You told him he was hypogonadal (a medical diagnosis that may or may not be correct). Then you said that diet and exercise dont fix dysfunctional testes. (In the strict sense that may be true.) That it is clearly implying that his testes ARE dysfunctional and NOT implying that his hormones may be out of whack for a completely different reason and that his testes may work just fine.
So while a diet may not fix a broken HPTA, there is no way you can know that his HPTA is broken. Therefore it is a possibility that his condition can be postively affected by diet and exercise.
And losing excess bodyfat will be the first thing a doctor recommends. Or if not the first thing, at least before TRT is discussed.
OP for the trigs and cholesterol, watch carbohydrates. Reducing bodyfat will postively affect both of those things as well. Fish oil is a very good addition.
You may want to look into D-aspartic acid for the testosterone boosting effects. Biotest also sells an herbal testosterone booster.