Not sure how much gut bacteria will help with weight loss, but it does seem to go the other way.

One of my favorite papers in the field in the last couple years shows a potential causal relationship between obesity and gut biomes by using artificial sweetener and a fecal transplant in mice.

Paywalled version in nature: http://www.nature.com/nature/journal/vaop/ncurrent/full/natu...

Unpaywalled version after googling: http://www.drperlmutter.com/wp-content/uploads/2014/09/Artif...

I believe it absolutely can. It has gone the other way where someone got FMT from an obese person and they needed up obese themselves! makes perfect sense since the gut bacteria is the actual digester of your meals. They will determine how to digest the various fat/protein/carb/sugar you eat. So people with say.. thyroid problem who typically gain weight out of their control probably stems from gut bac imbalance I'm conjecturing because believe or not the gut bac also has a say in productions of hormone from all your glands. I would bet those individuals if gotten FMT from a healthy donor would reverse that course.