A Detailed Look at Non-Starch Polysaccharides (NSP)
NSP, or non-starch polysaccharides, represents a historical and foundational approach to measuring dietary fiber. Developed primarily by researchers like Englyst and Cummings, this method focuses exclusively on the non-starch components found in the cell walls of plants. These components include cellulose, hemicellulose, pectin, and beta-glucans, which are resistant to breakdown by human digestive enzymes in the small intestine. The analysis is chemical-based, where starches are first enzymatically removed, and the remaining polysaccharides are hydrolyzed into their constituent sugars. These sugars are then measured using techniques like gas-liquid chromatography (GLC) or high-performance liquid chromatography (HPLC) to quantify the amount of NSP present. The NSP approach was valuable for understanding the properties and physiological effects of natural plant-based fiber, such as its impact on bowel function and cholesterol levels. However, it does not account for newer definitions of dietary fiber that include components outside of the traditional plant cell wall matrix.
The All-Encompassing Nature of AOAC Fiber Methods
AOAC, the Association of Official Analytical Chemists, has developed and refined a series of methods over time to provide a more holistic measurement of total dietary fiber (TDF). The evolution of these methods, including AOAC 991.43 and the more recent AOAC 2009.01 and 2011.25, reflects a broadening scientific definition of what constitutes dietary fiber. The key difference lies in the inclusion of several components that the NSP method excludes.
Unlike NSP, AOAC methods quantify:
- Resistant Starch: This type of starch escapes digestion in the small intestine and is fermented in the large intestine, offering health benefits similar to other fibers.
- Lignin: A complex polymer that is part of the plant cell wall but is not a carbohydrate. AOAC methods include it, while NSP does not.
- Isolated or Synthetic Non-Digestible Carbohydrates: This is a crucial distinction. As food technology advanced, new types of non-digestible carbohydrates, like inulin, polydextrose, and resistant maltodextrins, were added to foods to boost fiber content. AOAC methods are designed to capture these newer functional fibers, provided they demonstrate a physiological benefit.
AOAC analytical procedures use enzymatic digestion followed by gravimetric (weighing) and chromatographic techniques to measure high and low molecular weight fiber fractions. The result is a more comprehensive total dietary fiber value that aligns with modern nutritional definitions, including those from organizations like Codex and the European Food Safety Authority (EFSA).
Comparison Table: NSP vs. AOAC Fiber
| Feature | NSP (Non-Starch Polysaccharides) | AOAC (Association of Official Analytical Chemists) |
|---|---|---|
| Scope | Measures a narrower range, focusing on natural plant cell wall components like cellulose, hemicellulose, and pectin. | Measures a broader range, including natural plant fiber plus resistant starch, lignin, and functional, synthetic fibers. |
| Key Components | Cellulose, hemicellulose, pectins, and beta-glucans. | All NSP components, plus resistant starch, lignin, and low-molecular-weight, non-digestible carbohydrates. |
| Analysis Method | Enzymatic removal of starch, followed by chemical hydrolysis and measurement of constituent sugars via GLC or HPLC. | Enzymatic-gravimetric techniques, often combined with liquid chromatography (HPLC) for low-molecular-weight fibers. |
| Historical Context | Predates modern fiber definitions, reflecting an earlier understanding of plant-based fiber. | Developed and evolved to keep pace with changing definitions and the proliferation of functional fibers in processed foods. |
| Resulting Values | Typically reports lower fiber values for a given food product, especially those containing resistant starch or added functional fibers. | Typically reports higher total dietary fiber values due to its broader inclusion criteria. |
| Regulatory Use | Historically used in some regions for nutritional guidelines, such as by the WHO and FAO. | Widely used by regulatory bodies globally, including the FDA and EFSA, for food labeling and nutritional claims. |
Why Does the Measurement Method Matter for You?
The method used to measure fiber can have a significant impact on the total fiber content reported on a food label. This directly affects how consumers and nutritionists interpret the nutritional information of a product. For example, a food product containing added resistant starch or inulin will show a higher fiber count using the modern AOAC method than the traditional NSP method. This is particularly relevant for the growing market of fortified and functional foods.
For consumers, understanding the distinction is important for making informed dietary choices. If you are focused on consuming naturally occurring fiber from whole foods like fruits, vegetables, and whole grains, the distinction is less critical, as both methods will primarily capture the fiber content in these unprocessed foods. However, if you are consuming processed or fortified foods and are comparing products, knowing whether the fiber count is based on the broader AOAC standard can help explain variations in labeled fiber content.
For food manufacturers, the choice of method is critical for regulatory compliance and product development. In many countries, modern AOAC methods are the standard for declaring fiber content on nutritional labels. The ability of AOAC methods to capture a wider range of fiber types means manufacturers can more accurately report the fiber contribution of various ingredients, including functional fibers, which can be a key marketing point.
Conclusion: Different Methods for Different Fiber Perspectives
In summary, the core difference between NSP and AOAC fiber lies in their scope and the components they measure. NSP is a classic, narrower approach focused on the non-starch polysaccharides of the plant cell wall. In contrast, AOAC is a modern, more comprehensive set of methods that expands the definition to include resistant starch, lignin, and a variety of synthetic and isolated functional fibers. While NSP provides a valuable perspective on the fiber naturally present in plants, AOAC's broader approach reflects the reality of modern food processing and regulatory standards. For anyone interpreting food labels or discussing dietary fiber, recognizing this distinction is key to understanding the full picture of a product's fiber content.
How to Read Your Food Labels
- Recognize the standard: In many regions, the fiber value on the nutrition facts panel is an AOAC measurement, reflecting a comprehensive analysis.
- Look at the ingredients: Check the ingredients list for added fibers like inulin, polydextrose, or resistant starch to understand what is contributing to the total fiber count.
- Prioritize whole foods: Regardless of the measurement method, focusing on whole, unprocessed foods like vegetables, fruits, and whole grains ensures you are getting a rich, diverse mix of naturally occurring fibers.
- Be aware of older data: Some historical databases may use NSP values, which would appear lower than modern AOAC measurements for the same food.
- Consider fiber type, not just total grams: The different components measured by NSP and AOAC have different physiological effects. Soluble fibers (like those found in oats) can lower cholesterol, while insoluble fibers (like wheat bran) aid in laxation. The AOAC method can be further specified to break down into soluble and insoluble fractions.
- Don't be fooled by supplements: While some added fibers offer health benefits, they may not provide the same spectrum of nutrients as fiber naturally packaged in whole foods.
