Just how (bio)available should thickened liquids be in life?

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Title: Thickening agents used for dysphagia management: effect on bioavailability of water, medication, and feelings of satiety
Authors: Julie Cichero
Journal: Nutrition Journal
Year of Publication: 2013
Design Type: Narrative Review
Purpose: “This paper will review the literature for the impact of thickened liquids on hydration, medication bioavailability, and physiologic feelings of satiety.”

  • Only got a sec?
    • Many factors–including dehydration/malnutrition, thickening agents, drug administration, and palatability–need to be taken into consideration for any modification to liquid viscosity
  • Only got a minute?
    • “The literature on satiety suggests that dehydration may be due to physiological expectations that thick fluids will make them feel full. Flavour suppression associated with increasing thickness provides little motivation to drink. The mucoadhesive qualities of many thickeners leave the mouth feeling sticky after a drink rather than wet, resulting in continuing unresolved feelings of thirst.”
    • “Results consistently demonstrate that individuals who require thickened liquids consume less than if they were to consume unthickened liquids”
    • “The dietitian has an essential role in monitoring and preventing dehydration.”
    • “Drinks thickened with modified starch have been shown to be unstable, frequently continuing to thicken, or over-thicken, over time”
    • “Increasing viscosity impedes drug dissolution and disintegration..Administration of medication with thickened liquids needs careful consideration and consultation with a pharmacist.”
    • “Clinicians should strive to prescribe only the least thickened liquid required for swallowing safety and aggressively pursue treatments to improve functional return to normal, un-thickened liquids”
  • Got more time? Keep reading!!

How can one possibly know what to do/not do in situations if they aren’t aware of any problems or all the information? It happens all the time. Children need to be aware of what is right/wrong. Pets are made aware to not jump, bark, or get into the trash. I had to learn to be aware of when my car needed to be looked at. Now, do I know everything there is to know about my car? Sadly, no. But you can bet as I was nearing closer to getting my driver’s license, I intentionally and unintentionally had to learn more than what I had known such as the areas I was driving to/from, street signs, and which lights got busier around what time. Slowly, I started to increase my overall awareness around me as it related to the activity I was doing behind the wheel.

This is needed in an endless supply. It’s how we learn, adapt, develop, and grow. This is how we are able to teach our patients, families, colleagues, and communities the intricate, detailed information we are privy to in our SLP world in order to provide updated education or sometimes just to help others make the most informed decision.

My gut is starting to feel the queasiness from these heights, so I’ll step off that soapbox…….

Since Cichero’s article is a narrative summary (compared to systematic review), there’s not as much to pick apart in study design or methodology practices. However, there is a lot of information that some may already know and some may be hearing for the first time. Key players in the review revolve around concerns that we face daily with our patients such as dehydration, how thickened liquids affect medication release/activity, and the need to feel physiologically satisfied.

First thing’s first, vocab time for:


“In pharmacology, bioavailability is a subcategory of absorption and is the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered intravenously, its bioavailability is 100%”  Wikipedia

Hopefully, I’m not the only one when I say we’ve all been there, analyzing our oral motor and oropharyngeal movements to figure out what exactly is going on in there with that bolus as practicing clinicians and even students. With liquid, we may splash, twirl, hold, suck, squeeze, lift, or slide it around using our tentacle-like tongue intentionally. How we end up handling the liquid also depends on how it feels and tastes.

I am certainly gonna want the refreshing peach iced tea to run all over my tongue with a lasting after-taste versus the less appealing tomato liquid concoction that brings numerous reflexes to get it out of my system and body (no offense to all the tomato juice lovers, my senses just have complete power over me with some aversions😉). One might leave me feeling more fully satisfied, the other might mean unhappily craving something else to quench my thirst. Now, this normal physiological response doesn’t just disappear with our patients with dysphagia (sensory issues set aside). If anything, Cichero proclaims it can actually be more apparent and critical in our treatments.

So why exactly might patients with dysphagia consume less of something that their body is telling them to get rid of?

Cichero identifies 3 main culprits:

water patient

1. Access – this really made me aware of how I could retire early if I had a nickel for all the times I have had to give a patient liquids, had to open a container that’s been sitting on their meal tray for hours, or having to ask an aide or nurse to make sure to provide ice chips/liquids for patients. By being in the hospitalized setting (as well as other skilled facilities), the patients are inevitably at some sort of disadvantage first off.

Then, because of some type of disability (defined as ‘physical/mental condition that limits a person’s activities’), they also cannot open or access something to satisfy a basic need nor communicate to others to do this for them. Yes, it’s a lot of institutional change that typically needs to be looked at, but it’s still an easily changeable offense that should be discussed with those in decision-making positions (okay, just a quick hop on/off the soapbox again).

2. Unsatisfied thirst response


I couldn’t really say anything else that wasn’t already said here except I can’t wait to read more studies on this:🤓

“When the mouth is wet, as occurs in the influx of saliva and wetness provided by liquids, oral signals are conveyed to the brain to signal that thirst has been quenched and drinking behaviour can cease. Thirst will persist if the oral phase is bypassed, even if the person is physiologically hydrated by direct infusion of water to the stomach. Anecdotally, individuals with dysphagia complain of thirst and that thickened liquids leave a coating feeling inside their mouth. Interestingly, a study of healthy individuals demonstrated that thirst sensation progressively worsened with increasing viscosity.”  p.3

3. Decreased flavour/palatability – I wish I had more dietary-food-scientist-friends to know more about the “entangled polymers” and “electrical charges” that are involved to make my pizza slice taste so dang delicious, but for now I’ll have to interpret the article’s information simply as how the thickening agent particles (what I call the “bland-boring-Bettys”) bind and cover more and more of the yummy flavor/taste aspects of the liquids we know and love (all the food scientists out there can feel free to friend me anytime 😉 !!!).

An article I think worth checking out that’s referenced is Matta et al. (see article for full Reference list). Without getting into a great debate about gum versus starch thickeners, I’ll simply give the info provided on that article’s conclusions:

“Starch based thickeners were found to impart a starch flavour and a grainy texture for nectar and honey-like consistencies. Gum based thickeners did not produce any grainy textures, but did produce a higher ‘slickness’ than starch based thickeners. Flavour suppression was demonstrated for all thickening agents.”  p..4

Sitting there putting two and two together? Thinking that concerns for dehydration might also stem from the stripping away (availability) of water due to a thickening agent?

I’m a step ahead of ya……But first, let’s take a quick look back :

“Desirable water intake for older adults is calculated at 25-30 ml/kg/day. This equates to between 1.7-2 litres of fluid per day.”  p.2

I feel like this stat should have been ingrained in my brain long before the norms for verbal fluency because of its far-extending consequences. The article states that there have only been 2 studies that particularly look at the bioavailability of water when mixed with dysphagia-intended thickening agents (part animal/part human subjects used), both of which were using “pudding-thick” levels to make their conclusions that there is still water available despite being used with either gum or starch thickening agents (See article for specific details on studies).

Now, while I’m ecstatic that a glass of water thick enough to clump together forming a clear pudding-like substance onto a spoon still contains water, I’m also to-the-bottom-of-my-heart hoping that this consistency is not the norm across the populations we serve, and also believe in researchers to get studies going to support the same results with less-thick options and to what percentage water may be available across different consistencies (mind you this article was pulled from back in 2013) (See IDDSI for more information on recommended thickening levels !)

whats love

So, now we know patients, in general, have less access to liquids in medical facilities for starters, then on top of that using a thickening agent may put them more at risk for dehydration since their brain can experience a never-ending “thirst” feeling along with less desire to actually consume something that their tastebuds are screaming does not taste the way it should.

If those issues don’t bring heavenly signs of “quality of life” to mind, then a different route to consider may be: What’s thickening liquids with medications got to do with it?

Personally, a professional goal of mine is to increase my awareness and knowledge of the world of medications (I’m also accepting pharmacist friends as well! 😉 ), so I thoroughly enjoyed the mini human biology review from the article as it relates to medication administration.

The majority of medications are taken orally, as it’s typically easier, safer, more convenient, accessible, less expensive, and more frequently tolerated and adhered to. However, obviously, this directly impacts our patients with dysphagia if the risk is too severe to consume anything orally, especially the more medically fragile/complex populations. Some medications can be administered by other means such as IVs to the bloodstream, stomach, intestines, etc. However, even this bypass may impact how and when the medication is released into the system, which could have negative consequences down the line of care and is “a complex equation,” which is why we (SLPs) can lend a hand in the decision-making role when meeting with the medical team.

“For example, buccal or sublingual administration is designed to be absorbed through the oral mucosa and its rich blood supply. The stomach has a large epithelial surface, however, contents stay in the stomach for a relatively short period of time giving a short window for absorption.

Food delays gastric emptying. Medications that need to be absorbed quickly will be taken on an empty stomach. The small intestines provide for fast absorption and a large surface area. The time taken for medication to transit the small intestines will affect absorption rate and hence bioavailability of the drug. Other medications, such as sustained release doses, are best suited to absorption from the colon.”  p.4

To help grasp a bit better why absorptive sites of the body can play an essential part in boosting a medication’s effects, the article actually gives a nice ‘n easy-to-interpret Table explaining how permeable (i.e. let’s liquid absorb into it/penetrable) and soluble (i.e. dissolvable) different drug classification classes are with some general medication examples too (Class I, Class II, etc.). (see article for Table 3 Biopharmaceutics Classification System of medications, p. 4).

Overall, even different gum-based thickening agents can have different, unknown effects on the timing and absorption of medications, not to mention the different coatings that some medications are covered with, plus the practice of crushing medications and mixing with thickeners need to be considered (apparently future research on this is to come from Associate Professor Steadman at the University of Queensland!).


The last but certainly not the least by any means is how important the feeling of satiety is (I usually chase this feeling all day to avoid feeling the opposite-hangry). Another easily read Table (1) is provided as it relates to three levels of fluid thickness commonly used in dysphagia treatment and commercial comparisons, and is summarized below from the studies referenced:

“in healthy individuals 30-34% more thin liquids were consumed than semi-liquid and semi-solid products when all substances were equal for energy content, energy density, volume, and macronutrient composition. There were statistically significant reductions in amount consumed, despite similar subjective feelings of satiety.”

“Progressively less was consumed as fluid thickness increased. The test substances were similar in thickness to slightly thick, moderately thick and extremely thick liquids used in the management of dysphagia (Table 1).”  p.5

So, patients aren’t drinking enough because they don’t want to drink weird thick stuff, can’t get enough access to enough to stay hydrated, or get full too quickly (drinking less) with thickened liquids.

Which one of these can we change????

(Hint: All.)

To avoid stating the obvious, some alternative ways to overcome and reduce feelings of satiety are decreasing the introduction of air into the thickening process (less “bulk” mixing), being aware of fibre content of thickeners (gum vs. starch), and also being aware of a patient’s gastrointestinal abilities or deficiencies as it relates to gastric emptying and/or absorption of the intestines.

Okay, I’m going to stretch and just put a few toes on the soapbox….

My heartfelt question is—Is it always worth all the risks of having someone on a modified diet where their liquids are not appealing, not being consumed, and not satisfying a basic need of the human body, just to avoid a *possible* (aspiration) monster? There’s obviously more to consider here, and I can absolutely appreciate the time and a need for everything, especially during critically acute stages in recovery. However, with any recommendations, considering only ONE FACTOR like if they will aspirate or not versus a patient’s case holistically, sometimes feels all too similar like when I’m trying to be persuaded into investing in a fallout shelter to protect myself from the possibility if zombies come attacking  (zombies just ain’t my thang guys…) (Please search Langmore, 1998 Predictors of Aspiration to get more where I’m coming from.)


To go further, if there was a soupy-applesauce-looking liquid in a cup, would you feel motivated to down it? Or, do you think you might take as few and tiny sips of it as you can because your lips, tongue, and throat just can’t possibly stand any more of that negative sensory experience, so it switches on the “I’m full” light to put an end to the gross torture? (like ME as I’m writing this since my smoothie turned out to be a flop, and even though both you and I know I am in NO WAY full! 🙂 )

“The hypothesis put forward here is that sensation from the oral phase, through associative learning, triggers feelings of satiety rather than simply relying on signals from the stomach or small intestines.”  p.6


One last study reference by McCrickerd et al. informed me that participants “expected to feel more full from ingesting the thicker drinks” just by looking at them!!! So why are we constantly trying to trick our patients???

At the very least, trying to understand both sides of the equation and considering all aspects of a patient’s clinical case can put a clinician in a better position to educate and inform their patient, families, and medical professionals just what options are available to them for their quality of life.

How can you use this article?!?

Maybe to talk with administrators about changing strict policies?

Discussions about the purpose of /ineffectiveness for diet waivers?

Looking into more research on different consequences from thickened liquids?

Or even who might benefit MOST/LEAST from them?

“Awareness precedes change.”   Robin Sharma

Article Referenced: [FREE ACCESS]

Cichero, J. (2013). Thickening agents used for dysphagia management: effect on bioavailability of water, medication and feelings of satiety. Nutrition Journal12(1). doi: 10.1186/1475-2891-12-54

♦♦While the main idea of this review for the article was to have clinicians start thinking if a patient actually needs any thickened liquid, I fully realize that some patients may actually prefer this for a variety of reasons and this still is under individualized/holistic care😊♦♦

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