What is Metabolism? The Science Behind How the Body Burns Calories

Metabolism is often associated with weight loss and calorie burning, but it’s much more than that. Every breath we take, every muscle movement, and even digestion depend on metabolism to convert food into usable energy. While some people seem to have a naturally fast metabolism, others struggle with a slower rate, making weight management challenging. That said, understanding how metabolism works can help individuals make informed choices for better energy levels, improved health, and sustainable weight management. In this article, we’ll break down the science of metabolism, factors that influence it, common myths, and practical ways to maintain a healthy metabolic rate.

What is Metabolism?

Metabolism is the body’s internal energy system that keeps everything functioning, from breathing and digestion to cell repair and circulation. It is a complex network of chemical reactions that convert food into energy, which is then used for various bodily processes. Metabolism is divided into two main components:

1. Anabolism (Building & Storing Energy)

Anabolism is the constructive phase of metabolism, where small molecules combine to form larger ones. This process stores energy for future use and plays a vital role in tissue growth, cell repair, and hormone production. One example of an anabolic process is the synthesis of proteins from amino acids, which helps build muscle. Another example is the formation of fat stores from excess carbohydrates and lipids, allowing the body to store energy for later use.

2. Catabolism (Breaking Down & Releasing Energy)

Catabolism is the destructive phase of metabolism, where complex molecules break down into simpler ones to release energy. This energy is then used for physical activities, body temperature regulation, and essential organ functions. One example of catabolism is the breakdown of carbohydrates into glucose, which fuels various body processes. Another example is the conversion of fat stores into energy, which occurs during periods of fasting or exercise when the body needs additional fuel.

These two processes work simultaneously and in balance—when you eat, anabolism is at work storing energy, and when you move, catabolism breaks down stored energy to keep you active. In short, metabolism is what powers every cell in your body—from your brain to your muscles—making it essential for survival and overall well-being.

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) is the number of calories your body burns at rest to maintain essential functions like breathing, blood circulation, and cell production. Even when you’re not physically active, your body is constantly using energy to keep your heart beating, regulate body temperature, and repair tissues.

BMR is a key component of metabolism, as it accounts for the majority of the calories your body burns daily. A higher BMR means your body naturally burns more energy at rest, contributing to a faster metabolism, whereas a lower BMR indicates a slower metabolic rate, meaning fewer calories are used for basic functions.

What Affects Your BMR?

Several factors influence how fast or slow your BMR is, including:

• Body Size and Composition: People with more muscle mass burn more calories, even at rest, since muscle tissue requires more energy than fat tissue.
• Age: BMR slows down with age due to a natural loss of muscle mass and changes in hormonal activity.
• Gender: Men generally have a higher BMR than women because they tend to have more muscle and less body fat.
• Genetics: Some people inherit a faster or slower metabolism from their family.
• Hormonal Imbalances: Conditions such as hypothyroidism (underactive thyroid) can slow BMR, while hyperthyroidism (overactive thyroid) can speed it up.
• Environmental Factors: Cold weather can slightly increase BMR because the body has to work harder to maintain warmth.

How to Calculate BMR

Basal Metabolic Rate (BMR) is the number of calories your body burns at rest to maintain essential functions like breathing, circulation, and cell repair. Calculating your BMR helps determine how many calories your body requires daily, allowing you to make informed decisions about diet and exercise.

Formula for BMR Calculation

The most commonly used method to estimate BMR is the Harris-Benedict Equation, which differs based on gender:

• For Men: BMR = 88.36 + (13.4 × weight in kg) + (4.8 × height in cm) – (5.7 × age in years)
• For Women: BMR = 447.6 + (9.2 × weight in kg) + (3.1 × height in cm) – (4.3 × age in years)

Factors Affecting Metabolism

Metabolism is not the same for everyone—it varies based on a combination of biological, lifestyle, and environmental factors. Some people seem to burn calories effortlessly, while others struggle with weight management despite a similar diet and activity level. Understanding these factors can help in making informed lifestyle choices to support a healthy metabolism.

1. Muscle Mass

Muscle burns more calories than fat, even when the body is at rest. The more muscle a person has, the higher their metabolic rate, which is why strength training can help boost metabolism. As people age, they naturally lose muscle mass, which slows down metabolism. However, regular exercise, especially resistance training, can help preserve muscle and maintain a healthy metabolic rate.

2. Physical Activity

The more you move, the more calories your body burns. Aerobic exercises like running, cycling, and swimming increase calorie expenditure during the activity, helping with weight management and overall fitness. On the other hand, strength training exercises such as weightlifting and resistance training help build muscle, which in turn raises the resting metabolic rate, allowing the body to burn more calories even at rest.

3. Age and Gender

Metabolism naturally slows down with age due to muscle loss and hormonal changes. As people get older, their bodies tend to burn fewer calories at rest, making it easier to gain weight. Gender also plays a role, as men generally have a higher metabolism than women due to greater muscle mass and lower body fat percentage.

4. Hormonal Balance

Hormones play a critical role in regulating metabolism. Thyroid hormones (T3 and T4) control metabolic rate, with hypothyroidism slowing metabolism and hyperthyroidism speeding it up. Additionally, insulin resistance, often associated with obesity and diabetes, can make it harder for the body to use energy efficiently, leading to metabolic imbalances.

5. Genetics

Some people inherit a naturally faster or slower metabolism from their family. While genetics play a role, lifestyle choices such as diet, exercise, and sleep patterns can still influence metabolic rate. Even those with a slower metabolism can improve their energy expenditure through consistent physical activity and muscle-building exercises.

6. Diet and Hydration

What you eat and how well you stay hydrated directly impact metabolism. Protein-rich foods require more energy to digest due to their high thermic effect, which can slightly increase calorie burn. Spicy foods, such as chillies, may temporarily boost metabolism, but the effect is minimal. Staying hydrated is essential for all metabolic processes, as dehydration can slow down the body's ability to break down and utilize nutrients effectively.

7. Sleep and Stress

Lack of sleep can disrupt metabolism by affecting hunger-regulating hormones like ghrelin and leptin, leading to increased food cravings and potential weight gain. Chronic stress raises cortisol levels, which can promote fat storage and slow metabolic function over time. Ensuring adequate sleep and managing stress through activities like meditation or exercise can help maintain a healthy metabolic rate.

Tips to Support a Healthy Metabolism

While genetics and age play a role in metabolism, lifestyle choices can significantly influence how efficiently your body burns calories. Simple, sustainable habits can help maintain or even improve metabolic function. Here are some practical ways to support a healthy metabolism:

Engage in Regular Physical Activity

• Strength training – Lifting weights or doing resistance exercises builds muscle, which increases the resting metabolic rate.
• Aerobic exercises – Activities like running, cycling, and swimming help burn calories and improve overall metabolism.
• Stay active throughout the day – Avoid prolonged sitting by walking, stretching, or standing between work sessions.

Eat a Balanced Diet

• Prioritise protein – Protein-rich foods (eggs, fish, legumes, dairy) have a high thermic effect, meaning they require more energy to digest.
• Stay hydrated – Water is essential for all metabolic processes; dehydration can slow metabolism.
• Don’t skip meals – While fasting occasionally won’t harm metabolism, extreme calorie restriction can slow down energy expenditure over time.

Get Enough Quality Sleep

• Lack of sleep disrupts hormones that regulate hunger and metabolism (ghrelin and leptin).
• Aim for 7-9 hours of quality sleep per night to support metabolic function.

Manage Stress Levels

• Chronic stress increases cortisol levels, which can lead to fat storage and slower metabolism.
• Practices like meditation, yoga, and deep breathing can help lower stress and improve metabolic efficiency.

Include Metabolism-Supporting Foods

• Green tea and coffee – Contain compounds that can slightly enhance calorie burning.
• Spicy foods (chillies, ginger, turmeric) – Have a mild thermogenic effect that can increase metabolism temporarily.
• Fibre-rich foods – Whole grains, fruits, and vegetables aid digestion and prevent energy crashes.

When to See a Doctor About Metabolism Issues

While fluctuations in metabolism are normal, certain signs may indicate an underlying health condition that requires medical attention. If you experience unexplained changes in weight, energy levels, or body functions, consulting a doctor can help identify any metabolic disorders and provide appropriate treatment.

Signs That Require a Doctor’s Consultation

1. Unexplained Weight Changes – Sudden weight gain or weight loss without changes in diet or activity level could indicate thyroid issues, hormonal imbalances, or metabolic disorders.
2. Extreme Fatigue and Low Energy Levels – Constant tiredness, sluggishness, or difficulty staying active despite adequate rest may be a sign of slow metabolism, iron deficiency, or underlying medical conditions like hypothyroidism.
3. Difficulty Losing or Gaining Weight – If diet and exercise changes don’t seem to impact weight, it could indicate insulin resistance, hormonal imbalances, or metabolic adaptation.
4. Frequent Cold Sensations or Excessive Sweating – Feeling unusually cold all the time may suggest a slow metabolism (hypothyroidism), while excessive sweating or heat intolerance could indicate an overactive thyroid (hyperthyroidism).
5. Irregular Heart Rate or Blood Pressure – A consistently fast or slow heart rate, unexplained dizziness, or high blood pressure fluctuations may be linked to thyroid dysfunction or other metabolic disorders.
6. Persistent Digestive Issues – Slow digestion, bloating, constipation, or frequent digestive discomfort may indicate metabolic imbalances or nutritional deficiencies.
7. Uncontrollable Hunger or Loss of Appetite – A sudden increase or decrease in appetite without a clear reason could be linked to hormonal issues, blood sugar imbalances, or thyroid dysfunction.
8. Hair Thinning, Dry Skin, or Brittle Nails – Metabolic issues can affect hair, skin, and nail health, especially if caused by nutritional deficiencies, thyroid disorders, or hormonal changes.
9. Frequent Mood Swings or Brain Fog – Memory issues, trouble concentrating, or emotional imbalances could be linked to hormonal shifts or nutrient deficiencies affecting metabolism.
10. Family History of Metabolic Disorders – If you have a family history of thyroid disease, diabetes, or metabolic syndrome, regular check-ups are important to monitor any potential risks.

Common Myths About Metabolism

Metabolism is often surrounded by misconceptions that can lead to confusion about how the body burns calories. Let’s break down some of the most common metabolism myths and uncover the truth.

Myth: “Eating small meals at short intervals boosts metabolism”

Many people think that eating every 2-3 hours keeps metabolism active and helps burn more calories throughout the day. However, research shows that meal frequency has little effect on total calorie burn. What truly matters is overall calorie intake and nutrient balance, not how often you eat.

Myth: “Certain foods can significantly speed up metabolism”

Some claim that foods like green tea, chilli peppers, and coffee can drastically increase metabolism. While these foods have a small thermogenic effect, the impact is temporary and minimal. Instead of relying on specific foods, a well-balanced diet and regular exercise are the most effective ways to support metabolic health.

Myth: “People with a slow metabolism can’t lose weight”

A slow metabolism is often blamed for weight gain, but it’s not the sole factor. While some people naturally burn fewer calories due to genetics or medical conditions, weight loss is still possible with calorie control, strength training, and an active lifestyle. Metabolism can be improved over time with the right habits.

Myth: “Skipping meals slows down metabolism”

It’s commonly believed that missing a meal will cause the body to go into “starvation mode” and slow metabolism. In reality, occasional fasting does not significantly impact metabolic rate. However, long-term extreme calorie restriction can cause the body to conserve energy, making weight loss more difficult. Eating balanced meals at regular intervals is ideal for sustaining energy levels.

Myth: “Thin people have a fast metabolic rate”

Many assume that thinner individuals must have a naturally fast metabolism, but this isn’t always true. Metabolic rate depends on muscle mass, age, activity level, and genetics—not just body size. In fact, larger bodies burn more calories at rest because they require more energy for basic functions.

Conclusion

Metabolism is at the core of how your body converts food into energy, impacting everything from weight management to overall well-being. While factors such as age and genetics play a role, your daily lifestyle choices—exercise, diet, sleep, and stress management—can significantly influence your metabolic rate. If you're struggling with unexplained weight changes, fatigue, or metabolic health concerns, it’s essential to seek expert medical guidance. At Max Hospitals our team of experienced endocrinologists and nutritionists provides comprehensive metabolic assessments, personalised diet plans, and advanced treatments to help you achieve optimal metabolic health. Book an appointment with Max Hospitals today for expert guidance on maintaining a healthy and active lifestyle.

FAQs about Metabolism

Q. Can metabolism change over time?

Yes, metabolism naturally slows down with age due to a gradual loss of muscle mass and hormonal changes. However, regular strength training, staying active, and maintaining a balanced diet can help sustain a healthy metabolic rate. Certain medical conditions, such as thyroid disorders, can also cause metabolic fluctuations, which may require medical intervention.

Q. Does drinking cold water boost metabolism?

Drinking cold water may slightly increase calorie burning, as the body uses energy to warm the water to body temperature. However, the effect is very minimal and not a significant way to boost metabolism. Staying hydrated in general is far more important for maintaining an efficient metabolism.

Q. Can lack of sleep affect metabolism?

Yes, poor sleep quality or sleep deprivation can slow metabolism by disrupting hormonal balance. Lack of sleep increases ghrelin (hunger hormone) and decreases leptin (satiety hormone), leading to increased appetite and potential weight gain. Prioritising 7-9 hours of sleep per night is essential for metabolic health.

Q. Do artificial sweeteners impact metabolism?

There is some debate about the effects of artificial sweeteners on metabolism. While they do not contain calories, some studies suggest that they may alter gut bacteria, potentially influencing insulin response and appetite regulation. However, occasional use in moderation is unlikely to have a significant effect on metabolism.

Q. Can certain medications affect metabolism?

Yes, some medications can increase or decrease metabolic rate. For example:

• Steroids and antidepressants may slow metabolism and contribute to weight gain.

Stimulants, some thyroid medications, and certain diabetes drugs can increase metabolism.
If you suspect your medication is impacting your metabolism, consult a doctor for alternative options or adjustments.