nginx 反代 google，为啥入流量和出流量不一致？

想要节省流量和加快速度，但是发现在 nginx 服务器上，流入流量要比流出高出 2-4 倍。 反代其他网站也是，怀疑是后端（ google 等）的响应没有 gzip ？但是我请求是带了 gzip 啊，这是我的配置：

worker_processes 1;

error_log /var/log/nginx/error.log warn; pid /var/run/nginx.pid;

worker_rlimit_nofile 1024; events { worker_connections 1024; } http { include /etc/nginx/mime.types; default_type application/octet-stream;

log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                  '$status $body_bytes_sent "$http_referer" '
                  '"$http_user_agent" "$http_x_forwarded_for"';

access_log  /var/log/nginx/access.log  main;
sendfile        on;
tcp_nopush     on;
keepalive_timeout  120;
gzip  on;
gzip_types application/json text/plain application/x-javascript application/javascript text/javascript text/css application/xml text/xml;
gzip_min_length 1k;
server_tokens off;
upstream backend{
    server google.com;
	keepalive 120;
}
proxy_temp_path /tmp/cache_tmp;
proxy_cache_path /tmp/cache levels=1:2 keys_zone=cache1:100m inactive=20m max_size=5g;
server{
    listen 80;
    location / {
        proxy_pass https://backend;
		proxy_http_version 1.1;
		proxy_set_header Range $http_range;
		proxy_set_header If-Range $http_if_range;
		proxy_set_header Connection "";
        proxy_set_header X-Forwarded-For $remote_addr;
        proxy_set_header Accept-Encoding "gzip";
		proxy_cache cache1;
        proxy_cache_key $uri$is_args$args;
        proxy_cache_revalidate on;
    }
}

}