Metabolic Health

Caffeine and Its Metabolic Effects: A Simple Guide

Lienna May

September 28, 2022

Caffeine is a stimulant found in more than 60 plant species, including coffee beans, cacao beans, and tea leaves. You can consume it through coffee, tea, or soft drinks. It is a central nervous system stimulant that can lead to enhanced attentiveness. One consumes caffeine to stay awake and alert, and overcome tiredness. It is the primary active ingredient in coffee. While other sources also have caffeine, an average cup of coffee carries 75-100mg of it. However, this level varies across the world as preferences differ. 

Metabolism involves a set of chemical reactions in the body. These processes produce and use energy. According to a study, metabolism depends on gender, race, exercise, diet, age, and diseases. As a result, the metabolic rate is different for different people. For example, some have a high metabolic rate, requiring food consumption more frequently than others. 

According to research, caffeine increases energy metabolism throughout the brain. In addition, caffeine has hormonal effects on our body, like activating noradrenaline neurons and releasing dopamine. Therefore, moderate caffeine intake may cause positive physiological consequences like improved cognitive performance. But too much caffeine consumption can affect sleep and cause anxiety. 

Research has recently found that caffeine can increase metabolic rate and influence weight loss. For example, one study found that in lean and post-obese (not obese anymore) individuals, 100g of caffeine increased the metabolic rate by 3-4%. Since increased metabolism aids in losing weight, caffeine can also regulate metabolism for weight loss. However, taking precautionary measures while using caffeine is better because it can cause some adverse effects. 

You can use HealthifyPro’s CGM-based BIOS, a wearable device, to know the impact of caffeine on the body and blood glucose levels. For example, having coffee on an empty stomach before or including a cup of black coffee as a mid-morning drink after breakfast will significantly impact blood glucose levels. Reading the real-time oscillation in blood glucose levels, combined with HealthifyPro’s real-time feedback from our top fitness and nutrition coaches, can be very effective in helping you choose the best way to plan meals. So it is not only about the eating right food. It is eating at the right time in correct proportion. 

Caffeinated Products

You can find caffeine in coffee, tea, chocolates, etc. The amount of caffeine in each product will vary. You can use the following chart to know approximately how much caffeine is in these beverages. The information is according to research in the United States, so the amount of caffeine in India might vary slightly. 

In 12 oz (around 350ml) of these drinks, the amount of caffeine present (in milligrams) is: 

  • Instant coffee: 140mg
  • Expresso: 480mg
  • Plain or brewed coffee: 200mg
  • Green tea: 68mg
  • Black tea: 72mg
  • Brewed tea: 80mg
  • Coca-cola classic: 35mg

Despite the amount of caffeine in different drinks, expresso has the highest amount, followed by brewed coffee and soft drinks. According to the USDA (United States Department of Agriculture), 100g of dark chocolate contains 43 mg of caffeine, and 100g of milk chocolate contains 20g. It would help if you kept these in mind because too much caffeine (more than 400mg) can be harmful.

Careful Caffeine Consumption

Caffeine has positive and negative effects on the body. Therefore, to avoid the harmful effects of caffeine, one must be aware of how much of it  one consumes. 

The European Food Safety Authority (EFSA) published a study in 2015 on safe levels of caffeine consumption. According to this study, for an adult weighing 70kg, doses of caffeine up to 200mg are not a concern. For women who are not pregnant and men, up to 400 mg of caffeine per day wouldn’t cause any issues. For pregnant women, up to 200mg per day might be accepted but not more than this level. Additionally, the EFSA cautioned that, in some adults, a single intake of 100 mg of caffeine could shorten sleep duration. 

The allowance of children to consume caffeine in the form of coffee or tea is still a topic of debate. One review of studies points out that caffeine affects children’s growth and development in a positive way. It  found that you can use caffeine to treat Attention-deficit Hyperactivity Disorder (ADHD) as it increases arousal. In addition, children who consumed caffeine had more strength and physical performance during exercise. However, it causes negative disturbances in the sleep cycle and might increase symptoms of depression. 

Most paediatricians do not recommend caffeinated products, especially energy drinks and coffee, for children under 12 years of age. For those aged 12-18, the caffeine consumption limitations are 100mg daily. However, it is essential to note the sources and amount of caffeine to ensure that there is no overdose. 

Caffeine Consumption and its Effects

Caffeine goes into the bloodstream and body tissues after oral ingestion. Around 45 minutes to 1 hour after intake, absorption is complete. This time frame may be shortened or lengthened in specific populations, including pregnant women, smokers, and those with impaired liver function. The effects of caffeine can be observed as little as 20 minutes after consumption. Caffeine has a half-life of around 5 hours. It means that after 5 hours, half of the caffeine consumed is still in the body. The excess caffeine that is present produces effects that last longer than 5 hours.

Research has shown that consuming caffeine can reduce symptoms of Parkinson’s disease, such as tremors. It also acts as a protective factor against the onset of this disease. Other benefits include improvement in mood, reaction time, the speed at which one can process information, attention, and awareness.

The role of caffeine in weight loss and increasing metabolism is now the focus of research. Since maintaining proper body weight will reduce the risk of obesity, being overweight, cardiovascular diseases, diabetes, stroke, and metabolic syndrome. 

One study found that lean women who consumed coffee burned more calories than obese women who also had coffee. Although obese women burnt calories, it was a smaller amount. In thin women, the effects of caffeine lasted longer (during the night), which helped in burning more calories. 

According to a study, caffeine similarly influences the metabolism of older and younger adults. However, in older adults, there is a more significant impact on calcium metabolism and its effect on bones. In addition, other factors like gender, hormonal levels, medications, liver disease, smoking, diet, and obesity also influence how caffeine works in individuals. 

Consuming caffeine might be beneficial for various reasons in the short term. However, with continuous consumption, ‘caffeine tolerance’ develops. That is when the effects of caffeine diminish with time. Therefore, the person needs to consume more caffeine to have the same effects as the first few times. 

Some people may have undesirable side effects if they consume caffeinated foods or beverages in excess. These include anxiety, hyperactivity, agitation, and having trouble sleeping.

There are a few adverse effects of excess caffeine consumption. These include:

  • It might overstimulate the brain and lead to confusion.
  • Can cause headaches and irritability
  • Palpitations or irregular heartbeats and a rapid heart rate might occur because of an increased amount of caffeine in the body. 
  • Nausea, vomiting and diarrhoea
  • Increased urination
  • It might cause anxiety or sometimes even panic in susceptible individuals, e.g., those with anxiety or panic disorders

If people who have consumed caffeine in large quantities suddenly stop drinking caffeine, they might experience ‘caffeine withdrawal’. The symptoms are anxiety, confusion, irritability, vomiting, sleepiness, and in some cases, tremors and hallucinations. 

The HealthifyMe Note

You can primarily find caffeine in coffee, tea, energy drinks, and chocolates. It has positive effects such as increasing alertness and reaction time, reducing tiredness, facilitating weight loss by increasing metabolism and improving mood. The recommended level of caffeine for adults is up to 400 mg daily. Consuming more caffeine will result in adverse effects like anxiety, increased urination, tremors, etc. Caffeine consumption is not advisable for children. 

Relation Between Metabolism and Caffeine

Metabolic health signifies the balance in the rate of metabolism. Conversely, a person with poor metabolic health is likely to have high blood pressure, high cholesterol levels, low levels of good HDL cholesterol, high blood sugar, and a large waistline. 

Caffeine increases metabolism, thereby helping in weight reduction by burning more calories. According to a study, metabolic rate increased significantly 3 hours after caffeine ingestion in normal and obese individuals. In addition, in those with average weight, there was greater fatty acid breakdown (which helps reduce weight) than in obese individuals. 

Data suggests that genetic factors also play a crucial role in how a person reacts to caffeine and in evaluating how much coffee the person wants to have. Therefore, problems with these genes will lead to disturbances in metabolism after consuming caffeine. 

Type 2 diabetes results from high blood sugar levels. It, in turn, influences metabolism. One study found that the risk of type 2 diabetes decreased in young and middle-aged women when they moderately consumed caffeine. However, these results were obtained only in participants drinking coffee but not tea. These studies show that there is an association between metabolism and caffeine.

Effects of Caffeine on Metabolic Health

Increased Metabolic Rate

The Resting Metabolic Rate (RMR) refers to the rate at which calories are burnt by the body when at rest. A person’s ability to lose weight and the quantity of food they consume without gaining weight depends on their metabolic rate. Caffeine increases the RMR by about 3-11%, and higher doses have a more significant impact. It is because caffeine increases the calories burnt while at rest by rising RMR. The rise in metabolism is because of a boost in fat burning. 

Unfortunately, this increase in metabolism is less noticeable in those who are overweight or obese. According to a study, coffee enhanced fat burning by up to 29% in lean individuals while only increasing it by 10% in obese people. The impact is more significant in younger people and also seems to diminish with age. Nevertheless, caffeine in most people increases the metabolic rate. 

Fat Tissue Breakdown

Caffeine stimulates the neurological system, which signals the fat cells. You can achieve this signalling by increasing the adrenaline levels in the blood. Adrenaline is the hormone that signals the fat tissues to start breaking down fat and release them into the bloodstream. 

A negative energy balance occurs when a person consumes fewer calories than what is required by the body. That is where energy input is less than the energy expenditure. This type of energy balance usually results in weight loss. You can achieve this negative energy balance by consuming less or exerting more through physical activities. Drinking a cup of coffee or tea can also help boost metabolism and aid in weight loss.

Long-term Weight Loss Effects

Humans develop a tolerance to caffeine’s effects over time. Caffeine tolerance occurs when the impact of caffeine decrease over time with regular consumption.

Even if caffeine doesn’t help long-term to burn calories, it has the potential to reduce one’s appetite. A study found that a moderate amount of coffee (which contains caffeine) can reduce energy intake in the next meal and throughout the day. This effect was prominent in obese and overweight individuals. 

You can do ‘caffeine cycling’ by reducing the amount of caffeine intake or by stopping caffeine consumption for a while. This period can be between 2-8 weeks, depending on caffeine consumption. This cycling will help sustain caffeine’s effects, including increased alertness, weight loss, and mood improvements. 

The HealthifyMe Note

Caffeine intake increases metabolism, reduces fat tissues, and provides long-term weight loss results. Effects are more visible in lean people than in overweight or obese individuals. You can do caffeine cycling to sustain the effects of caffeine for a long time. That is where a person stops or gradually reduces caffeine consumption for a while. 

Factors Affecting Caffeine Consumption and Digestion

How caffeine gets digested in the body depends on various factors. Below are some of how caffeine may be processed and utilised by the body and can be affected by various individual, non-genetic factors. 

Liver Illness

The primary organ involved in the metabolism of caffeine is the liver. Research on the possible effects of specific liver conditions, such as cirrhosis and hepatitis B or C, reveals that they may cause impaired caffeine elimination in proportion to the severity of the disease. 

Smoking History

According to research, smoking increases the rate of caffeine digestion due to enzyme activation and speeds up caffeine clearance. Therefore, it will result in diminished effects of caffeine. Conversely, if a person stops smoking, it decreases caffeine clearance. Consequently, it also restores the natural rhythm of caffeine metabolism.


Several dietary variables may also impact the metabolism of caffeine. For example, consuming grapefruit juice increases half-life by 31% and reduces caffeine clearance by 23%. It simply means that caffeine stays in the body for longer, producing long-lasting effects. 

Brassica vegetables include cabbage, broccoli, cauliflower, turnip, brussels sprouts, kale, etc. A study found that consuming brassica vegetables stimulates caffeine metabolism. In addition, plasma caffeine levels (in the blood) increased in participants who consumed caffeine. 


Caffeine metabolism slows down during pregnancy, especially in the third trimester. It results in an increase in caffeine half-life and a decrease in the activity of the critical enzyme involved in caffeine metabolism. A few weeks after childbirth, the metabolism of caffeine returns to normal. Caffeine half-life is nearly doubled by oral contraceptive use, especially in the second half of a menstrual period (the luteal phase).

Alcohol Consumption

Caffeine does not alter the motor or psychiatric symptoms of alcohol intoxication. It also doesn’t reverse the negative impact of alcohol on physical abilities. 


Some medications may change caffeine’s pharmacokinetics (absorption, metabolism, excretion, and spreading of drugs). Therefore, healthcare practitioners should examine how specific drugs would affect caffeine consumption. In addition, consulting experts would help better understand the possibilities of taking medication alongside caffeine consumption. That is especially so if the effects of caffeine are not very evident even after consuming moderate to large quantities. 

Genetic Issues

Genetics can influence whether a person develops side effects. It is rarely the case, but it might be safer to have an allergy test before consuming caffeine.


Caffeine might temporarily increase your metabolism; this impact is less in long-term coffee drinkers due to tolerance. It is imperative to note the amount of coffee consumed daily. It is safe to consume up to 400 mg daily and in single doses of 200 mg. There are also weight loss results from consuming caffeine. Still, it is primarily in individuals who are not obese or overweight. Cycling caffeine can be a way to avoid developing tolerance and sustaining weight loss effects. The optimum cycles might be two-week cycles with two-week breaks.

About the Author

Received Master’s Degree in Nutrition from the University of Bridgeport - one of the most advanced scientific and evidence-based nutrition programs in the US. Lienna is also board-certified in Clinical Nutrition (CNS) by the American Nutrition Association and a licensed clinical dietician/nutritionist in the State of Florida. She is also certified by Yale University in 'The Science of Well-Being.' "I help my clients uncover the root causes behind their symptoms, understand their motivations, and help them break down big goals into manageable steps! My passion is to share the power of food and lifestyle as a form of medicine."

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