Biggest diet culprits: under-eating & low-carb
Based on my observations, asking many people here, and from my own experience, the two most common diet-related themes I've found with people who are still struggling with health problems at this forum are:
#1. Under-eating/calorie-restriction
#2. Low-carb/high-fat diets
I'm not saying everyone's health problems are caused by either of these two things, or that my findings & observations are necessarily accurate, it's just that in my attempt, these are the top two common diet-related traits I've found in people here that aren't improving, or getting worse. Most of my observations and the people I have asked have come from the AF, CFS, candida, and
parasite sections.
To make sure you're not under-eating, here's an official U.S. guide to how many calories people should at least be getting per day:
http://www.nhlbi.nih.gov/health/educational/wecan/healthy-weight-basics/balan...
If your life is very busy, stressful, or physically demanding, you may need even more calories per day than listed in the above link. Some simple ways to know you're getting enough to eat is you stop having food cravings at night and you're sleep stops getting disturbed.
If you've been on some kind of low-carb or high-fat diet and it doesn't seem to be working very well for you, I suggest trying a diet in the direction of high-carb/low-fat. How "low-fat" may depend on your body or circumstances, but "low-fat" is generally regarded as anywhere between 10-20% of total calories coming from fat, depending who you listen to.
Whatever diet you try, just make sure you're getting enough calories, or any diet will eventually fail you.
Other pieces of health advice, stay well hydrated and get plenty of rest.