High-end grocer Whole Foods is already poaching new customers from Walmart (WMT) and other competitors as the result of its new owner Amazon (AMZN) cutting prices, according to a report from Thasos Group, a data intelligence firm founded at MIT.

Beginning Aug. 28, Whole Foods, which had earned the nickname “Whole Paycheck,” slashed prices on some of its best-selling staple items, including avocados, bananas, organic brown eggs, Fuji and Gala apples, almond butter, and farm-raised salmon and tilapia.

Whole Foods immediately experienced a 17% increase in foot traffic year-over-year for the week beginning Aug. 28, the Thasos report found.

Of that foot traffic, new customers came primarily from Walmart, accounting for 24% of the new shoppers that week, while Kroger (KR) shoppers accounted for 16% and Costco customers for 15%.

Some of the Whole Foods’ other competitors also saw significant defections during that time. Nearly 10% of Trader Joe’s daily customers shopped at Whole Foods during the first week of price cuts, while 8% of Sprouts (SFM) and 3% of Target (TGT) customers did so.

Traffic has since subsided from its initial spike but remained at elevated levels of 4% year-over-year as of the week ending Sept. 16.

The profile of the Whole Foods’ customer didn’t change. Most of the shoppers were the wealthiest regular customers at the other stores, the report noted.

Thasos uses real-time location data from mobile phones for its reports.

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Julia La Roche is a finance reporter at Yahoo Finance.

Read more:

• What Whole Foods looks like now that Amazon owns it

• Despite Amazon’s price cuts, Whole Foods is still expensive