tl;dr: Excess body fat and obesity are an immune response to gram-negative gut bacteria, not a metabolic problem. Fix it by taking oral polymyxin, or a comparable antibiotic. Further research into good antibiotics for this purpose would be appreciated.
Earlier this year, an article found that bacteria from an obese human could cause obesity in mice. They isolated the bacteria, put it in some randomly chosen mice, and after a few months the mice with the bacteria were fat and had diabetes problems while the control group was healthy. With a second experiment they found that the mechanism is the molecule lipopolysacharride (LPS aka endotoxin), found in the membrane of all gram-negative bacteria. When gram negative bacteria become established in the gut, the LPS triggers a inflammation response from the immune system which causes both fat accumulation and diabetes in the long run. So they've established very firmly that gut bacteria are sufficient to cause excess body fat, but whether that's the main source in the general human population is unknown. (source: http://www.nature.com/ismej/journal/v7/n4/pdf/ismej2012153a.pdf, apologies if it's behind an academic firewall)
So how does one get rid of gram-negative bacteria? It turns out that there is a common antiobiotic, polymyxin, which specifically targets LPS itself and kills bacteria which produce LPS. Polymyxin is among the most common topical antibiotics (along with neosporin), and can also be taken intravenously or orally. Intravenously it is a mild neurotoxin, but this is not an issue if taken orally.
Finally, it turns out that a study published back in 2006 administered polymyxin intravenously to rats. They found a 46% drop in adipose fat mass in rats given polymyxin. They had no idea what the mechanism was, hypothesized some vague connection to insulin signalling, and it just went down as one of those weird results. But now, in light of the more recent results, we can be pretty sure that gram-negative gut bacteria were the issue. The importance of this study is that it suggests gram-negative bacteria are a major cause of excess body fat in the general rat population, not just a special case of the 2013 study. So, it's reasonable to suspect that polymyxin would fix most human obesity too. (source: http://link.springer.com/article/10.1007/s10989-005-9009-9)
My basic sanity check for any sort of experiment purporting to show a new mechanism responsible for obesity, is "under this mechanism, does it make sense for lots of people to be obese now in America, but hardly anyone a hundred years ago in America, or today in countries like Japan where people have high access to resources but eat less?"
If a mechanism for obesity leaves you confused by the patterns of obesity that occur in the real world, then it's probably better not to afford it much likelihood.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.