Let $\Phi$ be a *Youngs's function*, i.e.
$$ \Phi(t) = \int_0^t \varphi(s) \,\mathrm d s$$
for some $\varphi$ satifying

- $\varphi:[0,\infty)\to[0,\infty]$ is increasing
- $\varphi$ is lower semi continuous
- $\varphi(0) = 0$
- $\varphi$ is neither identically zero nor identically infinite

and define the *Luxemburg norm* of $f:\Omega\to\mathbb{R}$ as
$$ \lVert f \rVert_{L^{\Phi}} := \inf \left\{\gamma\,\middle|\,\gamma>0,\,\int_{\Omega} \Phi\left(\frac {\lvert f(x)\rvert}{\gamma} \right)\,\mathrm{d}x\leq 1\right\}.$$

Question: What can we say about $\Phi\left(\lVert f \rVert_{L^{\Phi}}\right)$? In particular, I'd like to know, if $$\Phi\left(\lVert f \rVert_{L^{\Phi}}\right) \leq C \int_{\Omega}\Phi(\lvert f(x)\rvert) \,\mathrm d x$$ holds for some $C$ independent of $f$.

Any idea or hint for a reference is welcome!

**Notes**:

- The above inequality trivially holds for $\Phi(t) = t^p$, where $p>1$
- Maybe it's appropriate to consider this question in the more general framework of Musielak-Orlicz spaces. However, e.g. in Lebesgue and Sobolev Spaces with Variable Exponents I was unable to find an appropriate result.
- I have asked this question on Math.Stackexchange without luck, so I'm trying here.