This week, ending decades of confusing and often-contradictory dietary advice, the federal government finally issued its long-awaited Dietary Guidelines.

The guidelines urge Americans to avoid "tomatoes, peppers, mushrooms, or eggplants…. [because t]hey cause inflammation. What else? No coffee. No caffeine. No fungus. No dairy."

Oh, wait. Nevermind. That was Tom Brady's nutritionist, Allen Campbell, talking this week about what he cooks up for Tom, his supermodel wife, Gisele, and their family.

Instead, the new federal Dietary Guidelines, which the federal government updates every several years as "an important resource to help our Nation reach its highest standard of health," urge all Americans to adopt a healthier diet.

What does that mean, exactly? The definition of a healthy diet appears to be much like the date on which Easter falls: it's a moveable feast.

Cholesterol had long been painted as a villain in the federal guidelines. No longer. Coffee was of questionable merit. It, too, now gets the green light.

In their place, sugar and protein—the latter a surprise to many—have emerged as areas of concern.

Does this mean cholesterol and coffee are good, and that protein and sugar are bad? Maybe so. Maybe not. It depends.

Critics have long pointed out the many, many ways Dietary Guidelines have been wrong over the years. Every revision and update of those guidelines is, at least in part, an admission that some or all of the previous advice was flawed.

I have little problem, at the theoretical level, with the government proposing broad dietary advice, provided a couple things. First, the advice must be based on sound science. It's better to give millions of people no advice than to give them all bad advice. Second, the advice should recognize and embrace the fact that dietary choices are like snowflakes. No two are alike. And the guidelines should never attempt to coerce anyone to adopt a particular diet.

But these Dietary Guidelines fail on both counts.

First, there's the issue of bad science. The guidelines claim to be "informed by a critical, and transparent review of the scientific evidence on nutrition."

I spoke with two key critics of the federal government's development of dietary advice this week. I'd previously written pieces on the issue that quoted Nina Teicholz, science journalist, author of The Big Fat Surprise, and board member of The Nutrition Coalition, and Edward Archer, Ph.D., a researcher and leading author on dietary science.

"Clearly there is not 'significant scientific agreement' on several key recommendations made by the [Dietary Guidelines], so it's not clear that they meet the standard that Congress requires to appropriate funds for them," says Teicholz, in an email to me this week.

Teicholz points to the fact federal dietary recommendations for salt consumption conflict with the government's own research on salt and the "significant disagreement" over the science of saturated fat, which the federal government treats as a settled matter.

"Until our national health policy is based on solid science," Teicholz tells me, "it seems questionable that it will do a better job of fighting obesity, diabetes as well as other nutrition-related diseases."

Archer lobs a similar complaint.

"The greatest problem with the DGA is the confluence of intellectually inferior and scientifically incompetent research with the politics of self-interest enforced by the power of the Federal Government," Archer tells me, also in an email this week.

The lack of agreement about just what constitutes a "healthy diet," coupled with the legal and policy implications of that disagreement, have long made federal dietary recommendations a decidedly lousy effort.

This week, just before the Dietary Guidelines were released, both the New York Times and FiveThirtyEight, the ESPN-affiliated website headed by stats geek Nate Silver, published lengthy pieces exploring just what makes for the most effective diet.

The Times piece suggests that what's deemed healthy or unhealthy food is made up of the "best guesses" of experts, many of whom disagree with each other.

That's not necessarily because there's a right or wrong answer.

"[L]ife is complex," the article notes, "and… we are more than what we eat."

The FiveThirtyEight piece, by Brown University economist Emily Oster, concludes that no single diet appears significantly better than any other. Instead, writes Oster, "the particular diet you choose is likely less important than choosing one you can actually stick to."

I'm quoting Oster five days into a weeklong no-booze, all-liquid diet.* It's a great way to lose the pounds I gained over a holiday season spent gorging on anything and everything. It's a diet, but it's no diet I could (or should) stick to for any length of time. In that way, it very much resembles the ever-changing dietary advice served up by our federal government.

*Since you're no doubt wondering, dinner last night was homemade roast butternut squash soup made with cream, butter, chicken broth, and leftover bacon (pulverized sufficiently that I could count it as liquid). Breakfast this morning was a few gulps of plain, full-fat kefir. For lunch, I juiced a cucumber, an orange, three carrots, and a nub of ginger.