Understanding the IDDSI Framework
For many years, the classification of thickened liquids varied widely, causing confusion and potential safety risks in healthcare settings. To address this, the International Dysphagia Diet Standardisation Initiative (IDDSI) developed a global framework to provide standardized terms, definitions, and testing methods. This system is now widely adopted and has replaced older, more subjective systems like the National Dysphagia Diet (NDD). The IDDSI framework uses a simple numbering system from 0 (Thin) to 4 (Extremely Thick) to define the consistency of liquids. A speech-language pathologist (SLP) evaluates a person's swallowing ability and recommends the appropriate IDDSI level to ensure safety and comfort. The thickness of the liquid provides more control during swallowing, slowing down the movement of the fluid and giving the individual more time to protect their airway.
The Stages of Thickened Liquids (IDDSI Levels)
Level 0: Thin
This is the baseline, representing regular, un-thickened liquids that most people drink every day. Examples include water, coffee, tea, and juice. For a person with dysphagia, thin liquids can move too quickly and potentially enter the airway, a complication known as aspiration.
Level 1: Slightly Thick
At this stage, the liquid is thicker than water but can still flow through a straw or a standard cup. It is often described as similar to a fruit juice that is naturally a little thicker than water, like V8. For some individuals, this slight thickening is enough to slow the flow and improve control during the swallow, providing a safer option than thin liquids.
Level 2: Mildly Thick
This consistency is thicker than Level 1, and while it pours quickly from a spoon, it is slower than a slightly thick liquid. It can be sipped from a cup, but requires more effort to drink through a standard straw. Many fruit nectars or thick milkshakes are naturally at this consistency. IDDSI recommends the Flow Test for this level, where 4-8mL of liquid should remain in a 10mL syringe after 10 seconds.
Level 3: Moderately Thick
Liquids at this level pour slowly and can be drunk from a cup or eaten with a spoon. They are very difficult to suck through a straw. The consistency is similar to honey and holds together well. The IDDSI Flow Test for this level shows a larger residual volume in the syringe (>8mL). At this stage, liquids start to drip in dollops through the prongs of a fork rather than flowing freely.
Level 4: Extremely Thick
This is the thickest stage of liquid, comparable to pudding. It is not pourable and must be eaten with a spoon. It holds its shape on a spoon and does not drip through the prongs of a fork. This level is used for individuals with significant swallowing difficulties and poor tongue control. It is important that this consistency is not sticky, as this could cause residue to remain in the mouth or throat.
Comparing IDDSI with the Old NDD System
To help those familiar with older terminology, the following table shows how the new IDDSI framework aligns with the previous National Dysphagia Diet (NDD) system.
| IDDSI Level | Description | Corresponding NDD Term | Key Characteristics |
|---|---|---|---|
| Level 0 | Thin | Thin | Flows like water |
| Level 1 | Slightly Thick | - (New category) | Thicker than water; flows through a straw |
| Level 2 | Mildly Thick | Nectar-thick | Flows quickly off a spoon; can be sipped |
| Level 3 | Moderately Thick | Honey-thick | Pours slowly; eaten with a cup or spoon |
| Level 4 | Extremely Thick | Pudding-thick/Spoon-thick | Holds its shape; must be eaten with a spoon |
The Role of Thickeners and Safe Preparation
Commercial thickeners are available in powder or gel form and are categorized into two main types: starch-based and gum-based.
- Starch-based thickeners: These are typically made from modified maize starch and can sometimes have a grainy texture. A key drawback is that saliva contains an enzyme called amylase, which can break down the starch and cause the liquid to thin over time.
- Gum-based thickeners: These are often made with xanthan gum and are known for producing a smoother, more consistent texture that remains stable longer. They are generally preferred for their reliable consistency.
Regardless of the type, always follow the manufacturer's instructions for mixing to achieve the desired IDDSI level. Factors like temperature and the type of liquid (e.g., milk vs. juice) can influence thickening, so careful preparation and testing are essential for safety. For verification, the IDDSI Flow Test and Fork Drip Test provide objective ways to check the consistency at the point of service.
Importance of Medical Oversight and Potential Risks
While thickened liquids are crucial for managing dysphagia, they are not without potential challenges. Studies have shown they may be associated with a higher risk of dehydration because people often drink less due to altered taste, texture, or early satiety. Thickeners can also affect the dissolution and absorption of certain oral medications, so it is vital to communicate this to a pharmacist. For these reasons, all decisions regarding thickened liquid consumption must be made in consultation with a healthcare professional, and the diet should be regularly monitored. Informed consent and consideration of the impact on quality of life are key components of proper care. For more information on the official framework and testing methods, visit the International Dysphagia Diet Standardisation Initiative website.
Conclusion
The IDDSI framework has brought much-needed clarity and safety to the management of dysphagia by providing clear, standardized stages of thickened liquids. Understanding these stages, from Level 0 (Thin) to Level 4 (Extremely Thick), is essential for both healthcare providers and caregivers. While thickened liquids are an effective tool for preventing aspiration, their use requires careful preparation, regular testing, and ongoing medical oversight to manage potential side effects like dehydration. Ultimately, tailoring the fluid consistency to an individual's specific needs, under the guidance of an SLP, is the best approach for ensuring safe and effective hydration.
Naturally Thick Liquids
- Level 2: Mildly Thick: Some fruit nectars like apricot or peach, creamy soups, and some milkshakes.
- Level 4: Extremely Thick: Thicker pureed fruits like bananas, some smoothies made with thicker ingredients, and commercial pudding.
Hot and Cold Preparation
- Hot drinks: When thickening hot beverages like coffee or hot chocolate, ensure you add the thickener according to the manufacturer's instructions, noting that some liquids may thicken more as they cool.
- Cold drinks: For cold items like ice cream or gelatin, remember that these melt into a thin liquid and must be thickened after melting, or thickened water can be frozen into ice cubes to prevent dilution.
International Dysphagia Diet Standardisation Initiative (IDDSI) website
Importance of Hydration Monitoring
Individuals on thickened liquids may reduce their fluid intake, so it's critical to monitor their hydration status to prevent dehydration. Increasing frequency of offerings, adding flavor enhancers, or using different thickener types can help improve palatability and fluid consumption.
