There's definitely something I'm missing here.

Since calories is a unit of measurement for energy, and caffeine seemingly gives you a lot, how can the labels on caffeinated products have such a low calory count?

I would presume that caffeine doesn't really have as much energy as it seems to give you? In which case, what does it do?

Thanks in advance!


I agree with @inf3rno: caffeine is a stimulant that acts on the brain and various other parts of the body (Snyder et al., 1981) and I wish to elaborate on its psychopharmacology. Caffeine's effects in the brain are mediated through adenosine A1 and A2 receptors (Daly et al., 1983). This results in a variety of actions (Fredholm et al., 1999). Most notably, adenosine inhibits neurotransmitter release in various brain structures including the acetylcholine release in the mesopontine projection neurons. Caffeine blocks these adenosine receptors, in turn leading to an increase in acetylcholine release in the cortex and hippocampus. This increases vigilance and information processing. Increased acetylcholine release in the prefrontal cortex may lead to increased attentional abilities. Adenosine also inhibits the effects of dopamine released by the striatium, ultimately leading to disinhibition of motor output in the brainstem. This in turn increases motor activity (Fisone et al., 1997). In all, caffeine does not exert its stimulant effects through its metabolic energy content, but due to its pharmacologic effects on adenosine receptors.

  • $\begingroup$ Excellent answer. I had to look up most of the words, but the bottom line summed it up nicely. $\endgroup$ – Alec Nov 5 '14 at 10:42

Caffeine is a stimulant, which helps you release the energy your body stored.

Caffeine is a central nervous system and metabolic stimulant,[12] and is used both recreationally and medically to reduce physical fatigue and to restore alertness when drowsiness occurs. It produces increased wakefulness, faster and clearer flow of thought, increased focus, and better general body coordination.[13] The amount of caffeine needed to produce effects varies from person to person, depending on body size and degree of tolerance. Effects begin less than an hour after consumption, and a moderate dose usually wears off in about five hours.[13]

Caffeine has a number of effects on sleep, but does not affect all people in the same way. It improves performance during sleep deprivation but may lead to subsequent insomnia.[14] In shift workers it leads to fewer mistakes caused by tiredness.[15] In athletics, moderate doses of caffeine can improve sprint,[16] endurance,[17] and team sports performance,[18] but the improvements are usually not very large. Some evidence suggests that coffee does not produce the ergogenic effects observed in other caffeine sources.[19] High doses of caffeine, however, can impair athletic performance by interfering with coordination.[20] There is also evidence that caffeine may be helpful at high altitude.[21]

  • $\begingroup$ Two excellent and sourced answers. I can only pick one as accepted, but I found a lot of value in your citations. Especially the 2006 one, which inadvertently also answered an unasked question about caffeine intake possibly increasing one's metabolic rate. $\endgroup$ – Alec Nov 5 '14 at 10:43

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