Dietary restrictions

Edit:  I've been limiting myself to drinking water only and it just might be the final step needed to get off these pills once and for all!

I went to a health screening recently as is required for my job to get a discount on insurance.  As usual, my numbers looked very good.
Height (no shoes) 5' 11"
Weight (clothes) 154 lbs.
BMI: 21.5
BP: 120/80
Cholesterol: 162
Triglycerides: 50
Chest: 38"
Waist: 29"
  The nurse even asked me if I was a runner because she said that it's usually the only time she sees numbers that good all the way around.  I am satisfied with how my body looks on the outside.  Of course, I'm thin but not so much that I look unhealthy. I'm often told by other runners that I "look fast." My BMI is right where it should be right now (20-25).  I was underweight when I was younger but have never been overweight.  I normally feel best around 155 lbs. but if I go above 160 or below 150, I can feel a difference.  Because I burn so many calories and I have a naturally high metabolism, I can eat pretty much whatever I want and as much as I want and I am still more likely to drop below 150 than get above 160.  There's not much threat of high cholesterol or triglycerides either.  When it comes to drinking, I'm not so lucky.  The following items must be avoided pretty much altogether: energy drinks, soda, sweet tea, coffee, liquor, beer, pretty much anything with sugar and/or caffeine or alcohol.
  As hard as it is to avoid all that, it can be tricky.  Just like anyone else on a diet, I can cheat every once in a while (maybe up to 1x per week) and get away with it.  The more that you get away with it, the more you feel that you can afford to cheat.  Then before you know it, you've re-gained 10 lbs. or in my case, slowed down by 10 sec/mile.  Over the last few months, I cheated about 1 in 3 days, sometimes as much as 1/2 and I've paid the price.  Again, I will stay accountable on this blog.  No more energy drinks period.  No more soda or tea period.  I never have liked coffee and don't want to stain my teeth.  As for alcohol, I can cheat for social gatherings or special occasions but those times must be rare (less than 2 times/month) with moderate consumption (no more than 3 beers).
  Recently, somebody posed a question regarding the effects of quitting soda on Runner's World Online.  Most reported that they have gone off and on with soda and though they felt better and lost weight while off, it did not significantly improve their running.  I've always run MUCH better when I go completely cold turkey and the greatest effects often come after 3-4 weeks.  Oh well, I guess everybody's different.  A lot of people say that they'd kill to be able to eat like I do and not gain weight.  Would they want to trade it for other tough dietary guidelines and the need to take precise amounts of pills which must be adjusted periodically and without notice?  I don't think so.
  I once read that quitting sugared drinks can improve your VDOT by up to 2 points with some benefitting more than others.  I figure that if I went out slower in Tupelo, I could have done a low-mid 41.  Without the 1/2 extra magnesium, possibly under 41:00.  That's about 50.5 on Daniels' VDOT scale.  52.0 is a 39:59.  Can it be done with this one change?