealing with protein and fats still leaves a massive amount of left over Calories for the good stuff (carbohydrate). At this stage you might realise that carbs and fats are almost fixed with total energy needs being a case of manipulating carbohydrates, meaning carbs and Calories go almost hand in hand. While there are limitations to this, more or less this is a great way of going about it.
So now we know what our underlying limit to carb intake is we can get to the point and work out how much rice, and pasta we can eat. So who gets how much?
General recreational gym-goer, CrossFit dad, daily jogger, Sunday cyclist with the lycra boys.
Yeh, so you train for general health, fat loss and enjoyment. Your exercise intensity is challenging and indeed hard enough to warrant a decent hit of carbs. But you don't exercise for hours and hours and relative to athletes you don’t 'really' exercise that hard. Carbs yes, but your requirements can likely be achieved through simply eating “healthy” as per the general government guidelines ranges. Which basically means sufficient fruits (2 serves, totalling ~ 300g), vegetables (5 serves, totalling ~400g) [8], beans, legumes, and whole grains will cover you off without the need for anything additional. Eating a varied, healthful wholefoods diet with heaps of whole grains and fibrous plants will likely do the job. For most general folks exercising mostly for health, total carbohydrate requirements might fall between ~1-4g per kilogram of body weight per day.
Gym bro, trying to get jacked?
You train really hard, bodybuilding style and there is nothing more important in life than getting jacked, so you can impress your mates and absolutely zero chicks. In reality, your training isn't that glycogen depleting and nowhere near that of certain other sporting endeavours. With that in mind if you’re trying to gain muscle mass, it’s a good idea to be in a surplus of Calories. Growing muscle can become quite an energy intensive process, especially when combined with the positive metabolic adaptations to overfeeding. Calorie and therefore carbohydrate needs can become pretty significant warranting the use of yummy, high Calorie per bite foods to viably meet high carbohydrate demands. For muscle growth once sufficient protein & fats have been dealt with you probably have enough room within your Calorie needs to consume anywhere between ~2-6g per kilogram of body weight in carbohydrates.
You're an athlete, who takes sports seriously. You might even be a pro.
The range of carbohydrate needs with in this category is broad because the amounts of exercise athletes do varies so much depending on how 'high level' they are, the sport they do and how much they train. The needs of a professional ultra-endurance runner during a race far exceeds someone like a crossfitter even if they train multiple times a day by several-fold. Athletes in hard training blocks, doing hours and hours of training per day may need up to if not more than 12g per kilogram of body weight as carbohydrates [11].
For our 75kg athlete mentioned before who was shocked at the idea of necking 3.5 full-sized Monster energy drinks before his mountain bike race, this equates to a very significant 900g of carbs per day. This is a lot of food, which will require food selection that can be easily consumed in great amounts with higher Calorie yields like sports drinks, bagels w jam, ‘sugary’ cereal, and white rice with maple syrup all over said rice, to viably meet needs. If you think it's possible to do it through wholemeal bread and baked potato, you're straight-up kidding yourself. Unless of course, you want to perform like shit because you've got about 20 kilos of food sitting in your gut, and you like the idea of coughing up blood because the several hundred grams of dietary fibre has completely fried your insides. So if you're an athlete with these massive needs, 'sort of liking junk food' probably won't cut it. You need to love the thought of CocoPops for breakfast and Weis fruit sorbet for dessert, not only is meeting needs important for your performance but also your health with low energy available in sports (LEA, or RED-S) being such a prevalent, very damaging and unrecognised issue. [12]
Okay, so we know roughly who needs what amounts of carbohydrates. Does timing matter?
Prefix to this timing and type section: Dose is king!
The higher the required dose, the longer the carbs will need to get past the blood and into the gut. It gets a little more complex because different carbs need different times to be available for use. As you can see all variables need to be considered, therefore the recommendations below regarding timing and type are rough broad ranges. An understanding of dose first, and time frame second will dictate the type.
Carb timing
Remember I mentioned glycogen, and how it's stored within the muscle and liver? Well if you deplete glycogen through exercise and then eat carbs to replete glycogen but don't exercise after that, muscle glycogen will still be full for ages and ages. However the body uses liver glycogen at rest which means even after an overnight fast where you've slept in bed doing nothing, liver glycogen stores become depleted. One of the main roles of liver glycogen is to regulate blood glucose concentration or the amount of glucose in the blood (blood sugar) [10]. This may indeed be impaired a little bit when you wake up, but for many instances, what's in the muscle is sufficient to fuel exercise.
Carbs in the hours prior to exercise. (pre-workout)
General recreational gym-goers, CrossFit dad, daily jogger, Sunday cyclist with the lycra boys.
For most folks there is more than enough glucose available in the muscle to fuel any exercise you do, so a reasonably high level of exercise performance can be achieved even in a fasted state after a nights sleep. But it doesn't hurt to eat more carbs and it might help you exercise harder even if it's mostly placebo, so having carbs in the hours before exercise is a good idea and something I would advise if it’s practically feasible, but I wouldn’t lose sleep over it (literally). If you have to be in the office by 8am and have no time to eat before your 6am gym session, don't worry about waking up at 4am to eat, the glucose you synthesised from carbs feedings the day prior has you covered. If you really want some glucose prior to exercise, maybe even because you just like it, and feel good when you do. Just drinking a bottle of sports drink upon waking is a good idea, and something that’s recommended for hydration after a full night of sleep.
Gym bro, trying to get jacked?
Unfortunately for Gym bro, most of the time the above still applies. You probably don’t need carbohydrates in the hours before exercise to perform reasonably well. But as mentioned carbohydrates in the hours prior to exercise has benefits within and outside of glucose availability, and are certainly worthwhile if feasible [10]. Carbohydrate ingestion in the hours prior to exercise, even if muscle glycogen is already full, offers performance benefits via the central nervous system [11] which I think in the context of someone who has a respectable interest in maximising training adaptations is worthwhile considering. Even the notion of ‘carbs before training makes you feel good’ alone makes it worthwhile nailing, especially if you need every helping hand you can get to make it through some tough sessions. So again, while pre exercise carbohydrates are not a ‘do or die’ factor, here is the thing though… The whole purpose, and idea of bodybuilding is to stand out, so meeting ‘baseline needs’ doesn't cut it. With that said, consuming carbohydrates in the hours prior to exercise now matters a whole lot more. They’re a fantastic idea and absolutely worth it, if you’re serious about getting the most from your hard efforts in the gym.
You're an athlete, who takes sports seriously. You might even be a pro.
You use a lot of carbs, and you're about to use a shit load more so you need every 'storage tank' of carbs fully topped up prior to the exercise or you might ‘run out of fuel’. Granted even elite level athletes will need to exercise for several hours to get close to depleting stored glycogen, so in that light, carbohydrates in the hours prior to exercise are still only a big factor for endurance sports. Yes, for these endurance, long duration folks, you can turn to fats for fuel, but it's at this point where the duration of exercise is so long the intensity will probably be low enough where fats can actually be oxidised fast enough to regenerate ATP as a sufficient rate in those who are well trained.
So does this mean pre exercise carbohydrate is only a consideration for athletes about to run for ~3 or more hours? No, because as mentioned previously liver glycogen depletes even at rest, so you’ll want to ensure you’re ‘topping the tanks up’.
Furthermore carbs aren't just stored in the muscle and liver, we can store smaller amounts in the blood. As mentioned, elevations in blood sugar concentration when starting exercise has its own central nervous system related performance benefits.
Carbohydrates in the hours prior to exercise are worthwhile and again just a great time to eat carbs in general from a practical perspective.
Intra workout carbs.
Anyone who trains hard for less than an hour.
While the athlete's fitness, along with exercise type, and intensity are important factors. It's still heavily secondary to duration. In short, exercise that lasts longer than an hour can benefit from some 'during exercise' carbohydrate ingestion, but 'intra' carbs for exercise that lasts less than an hour probably won't help much at all [11]. But again we ask the practical question; does that mean carbs during exercise is bad if you train less than an hour? No, but there probably isn't a massive need for it in order to maximise performance. This almost certainly covers off the 'average Joe' category and more or less most recreational gym-goers interested in muscle growth.
Anyone who trains hard for more than an hour.
Pretty much the only time when drinking carbs whilst exercising helps to a notable extent is if you're training for more than ~60 minutes. For exercise lasting 1-3 hours, ~30-60g per hour is the upper end of what 'you can handle' (more on this later). For exercise that spans beyond 3 hours up to ~90g of carbohydrates per hour can be consumed.[11]
Post-workout carbs
Here's the thing, pre-workout carbs starts when the last bout of exercise finished... Which means post-workout carbs are actually pre-workout carbs. Keep that in mind when you read this section if your brain hasn't already exploded from that concept.
Anyone who trains once a day.
If you exercise once a day or not that frequently, just eating carbs over the day after your exercise session gets you the replenishment you need. You have plenty of time to replete glycogen, there is no rush, so timing really doesn't matter. This covers off 'general recreational gym-goer, CrossFit dad, daily jogger, and Sunday cyclist with the lycra boys'.
I train once a day but I'm a 'gym bro, trying to get jacked', I need carbs after training don't I?
I know it's cool to post about the fact you ate a whole box of CocoPops post-training (shit I was that asshole), but you probably don't you need carbs to maximise post-workout anabolism. But what about that thing... you know "something to do with carbs putting stuff into cells". If the objective is muscle functional adaptations for endurance sport, growth for performance or aesthetics, or muscle retention during fat loss, the goal is to create a net positive balance of protein turnover on average over time. Which means muscle protein synthesis or building (MPS) exceeds muscle protein breakdown (MPB). In a nutritional sense this is a factor of protein ingestion, carbs don't boost MPS, but it's been said carbohydrates post exercise arrests MPB. However, post exercise carbohydrates still probably aren’t needed with research showing MPB is maximally suppressed through protein alone. So post-workout carbs probably matter less. [13]
But that 'driving nutrients into cells thing'? Yes, carbohydrate ingestion increases blood sugar concentration which triggers the beta cells of the pancreas to secrete insulin. Insulin acts as an Uber driver who drives the sugar around ‘the town’ to the cell entrance (the night clubs).Upon arrival said sugar is greeted by the bouncer who has come to the club entrance to let sugar in. This bouncers name is GLUT4, and his job at the club (the cell) is to let the sugars in. This process of him leaving the inside of the club (the D floor) to greet guests at the door is called 'GLUT4 translocation'. This is a valid reason to need carbs post-training, but exercise alone causes GLUT4 translocation [14].
So does this mean post-workout ingestion of carbs helps grow muscle? Maybe, but probably not a whole lot. Does this mean post-workout carbs don't matter? Probably not needed to maximise adaptations to the previous exercise bout. But if you're a big guy/girl who has a lot of Calories to work with, and therefore carbs to play around with, having a decent chunk of your daily targets post-exercise is a great idea, even on a practicality level.
Anyone who trains multiple times a day or has two very hard bouts of exercise close to each other in terms of time proximity.
This is when timing matters. Why does it matter? Because you have limited time to replace the glucose you previously used. Those storage tanks within the muscle and liver need to be refilled before your next bout of activity. The closer to the end of the workout you ingest carbs the greater the rate at which you'll replenish glycogen [16]. Adding caffeine to the mix may enhance this rate even more.[15] If this is you, get those carbs in fast, but carb timing is 3 dimensional and goes hand in hand with 'carbohydrate type'. (see below)
Carbohydrate type
When we refer to the 'carbohydrate type', we’re technically talking about different saccharides, combinations of, or the difference between simple sugars and complex carbs. In layman's terms we’re talking 'quick' vs 'slow' carbs.
You might have heard about the terms 'high and low GI', you might have seen food marketing based on this thing called 'GI'. As you may have guessed GI basically refers to the 'quickness' of the carb. Lower GI carbs typically represent themselves as high fibre plants and grains whereas higher GI or 'quick' carbs present themselves in the form of 'whiter, junkier, sugary, style carb-dense foods. It's important to note that carb-dense foods fall on a continuum within this range so it’s not exactly a matter of quick or slow, but more so how quick/slow.
The difference on a slightly more technical level refers to how rapidly the food empties the stomach, the rate at which it's absorbed through the intestinal wall, how rapidly it enters the blood, how quickly it increases blood sugar concentration and therefore and most importantly how quickly it can be available for use or storage. Any carbohydrate we ingest is basically glucose by the time it gets into the bloodstream. Any carbohydrate that is already that or something very close to it, doesn’t need much ‘processing or breaking down’, within the ‘processing plant’ that is the digestive tract, so it’s a relatively quick process. If something enters the gut in a ‘very unprocessed’ state, a lot of ‘stuff’ needs to happen before it is ready for the blood stream, which takes time.
At the end of all this ‘processing’ that occurs in the gut, the single overarching limiting factor of how quickly we can ingest carbs for use, is how rapidly the cell can use them. At the muscle cell level, the upper-end rate of carbohydrate oxidation is around ~2g per minute [16]. But almost always the actual limiting factor is the gastrointestinal part of the process. (more on this later)
The tricky part here is, appropriate selection of a carbohydrate-dense food source depends mostly on timing but also dose. The goal is to a) have the carbohydrates ready for use when it’s time to exercise, and b) consider the cross over of dose and time frames to avoid the occurrence of uncomfortable amounts of food just sitting in the gut during exercise and the performing impairing gastrointestinal stress that come with that.
If we remember that pre workout nutrition starts when the last workout ended we realise that much of this rides on how far away your next exercise bout is, and how quickly you need to repleat the ‘carbohydrate tanks’ to ensure fuel is available.
So let's cover what is appropriate when.
'Mega quick carbs'
When: Less than 60 minutes before the workout, during the workout (if exercising for ~<1 hour) or when massive amounts of carbs are needed.
Sports drink, or something ‘really sugary’ like energy gels and maybe lollies (if you’re okay with being ever so slightly suboptimal). These are the food sources that can be available for use by the contracting muscle as soon as possible. They’re nothing but carbohydrates and come with no baggage in the form of fibre, protein and fat, that’ll slow things down. If you need glucose, you need it quick, then this will do the job in a way that will least likely cause gastrointestinal stress because it doesn’t pose much workload on the gut, as minimal ‘processing’ is needed to get it ready for the bloodstream.
'Quicker carbs'
When: ~1-3 hours before exercise, upper end of time frames if larger dose is needed.
Sugary cereal, bagels with jam, white rice with maple syrup. ‘The whiter carbs’. These foods contain mostly carbs, very little to no fibre and not much of anything else (Protein & fats), their surface area is often relatively low compared to their Calorie content, so they’re Calorie dense. Due to the aforementioned their ability to very quickly pass the gut, get into the blood, and be available for use makes them appropriate for those who need large amounts quickly. If you’ve just finished hard exercise and have another one coming up very shortly these tick the box. But they’re almost always not appropriate as during exercise carbohydrates. So if intra exercise carbs are needed you’re best sticking with sports drinks (which will also provide hydration) and things like ‘energy gels’.
'Slower 'healthy' carbs'.
1 hour before exercise at the very least, only if the dose is very low, but most often several hours are needed between ingestion and exercise with these ‘slower, healthier carbs’.
This category covers high fibre whole grains and plants in the form of fruits and veg. So basically ‘healthy eating’. These foods have relatively higher surface areas and require more processing to be converted into a form that's compatible with the working muscle cell. They’re low Calorie per bite and physically difficult to ingest in large amounts. So if you need a lot of carbs quickly these are not for you. Most folks can stomach the ‘most people’ requirements of carbs that is probably around 1-4g of carbohydrates per kilogram of body weight through exclusively ‘healthy carbs’ without the need to swap things like sweet potato for white rice.
After the workout....
As mentioned before, post exercise is just another word for pre exercise, but often many hours if not days pre exercise. If you need glucose fast, refer to the timing part. If you need large amounts of glucose fast, refer to the type part, with timing in mind. If you don’t need glucose that fast, then post workout carbs isn’t a big concern. Simply just eating enough carbs over the next ~24 hours is all you need to do. If you have heaps of time but a lot of carbs to refill, then you might want to start now, and often with things that require very little work from the gut.
Why is carb type and timing important?
Availability for use, rates of gastric emptying, intestinal absorption and GIS.
As mentioned before the rate at which glucose can be ingested is limited by the amount that's needed and the rate it can be used. But beyond a certain reasonable point the delivery of the fuel to the bloodstream is the limiting factor. What I mean by that is the gut, or how quickly carbs can go from you mouth to floating in the blood.
Why does this relate to gastrointestinal stress (GIS)?
An estimated 30-50% of distance runners experience intestinal problems [18]. While less-so a concern and prevalence in other sporting endeavours, it’s still very much something to consider because no one likes being all bloated and gassy when they exercise, and it’s occurrence will likely limit ability to perform. The gut doesn’t like being overworked and forced into overdrive. If you give it too much to process, too fast it’ll get angry. If you give it something that doesn’t require much ‘processing’ you can get away with giving it a lot and it won’t get angry. Furthermore the gut, gets ‘less workers’ during exercise, that's because the body is a little more focused on the task at hand being… the exercise itself. When I say workers I’m talking blood flow. During exercise blood flow to the gut is reduced which therefore means the work capacity of the gut is significantly impaired. During prolonged hard exercise blood flow can be reduced to the gut by up to ~80%. [19]
If you’ve got food in the gut waiting to be processed while you’re exercising the stomach starts to ‘bitch and moan’, by going into a state of gastrointestinal stress. Obviously this makes you feel like shit, which even practically speaking certainly impairs your exercise performance potential. Furthermore, that fuel you’ve got sitting in the gut there probably won’t get absorbed into the blood to its full extent, so now you’ve got fuel you ingested being ‘ejected’ from the body unused. What I mean here is malabsorption.
Outside of a few obvious things like eating a sufficient fibre intake to promote healthy general gastrointestinal function and health (‘gut health’) mostly from plant matter, getting enough sleep and managing stress. Avoiding NSAIDs close to exercise [4] and staying hydrated (with a 6-8% carbohydrate concentration if the fluid itself contains them) are worthwhile considerations in avoiding GIS occurrence during exercise.
So there you have it, fuelling exercise 101 for best sports performance. The best thing to do from here is refer back to your situation and determine where you sit on each continuum. Then from there you can determine your requirements (dose) and fit type and timing into your eating, training and ‘life’ routine. Do the basics well, sprinkle a bit of caffeine on top, stay hydrated and you’re pretty much the whole way towards best fuelling exercise through a bit of extra trial and error. So do be prepared to try a few dose, time and type combos to get an idea of what works best for you and what you can and can not tolerate.
Key take home points.
1. Hydrate to thirst, in a proactive manner, especially in and around exercise with an awareness of internal cues. Consider climate, exercise duration, sweat rates & avoid hyper-hydration.
2. Aim to maximise fuel availability prior and during exercise. Start exercise in a glycogen depleted state and replace what you use. Consider carbohydrate dose, timing & type.
3. High level endurance athletes in certain training blocks may benefit from some training in low glucose availability. Carbohydrate availability is needed in most instances.
4. Carbohydrate dose meets demands as a linear relationship, with an overarching cap based on situational Calorie ceilings. Most folks do fine w 1-4g/kg, some athletes may need 12+g/kg.
5. Failing to meet energy requirements can lead to health and performance decrements (LEA & RED-S). The use of ‘junky’ foods makes meeting higher carbohydrate requirement feasible.
6. Carbohydrates in the hours before training are often a very worthwhile thing. Their benefit differs depending on the situation, but they’re not worth stressing over in most instances.
7. Caffeine is effective, use the ergogenic dose (3-6mg/kg when appropriate). This is a high intake so consider the tolerability of the ingestion methods (pills, coffee, energy drinks etc)
8. If exercise is less than <60 minutes during exercise carbohydrates are not needed. 30g/hr appropriate for 60-120 minutes, 60g/hr 120-180 minutes and 90g/hr if exercising for >2.5 hours.
9. Consider carbohydrate to fluid ratio in ‘during exercise’ carbohydrate drinks. Concentrations beyond 6-8% may cause gastrointestinal stress, malabsorption, & dehydration.
10. Gastrointestinal capacity is impaired during exercise. Consider the tolerability of foods you ingest in and prior to exercise. Consider rates of gastric emptying & intestinal absorption.
11. Carbohydrate type relate to rates of absorption, & GI & are mostly dictated by how quickly fuel availability & replenishment is required.
12. Pre exercise nutrition starts when the last exercise bout ended. Consider dose, and time frames when deciding on timing, and type of carbohydrate ingestion after exercise.
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