|Image 1: Starving + indulgence, even without|
over-indulgence, leads to obesity. (Image from
Hieronymus Bosch's The Seven Deadly Sins
and the Four Last Things)
So, if high ghrelin levels make you eat everything that cannot escape fast enough, it seems quite obvious that this would be the underlying reason for obesity in rats injected with exogenous ghrelin.
This, however, was not the case in a recently conducted study by Perez-Tilve et al. from the Department of Internal Medicine at the University of Cincinnati (Perez-Tilve. 2011).
|Figure 1: Food intake of ghrelin injected or control rats on low fat or high fat diets. |
(data adapted from Perez-Tilve. 2011)
The scientists had administered intracerebroventricular ghrelin injections to two groups of rats. One group received a low-fat chow, while the other was on the famous high-fat diet scientists use to emulate our modern westernized gluttony (cf. yesterday's news, fig. 1). As expected, the rats that were fed the low-fat chow significantly increased their food intake (cf. Figure 1). Unexpectedly, though, ghrelin failed to statistically significantly increase food intake in the high fat diet group, yet ...
in rats fed the HFD, ghrelin nonetheless increased adiposity [fat mass increase of 14±2 g (ghrelin+HFD) vs. 1±1 g (saline+HFD), P<0.001] up-regulating the gene expression of lipogenic enzymes in white adipose tissue.These results are of great interest, because they clearly show that your typical "fast", where you diet really hard for a few days (and thus increase your ghrelin levels), until you get so ravenously hungry that you end up (deliberately or not) "refeeding" yourself with pizza and ice-cream set the scene for further undesirable fat gain by setting your body's metabolic switches to fat storage mode.