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Metabolism: What is it, and how does it affect our bodies?

| Healthy You | Weight Loss | Wellness

Pink highlighter pen marking the word "metabolism" on a printed page

This vital function helps our bodies create and spend energy.

We’ve heard people talk about metabolism. “She can eat anything. She has a fast metabolism,” or “Our metabolism slows as we age; that’s why we gain weight.” But do you really know what your metabolism is or how it affects our bodies? Read on as we explain metabolism, how it works, and what you can do to improve it.

“Metabolism is a vital tool our body uses to create and spend energy,” says Jendy Newman, RD, CDE, at PeaceHealth Southwest Specialty Clinic in Vancouver, Washington. “It’s often misunderstood and thought of as pure genetics, but there are many things you can do to affect your metabolism.”

What is metabolism?

Metabolism is a series of chemical reactions that occur in your body. The three primary purposes of metabolism are the conversion of the energy in food to energy available to run cellular processes; the conversion of food to building blocks for proteins, lipids, nucleic acids and some carbohydrates; and the elimination of metabolic wastes.

Metabolism is broken down into two processes: anabolism and catabolism.

  • Catabolism is the process in which proteins, fats or tissues break down into smaller cells (cells or fatty acids). This occurs when you digest food (ex., bread broken down into glucose).
  • Anabolism is the process in which smaller cells (nutrients, cells or amino acids) are bonded together to create bigger structures (ex. When your body is trying to heal a cut by adding tissue and structures around the wound).

Your basal metabolic rate (BMR) is the number of calories your body needs to accomplish its most basic (basal) life-sustaining functions, such as breathing, circulation, nutrient processing and cell production. Your BMR can be used to help you gain, lose or maintain your weight. There are multiple ways to calculate your BMR; the Mifflin-St Jeor Equation is considered the most accurate. Calculate yours using this online calculator.

“Even the best BMR calculators provide only an estimate that should be used as a guide,” says Newman. “Meeting a registered dietitian and discussing your lifestyle habits and goals will help them form a nutrition plan to meet your needs.”

What affects your metabolism?

The general factors that affect metabolism are:

  • Genetics. A handful of genetic factors determine how much energy your body needs and your ability to build muscle mass.
  • Body size and muscle mass. Larger bodies have more metabolic tissue and a higher basal metabolic rate requiring more calories. Muscles burn calories faster than fat cells.
  • Sex. Generally, men have faster metabolisms because their bodies are larger and have more muscle mass than most women.
  • Physical Activity. Exercise causes your body to burn more calories than when you’re sedentary.
  • Age. A common myth is that your metabolism slows as you age, but age isn’t the problem. As you get older, you may not be as physically active or you may have less muscle mass, or your diet may not have changed to meet your body’s needs.
  • Smoking. Smoking cigarettes increases your heart rate, resulting in faster metabolism and more calories burned. This is why people who quit smoking often put on weight. The health consequences of smoking (cancer, high blood pressure, heart disease) far outweigh the health consequences of a few extra pounds. Watching what you eat, and exercising can help keep the weight off. 
  • Sleep. Sleep helps regulate your blood sugar. A lack of sleep causes your body to have trouble with blood sugar levels, leading to a lack of energy.

Certain endocrine disorders, such as hypothyroidism, can affect metabolism, causing it to be slower. In addition, several metabolic disorders can also affect the body. These disorders may cause a buildup of fatty substances in organs or an excess of minerals.

The relationship between metabolism and your weight

The relationship between metabolism and weight is often misunderstood. It’s easy to blame problems with weight on metabolism. But maintaining weight is a complex process involving genetics, hormones, diet, lifestyle, sleep, physical activity and stress.

Having a fast metabolism does not necessarily lead to thinness. In fact, studies show that people who are overweight/obese often have fast metabolisms. Their bodies need more energy to keep essential body functions going.

A lack of activity combined with lower energy needs creates a slow metabolism (meaning your body needs fewer calories to energize its essential functions). If you give your body too much energy in the form of calories, that energy has nowhere to go and is stored as fat leading to weight gain. Take in fewer calories than you burn, and you lose weight. 

Your metabolism is working to maintain your weight. Extreme dieting often leads to weight loss consisting of muscle mass and not fat. You can’t change your routine for a few days and expect significant changes. Balancing good habits will help your metabolism recognize a new ideal weight.

How can you improve your metabolism?

No miracle drug will improve your metabolism. But there are healthy lifestyle habits that will help improve your metabolism.

  • Exercise. Add strength training or other weight-resistance exercises to your routine to help build muscle. High-intensity interval training (for example, when walking or running, speed up for 30-60 seconds, then slow down to your regular pace, repeating for eight to 12 cycles) may also help boost your metabolism.
  • Eat a healthy diet. We eat to provide energy to our bodies. Fuel your body with lean protein, fresh fruits and vegetables and healthy carbohydrates and fats.
    • Lean protein takes longer for the body to burn and absorb than fat and carbohydrates; combine an increased protein intake with weight training to increase muscle mass.
    • Healthy carbohydrates in beans and legumes, fruits and vegetables, and whole grain products take longer for the body to process and provide more nutrients than simple carbohydrates in many processed foods.
    • Healthy fats are found in whole/unprocessed plant foods like avocados, coconuts, nuts and seeds, as well as animal foods, including meat, poultry, fish and dairy. Minimally processed oils (unrefined or cold pressed) can also be a healthy source of fat.
    • An increase in fiber can help burn fat by 30%. Fiber is found in many plant-based foods, such as fruits, vegetables, nuts, and whole-grain products. Animal products, including dairy products and meats, have no fiber.
  • Don’t skip meals. Eating proper meals boosts our metabolism and keeps us energetic throughout the day. Skipping meals and restricting too many calories forces your body to break down muscle for energy. 
  • Sleep. A lack of sleep affects your brain’s frontal lobe, which may decrease impulse control and decision-making ability.

“Metabolism is a complex process, but one that can be improved with some basic healthy lifestyle habits that will also help improve your overall health,” says Newman. “It takes time for your metabolism to adjust, so make one or two small habit changes and give your body time to adjust.”

If you want a healthy metabolism, eat fiber and nutrient-rich foods, avoid smoking and exercise moderately. Talk with your primary care doctor or a dietitian if you want to learn more.

Sources: Mayo Clinic, Cleveland Health, CDC