Dietary fiber effect on fluid retention

A Trek-Segafredo nutritionist said in an interview:
“On the biggest mountain stages, it’s preferable that the riders don’t consume foods with a lot of fiber,” Scheirlynck says. "If you eat a lot of fiber — like oats and whole grain pasta and bread, or certain kinds of fruits and vegetables — your body will maintain more fluids, and you are therefore heavier. This could mean that you’ve been working 12 weeks to get to your perfect race weight, and then the evening before a mountain stage, you gain two kilos.”

For those of us who don’t race, a couple of questions:

  • Are there high-carb low-fiber pre-ride food options that aren’t at the top of the glycemic index? All of the slower-absorbing “real food” carb sources that I can think of, like sweet potatoes and whole grains, are also fairly high in fiber.

-Can my body use that retained water to help maintain hydration? Is starting a long ride with extra water in my gut functionally equivalent to having an extra bottle on my bike?


Fluid needs time to get in the right place… Actually your body needs time to put it in the right place. Isotonic fluid can be processed faster than plain water and contains more ingredients you need.
You should hydrate starting 1.5 hours before riding and take the last 0.5 liters just 30 minutes before riding.
If going longer than 60 minutes, try to drink every 15 to 30 minutes. The amount should depends on your sweat rate (measure it using a scale).
Research indicates it doesn’t really matter if you drink to thirst or on time, just drink enough.

Trading your gut by using isotonic fluid during the ride. Eating is not necessary unless you are going long…(i don’t know how long)

The calculation of the number of carbs required per hour is quite simple to predict IMO, and therefore how much energy required on a long ride can be “fairly well guestimated”. If I’ve got anything wrong, let me know.

Energy as you know it for your house is measured in kWh, but the actual unit is Joule.
1 J = 1 Ws (Watt.second)
3600 seconds in an hour so:
3.6 kJ = 1 Wh

If we are working towards energy burned (not just energy pumped into the pedals), and taking into account that we (humans) are not efficient machines; somewhere between 20-25%. It means we need to multiply this value by something between 4 and 5.

To get to food calories you would then divide this again by 4.184. Let’s assume 4.667 as your efficiency then we have:

  • 1Wh (into the pedals) = 4 Cal (energy required)
  • Carbohydrates come in at 4 Cal/gram, so:
  • 1Wh (into the pedals) = 1 gram of carbs required.
  • The range would be 0.86 - 1.07 grams per hour.

So, riding for 2 hours at 200W (NP) should require 200g of carbs per hour, or 400g total carbs for the ride. There will be some fat metabolism, but not a lot if the intensity increases, like in a race. So let’s err on the side of caution and assume all our energy is coming from carbs. A well rested cyclist will have +/- 500g already stored (100g in the liver and 400g in the muscles). So we have sufficient energy to not consume any nutrition, but is it advisable to ride down to 100g (almost fully depleted; possibly not a good idea)?

Let’s say this becomes a 4 hour ride, also at 200W (NP). We will need 800g of carbs, less the 500g already loaded and ready to go. That’s 300g, or 75g per hour. Having a good breakfast before the ride means having a little more in the tank, and needing less on the ride.

My caveat:
The above excludes any fat we would burn off, but should cover how many carbs required per hour. The problem I’ve seen on many club rides are the guys that take 1 bottle of water and 1 bottle of mix (50g) on a 4 hour ride, and thinking they have enough.

Then racing becomes even more complex, as the intensity is higher, so the energy required will be more. The guys trying to race on the same single bottle of mix, a bottle of water, and a couple gels (22g per gel) often find thy have no energy at the pointy end of the race.

@Angstrom, welcome to the forums!

So when talking about fiber, carbs, and glycemic index, you really can’t consider them in isolation. They need to be taken as a whole. Glycemic index doesn’t really matter unless you’re consuming carbs in isolation. That’s where you can take something like sweet potato and compare it to table sugar. Although the sweet potato is actually still moderately high (~60), and that number increases depending on how it’s cooked. Whenever you consume some real food (let’s say white, cooked pasta) it’s rare that you would boil the pasta and just eat it plain. You might add sauce, vegetables, maybe meat (bolognese, anyone?). By doing this, you’re effectively lowering the glycemic index of the meal as a whole, slowing the digestive process. Protein has quite a large effect on this, which is why some recommendations for people with diabetes include consuming protein with their carbohydrate sources to stabilize the blood sugar response.

So when we’re talking about absorption for endurance performance, get it in there and through the gut as quickly as possible. This is easy with iso- or hypotonic sports drinks as @kjeldbontenbal said, since it’s a deliver issue to support the exercise demand. Pre-ride, I think about 2-3 hours out as your larger meal that contains more “real” food. The type doesn’t really matter - mostly carbs (oats, fruits, some vegetables, pasta, whatever…), some fat and protein (these will change that glycemic response), and low fiber (to prevent larger reductions in gastric emptying and potential for bloating). That way you don’t have to worry about negative effects while you’re fueling with primarily what the body will use during exercise. ~30-60 minutes out change to more of the “engineered” products, so carb-electrolyte beverages, fruits, a bar, gel, etc. if necessary. That’s going to get the energy on board, and every time you’re fueling, you’re drinking fluid, so you’re covering the pre-ride hydration needs too.

If we’re consuming higher-fiber foods before or during exercise, then there could be potential for fluid retention to some degree because increased fiber intake should come with increase fluid intake (and if you’re topped off on glycogen, then you’re going to bind more water molecules to the glycogen, increasing fluid retention that way actually). In terms of binding water, I haven’t seen that as the case where we actually retain additional fluid due to fiber per se. It’s likely because we are consuming additional fluid and/or gaining fluid storage through increased glycogen storage. However, the increase in fiber (and dependent upon the type, soluble vs. insoluble) can bring with it the feeling of bloating or fullness in the GI tract as that soluble gel is formed. I’m not sure the “camel” approach is going to be a useful strategy pre-ride when approached through increased fiber intake due to the potential for negative side effects (e.g., GI distress) associated with slower passage of fuel and fluid through the stomach.

Instead, you could try to ingest additional sodium and fluid pre-exercise which will increase plasma volume and get some of that functional effect you’re looking for. That way it’s coming from more useful components (e.g., sodium, sugar, and water) that will result in comparatively less risk for GI distress during exercise.

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