In a preliminary test, 16 male volunteers tasted samples of a soup with graded doses of red pepper in order to define a moderate and a maximum tolerable dose of red pepper.
On the day of the experiment, the researchers gave all volunteers the same breakfast. At lunchtime, the subjects ingested one of four experimental soups containing either a placebo, a moderate or a strong dose of red pepper plus placebo capsules, or a placebo soup plus capsules delivering a strong dose of red pepper.
The amount of food, protein and carbohydrate ingested was similar for all conditions. Energy and fat intake were similar after the ingestion of the moderate soup compared with placebo.
However, the strong soup significantly lowered fat intake compared with placebo and ingestion of strong capsules also tended to suppress it, the team writes in this month's British Journal of Nutrition (pp 991-995).
Moreover, energy intake after strong soup and capsules tended to be lower than placebo.
The results indicate that the maximum tolerable dose is necessary to have a suppressive effect of red pepper on fat intake, said the researchers based at Japan's Fukuoka University, but they concluded that the main site of the action of red pepper is not in the mouth.
The findings support previous results showing that red pepper decreases appetite and subsequent protein and fat intakes in adults.
Another Japanese team reported two years ago that the essential oil of raspberries melts human fat more than three times as much as capsaicin however.