Investing.com -- As U.S. consumers pour more than $1.5 trillion annually into packaged food, drinks, and household essentials, retailers like Walmart (NYSE: WMT ) and Costco (NASDAQ: COST ) are emerging as the biggest winners, Bernstein said.

The brokerage said a long-running power shift is playing out between consumer goods manufacturers and retailers, with the balance steadily tilting in favour of large-scale retailers.

While raw materials and logistics players capture about 40% of consumer spending in this space, the remaining 60% is split between manufacturers, which has roughly 35% share and other 25% by retailers.

That retailer slice, however, is growing.

Retailers have increased their share of the pie from about 34% to 38% over the past 15 years, Bernstein wrote, attributing the trend to scale advantages, stronger supplier bargaining, and the rise of private labels.

Mass merchants and warehouse clubs, in particular, have used their size to secure better pricing and pass savings on to shoppers.

Bernstein estimates identical baskets of consumer goods are 3% to 27% cheaper in club and mass retail channels compared to others.

Within its coverage, Bernstein flagged Walmart and Costco as best positioned to continue gaining share, citing their bargaining leverage and price leadership.

Meanwhile, food manufacturers, especially those in processed categories, have seen margin pressure and waning pricing power.

CPG companies are under pressure on factors such as retailer consolidation, shifting consumer health trends, the rise of challenger brands, and digital disruption.

Large food brands, in particular, face an uphill battle as they lose market share to both private labels and newer, wellness-focused competitors.