Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to invest in defensive stocks that tend to hold up better than others in tough economies -- and still grow over time -- the iShares S&P Global Consumer Staples ETF (NYSE: KXI) could save you a lot of trouble. Instead of trying to figure out which companies 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. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.48%.

This ETF has performed rather well, beating the world market handily over the past three and five years, as well as the past year. 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.

With a very low turnover rate of 4%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Several consumer staples companies had strong performances over the past year. Philip Morris International (NYSE: PM), for example, surged 36%, and some think it's no longer a bargain at current levels. Others, though, like the fact that it's focused outside the U.S., where a shrinking base of smokers, coupled with growing regulations and rising taxes, threaten profitability. They also like its growth rates (double digits for revenue and earnings over the past three years) and powerful brand names, which can help it command premium prices.

Western Gas Partners (NYSE: WES) gained 26%, and has also posted strong growth rates, with revenue climbing by more than 30% on average over the past three years, and earnings averaging 14%. With its last earnings report, management noted pressure from the low price of natural gas, but said that the company is performing well enough that it's maintaining the projections it laid out in February. Meanwhile, patient investors can collect a dividend yield topping 4%.

Tractor Supply (Nasdaq: TSCO), at whose store I once spied a barrel of "pork femurs" for sale, advanced 19%. It has been a long-term winner, averaging annual gains of 26% over the past decade as it operates retail stores in America's rural areas (and elsewhere). The company is planning to add 90 more stores next year, and, over the long run, aims to up its store count from about 1,100 to 2,100.

Other companies didn't do as well last year, but could see their fortunes change in the coming years. Procter & Gamble (NYSE: PG), the quintessential consumer staples company, shed 2%, as its earnings declined a bit and dividend growth slowed. Still, revenue is growing, and the company collects a significant chunk of it from emerging markets, which are growing relatively rapidly. The stock has been rather stagnant in recent years, and some expect a new CEO in the near future, which may usher in a period of stronger growth.

The big picture
Demand for consumer staples, as implied by the sector's name, isn't going away anytime soon. 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.

Many consumer staples companies dominate their industries, and have made many shareholders rich as they grew. In our special new report, you can discover the "3 American Companies Set to Dominate the World." The report's free today, but it won't be for long -- so click quickly.