I know reduced sex drive is a common side-effect of "calorie-restriction with optimal nutrition (CRON)". Is it caused by cortisol or overall not getting enough calories?

Either way, my own advice is

1. Don't fast until the problem goes away
2. Add more calories
3. Give yourself at least two days of rest a week
4. Be less strict with paleo. The addition of yams or dairy might help.
5. There is evidence that proximity to new hot women can increase testosterone.
6. Less running. Ladies...when was the last time you saw a long-distance runner that was "hot?"
7. More strength training. I don't do Crossfit, but it seems many hot guys do.

When I was eating SAD and running competitively I never noticed a reduction in sex drive. If anything I have always found that moderate exercise enhances it. Maybe you are going beyond the level that is optimum for health?

I did experience a dramatically-lowered sex drive once, when trying out a low-fat CRON-ish diet (Melissa mentioned that already). It's very obvious when it happens, not easy to miss. May take some time to recover if you are coming from a vegetarian diet.

Would a PaNu diet affect reproduction? Kurt Harris says:

Insulin is a phylogenetically old hormone. It is a biological messenger that in excess, is metabolically saying the following to your tissue and organs: "Go ahead and store energy, mature, reproduce and die." source article

Does such a message at the cellular level directly correspond to reproduction at the organism level? Doubtful, although you can find interesting research in that vein if you dig around:

Since the phenotype of leptin-deficient ob/ob and leptin-resistant db/db mice is also characterized by hypothalamic hypogonadism, deficiency of either leptin or insulin action in the CNS is sufficient to impair reproduction. source article

Would be interesting to know how much insulin affects sex drive.

EDIT: Here is an excerpt of some notes from GCBC I was just reading:

The Carbohydrate Hypothesis, III: Hunger and Satiety

• nutrition and fertility are closely linked
  • Le Magnen's hypothesis implies that fertility is mainly influenced by the immediate availability of fuel, not by body fat stores
  • experiments confirm: animals become infertile without food (regardless of body fat); the more food, the more fertile
    • insulin stores fuel (makes it unavailable): infusing insulin into animals shuts down their reproductive systems
• thus, low-carb has clear implications for infertility treatment

Fertility is not the same as sex drive obviously, but quite interesting nonetheless

It is said that excessive steady state cardio can lower testosterone, which would lower libido.

Here is one of many articles that reports this, but without references. I'll comment back later if I find any more solid evidence.

Long hours of exhausting exercise, sometimes called 'chronic cardio' is not considered a paleo type of lifestyle. According to paleo thought processes, this is an unnatural strain on the body and exercise in moderation is preferred. If you look at hunter gatherer societies, most types of daily work and exercise are not of the glycogen depleting kind.
-Eva

J--

Stress and fertility are intimately tied pun intended.

Going paleo and/or lower carb can be 'stressful..' unfortunately. If you followed strict panu, the carbs may have been too low combined with the lack of keto-adaptation which dpending on one's hormonal status/stress/sleep, may take 2-4 months from what I've read.

Personally I burned my adrenals out with excessive IF, ketosis, caffeine then a nasty bike spill.

I suspect your adrenals are burnt. The adrenals produce the sex hormones -- pregnenolone, dhea, testosterone and progesterone.

Consider some alleviation for adrenal fatigue -- listen to Andy Deas (he has good advice) from the Robbwolf.com podcasts.

What helps that I found is:

--rest relax yoga sleep and more sleep

--do NOT underestimate the value of UNDERTRAINING for better/optimal recoveries and limiting organ damage/injuries. Limit strong lifting to once every 10 days. Eat some carbs prior to anaerobic work until things are better. Skip IF (intermittent fasting) or ketosis until your testosterone is back on track like 1-3 months.

--vitamin C 2 g twice daily or more (adrenals use this up like candy to produce adrenalin for the times your body is feeling poopy and for endurance events) American Indians avoided scurvy in the winters buy cutting up the adrenals of hunted prey and divide up pieces for each tribe member. Adrenals are the richest organ source of vitamin C.

--adaptogens (Gaia adrenal is excellent -- in < 1 wk it kicked in)

--low dose activated B complex (ultrabotanicals and jarrow's are good)

--vitamins ADEK1 K2

--eat essential fats incl cholesterol, saturated fats, ALA, and omega-3 fish oil EPA + DHA (taking 7g lowered/normalized cortisol in stressed men, Poliquin wrote about once -- haven't dug out that article). Cholesterol is the precursor of cortisol and all the sex hormones.

--pantothenic acid 1 g twice daily (precursor to AcCo -- the energy substrate of mitochondria)

--maca -- do you know about the magic of maca? it's an adaptogen from peruvian tubers (like ginseng) which is rich in b-vitamins and plant sterols. It helps with not only adrenals but gonadal and thyroid function. it keeps me 'perky' haa and I aint talkin only my adrenals...

Hope you better soon... That s*cks...!!

-G

Not to be blunt, but what are your goals with your nutrition? Do you want to enhance your running or your sex life? You say that you "generally feel fine doing this" but here you are complaining that, in fact, you don't.

Are you sure you're eating enough protein to support your athletic activities? How much per pound of your bodyweight? High fat and lower protein is fashionable in the low-carb and paleo worlds right now, but that doesn't mean that it will actually work for you.

Your total calories and protein are not at all clear from any of your comments or from your original question. Are you actually eating enough, full-stop? Are you sure? How many calories? What is your actual workout volume per week?

Re: cortisol

I was fortunate enough to be able to attend Robb Wolf's Paleo Seminar on Saturday, and I got to ask him my big question. The answer does involve cortisol, so maybe it will be meaningful to you in some way.

I have found that I cannot shed fat on a ketogenic diet. I could when I was fat, but I can't now that I've only got a few pounds of fat that I'd like to turn into muscle. I feel good once I get keto-adapted, and while I'm slow to get going while working out, once I do, I do fine. The problem is that I do not make progress, and I stay sore for days after a big workout. I also get a reduced effect from my thyroid meds and progesterone supplementation, so all manner of important hormones are being effected and not positively!

I don't mind eating closer to Cordain's recommendations in The Paleo Diet - in fact, I much prefer it, but I could not understand why low-carb paleo would cause me to look, feel and perform worse than higher carbs and protein and lower fat. According to Robb, forcing your body to get sugar out of protein increases cortisol. We all know what that does to your body shape, and none of our hormones act alone.

So, it's possible your whole program is actually stressful and is suppressing sex hormones.

Jason,

Are you still vegetarian? I think it is possible but VERY very very hard since both Neanderthals and modern humans show evidence in 13C and 15N isotopes that our ancestors resemble obligate carnivores for the last 20 to 100,000 years ago prior to neolithicism... (Trinkaus et al PNAS 2009; Trinkaus et al PNAS 2000). imho We are not adapted well to 100% veg omnivorous yet.

fyi Vegetarian diets are the fastest way to kill adrenal glands... and thyroid... and gonads...

http://educate-yourself.org/cn/adrenalburnout19apr05.shtml

The above link is from Dr. Larry Wilson MD, a low carb, minimal fruit, no cow dairy/no grains evo/paleo type practitioner. There are other good threads here at paleohack on veg. diets you might consider checking out like HERE and HERE.

Are you consuming soy? Soya affects sex hormones and contains HIGH amounts of xenoestrogens and goitrogens -- makes boys into girls and girls into boys (e.g. PCOS).

-G

There has been lots of good answers here, I'll just add my personal experience... I am an endurance athlete (cyclist). I notice a BIG difference if Im riding a lot or if Im in the gym lifting heavy weights in the winter. Much more sex drive when im riding less.

I can only speak from experience, but when I went on a chronic cardio state and lost a bunch of weight, I might as well have been neutered. I came back to a more "normal" weight (i.e. 165ish for a 5'11" 34 year old male) and recovered some drive. In the last month, I have adjusted my workouts and diet to be more conducive to some weight gain with more meat and some post workout squashes, more meat and fat while focusing more on lifting and a little less (still doing a fair amount) of running. Ummmmm. This last month I've rediscovered "it." Feeling pretty randy.

How lean are you? If you're too lean, your body just won't have enough fat to produce sex hormones. If you're utterly ripped and "sexy", you just might not feel as sexy. That's pretty much ^Tom R.'s experience, and maybe yours' too.

Yes there is an it has zero to do with if you are low or high carb. It has to do with pregnenolone steal syndrome. Here you can read about it with links to other places that give you a deeper understanding of why it happens and what you can do about it.

http://jackkruse.com/cellular-depletions-why-should-you-care/

Vitamin E is a powerful antioxidant that helps improve circulation. Apart from sexual desire itself, circulation is the most important component of sexual function.Endurance athletes don't need bulky muscles -- they'll only get in your way and add extra weight that will slow you down.Sex is a natural and enjoyable function of the body, and there are many vitamins that can help restore balance and increase stamina and endurance.