The S&P 500 Consumer Staples index inched down 1.5% in September but still outperformed the wider S&P 500's 3.8% loss, according to data compiled by S&P Global Market Intelligence.

However, only nine of the 33 constituents of the consumer staples index posted positive share-price returns during the month.

Lamb Weston Holdings Inc. and Archer-Daniels-Midland Co. were the best-performing stocks in the S&P 500 Consumer Staples index in September. Both companies boosted their liquidity amid the COVID-19 pandemic.

Lamb Weston recorded a 5.4% share price increase during the month. The potato products company secured a further $750 million in revolving credit on Sept. 17.

Archer-Daniels-Midland was the second-best performer with a 3.9% gain. On Sept. 22, the agricultural products group priced and upsized its tender offer for up to $664.8 million in debentures and notes.

Sysco Corp., which led the S&P 500 Consumer Staples index in August, posted a 3.5% share price rise in September.

Meanwhile, The Kraft Heinz Co. was the worst-performing stock in the consumer staples sector with a decline of 14.5% during the month. On Sept. 15, the food company announced a plan to cut nearly $2 billion in costs through 2024. It also agreed to sell some of its cheese businesses to a Groupe Lactalis SA affiliate for $3.2 billion.

Shares of brewer Molson Coors Beverage Co. fell 10.8% in September, while tobacco company Altria Group Inc.'s stock declined 9.9%. The maker of Marlboro cigarettes on Sept. 9 warned of a potential write-down on its investment in Juul Labs Inc., which is reportedly ramping up job cuts and considering pulling out of 11 markets.

Only the S&P 500 Materials and S&P 500 Utilities indexes recorded positive returns in September.

Restaurant operator Darden Restaurants Inc. soared to the top of the S&P 500 with a gain of 16.2%. On Sept. 24, the Olive Garden parent reinstated its quarterly dividend and posted fiscal 2021 first-quarter adjusted diluted EPS that beat estimates.

Oil and gas company Apache Corp. was the worst performer in the index, posting a 36% loss during the month. U.S. oil producers continue to struggle from the effects of the COVID-19 pandemic.

In September, eight of the 10 worst-performing stocks in the wider S&P 500 index were energy companies.