Caffeine’s affinity for stimulating energy is no secret. Caffeine is one of the most commonly used ingredients in weight loss supplements. It is a naturally occurring crystalline xanthine alkaloid that is regularly consumed worldwide. Not only does it provide an obvious short-term energy boost, it also provides many potential health benefits. Caffeine has many valuable effects on exercise performance and energy. It stimulates the Central Nervous System and activates the metabolism. By improving metabolic capacity it may even ameliorate risk factors related to obesity and type 2 diabetes mellitus. Caffeine increases metabolic rate, which causes you to burn more calories and potentially lose weight. It is believed to increase metabolic rate of muscle via the release of catecholamines – chemicals that function as messages between brain cells and tissues – such as adrenaline. Even conferring a small increase in metabolic rate can cause the body to release energy as heat via thermogenesis, rather than the unfortunate alternative – converting it into body fat. Research has even shown caffeine’s uncanny ability to increase metabolic rate for up to a day following ingestion.
In addition to its influence on metabolism and the central nervous system, this mild stimulant may also potentially improve neuromuscular performance. Analyses of the extensive past research on caffeine has revealed that workout endurance could be improved by up to 12% with prior ingestion of caffeine. Caffeine decreases fatigue, increases energy, and improves reaction time by enhancing mental focus and concentration.  One study found that a single scoop of a caffeine ingested 20 minutes before the start of exercise could result in an increase in total work, performed at a higher quality. This performance enhancement occurred secondary to suspended fatigue and the ability to preserve increased energy levels. What’s even better is that taking caffeine before exercising can also help burn the fat that is stored around the organs. This is referred to as visceral fat and it is detrimental to health, which emphasizes the benefit conferred by breaking down these harmful fats.
Speaking of unhealthy fat, caffeine is also an anorectic – an agent that suppresses appetite. Caffeine is able to delay the onset of hunger. When it is taken before meals, it can reduce the amount of food required to feel satisfied. After eating the brain releases serotonin and other neurotransmitters (brain cell chemical messengers) that determine whether we feel satiated. Low serotonin levels can cause people to crave food, which are particularly increased by eating foods rich in carbohydrates. Yet rather than reaching for carbs, caffeine can quell the serotonin-motivated craving. Caffeine additionally stimulates hormones such as cholecystokinin and delays gastric emptying, together making you feel full after eating, thereby preventing continued consumption following a meal.
Delving deeper into the science…
After ingestion, caffeine is metabolized by the body mainly into the chemical compound paraxanthine. This chemical has been shown through scientific study to be directly responsible for the increase in lipolysis associated with caffeine ingestion. As caffeine is broken down forming paraxanthine, an increase in free fatty acid levels is noted to occur simultaneously, which suggests that paraxanthine is an active lipolytic agent promoting fat burn. Free fatty acid turnover has been found to double following caffeine ingestion due to increase in fatty acid oxidation and recycling. Plasma free fatty acids impact their own oxidation, while resting conditions require large increases in lipid turnover to induce a slight increase in lipid oxidation.
Caffeine stimulates lipolysis by reducing the degradation of cyclic adenosine monophosphate (cAMP) through beta-adrenergic independent pathways and increasing cAMP production via beta-adrenergic dependent pathways. Adipocytes (fat cells) have receptors that are regulated by the surrounding hormonal and chemical environment. Both adipocytes and muscle cells possess adrenergic (adrenaline-responsive) receptors, in the form of alpha and beta. Alpha adrenergic receptors make and store fat when activated, whereas the beta adrenergic receptors break down fat when activated. The beta receptors are activated by the sympathetic nervous system, which controls the “fight or flight” response to stressors. When triggered, the SNS releases catecholamines epinephrine and norepinephrine (aka adrenaline) which operates through a biochemical cascade involving activation of the enzyme adenylate cyclase, which catalyzes the conversion of adenosine triphosphate into cyclic adenosine monophosphate, which serves as a second messenger, ultimately facilitating the release of fat stores from adipocytes.
Caffeine’s beta-adrenergic independent effects are likely the result of caffeine’s ability to directly inhibit cAMP degradation, by inhibiting the cyclic nucleotide phosphodiesterase and blocking adenosine receptors. The adenosine receptor also inhibits lipolysis via adenylate cyclase. As an adenosine antagonist, caffeine stimulates lipolysis. A large increase in free fatty acid turnover following caffeine ingestion is presumably a result of the combined effects of caffeine on beta-adrenergic stimulation on lipolysis and on inhibition of the anti-lipolytic effects of adenosine. Beta-adrenergic receptor inhibition results in relatively significant increase in plasma glucose concentrations. Caffeine also stimulates an increase in catecholamine release, possibly secondary to the adenosine blockade. In addition to stimulating resting energy expenditure, caffeine’s increase in cellular thermogenesis also results in an increase in fatty acid turnover and lipid oxidation. Caffeine’s effect on lipid and energy metabolism appears to have both sympathetic and nonsympathetic components. It also inhibits the activation of phosphodiesterase, which stimulates cAMP degradation. Caffeine clearly has positive implications for lipid mobilization.
So to review, caffeine’s power as a supplement involves increased metabolic rate, improved energy and energy expenditure during exercise, as well as appetite suppression by making you feel satiated more rapidly and for an extended period of time. Though it unlikely comes as a surprise that caffeine provides your body with quite the boost, the extensive scientific evidence supporting its immense positive health implications may very well have given you a newfound appreciation for this its undeniably significant role in the world of exercise and nutrition.
 K Acheson et al. Metabolic effects of caffeine in humans: lipid oxidation or futile cycling? Am J Clin Nutr 2004;79:40–6.
 Benowitz NL, Jacob P, Mayan H, Denaro C. Sympathomimetic effects of paraxanthine and caffeine in humans. Clin Pharmacol Ther 1995; 58:684–91.