In A Nutshell

Mother Jones has recently run a lovely article (reprinted on Alternet) about a suite of seven reports run in BMJ (formerly the British Medical Journal).

And who knew there was something called the Gatorade Sports Science Institute? According to the BMJ investigation, "one of GSSI's greatest successes was to undermine the idea that the body has a perfectly good homeostatic mechanism for detecting and responding to dehydration—thirst." The article quotes the institute's director as having declared, based on little reliable evidence, that "the human thirst mechanism is an inaccurate short-term indicator of fluid needs."

Another study in the BMJ package finds that the European Food Safety Authority, which is authorized to assess health claims in food labels and ads, has relied on a seriously flawed review process in approving statements related to sports drinks. A third study reports that hundreds of performance claims made on websites about sports products, including nutritional supplements and training equipment as well as drinks, are largely based on questionable data, and sometimes no apparent data at all. One overall theme emerging from the various papers is that much of the research cited was conducted with elite and endurance athletes, who have specific nutritional and training needs; any such findings, however, should not be presumed to hold for the vast majority of those who engage in physical activity.

[...]"Humans do not regulate fluid balance on a moment to moment basis," Noakes writes. "Because of our evolutionary history, we are delayed drinkers and correct the fluid deficits generated by exercise at, for example, the next meal, when the electrolyte (principally sodium but also potassium) deficits are also corrected…People optimize their hydration status by drinking according to the dictates of thirst. Over the past 40 years humans have been misled—mainly by the marketing departments of companies selling sports drinks—to believe that they need to drink to stay 'ahead of thirst' to be optimally hydrated."

So why do I care? Because this, in a nutshell, is what the entire nutritional and industrial food complex has spent the last half-century doing—lying to the consuming public.
How do we know? Well, for one thing, we've only done one proper experiment on nutrition, and that would be the famous vitamin C/scurvy study done by the British navy. That was the last time it was considered possible or moral to do human experimentation. Everything since then is best guess and supposition blown up by marketing departments.
What's worse, we can't even trust basic food like tomatoes and potatoes. Recent research has cast significant doubt on the nutritional content of foods. Most have seen distinct drop off in nutritional composition over the last fifty years—and yet the old data is what we're relying on to make "informed" dietary decisions.
Grow your own damn food. If you can't or don't want to, pay someone a reasonable amount to grow heritage varieties for you. It really is about that straightforward.