Caffeine is a stimulant and can be found in coffee, tea, soft drinks, chocolate, caffeine pills, sports supplements, gums, energy drinks, and more. Coffee is the most widely consumed caffeinated beverage in the world. Most people use caffeine as a performance aid, a tool to increase their focus, and also as an appetite suppressant. Caffeine metabolizes primarily in the liver and is absorbed quickly, therefore having an effect on reducing fatigue, improving endurance, and increasing energy and focus.
Some studies suggest that caffeine can aid in weight loss; however, the effect can vary greatly between individuals. For example, some individuals can see improved metabolism; however, regular caffeine consumption could decrease benefits. Most athletes use caffeine for its ergogenic effect; they stop consuming caffeinated products and drinks so that when they need them for competition day they can maximize the performance effect of caffeine. The same goes for weight loss purposes, as benefits can diminish over time.
The potential of caffeine’s weight loss effects can be attributed to several factors. Through the thermogenesis effect, caffeine can increase the body’s production of heat which results in higher caloric expenditure and can potentially lead to weight loss. Through lipolysis, caffeine can enhance the mobilization of free fatty acids and thus promote fat oxidation and utilization as an energy source. And through appetite regulation, caffeine can contribute to appetite suppression, which leads to a reduction in food intake and subsequent weight loss. However, most studies are not conclusive, and the long-term effectiveness of caffeine for weight loss is still unclear.
The body is also able to develop a tolerance to caffeine, which may reduce its weight loss benefits over time. Additionally, excessive caffeine intake can lead to negative side effects including increased heart rate, anxiety, and sleep disturbances. Caffeine can also have a laxative effect in some individuals, and caffeinated beverages can increase the risk of developing gastroesophageal reflux disease (GERD), especially if consumed on an empty stomach. Caffeine can also inhibit the absorption of some vitamins, including iron, calcium, and B vitamins.
Earl Grey tea (one cup) contains about 30–40 mg of caffeine, while espresso contains 125–150 mg of caffeine. However, energy drinks and pre-workout supplements can contain 300–400 mg of caffeine per serving.
Studies also show that caffeine may increase energy but not metabolism. Some people with specific variants of the gene type CYP1A2 are slow metabolizers of caffeine, which means that the clearance of caffeine is slow (AC or CC genotype) while others can metabolize caffeine more quickly (AA genotype) and will see more benefits than the slow metabolizers. For example I am a slow metabolizer, which means that if I consume more than 150–200 mg of caffeine per day the effects can become negative.
There are other substances that may enhance weight loss when taken in conjunction with caffeine. Green tea extract contains the compound epigallocatechin gallate (EGCG) which may enhance thermogenesis and fat oxidation when combined with caffeine. Capsaicin, which is responsible for the strong taste in chili peppers, has been shown to increase thermogenesis and energy expenditure when combined with caffeine. And L-carnitine, an amino acid involved in fatty acid transportation into cells for energy production, has been shown to enhance fat oxidation and weight loss when taken alongside caffeine.
So caffeine may contribute to weight loss through various mechanisms, including thermogenesis, lipolysis, and appetite regulation, however its long-term effectiveness remains uncertain due to factors such as tolerance development and potential side effects. There is strong evidence to show that the combination of caffeine with certain other substances may enhance weight loss, but further research is necessary to establish the most effective dosages, combinations, and long-term implications of which substances and combinations would be ideal for weight management.
Of course, caffeine and other substances are only one tool in the toolbox so regardless of how much of an effect it might have you still need to approach weight loss with healthy eating habits and being physically active so that you can sustain your new weight and not rely on any other supplements.
The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials. Critical reviews in food science and nutrition. https://pubmed.ncbi.nlm.nih.gov/30335479/
Coffee, CYP1A2 Genotype, and Risk of Myocardial Infarction. https://jamanetwork.com/journals/jama/fullarticle/202502
Metabolic effects of caffeine in humans: lipid oxidation or futile cycling? https://academic.oup.com/ajcn/article/84/4/682/4633022