Cosinor analysis of feed intake cycle of rats fed a zinc-deficient diet and the effect of zinc supplementation

Rats fed a Zn-deficient diet develop a characteristic cyclic variation in feed intake (Mills et al., Am J Clin Nutr 22: 1240-1249 (1969). A preliminary analysis (Tamaki et al., Br J Nutr 73: 711-722 (1995)) of the cyclic variations was followed with a personal computer. Cosinor analysis revealed that the cyclic period of the feed intake of male rats was 3.5 +/- 0.05 d. The mesor, amplitude and acrophase value were 10.0 +/- 0.3 g/d, 4.4 +/- 0.2 g/d and 3.5 +/- 0.3 radian, respectively. The cycle of body-weight change of the Zn-deficient rats was well synchronized with that of feed intake. The parameters of the feed intake cycle had a high correlation to the corresponding parameters of body-weight change (mesor: r = 0.846; amplitude: r = 0.771; period: r = 0.925; acrophase: r = 0.452). With the supplementation of Zn (0.95-3.80 mg/kg of the Zn-deficient diet), cyclic variations in feed intake and body-weight change were also found. The mesor, amplitude and period of feed intake cycle were is good correlation with Zn intake (r = 0.856, p < 0.001, r = 0.804, p < 0.001 and r = 0.613, p < 0.01, respectively). The cycle of feed intake of the rats fed a Zn-free diet was simulated to be: mesor 9.7 +/- 0.1 g/d, amplitude 6.5 +/- 0.1 g/d and period 3.4 +/- 0.02 d. The concentration of Zn intake given the half-maximal value of the amplitude was assumed to be 56 +/- 1 microgram/d.