The Nasdaq-100 is an index designed by the Nasdaq company to follow the biggest, most innovative companies in the market. And over the past decade, it's trounced the S&P 500 index, generating returns of 382% versus 239% for the broader index.

If you're looking for a chance to buy shares of great companies at a discount, now may be the time. Even though the Nasdaq-100 has generated strong returns over the last decade, it's down sharply and underperforming the S&P 500 in 2022. This means that many of the companies in this index are also down.

That includes Latin American e-commerce and financial technology (fintech) company MercadoLibre (MELI 0.10%) and video-conferencing platform Zoom Video Communications (ZM -0.34%). Both MercadoLibre and Zoom are worth doubling down on in December. Here's why.

1. MercadoLibre

MercadoLibre's stock is down 33% year to date. But the company has positioned itself perfectly to profit from promising trends in Latin America in the coming decade. 

When it comes to e-commerce, MercadoLibre is excelling. It reached a record 43 million buyers in the third quarter of 2022. But gains appear to be ongoing. Consider that on Black Friday, Brazilian e-commerce sales as a whole fell 23% year over year. By contrast, Brazilian e-commerce sales for MercadoLibre were up 10%, suggesting it's gobbling up market share.

MercadoLibre is excelling with fintech, too. At the end of Q3, it had 41.6 million users of Mercado Pago, up 32% year over year. Helping boost adoption is an increasing suite of services offered by the company. Not only can customers deposit paychecks and get debit cards, but they can also buy insurance and take out loans in some markets -- MercadoLibre aims to keep expanding its reach with these products.

The shares are down in part due to fears regarding its lending business. For context, its portfolio of loans through Mercado Credito is at an all-time high of almost $2.8 billion. But roughly $1 billion is considered past due. Investors fear this is an imminent crisis.

Management acknowledges the need to be more selective in its lending process, as evidenced by its decision to slow loan originations in the third quarter. That said, investors need to keep things in perspective. In Latin America, lenders like MercadoLibre expect higher default rates than what's considered normal in the U.S. And for this increased risk exposure, they're compensated by charging higher interest rates. The reward offsets the risk.

The good news for MercadoLibre shareholders is that many of these loans are in Brazil, and the Brazilian economy seems poised for a rebound. According to Reuters, Brazil's Economy Ministry is predicting economic growth in 2023. And MercadoLibre's management believes that Brazil's interest rates are close to peaking, if they haven't already. Both economic growth and an interest rate reduction would help consumers and reverse the trends that are causing default rates to rise on MercadoLibre's loan portfolio. 

MercadoLibre is growing admirably right now, and some of the factors holding the company back from even greater gains appear to be improving. That's why it's a great stock to double down on in December.

2. Zoom Video Communications

One of the most prominent beneficiaries of pandemic was Zoom, the now-ubiquitous video-conferencing platform that kept people in touch while apart. With normal life gradually resuming, ts shares have plunged 62% year to date. But I believe further downside risk is low due to the strength of its business.

Here's a big reason Zoom stock is down: Its profit margins are deteriorating. Through the first three quarters of its fiscal 2023, research and development expenses have more than doubled from the comparable period in fiscal 2022. And sales and marketing spending is up 47% during this time.

ZM Operating Margin (Quarterly) Chart

ZM Operating Margin (Quarterly) data by YCharts

That has been discouraging to some investors because Zoom's year-to-date revenue is only up 8%. In other words, the company is spending on growth that isn't manifesting itself.

Or is it? Zoom signs long-term contracts with businesses and then recognizes revenue over the life of the contract. Therefore, revenue right now doesn't tell the whole story -- there are still remaining performance obligations (RPO) to consider.

For Zoom, its RPO reached an all-time high of over $3.2 billion Q3, up 32% year over year. RPO growth still trails the increase in marketing spending. But it's a far more palatable disparity. 

And here's another silver lining for Zoom investors. Yes, growth has slowed in its core business. But its investment in research and development can pay off with renewed growth in ancillary products and services over time.

Moreover, while shareholders await reinvigorated growth, Zoom is still profitable and in a strong financial position. The company ended Q3 with over $5 billion in cash and investments. And it had a net increase of over $162 million during the quarter.

In summary, Zoom is on strong financial footing, getting stronger, and is still spending liberally on the next phase of its growth. For me, this makes Zoom stock just as double-down worthy as MercadoLibre stock. And I'd buy more of both for the long term today.