In case you haven't noticed, lending rates are historically low and growth stocks are in demand. With the ability to borrow money still relatively cheap, growth stocks have handily outperformed value stocks since the end of the Great Recession. 

But as long-term investors, we understand that this isn't a sprint -- it's a marathon. We want high-quality growth stocks in our portfolios that can stand the test of time and deliver market-topping returns. 

With this in mind, we asked three Motley Fool investors to name growth stocks you should consider buying and holding for the next 50 years if they want to rack up some serious profits. Making the grade were robotic-assisted surgical system developer Intuitive Surgical (NASDAQ:ISRG), theme park and media industry giant Disney (NYSE:DIS), and China's search engine market-share leader, Baidu (NASDAQ:BIDU)

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The surgery trend is your friend

Sean Williams (Intuitive Surgical): There aren't many growth stocks whose margins have an opportunity to improve with each successive year, but one such company where that is possible is robotic-assisted surgical system developer Intuitive Surgical.

To begin with, you have to understand how the company makes its profit. Though it generated $910 million of its $3.12 billion in total sales in 2017 from the sale of its da Vinci surgical systems, which range from $0.5 million to $2.5 million in cost, these are generally low-margin machines. It takes a lot of research and development, along with high-cost equipment, to develop robotic surgical systems. The bulk of its margin is derived from instrument sales for each procedure performed on the da Vinci surgical system, along with servicing needs. These higher-margin line items are growing larger each year as the number of installed da Vinci surgical systems grows. This is primarily why Intuitive Surgical should be able to grow its earnings per share at a quicker rate than its total sales for years or decades to come. 

Secondly, it has unbelievable competitive advantages. If we were to take all of Intuitive Surgical's primary rivals and stack them up against the da Vinci surgical system, which had 4,409 installed systems as of Dec. 31, 2017, the competition would be but a blip. Intuitive Surgical has a long history of building rapport with the medical community, and the time and effort put into training surgeons on its expensive machinery essentially lock in those clients for the long haul. 

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Next, don't discount an aging global population. With few exceptions, the global population is living longer and slowly but surely gaining access to medical care. It's a long-term process that sets up the expectation of more surgical procedures being needed as time passes. That creates a steady stream of demand for new da Vinci systems and the juicy instrument and service margins that accompany that order.

Lastly, the company has ample opportunity to expand into new soft-tissue surgeries in the years to come. While it's hitting its stride in urology and gynecology surgeries, it's only touched the surface with regard to cardiothoracic, colorectal, and general surgery. An expanded surgical profile would go a long way to boosting robotic-assisted system use.

If you want a set-it-and-forget-it growth stock for five decades, Intuitive Surgical could be it.

The media industry's growing powerhouse

Travis Hoium (Disney): I don't think there's any company in the media industry better prepared to adapt to new consumer trends in streaming TV, sports, and movies than Disney. The company has some of the best content franchises, with Lucasfilm, Pixar, and Marvel augmenting the traditional Disney studios, plus the potential addition of most of Twenty-First Century Fox's most attractive assets if its acquisition goes through

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Some observers will argue that Netflix (NASDAQ:NFLX) is upending Disney's business, causing even more cord-cutting to hit cable networks and contribute to falling box office attendance over the long term. But Disney is better positioned to adapt to the changing market than its competitors. It's launching its own streaming services and will likely be able to charge significantly more than Netflix's $10.99 for an HD subscription and $13.99 for premium streaming content. It won't have the same reach immediately, but in time it could match Netflix on reach, too. 

Beyond streaming, Disney has a business model that acts like a waterfall, generating value every step of the way. It starts with box office releases, then moves to networks (eventually streaming), and then to theme parks. This creates three revenue touch points with consumers and each is incredibly profitable on its own. Together, they create the Disney juggernaut we know today. 

It's tough to predict exactly what Disney will look like in 50 years, but given its durable brands and multipronged business model in the media business, it's highly likely that Disney will be a winner for many decades to come.

Searching for the next big thing

Danny Vena (Baidu): Baidu may not be a household name to U.S. investors, but it's well-known to Chinese consumers. The company is the search leader in the most populous country, and has been called the "Google of China." While that analogy is entirely accurate, Baidu is positioned to capitalize on a vast number of opportunities beyond its core search.

An increasing portion of its revenue is spent on two strategic areas: research and development and content. Baidu's R&D expenditures grew to 15.2% of revenue in 2017, up from 14.4% in the prior year, while content spend skyrocketed to 15.8% of revenue, up from just 11.1% in 2016. What's driving these investments?

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Baidu subsidiary iQiyi is the leader in the direct-to-consumer streaming market, with 421 million monthly active users on mobile and 424 million on PC -- with more than 50 million paying subscribers. iQiyi's hybrid model is turning ad-supported users into paying subscribers. Its original programming took five of the top 10 spots in internet variety shows, and six of the top 10 internet drama series, so it's a hit with Chinese consumers. Baidu plans to spin off iQiyi sometime this year in a move expected to raise more than $1.5 billion.

The R&D spending is being driven by investments in artificial intelligence (AI), and it is widely acknowledged as the AI leader in China and among the top contenders in the world. Baidu has been investing across a broad spectrum of this nascent technology to improve its core search relevance, provide products to the consumer smart-home market, and develop self-driving cars.

Apollo, its open-source autonomous car unit, is the most advanced in China. Baidu has partnered with more than 80 companies on the technology and plans to sell a wide range of hardware that will plug into cars to run its self-driving systems. 

Baidu, as the industry leader in next-generation technologies in the Middle Kingdom, is a stock you might want to hold on to for the next 50 years.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.