Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some consumer staples stocks to your portfolio but don't have the time or expertise to hand-pick a few, the Fidelity MSCI Consumer Staples Index ETF (NYSEMKT: FSTA) could save you a lot of trouble. Instead of trying to figure out which stocks will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. This ETF, focused on consumer staples companies, sports a very low expense ratio -- an annual fee -- of 0.12%. The fund is new and small, though, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This consumer-staples ETF, launched in late 2013, is too young to have a sufficient track record to assess. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

Why consumer staples?
By definition, staples are items that we tend to buy no matter what the economy is doing. That makes companies making or selling staples attractive, as they add a defensive element to a portfolio, bolstering it in downturns. Consumer staples companies also often offer dividends, in part due to their relatively predictable income streams.

More than a handful of consumer staples companies had strong performances over the past year, with some notable exceptions. Tobacco giants Altria Group (NYSE:MO) and Philip Morris International (NYSE:PM) gained 12% and shed 9%, respectively. That's not what some might have expected, as Altria, selling tobacco products domestically, faces headwinds such as rising taxes, regulations, competition from discount cigarettes, and a shrinking smoker base. Philip Morris is its international counterpart, with seemingly greater growth potential as it operates in emerging markets where growing middle classes will smoke more cigarettes. But it, too, is increasingly challenged by taxes and regulations in some markets. Its last quarter featured results that topped expectations, but volumes have been shrinking. Altria's fourth-quarter results were disappointing, with Marlboro volume shrinking by 5.7% over year-earlier levels. Altria and Philip Morris remain solid dividend payers, offering yields of 5.2% and 4.6%, respectively.

Whole Foods Market (NASDAQ:WFM) surged 24.5% over the past year, but has slipped in the past few months, as its growth seems to be slowing. Still, it has been posting double-digit growth rates and management aims to more than triple its recent store count of 370 in the coming years. Boosted by the growing demand for organic foods, the company has enjoyed substantial pricing power, but with more conventional supermarkets now offering organic fare, it faces competition and pressured profit margins. (Meanwhile, Whole Foods and its peers are giving restaurants competitive headaches with their prepared foods.) Whole Foods' dividend yield is just 0.9%, but it has rewarded shareholders handsomely through share-price appreciation, averaging annual growth of more than 17% over the past 20 years.

Other consumer staples companies that didn't do quite so well over the last year include Sysco (NYSE:SYY), up just 6.5%. Sysco leads in delivering foods and other supplies to restaurants and institutions. In its second quarter, its earnings were down 4% over year-ago levels, but still exceeded expectations, while its 4% growth in revenue didn't meet projections. Some see it as a good company in an unappealing industry and worry about how rapidly it can grow. Its fans, though, love its market dominance, consistent profitability, and reliable quarterly payout, which recently yielded 3.2%. Sysco is aiming to buy its biggest rival, US Foods, for around $8.2 billion, but it's meeting some opposition on that front from customers and some attorneys general.

The big picture
If you're interested in adding some consumer staples stocks to your portfolio, consider doing so via an ETF. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.