UK equity funds have had a tough time in recent years
Savers putting their money in funds investing in UK stocks and shares would have made more money since 2000 by putting it in savings accounts instead.
If £1,000 was invested at the start of the decade, it would now be worth £1,094 in an average UK unit trust but £1,358 in a typical savings account.
The research by Thomson-Reuters Lipper, commissioned by the BBC, questions the returns from long-term investments.
But industry experts say that timing was key to how much money can be made.
The same calculations, but up to July 2007, would have seen shares perform comfortably ahead of cash, according to Jane Lowe, director of markets at the Investment Management Association (IMA).
The exclusive research for the BBC found that £1,000 invested in a UK equity income fund would also have made less than in an instant savings account - now being worth £1,302.
But if anyone made the unusual decision at the time of investing in a commodities or natural resources fund eight years ago, their £1,000 would now be worth £3,260.
The fund management industry often suggested that over the long-term shares would outperform a typical savings account.
Ms Lowe said that stocks and shares were not an investment for those wanting to make a "quick buck".
"It is a longer term question of when you are putting your money in and when you are taking money out," she said.
She said it was difficult to predict the peaks and troughs of the market, but over the long-term this form of investment was still a better bet than savings accounts.
She suggested that people drip-feed their investments into funds to flatten out the cycle.
William Claxton Smith, of Insight Investments, also pointed out that over the last eight years interest rates have been relatively high in the UK, leading to better returns from savings accounts.