Letters to the Editor

The role of carbohydrates in feline diets

In the Timely Topics in Nutrition review article “Evidence does not support the controversy regarding carbohydrates in feline diets,”1 the authors suggest that, for healthy cats, an upper limit of 50% of calories coming from carbohydrates in their diets is acceptable. But they also state that low-carbohydrate diets can help diabetic cats and achieve remission.1 How are we to know that a cat is diabetic until it has been fed a high-carbohydrate, diabetogenic diet, to which, admittedly, many cats adapt. But they can develop other health consequences, which these authors failed to address, their focus on dietary fat content and feline obesity being a distraction.

Many manufactured cat foods, especially dry kibble, contain phytates, which are present mainly in legumes (ie, soy) and cereals. These reduce the digestibility of proteins and mineral absorption.2 A net loss of body calcium, phosphorus, and magnesium during feeding of the fiber diet suggests that dietary inclusion of insoluble fiber could increase macromineral requirements of cats. Could this be a contributing factor to the widespread diagnosis of arthritis in cats?

Starch and fiber in diets potentially stimulate formation of struvite crystals.3 Hence, reducing dietary carbohydrate is desirable to prevent struvite urolith formation.

Considering the high incidence of hyperthyroidism in the cat population, the inclusion of soy as a cheap protein in many cat foods also needs to be questioned since soy does affect the thyroid gland.4

I am also concerned about irritable and inflammatory bowel conditions in cats and the immunological and behavioral consequences of intestinal dysbiosis, leaky gut syndrome, and autoimmune diseases possibly caused in part by lectins in the diet, as noted in human patients.5 This may result in such cats being euthanized, abandoned, or left at an animal shelter for unlikely adoption.

Michael W. Fox, BVetMed, PhD, DSc Animal Doctor syndicated column office Golden Valley, MN

  • 1.

    Laflamme DP, Backus RC, Forrester SD, Hoenig M. Evidence does not support the controversy regarding carbohydrates in feline diets. J Am Vet Med Assoc. 2022;260(5):506513.

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  • 2.

    Samtiya M, Aluko RE, Dhewa T. Plant food anti-nutritional factors and their reduction strategies: an overview. Food Prod Process Nutr. 2020;2(1):114. doi:10.1186/s43014-020-0020-5

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  • 3.

    Funaba M, Uchiyama A, Takahashi K, et al. Evaluation of effects of dietary carbohydrate on formation of struvite crystals in urine and macromineral balance in clinically normal cats. Am J Vet Res. 2004;65(2):138-42. doi:10.2460/ajvr.2004.65.138

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  • 4.

    Tonstad S, Jaceldo-Siegl K, Messina M, et al. The association between soya consumption and serum thyroid-stimulating hormone concentrations in the Adventist Health Study-2. Public Health Nutr. 2016;19(8):14641470. doi:10.1017/S1368980015002943

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  • 5.

    Morosi LG, Cutine AM, Cagnoni AJ, et al. Control of intestinal inflammation by glycosylation-dependent lectin-driven immunoregulatory circuits. Sci Adv. 2021;7(25):eabf8630. doi:10.1126/sciadv.abf8630

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The authors respond

We are writing in response to Dr. Fox’s commentary on our article.1 In his comments, he calls out a number of issues that he perceives to be associated with commercial cat foods, but most of his comments are not relevant to our review article on carbohydrates. However, they do bear addressing due to the misinformation suggested, so we’ll first respond to the comments directly related to our article, then to the rest.

Dr. Fox stated that “low-carbohydrate diets can help diabetic cats and achieve remission. How are we to know that a cat is diabetic until it has been fed a high-carbohydrate, diabetogenic diet, to which, admittedly, many cats adapt.” We will not address Dr. Fox’s clinical abilities to diagnose disease, but it appears that he has missed the point of the article, which is based on published scientific data. The data do not support that high-carbohydrate (even up to 50% of metabolizable energy) diets are diabetogenic. While very high-carbohydrate diets can result in postprandial elevations in blood glucose, such elevations are not sufficiently high as to cause glucose toxicity or diabetes. In fact, the highest peak elevations in blood glucose recorded in any of the studies exploring this issue was 241 mg/dL in obese cats fed a large meal of a food containing 51% of calories from carbohydrates and only 21% of calories from protein, following a 24-hour fast.2 As we point out in our article, there are a number of features from that study design that lead to a worst case scenario for postprandial blood glucose. Despite this, the peak blood glucose was well below that shown to cause glucose toxicity (450 to 540 mg/dL) or to have adverse effects on insulin secretion in cats.3,4

In addition to basic research relative to carbohydrates’ impact on blood glucose, several epidemiological studies have evaluated diet as a risk factor for feline diabetes.58 Two studies suggest that dry food (dry food being higher in carbohydrates vs wet or canned foods) may be a risk factor.5,6 However, one of these studies did not confirm that the diet reported was that fed prior to the diagnosis, as opposed to a diet prescribed after the initial diagnosis.5 The second of these studies showed that cases were more likely to be fed a dry food than the control cats.6 Unfortunately, the control group was not age-matched and averaged 13 years of age, compared to 10 years in the diabetic cats. Other evidence shows that older cats are more likely to be fed more wet food than younger cats,9 thus confounding interpretation of this finding. The remaining 2 studies found either no impact of diet or a suggestion that a greater proportion of diet from dry food was associated with lower risk for feline diabetes mellitus.7,8 Given that over 90% of cats in the US, Australia, and Europe consume at least 50% of their calories from commercial dry food,10 it seems reasonable to conclude that, if dry foods were diabetogenic, the evidence would be much stronger and overall prevalence of feline diabetes would be greater. Therefore, the sum of the evidence does not support the hypothesis that dry foods are diabetogenic.

Dr. Fox wrote that “they can develop other health consequences, which these authors failed to address, their focus on dietary fat content and feline obesity being a distraction.” We must clarify that the topic of the article was the role of carbohydrates in feline diets. No distraction was intended in mentioning fats or proteins. Dietary energy comes from any of the macronutrients: protein, fat, and carbohydrates. If a diet contains less of one of these (ie, carbohydrate), the remaining macronutrients (fat and protein) will be relatively increased. Therefore, low-carbohydrate diets tend to contain a higher percentage of protein and fat. Given that fat contains over twice the calories per gram compared to carbohydrate, low-carbohydrate diets tend to be higher in calories. Several studies have confirmed higher fat diets as risk factors for the development of obesity in cats.1114 Regardless of diet fed, it is important to feed cats an appropriate calorie intake to avoid obesity.

Dr. Fox goes on to discuss multiple issues that were not relevant to our article. However, we wish to address them. According to Dr. Fox, “Many manufactured cat foods, especially dry kibble, contain phytates, which are present mainly in legumes (ie, soy) and cereals. These reduce the digestibility of proteins and mineral absorption. A net loss of body calcium, phosphorus, and magnesium during feeding of the fiber diet suggests that dietary inclusion of insoluble fiber could increase macromineral requirements of cats. Could this be a contributing factor in the widespread diagnosis of arthritis in cats?”

It is true that phytates, a naturally occurring fiber in plant matter, can decrease digestibility of a diet and other components of that diet. Other dietary fibers can similarly decrease diet digestibility yet are important to gastrointestinal health and a healthy microbiome. Most commercial pet food manufacturers understand the impact that various ingredients can have and adjust formulas accordingly. Pet foods that have undergone Association of American Feed Control Officials feeding trials have demonstrated the bioavailability of the essential nutrients contained therein. There is no evidence to suggest that commercial diets lead to arthritis. Further, arthritis is an inflammatory condition of joints and not related to bone density, so this hypothesis lacks even physiological support.

Dr. Fox wrote, “Starch and fiber in diets potentially stimulate formation of struvite crystals. Hence, reducing dietary carbohydrate is desirable to prevent struvite urolith formation.”

There are many factors that can alter the likelihood of struvite formation. Urine pH is recognized as a major influencer on formation or dissolution of struvite. Animal proteins are naturally acidifying, as are certain minerals. Dietary base excess, which is driven by dietary minerals, is correlated with urine pH.15 In the study referenced,16 in addition to differences in protein and starch, the diets differed considerably in base excess. While the exchange of starch for protein in these experimental diets was associated with an increase in base excess, urine pH, and struvite formation, these effects are easily compensated for in properly balanced, nutritionally complete diets.

Dr. Fox wrote, “Considering the high incidence of hyperthyroidism in the cat population, the inclusion of soy as a cheap protein in many cat foods also needs to be questioned since soy does affect the thyroid gland.” Soy can provide a highly digestible source of many essential amino acids in diets for cats or dogs. Soy does have a mild impact on thyroid hormones and can decrease absorption of iodine and contribute to a deficiency if dietary iodine is marginal. This is well-known in multiple species. However, there does not appear to be a clinically significant impact from commercial dry cat foods, with or without soy proteins, on feline hyperthyroidism. In fact, multiple studies have shown that consumption of dry food is protective against feline hyperthyroidism, compared to consumption of wet cat foods.1720

Dr. Fox wrote, “I am also concerned about irritable and inflammatory bowel conditions in cats and the immunological and behavioral consequences of intestinal dysbiosis, leaky gut syndrome, and autoimmune diseases possibly caused in part by lectins in the diet, as noted in human patients. This may result in such cats being euthanized, abandoned, or left at an animal shelter for unlikely adoption.”

Lectins, such as haemagglutins, are examples of the many antinutritional factors that may be present in raw plant-based ingredients. In raw form, these compounds can inhibit protein digestion and even be irritable to the gastrointestinal mucosa. Fortunately, the vast majority of these compounds, including the lectins mentioned, can be destroyed by proper cooking. Extrusion, the cooking process used for the vast majority of commercial dry foods, has proven to be very effective at eliminating lectins and other antinutritive factors while increasing dietary digestion.21,22

In summary, we stand by our original review article and the conclusion that published evidence does not support adverse effects from carbohydrates within nutritionally balanced diets. In fact, over 90% of healthy cats consume at least 50% of their calories from commercial dry cat foods and there is no published evidence that such diets lead to disease. We appreciate Dr. Fox providing us with this opportunity to address these important issues for our veterinary patients.

Dorothy Laflamme, DVM, PhD, Dipl ACVIM (Nutrition)

Robert Backus, DVM, PhD, Dipl ACVIM (Nutrition)

Dru Forrester, DVM, MS, Dipl ACVIM (Internal Medicine)

Margarethe Hoenig, Dr Med Vet, PhD, Dipl ACVIM (Internal Medicine)

  • 1.

    Laflamme DP, Backus RC, Forrester SD, Hoenig M. Evidence does not support the controversy regarding carbohydrates in feline diets. J Am Vet Med Assoc. 2022;260(5):506513.

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  • 2.

    Coradini M, Rand JS, Morton JM, Rawlings JM. Effects of two commercially available feline diets on glucose and insulin concentrations, insulin sensitivity and energetic efficiency of weight gain. Br J Nutr. 2011;106(suppl 1):S64S77. doi:10.1017/S0007114511005046

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  • 3.

    Zini E, Osto M, Franchini M, et al. Hyperglycaemia but not hyperlipidaemia causes beta cell dysfunction and beta cell loss in the domestic cat. Diabetologia. 2009;52(2):336346. doi:10.1007/s00125-008-1201-y

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  • 4.

    Link KR, Allio I, Rand JS, Eppler E. The effect of experimentally induced chronic hyperglycaemia on serum and pancreatic insulin, pancreatic islet IGF-I and plasma and urinary ketones in the domestic cat (Felis felis). Gen Comp Endocrinol. 2013;188:269281. doi:10.1016/j.ygcen.2013.04.029

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  • 5.

    McCann TM, Simpson KE, Shaw DJ, Butt JA, Gunn-Moore DA. Feline diabetes mellitus in the UK: the prevalence within an insured cat population and a questionnaire-based putative risk factor analysis. J Feline Med Surg. 2007;9(4):289299.

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  • 6.

    Öhlund M, Egenvall A, Fall T, Hansson-Hamlin H, Röcklinsberg H, Holst BS. Environmental risk factors for diabetes mellitus in cats. J Vet Intern Med. 2017;31(1):2935. doi:10.1111/jvim.14618

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  • 7.

    Sallander M, Eliasson J, Hadhammar A. Prevalence and risk factors for development of diabetes mellitus in Swedish cats. Acta Vet Scand. 2012;54(1):61. doi:10.1186/1751-0147-54-61

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  • 8.

    Slingerland LI, Fazilova VV, Plantinga EA, Kooistra HS, Beynen AC. Indoor confinement and physical inactivity rather than the proportion of dry food are risk factors in the development of feline type 2 diabetes mellitus. Vet J. 2009;179(2):247253. doi:10.1016/j.tvjl.2007.08.035

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  • 9.

    Laflamme DP, Abood SK, Fascetti AJ, Fleeman L, Freeman L, Michel K. The effect of age on how cats are fed. Abstract in: Proceedings of the World Small Animal Veterinary Association World Congress. World Small Animal Veterinary Association; 2008.

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  • 10.

    Laflamme DP, Abood SK, Fascetti AJ, et al. Pet feeding practices of dog and cat owners in the United States and Australia. J Am Vet Med Assoc. 2008;232(5):687694.

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  • 11.

    Nguyen PG, Dumon HJ, Siliart BS, Martin LJ, Sergheraert R, Biourge VC. Effects of dietary fat and energy on body weight and composition after gonadectomy in cats. Am J Vet Res. 2004;65(12):17081713. doi:10.2460/ajvr.2004.65.1708

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  • 12.

    Backus RC, Cave NJ, Keisler DH. Gonadectomy and high dietary fat but not high dietary carbohydrate induce gains in body weight and fat of domestic cats. Br J Nutr. 2007;98(3):641650. doi:10.1017/S0007114507750869

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    Pereira-Lancha LO, Coelho DF, de Campos-Ferraz PL, Lancha AH Jr. Body fat regulation: is it a result of a simple energy balance or a high fat intake? J Am Coll Nutr. 2010;29(4):343351. doi:10.1080/07315724.2010.10719850

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  • 14.

    Farrow HA, Rand JS, Morton JM, O’Leary CA, Sunvold GD. Effect of dietary carbohydrate, fat, and protein on postprandial glycemia and energy intake in cats. J Vet Intern Med. 2013;27(5):11211135. doi:10.1111/jvim.12139

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  • 15.

    Jeremias JT, Nogueira SP, Brunetto MA, et al. Predictive formulas for food base excess and urine pH estimations in cats. Anim Feed Sci Technol. 2013;182(1-4):8292.

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  • 16.

    Funaba M, Uchiyama A, Takahashi K, et al. Evaluation of effects of dietary carbohydrate on formation of struvite crystals in urine and macromineral balance in clinically normal cats. Am J Vet Res. 2004;65(2):138142. doi:10.2460/ajvr.2004.65.138

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  • 17.

    Kass PH, Peterson ME, Levy J, James K, Becker DV, Cowgill LD. Evaluation of environmental, nutritional, and host factors in cats with hyperthyroidism. J Vet Intern Med. 1999;13(4):323329.

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    Köhler I, Ballhausen BD, Stockhaus C, Hartmann K, Wehner A. Prevalence of and risk factors for feline hyperthyroidism among a clinic population in Southern Germany. Tierarztl Prax Ausg K Kleintiere Heimtiere. 2016;44(3):149157.

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    McLean JL, Lobetti RG, Mooney CT, Thompson PN, Schoeman JP. Prevalence of and risk factors for feline hyperthyroidism in South Africa. J Feline Med Surg. 2017;19(10):11031109.

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  • 20.

    Bree L, Gallagher BA, Shiel RE, Mooney CT. Prevalence and risk factors for hyperthyroidism in Irish cats from the greater Dublin area. Ir Vet J. 2018;71:2. doi:10.1186/s13620-017-0113-x

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  • 21.

    Singh S, Gamlath S, Wakeling L. Nutritional aspects of food extrusion: a review. Int J Food Sci Technol. 2007;42(8):916929.

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    Ciudad-Mulero M, Fernández-Ruiz V, Cuadrado C, et al. Novel gluten-free formulations from lentil flours and nutritional yeast: evaluation of extrusion effect on phytochemicals and non-nutritional factors. Food Chem. 2020;315:126175. doi:10.1016/j.foodchem.2020.126175

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Ventral versus lateral approach for mandibular and sublingual sialoadenectomy in dogs

I wish to thank Dr. Swieton and her coauthors for their recent article.1 Their results appear to demonstrate that, at least for original sialocele surgery, there is probably no strong need for extensive rostral dissection to remove the entire course of the mandibular/sublingual duct and all of the polystomatic salivary glands to achieve a satisfactory outcome. In their description of the lateral approach they indicate that the duct was ligated and transected at the level where the lingual branch of the trigeminal nerve was identified. They did not comment on the methods that were used by the surgeons involved for getting far enough rostral to the digastricus muscle to permit this identification. The literature describes both transection of the muscle as well as the more elegant or less traumatic passage of the duct from lateral to medial around the digastricus to facilitate this, along with simply retracting the digastricus. It would be helpful to the reader to know whether these or any other methods were employed during the lateral approaches that were performed in this study. Furthermore, in the descriptions of the 2 approaches in their materials and methods, there was no mention of drain placement for either technique, whereas in the results it was apparent that some dogs did have postoperative drains. It would be helpful as well to know how many and what types of drains were used for each surgical approach and whether, for each approach, the decision to not place a drain in any way adversely affected the outcomes (the authors did report that use of a drain increased hospitalization time).

James M. Fingeroth, DVM, Diplomate ACVS

Orchard Park Veterinary Medical Center

Orchard Park, NY

1.

Swieton N, Oblak ML, Brisson BA, Singh A, Ringwood PB. Multi-institutional study of long-term outcomes of a ventral versus lateral approach for mandibular and sublingual sialoadenectomy in dogs with a unilateral sialocele: 46 cases (1999–2019). J Am Vet Med Assoc. 2022;260(6):634642.

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The authors respond

Thank you very much for your interest in our study and thoughtful questions. With respect to the methods involved in dissecting the salivary duct/gland complex rostral to the digastricus with the lateral approach, there was little description in the medical records of how this was achieved. In speaking with 2 of the individuals who performed the lateral approach, they indicated that dissection cranial to the digastricus was not possible with this approach and retraction was used to achieve visualization prior to amputation. The majority of the cases performed by a lateral approach in this study were performed by these individuals. We acknowledge this contributes to heterogeneity within each technique group and is a limitation of this retrospective study, but as our goal was to compare whether rostral dissection and therefore removal of the complete sublingual gland/duct complex affects local recurrence, we do not believe that this is an important factor in the utility of this study. In addition, since the goal of our study was not to describe the surgical technique itself, we would encourage you to consult previous publications for a more thorough surgical description.

On the basis of our results, we cannot make the argument that dissection and removal of the entire duct is necessary, although anecdotally we have seen cases where the sialocele appeared to be originating more rostrally in salivary tissue that was present rostral to the lingual nerve. In those cases we were performing a ventral approach and full dissection so we cannot know for sure whether this patient would have experienced local recurrence with a less-extensive dissection. Unfortunately, due to the retrospective nature of this study and lack of techniques to preoperatively identify the origin of the sialocele, we cannot make further recommendations for one technique over the other, aside from stating that the best technique is likely the one with which the surgeon is most comfortable. Notwithstanding, if a ventral approach is elected, the additional dissection to follow the duct to the oral cavity is minimal and will remove all salivary tissue.

To address your second question, drains were placed in 8 of 15 (53%) dogs with the ventral approach and 11 of 31 (35%) dogs with the lateral approach in this study. Drain usage appeared to be based on surgeon preference rather than specific patient characteristics. Closed suction drains were utilized in all ventral approach cases and in dogs with the lateral approach, 5 drains were closed suction, 3 were penrose drains, and the type was not available in 3. Only 1 drain was placed per sialoadenectomy procedure. Two dogs with the ventral approach developed a seroma postoperatively: one that had a closed suction drain removed 2 days prior to seroma development and the other without a drain. None of the dogs with the lateral approach developed postoperative seromas. Due to the low incidence of postoperative seroma formation, our results did not support that drain placement had an influence on outcome. This question would be an interesting topic of future prospective study.

Natalie Swieton, MSc, DVM

Michelle Oblak, DVM, DVSc, Diplomate ACVS-SA

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