It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term investors' portfolios.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

If you are looking to diversify your portfolio, consider Van Eck International Investors Gold A (INIVX). INIVX is classified as a Sector - Precious Metal fund, and these mutual funds invest in stocks with a focus on the mining and production of precious metals like gold, silver, platinum, and palladium. This fund is a winner, boasting an expense ratio of 1.31%, management fee of 0.65%, and a five-year annualized return track record of 28.2%.

Wasatch Global Value Investor (FMIEX Quick QuoteFMIEX - Free Report) : 1.1% expense ratio and 0.9% management fee. FMIEX is a Global - Equity mutual fund investing in bigger markets like the U.S., Europe, and Japan; these kinds of funds aren't limited by geography. With yearly returns of 13.3% over the last five years, FMIEX is an effectively diversified fund with a long reputation of solidly positive performance.

Emerald Large Cap Focused Inv (IAFMX). Expense ratio: 1.07%. Management fee: 0.7%. Five year annual return: 16.56%. IAFMX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.