Every grapefruit contains about 100 mg nootkatone, most of which is in the peel. Nootkatone is responsible for the refreshingly bitter taste of grapefruit, which the food industry has imitated in semi-synthetic form and loves to add to soft drinks and candy. According to the Japanese Kao Corporation, however, nootkatone is also a stimulant and slimming aid. But only in wildly high doses…
The Kao Corporation stumbled upon the interesting properties of nootkatone when looking for naturally occurring compounds that may be able to help in the fight against the obesity epidemic. To be more precise: the Japanese were looking for substances in our food which, like resveratrol and EGCG, activate the key metabolic molecule AMPK.
AMPK is activated when cells run low on energy as a result of extended periods of physical exertion or fasting. From the level of activity of AMPK the cell 'reads' whether it should be burning fats, becoming more sensitive to insulin, stepping up detoxification processes or repairing molecular structures. As a result of this mechanism fasting and physical exertion are healthy activities.
Many compounds in fruit, vegetables and herbs also activate AMPK. These compounds can boost the body's energy expenditure and enhance performance. So AMPK activators are potential slimming aids, which may also help us to be able to exercise for longer or more intensively.
The Japanese gave mice feed that consisted for 0.2 percent by weight of nootkatone for a period of 10 weeks. At the end of the period the researchers measured how long the mice were able to swim for – and compared their times with those of mice that had not received any nootkatone.
In another experiment the researchers gave mice feed to which extra sugar and fat had been added, for a period of 18 weeks. The mice that also got nootkatone mixed in their food remained as slim as the mice that got standard feed.
A dose of 200 mg nootkatone per kg bodyweight increased oxygen consumption almost immediately, the Japanese discovered. This dose also boosted AMPK activity in the muscles within half an hour, thereby boosting fatty acid burning too.
"Administration of nootkatone was beneficial toward the prevention of obesity as well as for improving endurance capacity", the researchers conclude. "These results support the idea that AMPK activators are useful as exercise mimetics or exercise-supporting drugs in treating obesity and for improving physical performance. The administration of nootkatone is a potential candidate treatment for metabolic syndrome."
It sounds promising, but there are toxic pitfalls involved. The human equivalent of the doses used is around 10-15 mg/kg bodyweight/day. The acceptable daily intake of nootkatone according to the Sixty-ninth report of the Joint FAO/WHO Expert Committee on Food Additives [who.int] is 0.1 mg per kg bodyweight per day.
Am J Physiol Endocrinol Metab. 2010 Aug;299(2):E266-75.