Reading through TheStreet.com's ratings this weekend, I came across something interesting:

Nutritional and personal care products developer USANA Health Sciences (NASDAQ: USNA) has been upgraded to a buy from a hold. Its revenue increased by 16.9% in the third quarter compared with the same period last year. Earnings improved to 70 cents a share from 55 cents per share over the same timeframe.

The company's return on equity improved to 184.53% in the third quarter compared with 78.97%, a signal of significant strength within the corporation. This return on equity greatly exceeds that of both the industry average and the S&P 500. USANA Health had been rated a hold since August 2007.

All of that is true and, as investors, we all know that a company that can earn high returns on equity is a wonderful thing indeed. If you don't believe me, take a look at the writings of Peter Lynch, Warren Buffett, Bill Miller, and just about any other great investor.

But at some point, a high return on equity becomes a red flag for fraud and/or an unsustainable business model. Can a company's management/business model be so amazing that the company can earn returns many times greater than industry peers or that market as a whole -- without any particularly important patents or competitive advantages to speak of? Does TheStreet.com really think that a ROE of 184.53% is sustainable? Are Dave Wentz and Gil Fuller (Usana's President and CFO, respectively) really more than eight times as good at deploying capital as Warren Buffett?

I somehow doubt it.

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