I am 48.
What you are concerned with and suffering from has been a very common theme of late. Here are several previous threads, which may be of some use to you.
http://cathe.com/forum/f95/am-i-just-getting-old-289062/
http://cathe.com/forum/f97/help-my-body-has-shifted-menopause-289136/
http://cathe.com/forum/f97/need-advise-cathletes-help-288226/
I'll be a broken record. I seem to be saying this a lot -
There is no one magic recipe or perfect solution. We are all different, with different chemistry, and as you pointed out, different genetics. Aspects of some dietary programs may work for you, while other aspects may not. Same is true with exercise; some people need high intensity effort while others become depleted by it.
The key here is to discover what works for you.
Like you, I cannot go carbohydrate free. I, too, lose energy and become lethargic, and I’ve discovered I also start to become a little –uh – too fragile, emotional, and overly sensitive. Our bodies and brains need carbohydrates for fuel, for repair, and for hormone productions.
It is worthwhile logging your calories and your macro’s on a nutrition tracking website to see where you are at with your energy in and energy out.
I attempt to keep my carbs and protein fairly balanced. I feel best when the ratio is close to 2:1...carbs to protein. What does this look like. 4 oz of protein with 50 grams of carbohydrate. I eat a good quality fat at each meal, 10 grams is about the right amount for me. (I just stumbled across this blog – that was informative – and echoes my experience:
Serotonin and the Carbohydrate to Protein Ratio – 180 Degree Health) I had a good laugh when I realized, just now, that my total ratios usually are very close to Sear's "Zone."
Much to my dismay I felt a lot better when I stopped running. I was becoming too depleted by long, sustained runs. I do a lot more weight lifting and a moderate amount of medium intensity cardio.
Finding that perfect balance is an ongoing puzzle. For example, if everything else stays the same – energy in/energy out – and I make a little change like I eat too many nuts or don’t take the dogs for a walk - the scale goes up.
But here are specifics for what is working for me (broken record, again):
I’ve had to eliminate – by exhaustive personal trial and error – the following foods:
Cow Dairy
Sugar in all forms – including fresh fruit, dried fruit, agave nectar
Corn
Legumes, especially peanuts
Grains (wheat –especially white flour, gluten grains...and lately even brown rice, but YMMV*)
Coffee and black tea
---what does that leave? ----
Veggies, eggs, and potato for breakfast
Veggies, salmon and sweet potato (yam) for lunch
Large green salad, protein of some variety for dinner
And Bowl of oatmeal at bedtime (to which I add 1 tsp coconut oil, ground flax seed, cocoa powder and stevia)
I hope this helps you on your personal journey.
Report back your own findings when you have the time. I know I'd like to hear what you've discovered.
(*YMMV- your mileage may vary)