This development is boosting wholesale demand from the food service segment by 4% to 5% a year across Europe, compared with growth in retail demand of 1 to 2 percent.

【翻译】这一发展使整个欧洲食品服务业的批发需求每年增长4%至5%，相比而言，零售需求增长是1%至2%。

by + 百分数：表示“增长或减少的幅度”。意为“增加了百分之几；减少了百分之几”等。

举个例子：

The number of online shoppers in the world's second largest economy grew by 13% to 374 million in the 12 months to June, according to the China Internet Network Information Center.

1. grew by 13% to 374 million 意为“增长了13%，达到374万人”。

2. in the 12 months to June 意为“到六月份为止的12个月里”。

翻译：据中国互联网络信息中心称，在到六月份为止的12个月里，世界第二大经济体在线购物者数量增长了13%，达到了374百万人。