As I mentioned, the use of kava (also known as kava-kava) is not
associated with weight gain, but there are numerous mentions of weight
loss in connection with this substance. I've gathered some excerpts
from online articles for you. It should be noted that some of these
refer to the drinking of a kava-based tea infusion rather than to the
consumption of a commercially manufactured extract, but the active
chemical ingredients are the same.
In collecting this information, I have omitted many references to
potentially dangerous health effects related to liver toxicity, since
you have stated that you are aware of that risk.
"Although Hawaiian healers used kava for dozens of purposes, there is
no question that its use to induce relaxation is not culture-specific.
Tests on animals show that extracts of the drug-but no single
identified compound-cause muscle relaxation to the point that animals
fall out of revolving cages. Methysticin and DHM protect animals from
muscle convulsions due to strychnine. Kava was used in Hawaii to
reduce anxiety, bring on sleep, counteract fatigue, and treat asthma,
arthritis pains, and urinary difficulties. Kava appears to act as a
diuretic, and the root was even used as a weight loss agent. Medical
tests suggest it may be helpful in treating psychosomatic symptoms in
menopause. Kawain acts as a local anesthetic, numbing the lips and
mouth. Food eaten after ingesting kava drink cannot be tasted."
"However, long term use of kava leads to a range of health problems
including malnutrition, weight loss and apathy."
"The study found that in addition to causing acute intoxication,
sedation and relaxation, a rash, and weight loss in long-term users,
kava may also cause liver and renal dysfunction, hematological
abnormalities, and possibly pulmonary hypertension."
Erowid Kava Vault
"Low to moderate use typically causes:
Higher doses are associated with intoxication and include:
reddened and dilated eyes
Long-term kava is associated with weight loss, malnutrition, liver
damage and scaly skin. Often health suffers and a disinterest in life,
family, etc. has been reported."
National Drug Policy New Zealand
"Kava is a diuretic. Being a diuretic, it is also used for weight loss."
"Although mild to moderate kava drinkers of kava are not known to have
significant gastrointestinal complications, recent adverse effects
have involved mainly heavy kava drinkers. There has also been
speculation about association of kava drinkers and weight loss. The
possible causes of this have included poor food intake, malnutrition
and the possibility of malabsorption."
Erowid Kava Vault
"Weight loss after using too much Kava extract for too long may occur."
"Kava can also reduce pain, relax the muscles and help with losing
weight... Kava often suppresses the appetite, an effect that was
noticed and written about as early as 1908. It also has a thermogenic
effect on the metabolism, helping the body to burn calories. And
anyone who overeats out of nervousness can calm their nerves with Kava
before meals, enjoy their food more, and experience less of a desire
to overeat. There are already health companies incorporating Kava as
the active ingredient in their weight loss formulas."
"Heavy chronic consumers of kava are more likely to suffer from
general ill health, at times losing up to 50% body fat and 20% of
their body weight. People affected by long term kava consumption are
generally undernourished, perhaps due to appetite suppression and the
fact that some kava drinkers prefer to spend time ingesting the
beverage in stead of nourishing themselves adequately."
My Google search strategy:
Google Web Search: kava "weight loss OR gain"
I hope this information will be useful. If anything is unclear or
incomplete, please request clarification; I'll gladly offer further
assistance before you rate my answer.