Hey Allen-
Being the Paleo Whore that I am I'm inclined to look for some answers to this question from that perspective.
Cordain makes the point that there is a seasonal ebb and flow to both total fat content and saturated fat content of wild game, with the peak for both occurring in the late fall:
http://www.thepaleodiet.com/faqs/#Fats
Total caloric intake, carbohydrate intake AND it would appear saturated fat intake can influence androgen levels in a few different ways. The first is raising or lowering total testosterone. The second is increasing FREE testosterone irrespective of total testosterone as a consequence of decreases in sex hormone binding protein (SHBP). If one buys into the seasonal availability of foods and the possibility that fertility in humans was historically tied to food availability, late fall would be the "go time" as relatively high levels of dietary carbohydrate, fat and saturated fat would be available.
If you buy into this perspective it makes sense that sat'd fat can increase testosterone levels.
As to Sat'd fats effects on LDL and heart disease I tend to fall back to the above information in that our ancestors simply did not get that much sat'd fat in the diet EVER, and the amount ingested was always a relatively low % as compared to mono's and polly's. That said it does appear that a very low insulin level may alter metabolism in such a way that high satd fat is either not or less harmful than under conditions of hyperinsulinism. Even under these scenarios its pretty easy to make the preponderance of one's fats come form mono's, even in a low carb situation.
As to the high protein leading to low testosterone levels...here is a guess. We have a protein ceiling of between 35-40% of calories. Above this intake level our livers can not deal with the urea that is a consequence of protein breakdown and we can experience protein toxicity commonly referred to as "rabbit starvation". Now this is a matter of %'s...so long as adequate fat or carbohydrate is present one can metabolize the protein. My guess is that once one reaches a certain protein intake this may register as a stresor as it would indicate inadequate food supply and the potential for impending starvation. Just a guess on this but it fits with the other information. I think it's interesting that protein recommendations for a 170lb male could range form a low of ~130g/day from a Zone perspective to 300g/day from a Cordain/paleo/John Berardi perspective. I think it particularly interesting that all recommendaitons deliver great results.
As always with science...more questions that answers.
Saturated Fat: Killer or Testosterone Booster?
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