Addition of fiber in diets formulated for dogs has been shown to affect ingesta viscosity,1–3 gastrointestinal motility,3–5 satiety,6,7 nutrient digestibility,8–10 and metabolic responses to feeding,9,11–13 as well as colonic bacterial populations and their products.14–17 Thus, supplementation with fiber may be useful in the management of diseases such as diabetes mellitus and obesity in canine patients.
In diabetic dogs, a diet with high IDF content is reported to improve glycemic control, evidenced by lower mean blood glucose measurements18; lower mean preprandial, postprandial, and 24-hour serum glucose concentrations19; and lower 24-hour urinary glucose excretion,19 compared with diets containing either very low concentrations of TDF18,19 or high concentrations of SDF.18 Lack of effect of dietary IDF on glycemic control in diabetic dogs has also been reported.20 In nondiabetic obese dogs, addition of dietary LMWSDF improved glucose tolerance as measured by the hypoglycemic-euglycemic clamp technique and by homeostatic model assessment,12 and plasma glucagon-like peptide 1 and insulin concentrations were greater in healthy dogs fed highly fermentable plant fibers than in dogs fed nonfermentable fiber.13 Microbial fermentation of some types of dietary fiber (generally SDF) results in production of short-chain fatty acids, some of which are involved in regulation of intestinal production of glucagon-like peptide,1,13 potentially modulating appetite, gastrointestinal motility, and insulin response to a meal.
Dietary fiber is also used in the management of obesity to achieve energy dilution as well as satiety. Although increased dietary fiber intake has often been reported to increase satiety in human studies,21,22 studies in dogs show mixed results. Some reports6,23 describe minimal to no decline in perceived hunger or food intake with supplemental fiber administration. However, obese dogs undergoing a weight loss program that were fed a diet with high fiber and high protein content achieved a greater degree of, and more rapid, weight loss than dogs fed an otherwise similar diet with moderate fiber content.24
Application of these findings to clinical practice is difficult because TDF is not reported for most commercially prepared diets for dogs. Pet food labeling regulations only require declaration of maximum CF concentration as part of the guaranteed analysis, although some manufacturers may voluntarily report TDF.
The CF analysis method captures variable portions of IDF (0% to 90% depending on the composition of the fiber source analyzed), without capturing any SDF25; therefore, CF underestimates the concentration of IDF and is a poor indicator of the TDF of pet foods.26–28 In contrast, the current standard analysis for foods intended for human consumption is a TDF method that quantifies IDF and HMWSDF (AOAC official methods 985.29 and 991.43) but not LMWSDF (eg, inulin and fructooligosaccharides). Separate assays were previously required if measurement of LMWSDF was desired; however, a newer assay that measures IDF, HMWSDF, and LMWSDF within the same method is now available (AOAC official method 2011.25).29
To more clearly define the effects of fiber in obese and diabetic patients, dietary fiber intake must be accurately described, both in terms of quantity and composition. The purpose of the study reported here was to examine the dietary fiber concentration and composition (measured with AOAC official method 2011.25 as IDF, HMWSDF, and LMWSDF) of commercially available diets formulated for management of obesity, diabetes mellitus, and dietary fat-responsive diseases such as pancreatitis and hyperlipidemia in dogs. Where dietary fat-responsive diseases are common comorbidities in both diabetic and obese patients,30–35 diets formulated with < 20% fat on an ME basis for treatment of these diseases are often fed to obese and diabetic patients. We hypothesized that LMWSDF would represent a substantial portion of dietary fiber in each diet type and that there would be significant differences in dietary fiber concentration and composition among diet categories.
Materials and Methods
Samples of veterinary therapeutic dry and canned diets formulated for management of diabetes, obesity, and dietary fat-responsive disease in dogs were donated by the faculty and staff at the Veterinary Medical Teaching Hospital of the School of Veterinary Medicine at the University of California-Davis or purchased from local veterinary clinics. All of the products were commercially available. Product name, type, lot number, ingredient list, guaranteed analysis, typical analysis, energy density, and expiration date were recorded from product labels, product guides, or manufacturer websites. Each product was assigned a sample number. Energy density was converted to a dry-matter basis by dividing the as-fed value by the dry-matter concentration (dry-matter concentration = 100% – measured moisture concentration). If TDF concentration and composition were not included in the typical analysis, manufacturers were contacted to obtain this information; when this was reported on an ME basis, it was similarly converted to a dry-matter basis. On the basis of the timing of sample collection (November 2012) versus the availability of the newer TDF assay (May to June 2012),29 reported TDF was assumed to be IDF + HMWSDF, and reported SDF was assumed to represent HMWSDF only.
Diets were considered to have been formulated primarily for management of diabetes (diets A–E),a–e obesity (diets F–O),f–o or dietary fat-responsive disease (diets P–S)p–s according to the indication listed first in the manufacturer's product guides at the time diets were collected (current as of November 2012). Quantitative diet categories were created on the basis of criteria for the AAFCO calorie content terms light, lite, or low calorie (diets A, B, F–I, and M–O; categorized as light diets) and fat content terms lean or low fat36 (diets A–C, F–K, M, and O–S; categorized as low-fat diets). According to AAFCO standards, light diets contain < 3,100 and 900 kcal/kg as fed for dry and canned, respectively, whereas low-fat diets contain < 9% and 4% fat as fed for dry and canned diets, respectively.36 Manufacturer-provided information was used for these category assignments. Diets were also categorized as having (diets C, E, J, and N–Q) or not having (all others) oligosaccharide sources listed in the ingredient declaration.
Approximately 200 g of each dry sample was placed in a sealed plastic bag labeled only with the sample number. Canned samples (unopened cans with manufacturer labeling removed, in a quantity sufficient to provide 738 g of each diet) were labeled similarly. Samples were submitted to an American Association for Laboratory Accreditation–certified reference laboratoryt and analyzed for moisture by use of a validated modification of AOAC International method 925.0937 for canned diets and the AOAC International Official Method 930.1538 for dry diets. Measured concentrations of IDF, HMWSDF, and LMWSDF were determined by AOAC International official method 2011.2539 and reported on a dry-matter basis. The measured TDF was defined as IDF + HMWSDF + LMWSDF. The measured SDF was defined as HMWSDF + LMWSDF. The composition of TDF was determined as the proportion of TDF represented by SDF, the proportion of SDF represented by LMWSDF, and the proportion of TDF represented by LMWSDF.
For TDF measurements, the reference laboratory provided a measure of uncertainty of 0.66. According to the laboratory, measure of uncertainty was calculated as follows for a reference sample:
Laboratory quality control measures included the use of 2 identical standard reference samples analyzed with each batch of test samples; the result for each sample was accepted and considered valid if the mean result for the reference samples was within 2 SDs of the reference sample mean.
Statistical analysis—Reported versus measured moisture concentration, reported CF versus measured IDF and TDF concentrations, reported TDF versus measured TDF and measured IDF + HMWSDF concentrations, reported IDF and SDF versus measured IDF and HMWSDF concentrations, and reported SDF versus measured HMWSDF + LMWSDF concentrations were compared by means of Wilcoxon signed rank tests. Diet type groups (canned and dry, presence or absence of added oligosaccharide sources, product guide indication, and categorization by AAFCO calorie and fat terms) were compared by means of Mann-Whitney tests for differences in energy density, TDF, IDF, HMWSDF, and LMWSDF concentrations; the proportion of TDF contributed by SDF; the proportion of SDF contributed by LMWSDF; and the proportion of TDF contributed by LMWSDF. All data are reported as median and range. Linear regression was performed to evaluate the relationship between dietary caloric content (kcal/kg of dry matter) and measured TDF on a dry-matter, as-fed, and ME basis. Commercial softwareu,v was used for all analyses.
Results
Four dry diets and 1 canned diet were donated. Seven dry and 7 canned diets were purchased. Four manufacturers produced the 19 diets (11 dry and 8 canned) examined; dry and canned diets from each manufacturer were included. The ingredient list, guaranteed analysis, typical analysis, and energy density were available for all 19 diets. Total dietary fiber concentration was available from 3 manufacturers for 14 diets (9 dry and 5 canned), with TDF composition available from 2 manufacturers for 5 of those diets (4 dry and 1 canned).
Reported energy density was 3,553 kcal/kg on a dry-matter basis (range, 2,889 to 4,376 kcal/kg) for all diets. Diets formulated for treatment of diabetes mellitus had significantly (P = 0.01) lower energy density (3,534 kcal/kg; range, 3,281 to 3,636 kcal/kg) than did diets for management of dietary fat-responsive disease (3,679 kcal/kg; range, 3,660 to 3,816 kcal/kg). All (canned and dry) light diets had significantly (P < 0.001) lower energy density (3,262 kcal/kg; range, 2,889 to 3,620 kcal/kg), compared with all non-light diets (3,672 kcal/kg; range, 3,534 to 4,376 kcal/kg). This was also true when only dry diets (3,224 kcal/kg [range, 2,988 to 3,281 kcal/kg] vs 3,671 kcal/kg [range, 3,534 to 3,927 kcal/kg]; P = 0.008) and only canned diets (3,454 kcal/kg [range, 2,889 to 3,620 kcal/kg] vs 3,685 kcal/kg [range, 3,660 to 4,376 kcal/kg]; P = 0.02) were compared. Comparison of other diet categories (dry vs canned, added oligosaccharide sources vs no added oligosaccharide sources [all, dry, and canned diets], diets for management of obesity vs diets for management of diabetes mellitus [all, dry, and canned diets], diets for management of obesity vs diets for managing dietary fat-responsive disease [all diets], and low-fat diets vs non–low-fat diets [all diets and dry diets only]) yielded no significant differences in energy density. Energy density was negatively correlated with TDF concentration on an as-fed, dry-matter, and ME basis for all diets (r = −0.48, −0.85, and −0.87, respectively; P = 0.040, P < 0.001, and P < 0.001, respectively), dry diets (r = −0.84, −0.87, and −0.90, respectively; P = 0.001, P < 0.001, and P < 0.001, respectively), and canned diets (r = −0.78, −0.85, and −0.86, respectively; P = 0.021, P = 0.007, and P = 0.006, respectively).
For dry diets, reported maximum moisture concentration on an as-fed basis (10%; range, 10% to 12%) was significantly (P = 0.001) higher than measured moisture concentration on an as-fed basis (7%; range, 6% to 11%). For canned diets, reported maximum moisture concentration on an as-fed basis (78%; range, 77% to 88%) was also significantly (P = 0.008) higher than the measured as-fed value (76%; range, 74% to 85%).
Reported maximum CF concentrations for all diets (13.1%; range, 3.3% to 30.5%), dry diets (10.7%; range, 3.9% to 21.5%), and canned diets (14.4%; range, 3.3% to 30.5%) were significantly lower than measured TDF concentrations for all diets (P < 0.001), dry diets (P = 0.001), and canned diets (P = 0.008), respectively, on a dry-matter basis (Table 1). The reported maximum CF concentrations were significantly (P = 0.002) lower than measured IDF concentrations for dry diets on a dry-matter basis, but maximum reported CF was significantly (P = 0.003) higher than measured IDF concentrations for all diets and not significantly different from IDF for canned diets. Reported maximum CF concentration represented 29% to 95% of the measured TDF concentration, with 1 exception: a dry obesity management diet, for which reported maximum CF content was 200% of the measured TDF content. Reported maximum CF concentration represented 56% to 423% of the measured IDF concentration, with 6 diets having a maximum CF concentration that exceeded measured IDF concentration.
Median (range) measured concentrations (percentage dry matter) of TDF, IDF, SDF, HMWSDF, and LMWSDF in diets used for management of obesity, diabetes mellitus, and dietary fat-responsive disease in dogs.
| Category | TDF | IDF | SDF | HMWSDF | LMWSDF |
|---|---|---|---|---|---|
| All diets (n = 19) | 17.2 (7.7–42.6) | 12.6 (3.6–37.5) | 4.6 (2.8–7.8) | 2.7 (1.2–5.6) | 2.1 (0.8–4.1) |
| Dry (n = 11) | 21.0 (9.3–34.5) | 15.4 (5.2–29.0) | 4.8 (3.0–7.8) | 2.4 (1.2–5.6) | 2.4 (1.1–4.1) |
| Canned (n = 8) | 16.6 (7.7–42.6) | 11.6 (3.6–37.5) | 4.6 (2.8–5.3) | 2.8 (1.5–4.0) | 1.5 (0.8–3.4) |
| Diets with added oligosaccharide sources (n = 7) | 15.9 (9.3–34.5) | 10.3 (5.2–29.0) | 4.8 (4.1–7.8) | 2.8 (1.7–4.7) | 2.4 (1.7–3.9) |
| Dry (n = 5) | 17.2 (9.3–34.5) | 9.4 (5.2–29.0) | 4.8 (4.1–7.8) | 2.4 (1.7–4.7) | 2.4 (1.7–3.9) |
| Diets without added oligosaccharide sources (n = 12) | 24.0 (7.7–42.6) | 18.0 (3.6–37.5) | 4.4 (2.8–6.9) | 2.6 (1.2–5.6) | 1.4 (0.8–4.1) |
| Dry (n = 6) | 24.9 (9.3–31.9) | 18.0 (5.3–28.9) | 4.4 (3.0–6.9) | 2.6 (1.2–5.6) | 1.9 (1.1–4.1) |
| Product guide indication | |||||
| Obesity management diets (n = 10) | 22.4 (7.7–42.6) | 16.6 (3.6–37.5) | 4.6 (3.5–6.9) | 2.8 (1.2–4.0) | 2.3 (0.8–4.1) |
| Dry (n = 5) | 27.5 (9.3–34.5) | 20.6 (5.2–29.0) | 4.9 (3.5–6.9) | 1.7 (1.2–2.8) | 2.4 (2.2–4.1) |
| Canned (n = 5) | 17.2 (7.7–42.6) | 12.6 (3.6–37.5) | 4.5 (4.1–4.9) | 2.8 (1.5–4.0) | 1.3 (0.8–2.6) |
| Diabetes management diets (n = 5) | 22.2 (17.2–31.9)* | 16.5 (9.4–28.9)* | 4.5 (2.8–7.8) | 2.8 (1.8–5.6) | 1.2 (0.9–3.1) |
| Dry (n = 4) | 21.6 (17.2–31.9) | 16.0 (9.4–28.9) | 5.6 (3.0–7.8) | 3.8 (1.8–5.6) | 1.4 (1.1–3.1) |
| Fat-responsive disease management diets (n = 4; dry and canned) | 10.7 (9.3–15.9)* | 5.6 (5.3–10.6)* | 5.0 (4.0–5.3) | 2.4 (1.9–3.2) | 2.3 (1.6–3.4) |
| AAFCO designation | |||||
| Light diets (n = 9) | 28.8 (14.9–42.6)† | 23.9 (10.3–37.5)† | 4.6 (2.8–6.9) | 2.8 (1.7–4.0) | 1.3 (0.8–4.1) |
| Dry (n = 4) | 30.4 (27.5–34.5)‡ | 26.4 (20.6–29.0)‡ | 5.2 (3.0–6.9) | 2.2 (1.7–2.8) | 3.0 (1.2–4.1) |
| Canned (n = 5) | 25.9 (14.9–42.6) | 23.1 (10.3–37.5) | 4.5 (2.8–5.2) | 2.8 (2.0–4.0) | 1.1 (0.8–1.7) |
| Non-light diets (n = 10) | 10.7 (7.7–22.2)† | 6.3 (3.6–16.5)† | 4.6 (3.5–7.8) | 2.4 (1.2–5.6) | 2.4 (1.1–3.4) |
| Dry (n = 7) | 10.2 (9.3–22.2)‡ | 6.7 (5.2–16.5)‡ | 4.5 (3.5–7.8) | 2.4 (1.2–5.6) | 2.4 (1.1–3.1) |
| Low-fat diets (n = 15) | 17.2 (7.7–42.6) | 10.5 (3.6–37.5) | 4.6 (2.8–7.8) | 2.7 (1.5–4.7) | 2.1 (0.8–4.1) |
| Dry (n = 7) | 17.2 (9.3–31.9) | 9.4 (5.2–28.9) | 4.8 (3.0–7.8) | 2.4 (1.7–4.7) | 2.4 (1.2–4.1) |
| Canned (n = 8) | 16.6 (7.7–42.6) | 11.6 (3.6–37.5) | 4.6 (2.8–5.3) | 2.8 (1.5–4.0) | 1.5 (0.8–3.4) |
| Non–low-fat diets (n = 4; all dry) | 21.6 (10.2–34.5) | 16.0 (6.7–29.0) | 5.0 (3.5–6.8) | 2.2 (1.2–5.6) | 2.0 (1.1–3.9) |
Measured concentrations of IDF, HMWSDF, and LMWSDF were determined by AOAC International official method 2011.2539: measured TDF was defined as IDF + HMWSDF + LMWSDF, and measured SDF was defined as HMWSDF + LMWSDF. The AAFCO designation categories were assigned on the basis of criteria for the calorie content terms light, lite, or low calorie (light diets) and lean or low fat (low-fat diets). Data are not presented for subcategories with ≤ 3 samples/group.
Within a column, values with the same symbol are significantly (P < 0.05) different.
For the 14 diets (9 dry and 5 canned) that had reported TDF concentrations (assumed to represent IDF + HMWSDF), the reported CF concentrations for all diets (13.1% [range, 3.3% to 30.5%]) and dry diets (10.7% [range, 3.9% to 21.5%]) were lower than the reported TDF concentrations for all diets (16.6% [range, 5.4% to 31.1%]; P = 0.017) and dry diets (19% [range, 6.1% to 31.1%]; P = 0.012), respectively, on a dry-matter basis. This difference was not significant for canned diets. The reported TDF concentrations were also lower than the median measured TDF concentration (which comprised IDF + HMWSDF + LMWSDF) for all 14 diets evaluated (16.6% [range, 5.4% to 31.1%]; P < 0.001) and all 9 dry diets (10.0% [range, 6.1% to 31.1%]; P = 0.004) in this group, but differences for canned diets were nonsignificant. When measured LMWSDF concentration was subtracted from measured TDF concentration, there were no significant differences between reported and measured TDF values for all diets, dry diets, or canned diets. For all diets and dry diets in the subgroup of 5 diets (4 dry and 1 canned) that had TDF composition reported, there were no differences between reported and measured IDF, reported SDF (assumed to reflect HMWSDF) and measured HMWSDF, and reported SDF and measured SDF (as HMWSDF + LMWSDF) concentrations on a dry-matter basis. Reported concentrations of SDF and IDF were available for only 1 canned diet, so comparison of canned diets was not attempted for these variables.
Soluble dietary fiber (HMWSDF and LMWSDF) constituted a median of 30.4% (range, 9.4% to 53.7%) of TDF, and LMWSDF contributed a median of 11.5% (range, 2.7% to 33.8%) of TDF. There were no differences in measured concentrations of TDF, IDF, HMWSDF, LMWSDF, SDF, the proportion of TDF contributed by SDF, the proportion of SDF contributed by LMWSDF, or the proportion of TDF contributed by LMWSDF between dry and canned diets when all foods were grouped into these 2 categories and compared on a dry-matter basis. Similarly, there were no differences in these variables between diets that had added oligosaccharide sources and those that did not (compared as all diets and dry diets only).
When diets were categorized according to their product guide indications (as diets for dogs with obesity, diabetes mellitus, or dietary fat-responsive disease), there were differences in concentrations of TDF and IDF, as well as TDF and SDF composition, on a dry-matter basis (Table 1). A significantly (P = 0.01) larger proportion of SDF was provided as LMWSDF by dry obesity management diets (59.2%; range, 44.8% to 69.7%) than by dry diets for dogs with diabetes mellitus (38.2%; range, 16.7% to 40.3%). When all diets for diabetes mellitus management were compared with all diets for management of dietary fat-responsive disease, diabetes management diets had greater TDF (P = 0.01) and IDF (P = 0.03) concentrations, but diets for dogs with dietary fat-responsive disease had significantly (P = 0.05 for all comparisons) higher proportions of TDF contributed by SDF (45.0% [range, 43.6 to 47.4%] vs 21.3% [range, 9.4% to 45.4%]), higher proportions of SDF contributed by LMWSDF (45.1% [range, 39.5 to 63.6%] vs 37.2% [range 16.7% to 40.3%]), and higher proportions of TDF contributed by LMWSDF (20.3% [range, 13.4% to 30.1%] vs 5.1% [range, 3.4% to 17.8%]). There were no significant differences in concentrations of SDF, LMWSDF, or HMWSDF between diets for management of diabetes mellitus and those for dietary fat-responsive disease.
Nine diets (7 formulated for dogs with obesity and 2 for dogs with diabetes mellitus) met criteria for the AAFCO calorie content terms light, lite, or low calorie (categorized as light diets). When all diets and dry diets were categorized as light or non-light, there were no differences in the concentrations of SDF, HMWSDF, or LMWSDF or in the proportion of SDF contributed by LWMSDF between categories; canned diets were not compared because of small sample numbers. However, the group of diets classified as light had higher concentrations of TDF (P = 0.002) and IDF (P = 0.001), lower proportions of TDF contributed by SDF (16.0% [range, 9.4% to 30.5%] vs 43.7% [range, 21.3% to 53.7%]; P < 0.001), and lower proportions of TDF contributed by LMWSDF (4.7% [range, 2.7% to 14.9%] vs 20.4% [range, 5.1% to 33.8%]; P = 0.003), compared with non-light diets. When dry light diets were compared with dry non-light diets, results were similar except that there was no difference in the proportion of TDF contributed by LMWSDF in dry diets. In contrast, when diets were grouped according to criteria for AAFCO fat content terms, there were no differences in concentrations of TDF, IDF, HMWSDF, LMWSDF, SDF, or fiber composition between low-fat and non–low-fat diets. Fifteen diets (including diets for management of obesity [n = 8], diabetes mellitus [3], and dietary fat-responsive disease [4]) were categorized as low-fat diets according to AAFCO criteria. All canned diets met the criteria for the low-fat designation, despite energy density ranging from 2,889 to 4,376 kcal/kg on a dry-matter basis and fat concentration on an ME basis ranging from 17% to 38%.
When canned and dry diets made by the same manufacturer with the same product name (8 diet pairs) were analyzed, dry diets ranged from having 13.80% lower (3 obesity management diets and 2 diets for fat-responsive disease management) to 19.68% higher (1 diabetes management diet and 2 obesity management diets; on a dry-matter basis) TDF concentration than their canned counterparts.
Discussion
As has been described for diets formulated to manage obesity and diabetes mellitus in cats,40 energy density of all diets formulated for dogs with diabetes mellitus, obesity, or dietary fat-responsive disease in the present study was negatively correlated with TDF concentration. Although this is not the only factor to affect energy density, it appears to have a role in the formulation of therapeutic diets for these indications, given that there were significant differences in composition and concentration of TDF among diet categories. Fat concentration, which was not measured for analysis in the present study, is another major contributor to energy density. However, none of the diets evaluated exceeded 40% fat (according to manufacturer-provided information as assessed on an ME basis). By evaluating diets for management of obesity, diabetes mellitus, and dietary fat-responsive disease, a sample of study diets in which TDF is relatively more important in determining energy density (compared with other types of diets) may have been selected, whereas TDF concentration was not shown to be strongly correlated with caloric density in a study26 of canine maintenance diets.
Differences between manufacturer-reported maximum moisture concentrations and measured moisture concentrations in the present study were consistent with results of other studies,26,40,41 as were differences between the reported maximum CF and measured TDF concentration.26,28,40 In canned diets only, reported maximum CF concentration was not different than measured IDF concentration, suggesting this value could potentially be used to estimate IDF content in similar diets. However, this was not supported by a previous study26 for a sample of canine maintenance diets. Reported CF concentrations in excess of measured TDF and IDF concentrations in canned diets were previously determined in a study40 evaluating fiber content and composition in feline diets for management of obesity and diabetes mellitus. The fact that the measured IDF concentration was greater than the reported maximum CF concentrations in dry diets but not canned diets in the present study appeared to be attributable to the reporting of maximums on an as-fed basis. This would cause the magnitude of the overestimate inherent in reporting a maximal value to be greater for a canned diet than a dry diet when converted to a dry-matter basis because of the large difference in moisture contents. Reported maximum CF concentration was lower than reported TDF concentration in all diets (n = 14) and dry diets (9) but not in canned diets (5) for which the information was provided, and this could also have been attributable to the inflation of reported as-fed maximal CF concentrations in dry-matter conversion calculations for canned diets.
When TDF measurements were adjusted to exclude LMWSDF, there was no difference between measured and reported TDF concentrations, supporting the assumption that reported TDF concentration was measured by the manufacturers of diets in the present study by use of an assay that detects IDF and HMWSDF. This was further supported by the fact that reported IDF and reported SDF concentrations were not different from the measured IDF and HMWSDF concentrations in all diets (n = 5) and dry diets (4) for which the manufacturer information was available (information was not available for enough canned diets to make this comparison). Even though reporting of TDF concentration as IDF + HMWSDF concentrations represents a vast improvement in provision of useful information about fiber concentration and composition, compared with a maximum CF concentration, the underestimation of TDF that occurs through use of an assay that does not detect LMWSDF may be important in diets for management of diseases where LMWSDF may be beneficial.
In diets with added oligosaccharide sources, the concentration of LMWSDF was higher than, albeit not significantly, that for diets without these products. The argument is often made that a finding of significance in a study does not necessarily translate to clinical importance. However, it is possible that a clinically important response can be obtained with diets where concentrations of components are not significantly different. This may be the case for diets with oligosaccharide sources in our study, considering that experimental diets with concentrations of oligosaccharides similar to those of the diets evaluated in this study were shown to have clinical benefits in dogs.12,42,43
Reported TDF concentrations were lower than measured TDF concentrations in all diets and dry diets but not in canned diets of the present study. Because the reported TDF data are from typical and not guaranteed analysis, they are not maximum values, so there would be no artificial inflation of TDF concentration associated with conversion to a dry-matter basis. In this case, the lack of a significant difference between reported and measured TDF in canned diets appears to be due to true differences in composition between dry and canned diets, with canned diets being lower in the LMWSDF (not included in the TDF concentrations reported by manufacturers).
Making accurate assumptions about dietary fiber concentration or composition in canned versus dry diets on the basis of our results is challenging, owing to the lack of differences in several variables (measured TDF, IDF, HMWSDF, LMWSDF, and SDF concentrations; the proportion of TDF contributed by SDF; the proportion of SDF contributed by LMWSDF; and the proportion of TDF contributed by LMWSDF) between these diet formulations. Further, within groups of diets categorized by product guide specifications, and even between canned and dry diets with the same product name, there was variation in dietary fiber concentration and composition. Veterinarians should not presume that a pet will always have the same response to dry and canned versions of the same diet or that all diets with the same indications will perform in the same manner clinically.
There were significant differences in dietary fiber content between diets for treatment of diabetes mellitus and those for treatment of dietary fat-responsive disease, with diabetes management diets having higher TDF concentration as a result of higher IDF concentration. This may be inherent in the formulation of diets for dogs with diabetes mellitus, given the evidence that IDF has the potential to improve regulation of blood glucose concentrations in diabetic dogs.18,19 Although diets for dogs with fat-responsive disease had lower TDF concentration, a larger proportion of TDF was contributed by SDF, particularly LMWSDF, compared with diabetes management diets. This may again be a design feature of these diets, which are formulated to be highly digestible; SDF may slow gastrointestinal transit and therefore increase digestibility.4,44 Also, given that these diets are intended to promote gastrointestinal health, the increased fermentability of a diet with higher SDF concentration would also serve this purpose.
When AAFCO calorie terms were used as objective measures for categorizing diets on the basis of caloric density, differences in TDF concentration between light and non-light diets supported the results of regression analysis indicating that TDF concentration was negatively correlated with energy density. Light diets were characterized by a higher IDF concentration and a lower proportion of TDF contributed by SDF, resulting in a lower proportion of TDF contributed by LMWSDF in all diets and canned diets. Although dietary fat concentration largely contributes to caloric density, it is not the only factor, given that none of the diets for management of dietary fat-responsive disease (all < 20% fat on an ME basis) met AAFCO criteria for designation as a light food. Notably, given that all canned diets included in the present study met criteria for the AAFCO low-fat designation, yet this group included diets containing up to 38% fat on an ME basis, practitioners should be aware that such diets may not provide adequate fat restriction for a given patient.
The difference between TDF concentration as IDF + HMWSDF + LMWSDF concentrations and as IDF + HMWSDF concentrations and the difference between CF concentration and TDF concentration (as IDF + HMWSDF + LMWSDF concentrations) is relevant not only to potential clinical effects of diet, but also to calculations of energy density. Carbohydrate content of a diet is not measured specifically but is determined by subtraction of percentage protein, fat, moisture, ash, and fiber from 100%. Discrepancies between actual and reported values for protein, fat, moisture, ash, and fiber can occur when guaranteed, rather than typical, analysis values are used or when the analytic method used to determine any of these values is inaccurate, as in the case of CF concentration. All of these imprecisions contribute to inaccurate estimation of carbohydrate concentration. Once carbohydrate concentration (termed nitrogen-free extract) is determined, modified Atwater factors (3.5, 8.5, and 3.5 kcal/g for protein, fat, and carbohydrates, respectively) are used to calculate the energy density of the diet. This is the approved calculation method per AAFCO, and many pet food manufacturers use this, rather than direct measurements, to determine energy density. As such, the calculated values overestimate the energy density of many diets and possibly result in errors in calculation of amounts to feed individual pets.
The sample of diets examined in the present study varied in fiber concentration and composition, often even within a category of diets described as indicated for the same disease as well as between dry and canned versions of the same diet. For these reasons, when recommending a diet for a canine patient, veterinarians should consider the nutrients of concern for the patient, and recommend diets on the basis of how well they meet targeted concentrations for those nutrients, rather than relying solely on the product guide indications. Veterinarians should request TDF data from manufacturers if it is not available in product guides. More consistent manufacturer reporting of TDF concentration and composition should be encouraged. This will allow for improved and individualized management of patients.
ABBREVIATIONS
| AAFCO | Association of American Feed Control Officials |
| AOAC | Association of Analytical Communities |
| CF | Crude fiber |
| HMWSDF | High-molecular-weight soluble dietary fiber |
| IDF | Insoluble dietary fiber |
| LMWSDF | Low-molecular-weight soluble dietary fiber |
| ME | Metabolizable energy |
| SDF | Soluble dietary fiber |
| TDF | Total dietary fiber |
Hill's Prescription Diet w/d Canine Low Fat-Diabetic-Gastrointestinal dry, Hill's Pet Nutrition Inc, Topeka, Kan.
Hill's Prescription Diet w/d Canine Low Fat-Diabetic-Gastrointestinal canned, Hill's Pet Nutrition Inc, Topeka, Kan.
Iams Veterinary Formula Glucose and Weight Control Optimum Weight Control/Canine dry, Procter & Gamble Pet Care, Cincinnati, Ohio.
Purina Veterinary Diets DCO Dual Fiber Control Canine Formula dry, Nestlé Purina Petcare Co, St Louis, Mo.
Royal Canin Veterinary Diet Diabetic dry, Royal Canin USA Inc, St Charles, Mo.
Hill's Prescription Diet r/d Canine Weight Loss-Low Calorie dry, Hill's Pet Nutrition Inc, Topeka, Kan.
Hill's Prescription Diet r/d Canine Weight Loss-Low Calorie canned, Hill's Pet Nutrition Inc, Topeka, Kan.
Purina Veterinary Diets OM Overweight Management Canine Formula dry, Nestlé Purina Petcare Co, St Louis, Mo.
Purina Veterinary Diets OM Overweight Management Canine Formula canned, Nestlé Purina Petcare Co, St Louis, Mo.
Iams Veterinary Formula Weight Loss/Mobility Plus Restricted-Calorie/Canine dry, Procter & Gamble Pet Care, Cincinnati, Ohio.
Iams Veterinary Formula Weight Loss/Mobility Plus Restricted-Calorie/Canine canned, Procter & Gamble Pet Care, Cincinnati, Ohio.
Royal Canin Veterinary Diet Calorie Control dry, Royal Canin USA Inc, St Charles, Mo.
Royal Canin Veterinary Diet Calorie Control canned, Royal Canin USA Inc, St Charles, Mo.
Royal Canin Veterinary Diet Satiety Support dry, Royal Canin USA Inc, St Charles, Mo.
Royal Canin Veterinary Diet Calorie Control CC High Fiber canned, Royal Canin USA Inc, St Charles, Mo.
Hill's Prescription Diet i/d Low Fat GI Restore Canine dry, Hill's Pet Nutrition Inc, Topeka, Kan.
Hill's Prescription Diet i/d Low Fat GI Restore Canine canned, Hill's Pet Nutrition Inc, Topeka, Kan.
Royal Canin Veterinary Diet Gastrointestinal Low Fat dry, Royal Canin USA Inc, St Charles, Mo.
Royal Canin Veterinary Diet Gastrointestinal Low Fat canned, Royal Canin USA Inc, St Charles, Mo.
Eurofins Scientific, Des Moines, Iowa.
Excel 2007, Microsoft Corp, Redmond, Wash.
Stata/IC, version 12.1, StataCorp LP, College Station, Tex.
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