Guar gum and cat age both shift nutrient availability in cats

Why the question mattered in the 1990s#

By the mid 1990s, dietary fibre had become a major topic in human nutrition research, with a body of published work linking soluble and insoluble fibres to various metabolic and intestinal effects. Soluble fibres such as guar gum and pectin were understood to behave differently from insoluble fibres such as wood cellulose or wheat bran: the soluble types tend to slow absorption in the small intestine, lengthen gut transit time and ferment readily in the colon, while insoluble types speed passage, resist fermentation and bulk out the faeces.

Far less had been published on fibre and cats specifically, even though canned cat food commonly contains soluble fibres such as guar gum, carrageenan, carob and xanthan as gelling agents to give the product its texture. Harper and Siever-Kelly set out to fill part of that gap, examining how a modest level of guar gum supplementation affected feed intake, the apparent digestibility of macronutrients, and faeces quality in healthy adult cats. They also deliberately recruited cats across a wide age span, since questions about digestive decline with age, and its implications for senior cat diets, were of direct commercial interest.

How the trial was designed#

The study used 48 healthy adult cats, 18 neutered males and 30 entire females, with a mean bodyweight of 3.7 kg, drawn from an age range spanning roughly a year and a half of age up through 13 years old. Before testing began, every cat received a dental check and, where needed, a teeth clean, plus a veterinary examination and blood tests covering routine biochemistry, haematology and thyroid hormones. All animals tested negative for feline immunodeficiency virus and feline leukaemia virus.

The cats were split into six age groups of eight animals each, spanning 1.5 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10 and 12 to 14 years. Each cat was fed, in turn, a standard canned Whiskas diet (total fibre content 0.2%) and the same product with 0.4% guar gum added (bringing total fibre to 0.6%), in a balanced design across two four-week feeding periods. Each diet exposure comprised a one-week pre-feed followed by a three-week faeces collection period, treated as three separate one-week collections so that three digestibility values were generated per diet for each cat.

Food was offered freely with water always available, and intake was recorded daily. Faeces were graded for consistency on a scale running from a very hard, dry motion at one end to diarrhoea at the other, then homogenised, freeze-dried and analysed for the same proximate nutrients measured in the diets. Comparisons between the two diets used paired t tests, while age-related patterns were examined first with simple regression and then, where a linear pattern was confirmed, with one-way analysis of variance across the six age groups.

What the fibre did and did not change#

Adding 0.4% guar gum made no significant difference to how much food the cats ate, across any age group. Mean food intake was 207 g/d on the standard diet and 280 g/d on the guar gum diet, and apparent digestible energy intake was similarly unaffected overall: 203.6 kcal/d on the standard product against 198.6 kcal/d with guar gum added.

Where the fibre did make a measurable difference was in protein digestibility, which was significantly reduced by the guar gum addition, most clearly in the 4-6, 8-10 and 12-14 year age groups. Fat, organic matter and energy digestibility all showed a similar downward trend with guar gum, though none of these reached statistical significance. The authors noted that even with these reductions, all digestibility coefficients stayed within normal ranges for the species.

Faeces quality showed a comparable pattern: there was a tendency toward wetter, poorer-quality faeces on the guar gum diet, and toward higher wet faeces output per 1000 kcal of digestible energy eaten, but neither effect reached statistical significance. The paper attributes the protein effect to the way guar gum raises the viscosity of gut contents, a property reported elsewhere to slow gastrointestinal transit and limit how well digestive products reach the gut wall.

What ageing did on its own to nutrient availability in cats#

Independent of which diet was fed, age had its own clear effects. Food intake climbed steadily with age, with cats in the oldest group (12-14 years) eating significantly more of either diet than cats in the other five age groups. At the same time, digestibility of protein, fat, organic matter and energy all fell steadily as age increased, a pattern confirmed statistically for both the standard diet and the guar gum diet.

The authors interpret these two trends together: older cats with reduced digestive efficiency appeared to compensate by eating more, which kept their apparent digestible energy intake broadly stable across the age range and explains why bodyweight did not change significantly over the nine-week trial for any cat, nor varied systematically with age.

Wet faeces output (per 1000 kcal of digestible energy eaten) climbed with age on both diets, a pattern the paper links directly to the decline in digestibility in older cats. Faeces consistency scores themselves, however, were not significantly affected by age.

How much weight these findings can carry#

The trial design has real strengths for a feeding study: a reasonably large sample of 48 cats, a wide age spread split into defined groups, triplicate faeces collections per diet per animal, and paired comparisons that let each cat act as its own control. Veterinary and blood screening before the trial also gives some confidence that the animals were a genuine cross-section of ageing cats rather than an unusually healthy or unhealthy subset; three cats showed mildly abnormal biochemistry suggestive of early kidney changes but were kept in the analysis as plausibly typical of older cats.

That said, we would treat the non-significant trends in fat, organic matter and faeces quality as suggestive rather than settled, since the paper itself reports these as trends only, not statistically confirmed effects. The guar gum inclusion level tested, 0.4%, was chosen as roughly the practical ceiling for a canned product before texture problems appear, so the results describe a commercially realistic but narrow dose range rather than a dose-response curve across higher fibre levels.

The study also sits within a single research setting using one commercial product line, which limits how far the specific digestibility figures can be generalised to other diets or fibre sources.

How this fits with earlier work#

The paper places its guar gum findings alongside earlier work on carrageenan in semi-purified cat diets, which reported a similar depression of nutrient digestibility that became more marked as the fibre inclusion level rose. It also draws on broader literature linking soluble fibre viscosity to reduced protein digestibility across species, consistent with the mechanism proposed for the drop seen here.

On ageing, the authors contrast their results with an earlier conference abstract that found no significant differences in digestive efficiency between cats aged around 1 year, 3-5 years and over 10 years, although even that study recorded a lower fat digestibility figure in its oldest cats than in its middle group. The present trial's larger, more finely graded age groups, and its use of regression rather than a simple three-way comparison, is offered as a possible reason for detecting an age effect where the earlier work did not.

The authors also tested, outside the main reported trial, diets containing 5% pectin, dried apples or dried sugar beet pulp, all of which cats refused, though they note the poor acceptance of the apple and sugar beet pulp diets may not have been due to fibre content alone.

What it suggests for diet formulation#

The practical implication the authors draw out most strongly concerns senior cat diets. Because protein digestibility fell with age independently of the fibre content of the diet, and because guar gum made this reduction worse, the paper recommends that protein levels in diets for older cats should not be cut back, and should at least match the levels used in adult maintenance products. This runs counter to a common formulation approach of reducing protein in senior diets as a precaution against compromised kidney function.

The authors also suggest that gelling agents such as guar gum should be kept to a minimum in products aimed at older cats specifically, given the combined effect of age and fibre on protein digestibility observed in this trial.

For readers following related nutrition and meat-quality research on this index, the present paper sits within a broader body of mid-1990s work collected in the RAAN Conference Proceedings and the wider Recent Advances in Animal Nutrition community, much of it concerned with how diet composition interacts with an animal's physiological state, a theme also explored from a different angle in the summary on glycogen metabolism in sheep and cattle.

Sources and further reading#

• Trove library search: find a library that holds the paper
• Feedipedia animal feed database: an open-access database of animal feeds

Questions#

— The Livestock Library team