I would like to know what came before this, because it seems a bit self contradictory.
多数人体重的增加会从周六开始,
the majority of participants will start to gain weight from Saturday,
那些体重减轻者和体重保持者
those who lost weight and those who maintained the same weight
Either: they gained weight, they lost weight, or they stayed the same. That is 100% of the participants, not 多数。
这项联合多所医学院校所做的研究发现,
This research, conducted in conjunction with various medical schools discovered,
除了个别人以外,
(that) apart from a few individuals,
多数人体重的增加会从周六开始,
the majority of participants will start to gain weight from Saturday,
而体重减轻则会从周二开始,
and will lose weight beginning Tuesday,
特别是对于那些体重减轻者和体重保持者来说更是如此。
this is especially so for those who lost weight and those who maintained the same weight.
特别(是): especially (don't need this 是)
对于[something]来说: regarding [something], concerning [something], as far as [something] is concerned
更是如此: even more so
Chinese likes to wrap phrases at both ends.
对于 [我] 来说,他是最合适的人。(I'm sure she's not talking about me!)
但对于 [我] 来说却是个好消息。
对于 [我] 来说,这是“第0步”。