Small food companies are gaining space in millennials' shopping carts, but hope for big companies is not completely lost, a research note from Goldman Sachs and Conde Nast says.

Sales for the leading packaged food companies that Goldman tracks have been disappointing, with the first quarter of 2017 seeing, in aggregate, an sales decline of 1.6 percent — which is an all-time low for growth.

Big brands still dominate, driving 80 percent of industry sales, according to the report. But smaller brands have gained momentum, gaining share in 62 percent of the top 50 packaged food categories.

Distributing and advertising products is easier than ever, the note said. That's allowed more companies to enter the market and easily reach consumers, particularly millennials. While newcomers have benefited, big brands have spent more than a decade trying to cut margins, leading consumers to consider their products "over-engineered," the note said.

Some of the up-and-coming brands are run by entrepreneurs, including Kind, Clif, and Quest bars, Amy's Kitchen in the frozen food aisle, and Siggi's yogurt, among others.