In a time when seemingly every kind of food or drink has something bad associated with it, you’d think at least water would escape unscathed. But one doctor reported in the British Medical Journal this July that advice to drink 8 glasses of water per day is “nonsense.” And drinking too much water could actually be harmful.

The lesson here isn’t that water is bad or that we shouldn’t drink it. Rather, it’s that the so-called experts on what we eat and drink can change their minds (and often do).

In the 1970s, eggs were considered unhealthy due to their cholesterol content. Since then, scientists figured out that dietary cholesterol isn’t the same thing as blood cholesterol, and the tables turned again: Eggs are now considered a health food.

Similarly, in the 1980s fat became the enemy and “low-fat” products spread like wildfire. Now that trend is starting to change as carbs are developing a stigma.

Despite how much money and expertise is poured into nutrition research, we should still be skeptical about jumping to conclusions about our food and health. Our understanding is always shifting, and it’s often muddled by activists with a dog in the fight.

Consider the case of high fructose corn syrup. People started to shun this corn sugar in favor of sugar from cane or beets after one hypothesis several years ago speculated that high fructose corn syrup might be especially fattening.

But once again, a nutritional about-face has occurred. Credible experts from the American Medical Association to the American Dietetic Association recognize table sugar and high fructose corn syrup are metabolized similarly by the body. And two authors of the original hypothesis later declared that sugar is sugar, whether it is made from beets, cane or corn.

These days, the newest party line is that we should reduce our intake of sodium. Sodium raises blood pressure, which in turn raises the risk of heart problems, or so the logic goes. Some “food police” activists want national salt control.

In reality, it appears that only 10 percent of the population is truly sensitive to sodium. Recently published research discovered that salt reduction in people diagnosed with heart disease is actually associated with a more than twofold higher risk of dying. Additionally, a 50 percent salt reduction was not associated with improved heart health in the general population.

And the conventional wisdom about fish consumption may soon change as well. According to a 2004 government advisory, pregnant women should eat at most two servings of fish a week due to the trace amount of mercury in seafood. Environmental and animal rights groups — concerned with preserving wild fish stocks — have latched onto this as a way to scare Americans away from eating fish.

But more than 100 experts signed an open letter last year asking the federal government to update its recommendations in light of newer research finding that the health benefits of eating fish far outweigh the hypothetical detriments. (There still hasn’t been a single case of mercury poisoning in the United States from commercially bought seafood.)

A 2007 Lancet study found “no evidence” for concern, and further discovered that of the 9,000 pregnant women studied, those who ate the most fish had kids with the highest IQs. (Japanese children eat plenty of tuna and seem to have little trouble with math.)

What else could lie on the food horizon? It’s hard to say. It may well turn out that saturated fat isn’t as bad as it’s made out to be.

Whatever the case, we should bet on “moderation” remaining the cornerstone of any diet. Anybody who tells you a food or ingredient is going to harm you generally has an agenda, and not your health, to promote.