Article originally found here (link will open in a new window). I am not the author of the following article.

The effect of caffeine, green tea and tyrosine on thermogenesis and energy intake
A Belza1, S Toubro1 and A Astrup1

1Department of Human Nutrition, Faculty of Life Sciences, University of Copenhagen, Copenhagen, Denmark

Correspondence: Dr A Belza, Department of Human Nutrition, The Centre for Advanced Food Studies, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark. E-mail: anbe@life.ku.dk.

Received 14 February 2007; Revised 8 July 2007; Accepted 20 July 2007; Published online 19 September 2007.

Abstract
Objectives: To investigate the effect of three different food ingredients tyrosine, green tea extract (GTE) and caffeine on resting metabolic rate and haemodynamics, and on ad libitum energy intake (EI) and appetite.

Methods: Twelve healthy, normal weight men (age: 23.72.6 years, means.d.) participated in a four-way crossover, randomized, placebo-controlled, double-blind study. Treatments were administered as tablets of 500 mg GTE, 400 mg tyrosine, 50 mg caffeine, or placebo, and were separated by >3-day washout. The acute thermogenic response was measured in a ventilated hood system for 4 h following ingestion. Blood pressure, heart rate (HR), and subjective appetite sensations were assessed hourly and ad libitum EI 4 h post-dose.

Results: Caffeine induced a thermogenic response of 6% above baseline value (7225 kJ per 4 h, means.e.) compared to placebo (P<0.0001). The thermogenic responses to GTE and tyrosine were not significantly different from placebo. Tyrosine tended to increase 4-h respiratory quotient by 1% compared to placebo (0.010.005, P=0.05). Ad libitum EI was not significantly different between treatments but was reduced by 8% (-403183 kJ), 8% (-400335 kJ) and 3% (-151377 kJ) compared to placebo after intake of tyrosine, GTE and caffeine, respectively. No significant difference in haemodynamics was observed between treatments.

Conclusions: Only caffeine was thermogenic in the given dose and caused no haemodynamic side effects. The sample size was probably too small to detect any appetite suppressant properties of the treatments. Further investigations are required.