My track coach banned caffeinated drinks like RedBull because of the inconsistency it can create; example- my teammate would run a 44 second 400m dash consistently, one day he tried redbull before one of his races, he ran a 42.5 (granted that's not all redbull's work), the next time he tried redbull in a race he ran a 47.8, the time after that he ran a 43.1, then he ran a 46.9. The point here being was that you had no idea how he would perform because either he would crash or get that "boost".
That can't be said definitively. There are too many variables to be able to blame caffeine for his performance.
And don't forget dehydration.
Boy, nobody ever gets dehydrated. Dehydration also effects performance too.
And with all that being said, caffeine isn't proven to be bad for you in moderation 1-2(though that's pushing it) cups a day
200-400mg which equal to roughly 2-4 cups of coffee is recommended dosage. 500-700mg (4-7 cups of coffee) can start to show side effects and/or possible adverse health effects. (Can be higher depending on your tolerance)http://www.mayoclinic.com/health/caffeine/NU00600
Also.. fat loss supplements are crap, but don't take my word for it, I'm just very biased because all they do is either a) dehydrate you b) dehydrate you or c) **** up your metabolism and cause hormone level abnormalities see hypothyroidism for example
It works fine as a weight loss supplement. Also why aren't 1/2 the people in the US including me suffering from hypothyroidism? Caffeine interfers with T3 levels for only a short period of time.http://www.obesityresearch.org/cgi/content/full/13/7/1195http://184.108.40.206/search/cache?ei=UTF-8&p=caffeine+cause+hypothyroidism&fr=yfp-t-501&u=www.csa.com/discoveryguides/thyroid/overview.php&w=caffeine+cause+hypothyroidism&d=fI16e_H_QdUx&icp=1&.intl=us
increasing the risk of heart disease
eating mcdonalds does but that doesn't seem to stop people
Filtered coffee doesn't which is what a majority of people drink.http://articles.mercola.com/sites/articles/archive/2001/02/28/coffee-cholesterol.aspx
stay with in the 200-400mg range, be active and you will be just fine.
arrhythmias and stress levels
Those are properties of caffeine, no big deal, take lower dosages if you want to avoid those effects