Dietary calcium affects body composition and lipid metabolism in rats

Calcium (Ca) intakes may affect cardiovascular disease risk by altering body composition (body weight and fat) and serum lipid profile, but results have been inconsistent and the underlying mechanisms are not well understood. The effects of dietary Ca on body composition and lipid metabolism were examined in rats. Male Sprague-Dawley rats were fed high-fat, high-energy diets containing (g/kg) low (0.75Ca, 0.86 ± 0.05; 2Ca, 2.26 ± 0.02), normal (5Ca, 5.55 ± 0.08) or high (10Ca, 11.03 ± 0.17; 20Ca, 21.79 ± 0.15) Ca for 10 weeks. Rats fed the lowest Ca diet (0.75Ca) had lower (p < 0.05) body weight and fat mass compared to other groups. Rats fed the high Ca diets had lower serum total and LDL cholesterol compared to rats fed normal or low Ca. Liver total cholesterol was lower in rats fed high compared to low Ca. In general, liver mRNA expression of genes involved in cholesterol uptake from the circulation (Ldlr), cholesterol synthesis (Hmgcr and Hmgcs1), fatty acid oxidation (Cpt2) and cholesterol esterification (Acat2) were higher in rats fed higher Ca. Apparent digestibility of total trans, saturated, monounsaturated and polyunsaturated fatty acids was lower in rats fed the high compared to the low Ca diets, with the largest effects seen on trans and saturated fatty acids. Fecal excretion of cholesterol and total bile acids was highest in rats fed the highest Ca diet (20Ca). The results suggest little effect of dietary Ca on body composition unless Ca intakes are very low. Decreased bile acid reabsorption and reduced absorption of neutral sterols and saturated and trans fatty acids may contribute to the better serum lipid profile in rats fed higher Ca.

钙（Calcium, Ca）摄入可通过改变机体组成（体质量与体脂）及血清脂质谱影响心血管疾病风险，但现有研究结果并不一致，其潜在作用机制仍未被充分阐明。本研究以大鼠为模型，探究了膳食钙对机体组成与脂质代谢的影响。选取雄性斯普拉-道来（Sprague-Dawley，简称SD）大鼠，饲喂高脂高能量日粮，其钙含量（单位：g/kg）分为低剂量组（0.75Ca组：0.86±0.05；2Ca组：2.26±0.02）、正常剂量组（5Ca组：5.55±0.08）及高剂量组（10Ca组：11.03±0.17；20Ca组：21.79±0.15），连续饲喂10周。结果显示，饲喂最低钙日粮（0.75Ca组）的大鼠体质量与体脂量均低于其余各组（p < 0.05）。饲喂高钙日粮的大鼠血清总胆固醇与低密度脂蛋白（Low-Density Lipoprotein, LDL）胆固醇水平均低于正常钙或低钙日粮组大鼠。相较于低钙日粮组大鼠，高钙日粮组大鼠的肝脏总胆固醇水平更低。总体而言，饲喂更高钙日粮的大鼠肝脏中，参与循环胆固醇摄取的基因（Ldlr）、胆固醇合成相关基因（Hmgcr与Hmgcs1）、脂肪酸氧化相关基因（Cpt2）及胆固醇酯化相关基因（Acat2）的mRNA表达水平均更高。相较于低钙日粮组大鼠，高钙日粮组大鼠的总反式脂肪酸、饱和脂肪酸、单不饱和脂肪酸及多不饱和脂肪酸的表观消化率更低，其中对反式脂肪酸与饱和脂肪酸的影响最为显著。饲喂最高钙日粮（20Ca组）的大鼠，其粪便中胆固醇与总胆汁酸排泄量最高。本研究结果表明，除非钙摄入量极低，否则膳食钙对机体组成的影响并不显著。胆汁酸重吸收能力下降，以及中性固醇、饱和脂肪酸与反式脂肪酸吸收减少，可能是高钙日粮组大鼠血清脂质谱得到改善的潜在原因。