The news this week that General Mills pledged to remove synthetic ingredients from its cereals, following similar commitments from companies such as Nestle, Hershey, Kraft and Pepsi, appears to be a sign of the times. For the first time since packaged foods took the American homes by storm in the 1950s, large food brands are losing market share to small, specialty and organic companies.

In response, big brands are taking big steps. Aside from cutting artificial ingredients, some are entering the organic market: General Mills bought organic pasta, meals and snacks company Annie’s Homegrown last year, while Campbell’s acquired organic baby food company Plum Organics in 2013 and launched an organic soup line in February.

Big brands will need to continue this trend if they hope to regain baby boomers and attract new millennial buyers. A 2014 report from financial analyst firm Jefferies, Food: the Curse of the Large Brand, found that large consumer packaged goods brands have lost market share in 42 of the 54 most relevant food categories over five years. The shift has been driven, in large part, by demographic changes.

By 2020, millennials above 25 years old are expected to comprise roughly 19% of the US population, up from just over 5% in 2010, and make up one third of the adults, according to the Census Bureau. The age of 25 is an important milestone, Jefferies analyst Scott Mushkin said, because it’s when “income and household formation start to accelerate, creating the catalyst for increased consumption”.

The millennial generation’s coming of age could have a big impact on packaged-foods companies. That’s because millennials have consistently shown a preference for locally grown, healthy foods.

At the same time, baby boomers have been growing more discriminating about their diet, increasingly opting for foods geared towards bolstering either brain health or physical activity. According to a recent survey by market research firm Alix Partners, 82% of baby boomers and 72% of millennials believe eating healthily is “extremely important”.

Both trends – the rise of millennials and the changing habits of boomers – are tipping the scales away from traditionally produced packaged foods.