EFFECTS OF A DIETARY LOAD OF ACID OR BASE ON CHANGES INDUCED BY LACTOSE IN RATS

Feeding lactose or other slowly digestible carbohydrates to adult mamm als may induce a variety of effects including hyperplasia and neoplasi a. The most fundamental effect probably is the increased production in the large intestine of short-chain fatty acids (SCFA) resulting from increased fermentation of carbohydrate residues. To find out whether t he increased production of these acidic compounds is involved in the i nduction of certain alterations caused by low-digestibility carbohydra tes, the modifying effects of an acidifying (NH4Cl) or an alkalizing ( KHCO3) diet supplement on lactose-induced changes in rats were studied . Three groups of 50 rats per sex were fed a 20% lactose diet unsupple mented or supplemented with 1% NH4Cl or 2% KHCO3, for at most 2.5 yr. One control group was fed the basal diet which contained wheat starch instead of lactose. Feeding lactose resulted in wet faecal pellets, re duced pH of the faeces, higher intake of food and water, lower body we ights, increased caecal weights and fewer deaths. These effects were n ot significantly modified by NH4Cl or KHCO3. Feeding lactose increased urinary calcium levels, the effect being enhanced by NH4Cl and reduce d by KHCO3. Lactose also tended to increase blood values of alkaline p hosphatase and to decrease those for bicarbonate and base excess. Thes e tendencies were generally more marked with NH4Cl, and less marked or absent with KHCO3. In addition, rats fed lactose showed decreased sev erity of nephrosis, increased mineralization and hyperplasia of the re nal pelvic epithelium, and relatively high incidences of Leydig cell h yperplasia and neoplasia. NH4Cl supplementation was associated with a relatively small number of single and multiple rumours, with decreased incidences of hyperplasia and mineralization of the renal pelvis epit helium and with a markedly reduced incidence of proliferative changes in the adrenal medulla. With the KHCO3 supplement the incidences of Le ydig cell proliferation and of bladder tumours were relatively high. T hese findings, in particular the differences between the diet groups i n urinary calcium levels and possibly also the variations in blood lev els of alkaline phosphatase, bicarbonate and base excess, suggest that the acidic end products of carbohydrate fermentation (SCFA) act as an acid load on the body.