AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 527-R535, Copyright © 1994 by American Physiological Society
Diet cycling and age alter weight gain and insulin levels in rats
B. E. Levin
Neurology Service, Department of Veterans Affairs Medical Center, East Orange, New Jersey 07018.
For assessment of the effect of diet cycling on body weight gain patterns,
3-mo-old male Sprague-Dawley rats were either cycled from chow to a
high-energy condensed milk (CM) diet, back to chow, and then back to CM
diet at 3-mo intervals (cyclers) or were fed chow to 9 mo of age and then
CM diet for 3 mo (noncyclers). Nine of 21 cyclers developed diet-induced
obesity (DIO), gaining 36, 59, and 281% more weight than chow-fed controls
(CF) at each cycle, respectively. Twelve cycled rats were diet-resistant
(DR) with comparable weight gain to CF rats after the first CM diet and
chow cycles. However, they gained 202% more than CF rats and 50% more, with
29% heavier retroperitoneal fat pads, than noncycled DR rats after their
second CM diet cycle begun at 9 mo of age. Enhanced weight gain in DR
cyclers was probably due to enhanced food efficiency in the last few weeks
of CM diet intake. Plasma insulin levels were 70% higher in cycled vs.
noncycled DIO and DR rats, and both were higher than CF rats. Unlike
6-mo-old DR rats in a prior study, 12-mo-old noncycled DR rats after 3 mo
on CM diet here had 45-172% higher alpha 2-adrenoceptors binding in 6 of 17
brain areas than noncycled DIO and/or CF rats. Thus age, diet cycling, and
brain alpha 2-adrenoceptors interact to affect long-term changes in weight
gain and metabolism.
