Many investors tend to stick with what they know, or what they feel they can trust.

Most investors will invest in popular shares, many of which would receive frequent attention from the financial media and would typically account for a large portion of the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO).

A survey by the SelfWealth network recently showed how the typical SMSF portfolio is constructed. Although the results were hardly surprising, it is alarming to note just how conservative the typical SMSF owner is with their investments, which could hinder their returns over the coming years.

As you would expect, Commonwealth Bank of Australia (ASX: CBA) and its big bank brethren were among the most popular shares held by SMSF owners. Telstra Corporation Ltd (ASX: TLS), Woolworths Limited (ASX: WOW) and Wesfarmers Ltd (ASX: WES) were also widely held, while BHP Billiton Limited (ASX: BHP) was at the top of the list.

Source: SelfWealth

Source: SelfWealth

In fact, SelfWealth said that BHP had been at the top of the super investors’ most favoured stocks list, even despite the negative media commentary on the business and the risks surrounding its involvement in the mine disaster in Brazil that killed more than a dozen individuals.

Many of these SMSF owners would have enjoyed BHP’s strong run-up in price in recent months as commodity prices have rebounded, but that means many are now also vulnerable to a pullback in the event that commodity prices do not hold around their current levels.

Similarly, the banks are facing an uphill battle to continue growing earnings and dividends, while Woolworths is also struggling with falling margins and sales.

Of course, many investors will feel most comfortable holding some of these businesses in their portfolios, and that is okay. In other words, there is no need to rush out and sell them all!

However, although investing in these businesses is often considered to be conservative and low-risk, it is important to realise they are still susceptible to risk. What’s more, they are not guaranteed to generate investors a profit, especially in the event that earnings growth does slow (or if dividends drop).

While holding some blue chips in a portfolio is okay, investors should ensure they are not too exposed to any one company or sector. One way to do this may be to explore some of the opportunities outside of the ASX 20, many of which still offer the opportunity for growth and income.

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Motley Fool contributor Ryan Newman has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.