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According to the latest research, more than 1 billion people around the world have obesity. It is considered a complex chronic disease defined by having excessive fat deposits that can negatively impact health. Obesity can increase a person’s risk of several health complications, such as type 2 diabetes, heart disease, and osteoarthritis. Recently, researchers have discovered that higher levels of caffeine in the blood over a long period of time may protect the body against obesity.

Caffeine Intake vs Circulating Caffeine

Caffeine is the most commonly used stimulant in the world, making caffeine intake fairly easy to study. However, caffeine intake differs from circulating caffeine, or caffeine levels in the blood (plasma caffeine). Plasma caffeine is caffeine that is active, allowing it to affect bodily functions. The level of plasma caffeine not only changes based on caffeine intake, but also on its metabolism influence by genetic variants. For example, there are genetic variants that may affect and break down plasma caffeine faster than others. Therefore, someone who drinks coffee every morning with a genetic variant that speeds caffeine metabolism may not have higher plasma caffeine than someone who drinks the same amount with a genetic variant that metabolizes caffeine at a slower rate. Additionally, most of the research that has been conducted on caffeine and obesity contains data on caffeine intake rather than plasma levels of caffeine. One meta-analysis from 12 studies revealed an association between coffee intake and lower body mass index (BMI) in men, but not in women. In the same study, higher coffee intake was associated with an increased risk of obesity in women, but not in men. It is possible that these inconsistencies are related to sex related differences in caffeine metabolism.

Plasma Caffeine and Obesity

A newer study from the United Kingdom (UK) published earlier this year (2024) revealed novel evidence suggesting that long-term increases in circulating caffeine may reduce body weight and the risk of osteoarthritis. In this genetic investigation, researchers studied the clinical effects of plasma caffeine in a phenome-wide association study (PheW) to better understand how genetics plays a role in the association between caffeine intake and obesity. They discovered that individuals with genetic variants that slow down caffeine metabolism have higher plasma caffeine, consequently lowering caffeine consumption. Alternatively, individuals with lower plasma caffeine (due to faster metabolism) tend to have higher caffeine intake. These findings suggest that consuming more caffeine does not necessarily suggest having high levels of caffeine. The results of their study concluded that long-term increases in plasma caffeine may help lower body weight, thus having a protective effect on obesity risk. These findings clarify that the association between lower obesity risk and increased plasma caffeine reflects slower caffeine metabolism. As always, it is important to keep in mind that these are cross sectional correlational studies, which don’t allow to make conclusion about caffeine intake being causally related to body weight.

How caffeine promotes weight loss has much to do with its influence over energy expenditure (EE), energy intake (EI), thermogenesis and fat oxidation. Caffeine has been found to increase EE and decrease EI. Since obesity is an imbalance between EI and EE, this makes caffeine a potentially useful tool for managing body weight. Additionally, caffeine can stimulate fat metabolism when binding to fat cells. This suggests that obese individuals may positively respond to caffeine if they have a genetic variant that slowly metabolizes caffeine, making it widely available in the blood for a sufficient amount of time for cells to use.

How Much Caffeine Should I Consume?

Understanding that genetic differences play a role in the amount of caffeine circulating in the blood makes healthy caffeine consumption look different for everyone. Some studies have demonstrated that consuming at least 3 milligrams (mg) of caffeine per kilogram (kg) of body weight is sufficient for increasing fat metabolism during low or moderate exercises. This finding highlights the importance of ingesting caffeine before a workout to maximize fat metabolism. Therefore, someone who weighs 68 kg (150 lbs) would need about 200 mg of caffeine a day, which is a little more than 2 cups of coffee. This may work for people who can metabolize caffeine quickly and without experiencing anxiety or jitters after drinking coffee. However, for those who do experience anxiety from caffeine consumption, it may be best to consider lowering the dosage to a quantity that promotes energy rather than anxiety.