Claudia A. Kirk, DVM, PhD, DACVN, DACVIM
The role of carbohydrates in the pathogenesis of feline disorders such as obesity, diabetes mellitus (DM), lower urinary tract disorders, and gastrointestinal diseases (inflammatory bowel disease, pancreatitis) currently is a topic of considerable discussion.1,2 The consumption of carbohydrates pet foods have been implicated as contributors for the increased occurrence of these disorders and that feeding low-carbohydrate foods is indicated to prevent or manage these conditions.2 The primary purpose of this review is to summarize what is currently known about the role of carbohydrates in the pathogenesis of feline diseases and to review evidence supporting feeding low-carbohydrate (LC) foods.
Do cats have a requirement for carbohydrates?
Cats are carnivores that have adapted to foods higher in protein and lower in carbohydrate compared with other species (e.g., dogs). The natural prey of cats contains around 55% protein, 45% fat, and little carbohydrate (1–2%) on a dry matter basis (DMB).2 No requirement for dietary carbohydrates has been demonstrated for adult cats, but may be conditionally essential during gestation and lactation. Despite altered carbohydrate metabolism (e.g., low hepatic glucokinase activity, decreased intestinal and pancreatic amylase activity), cats efficiently use carbohydrates.3–5 Dry foods containing 40% or more dietary carbohydrates with an average digestibility of 85% are well tolerated by normal cats.
What effects does spaying or neutering have on nutritional requirements of cats?
Spaying or neutering cats have been shown to decrease metabolic rate and increase food intake, body weight, body condition score, and amount of body fat.7–11 In one study, energy intake increased by 25% within 4 weeks of gonadectomy and by 50% within 12 weeks.7
Does increased carbohydrate intake cause diabetes mellitus in cats?
Several studies have evaluated the potential role of carbohydrates in the pathogenesis of DM in cats. Summarizing key findings:
An epidemiological study of cats from the Netherlands14 found indoor confinement and low physical activity and not amount of dry food were associated with DM. High carbohydrate intake was not considered a risk factor for feline DM. But recent reports from these investigators have suggested an association of high carbohydrate foods with calcium oxalate urolithiasis.
In cats fed a high carbohydrate/low fat (HC/LF) versus low carbohydrate/high fat (LC/HF) food13, cats eating the LC/HF demonstrated reduced insulin responsiveness during glucose tolerance testing compared with cats eating the HC/LF food. Dietary fat appeared to be related to insulin resistance and weight gain more so than carbohydrate intake.
A study comparing the effect of a HC/low-protein food vs. a LC/high-protein food on glucose and fat metabolism in lean and obese cats before and after weight loss.12 Obesity, but not dietary protein or carbohydrate content, led to severe insulin resistance in cats.
Effects feeding different amounts of carbohydrate and fat were evaluated in 24 cats before and after gonadectomy.7 Cats were fed either 4%, 27%, 45%, or 56% carbohydrate (DMB) by free choice. 1) High concentrations of dietary carbohydrate did not induce weight gain or increased plasma glucose and insulin concentrations prior to gonadectomy, 2) gonadectomy resulted in increased food intake weight gain, in which high dietary fat appeared more important.
Another study comparing a traditional high carbohydrate fiber enhanced weight control food with a low carbohydrate diet found similar weight loss when caloric intake was restricted to the same level.6
Current published evidence does not support a direct cause-and-effect relationship between increased carbohydrate consumption and DM or obesity in cats.1
Are low-carbohydrate foods effective for managing diabetic cats?
Nutrition, weight control and insulin treatment play a key role in successful treatment of cats with DM. Feeding increased fiber, which may delay or decrease carbohydrate absorption from the gastrointestinal tract, has been associated with improved glycemic control in cats with DM. Studies using LC foods to improve diabetic control and increase DM remission rates are summarized below:
In an uncontrolled study of 9 the daily dose of insulin had been decreased in 5 of 9 cats and insulin was discontinued in 3 cats.16 However, 6 of 8 cats that had their insulin dosage lowered were not well controlled based on blood glucose and fructosamine levels.
Diabetic cats were fed a LC food alone (6 cats) or LC and acarbose (18 cats), an α-glucosidase inhibitor that impairs intestinal glucose absorption.17 Of the 24 cats, 15 (62.5%) no longer needed exogenous insulin. All cats showed improved glycemic parameters with significant decreases in serum glucose and fructosamine concentrations; however, the best response (discontinuation of insulin) was observed in obese cats.
A study of 63 diabetic cats compare feeding a moderate carbohydrate (MC) food with a LC food for 16 weeks15 reported, 68% of cats in the LC group and 41% of the cats in the MC group no longer required insulin; the difference between groups was significant (P = 0.031).
Findings from these 3 studies described demonstrate low carbohydrate foods are valuable in the management of DM in cats.
What amount of carbohydrates is ideal for managing cats with DM?
Although some clinicians strongly recommend that diabetic cats be fed < 7% carbohydrates (DMB), the evidence supports that amounts ranging from 5 to 26% of calories as carbohydrates are associated with diabetic remission and improved glycemic control.15–17 In fact, the highest reported remission rate has been associated with feeding 12% of calories as carbohydrates.15 There currently are no published studies to show that feeding < 12% of calories as carbohydrates is more beneficial in managing DM in cats.
Should all diabetic cats be fed low-carbohydrate foods?
Although some LC foods may be effective for maintaining glycemic control, they may not be ideal for all diabetic cats. To maintain caloric content of LC foods, the amount of protein and/or fat must be increased and therefore are not appropriate for some cat's protein or fat intolerance. Proteins, amino acids, and fat stimulate pancreatic secretions and may not be appropriate for cats with acute or active pancreatitis, severe hepatic disease or hepatic encephalopathy or clinical signs of uremia in cats with chronic kidney disease. One option for managing cats with DM and chronic kidney disease is to adjust insulin therapy and feed the moist version of a therapeutic renal food.
Cats are carnivores naturally adapted to HP/LC foods. Nonetheless, they are able to efficiently use carbohydrates.2–5 The role of dietary carbohydrates in the pathogenesis of feline diseases, particularly obesity and DM, is controversial. The causes are multifactorial and high dietary carbohydrates may have a more indirect role due to free-choice feeding of dry food and subsequent obesity, which is directly associated with insulin resistance. Healthcare team members need to make appropriate recommendations to help pet owners maintain ideal body condition in their cats throughout their lifetime. Once DM occurs, weight management along with LC diets has beneficial effects, including diabetic remission in cats consuming between 5% and 26% of calories from carbohydrates.
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