I found this interesting. An article by Scratch Labs
Less is More:
frequently asked questions that we get are 1) why our Exercise Hydration Mix is
only 80 Calories per 500 ml (16.9 ounce) serving and 2) how to get more
calories in during long endurance events with our relatively low calorie sports
The short answer to the first question
is that our Exercise Hydration Mix is only 80 Calories per serving because it
is our experience that a 4% carbohydrate solution (4 grams of carbohydrate per
100 ml or 20 grams per 500 ml at 4 Calories per gram) is the highest concentration
of carbohydrate that we can have in our drink while still optimizing water or
fluid transport across the small intestine.
I’ll get to the science of it all
below for those who are interested, but for those who aren’t, the bottom line
is that in practice, when athletes I’ve worked with used solutions that were
concentrated with too much carbohydrate (regardless of type of carbohydrate),
most experienced gut rot – that bloated, sick, less than fresh, I don’t want to
drink anymore, stomach upset that is a problem common with many sugary sports
drinks and gels – a problem that motivated the development of our line of
anti-gut rot hydration products.
The answer to the second question is
that if you need more calories to meet your energy demands during a long
workout, what I’ve observed amongst Grand Tour riders, who require and consume
more calories while competing than almost any other group of athletes in the
world, is this - that for the same amount of energy, eating real food that forms
a bolus in the stomach and slowly trickles into the body always works better
than trying to drink that fuel or energy in a solution.
how does a lower calorie drink help to prevent gut rot? To understand that, you
need to know a little bit about how water gets transported into our body. In
short, water can be transported across the small intestine passively through a
process calledosmosisorco-transportedwith sodium and glucose.
& Semi-permeable Membranes:
is the movement of a particular fluid from an area of low concentration to an
area of high concentration across asemi-permeable membrane. A semi-permeable membrane allows the
fluid but not certain molecules to pass through it. When a membrane keeps
certain molecules from crossing it, differences in concentration can exist on
either side of the membrane. As a result, any fluid that can pass through the
membrane will move from the side with the lower concentration of molecules to
the side with the higher concentration to create equilibrium through the
process of osmosis. Examples of semi-permeable membranes include the walls that
form each of our body’s cells, the thin layer of film that is visible when you
crack an egg, and our small intestine, which is the primary gateway that water
uses to enter our body.
this in mind, one very important idea is that the inside of our belly or
gastrointestinal tract, where we stuff our food and drink into via our mouths,
is not the inside of our body. In fact, the GI-tract is simply a tube within
our body that is open to the exterior world at our mouth and anus. The
GI-tract, not only digests and processes the food we eat, it acts to
selectively transport fluid and nutrients from the outside world (which is the
inside of the belly) into our body primarily at the small intestine.
the small intestine can actively transport nutrients like sugars, amino acids,
and electrolytes, it also acts as a semi-permeable membrane where water flux is
strongly influenced by osmosis. This means that if you drink a solution with a
greater concentration than your blood or bodily fluids, water will flow out of
your body into your belly through osmosis to dilute that concentrated solution
unless the molecules or ingredients in that solution are permeable to your
small intestine or unless those molecules can be quickly and actively
transported to the other side to help pull water along.
another way, if your sports drink is “thicker” than blood, then water will flow
out of your blood stream into your gut, effectively dehydrating and bloating
you, especially if the concentration is so high that active transport of
solutes or particles in the solution can’t keep up with the initial water flux.
Ultimately, drinking a solution with a very high concentration of anything
(e.g., gels) is like throwing a lot of junk down your sink’s garbage disposal
and not having either enough water or a strong enough motor to keep the drain
that we don’t want to clog our drain, it’s critical that we also understand
what determines the osmotic pressure or force that a solution exerts. Simply,
osmotic pressure is a function of the total number of molecules (solute) that
end up dissolving into a fluid (solvent) to form a mixed solution. This osmotic
force or “thickness” can be measured as that solution’sosmolality.
Thus, if you want to ensure that what you drink is easily absorbed into your
body, then in theory the osmolality of that drink needs to be less than the
osmolality of blood or plasma, assuming that osmosis is the only mechanism for
water transport (more on this in a bit).
on one’s hydration state, blood osmolality can range anywhere from 275 to 295
milliosmoles per kg of water. Our exercise hydration drink has an osmolality of
280 to 285 milliosmoles per kg of water, primarily because of the lower
concentration of carbohydrate that we use, which is our main ingredient.
important, however, to realize that a solution’s osmolality is affected by all
of the molecules that enter into solution. This means that the osmolality of a
sports drink is determined not just by the amount and type of carbohydrate in
the solution but by all of the ingredients in that solution, from the
electrolytes to ingredients like preservatives, artificial sweeteners, flavouring
agents, and even food colourings. This is a key reason why we do not add
superfluous ingredients to our hydration products. This is also why gels and
heavily concentrated carbohydrate solutions that are already dissolved in water
can exert a greater osmotic force than a bolus of real food even when matched
for calories. And while we intentionally designed a drink with an osmolality
that favours the passive movement of water into the body, the favourable osmotic
gradient of our drink relative to the body is not the only factor that helps to
help optimize hydration and prevent bloating.
of Water with Sodium and Glucose:
can also move into the body through channels known as SGLT1 transporters that
actively transport sodium and glucose across the small intestine. These
channels use energy to move 2 sodium ions and one glucose molecule into the
body. As this happens, 210 molecules of water also move across, effectively
getting a free ride into the body as sodium and glucose pay a toll to gain
entry. While this seems like a lot of water relative to sodium and glucose,
this gateway is rate limited or locked by the availability of sodium and
glucose. Crunching the numbers, to move 1 litre of water across the gut through
this mechanism, just over 12 grams of sodium and close to 48 grams of glucose
(a 4.8% glucose concentration) would be needed. This is one reason why
oral rehydration solutions used to treat diarrheal diseases contain grams, not
milligrams of sodium in them along with some sugar or glucose to help take
advantage of this route.
our exercise hydration drink contains significantly more sodium (310 mg per ½ litre
or 16.9 ounces) than other sports drinks to help replace the sodium we lose in
our sweat as well as plenty of glucose, a relatively greater, albeit still very
small, amount of water (25 ml) can be theoretically co-transported through the
active transport of sodium and glucose. In theory, the active transport of
sodium itself along with other molecules like glucose also creates a more favourable
concentration difference for the flow of water into the body by osmosis. That
all said, starting with a sports drink with a concentration that is too high
and without enough sodium or salt makes this a real uphill battle despite
active transport systems that might help to facilitate water transport. This
significantly increases the risk of stomach problems especially over the course
of a really long day since water flow is still primarily dependent on osmosis.
Alone Can Kill You:
of this may lead people to think that if hydration were the primary goal then
just drinking water would be the quickest and most effective way to hydrate. In
fact, because water can be transported passively along its osmotic gradient and
also co-transported with sodium and glucose, having some salt and sugar in a
drink solution that is hypotonic (less concentrated) or even isotonic (same
concentration) compared to blood would actually be the fastest way to hydrate.
While drinking water alone is just fine if you’re sitting around or having
dinner at home, drinking water alone is not fine if you’re trying to rehydrate
when you’re sweating or have some illness or hangover that results in diarrhoea
or vomiting. In fact, drinking water alone when we are exercising can be risky
since we can lose an appreciable amount of sodium in our sweat (400 to 800 mg
per litre of sweat) and if we don’t replace that sodium then an influx of just
water can dilute the sodium in our body. This can lead to a scenario
called hypernatremia, which include symptoms like headache, confusion, a drop
in performance, fatigue, nausea, vomiting, irritability, muscle spasms,
seizures, coma, incontinence, and in some very rare cases death.