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 because of their defensive nature, the First Trust Consumer Staples AlphaDEX ETF (NYSEMKT:FXG) 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 First Trust ETF's expense ratio -- its annual fee -- is 0.70 %. The fund is a bit on the small side, too, 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 ETF has performed  rather well, beating the world market over the past three and five years. 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?
More than a handful of consumer staples companies  had strong performances over the past year. Philip Morris International (NYSE:PM), for example, soared 41%. The globally focused tobacco giant enjoys faster growth  rates and less restrictive regulations than its American-based cousin, Altria (NYSE: MO), but anti-smoking campaigns are gaining ground globally. Philip Morris has been raising its dividend and buying back shares aggressively,  and growth rates in emerging nations bode well for the company, too. Don't discount its brand power, either -- the Marlboro name is well known worldwide.

Monster Beverage (NASDAQ:MNST) gained 21%. The stock formerly known as Hansen Natural has bears worrying about slowing growth, but slower rates for the company are still very strong compared with many others. Energy drinks are a briskly growing niche, and Monster is a key player, but it has strong competition, too, from Starbucks (NASDAQ: SBUX), SodaStream (NASDAQ: SODA), and others. Its success has generated some speculation  that it may be taken over, though that wouldn't be an inexpensive proposition with the market cap recently above $10 billion.

Ingredion (NYSE:INGR), up 26%, specializes in starch and sweetener ingredients. In a sign of confidence, the company, formerly known as Corn Products International, recently raised its dividend  payout by 30%, so that it yields nearly 2% now. Its revenue and growth rates have sported double-digit averages over the past five years, and the growth rates have been accelerating, too. The company acquired  National Starch in 2011, and though it faces some challenges by the recent drought, it also locks in prices when possible via hedging .

Other companies didn't do as well last year, but could see their fortunes change in the coming years. Archer Daniels Midland (NYSE:ADM), for example, gained just 4%, punished to some degree by volatility in food prices, such as in corn and cocoa. Drought conditions in America's farm belt will likely make things worse, with ADM's Crop Risk Services unit likely to see claims rise. One boost to business in recent years has been the use of corn for ethanol, and the government's QE3 stimulus should boost agricultural spending as well.

The big picture
Demand for consumer staples isn't going away anytime soon -- by definition. 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.

Longtime Fool contributor Selena Maranjian, whom you can follow on Twitter, owns shares of Starbucks. The Motley Fool owns shares of ADM, Starbucks, and SodaStream and has options on Starbucks. Motley Fool newsletter services recommend Monster Beverage, SodaStream, and Starbucks. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.