My immune system has been horrible since I got mono really bad about 17 years ago. I got every cold and flu that anyone around me had and then some. I did a little better when I was working out heavily, but still got sick pretty often.
Since I changed last year to a strict ketogenic diet (CKD), I haven't been sick once, except for seasonal allergies, but even that was milder than usual. I recently attended a week-long training class where 13 of the 23 students had full blown flu and I felt great all week. This would have been a death sentence for me prior to this diet.
The gist is that I eat few carbs and lots of fat. I've lost a lot of weight (wasn't big to begin with though) while retaining muscle, and have not increased my exercise. I feel great! Lots of energy, I think more clearly, I'm very satisfied after eating, never crave sugar, and get to eat lots of bacon! I miss drinking whole milk, but with how good I feel, it's worth the sacrifice. Since it's a cyclical diet, I load up on carbs once or twice a month, which satisfies any urges I have toward carbs and I get my whole milk fix. The few carbs I do consume regularly are incidental and generally come from cheeses or vegetables. This lets me afford to have beer regularly without knocking me out of ketosis.
I'm not saying this is for everyone, but it's certainly working in many ways and is a sustainable long term solution for me.
