The treatment could be another option for people who want to lose weight.
Professor Steve Bloom and colleagues from England conducted a 4-week blinded trial in 26 people with diabetes who were all overweight or obese.
The researchers suggested that oxyntomodulin, which is naturally found in the intestine, could be a new way of tackling obesity.
The researchers had 14 of the patients inject themselves with oxyntomodulin 30 minutes before each meal, 3 times a day, for 4 weeks.
There were 12 controls who administered saline at the same frequency for the same period.
The researchers found that those on the hormone lost an average of 2 kg in 4 weeks, compared to 0.5kg for those on a dummy treatment.
| Those on the hormone lost an average of 2 kg in 4 weeks vs 0.5kg in the controls|
In addition, the team noted that the group taking oxyntomodulin also had a reduced appetite, but they saw no change in their enjoyment of food.
Levels of leptin, a protein known to be responsible for regulating the body's energy expenditure, were also lower in the group receiving hormone injections.
The team found that adipose hormones, which encourage the build up of a type of tissue where fat cells are stored, were lower with hormone injections.
Professor Bloom, senior researcher at Imperial College London and Hammersmith Hospital, who led the study, told the BBC: "We saw a dramatic rate of weight loss.”
"Oxyntomodulin is natural as its is released every time you eat lunch or supper, so it's not quite like a drug.”
"I would anticipate it being completely safe and also, since you have your own oxyntomodulin, it isn't likely to ever stop working, as is the problem with existing anti-obesity drugs.”
“Larger trials are needed to check the treatment was effective over longer periods.”
Dr Ian Campbell, president of the National Obesity Forum, added, “This study is exciting.”
"The weight-loss is significant, but questions need to be asked about what the weight loss would be with the additional lifestyle changes, and the efficacy over a period of time much longer than 4 weeks.”