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How Your Diet Affects Your Metabolism

Fitday Editor

Metabolism is the term used to collectively describe the various processes that take place in the body to sustain life and normal functioning. This includes numerous complex tasks including converting food into energy, making new cells and tissues, breathing, circulating blood, regulating body temperature, removing wastes, and much, much more.

Resting Metabolic Rate

Because all of this work requires energy, the body must use calories to carry out these processes. The number of calories burned when the body is at rest is called the "resting metabolic rate" (RMR), sometimes also referred to as the "basal metabolic rate" (BMR), and accounts for approximately 60 to 70 percent of calories burned each day. The RMR is the minimum amount of calories the body must have to function properly when at rest; this does not include the calories needed to perform exercise or other daily activities.

Each person's RMR will vary based on genetic predisposition, body size and composition, gender and age. Individuals who have larger and/or more muscular bodies will burn more calories at rest. Men typically have less body fat and more muscle than women, and therefore will burn more calories at rest since muscle tissue burns more calories than fat tissue. Additionally, as we age, muscle tissue tends to decrease while fat tissue may increase, thereby slowing down the metabolic rate.

Other factors like illness, drugs, dietary deficiencies and hormonal imbalances can also alter metabolism.

Diet and Metabolism

According to the Mayo Clinic, energy needs for the body's basic functions stay fairly consistent and aren't easily changed. However, shifts in diet and body composition can alter the body's functioning.

It is very important to meet RMR calorie needs daily. Eating too few calories, such as in extreme dieting, can actually slow the metabolism. Without enough energy, the body begins to conserve calories which can lead to a host of undesirable side effects including fatigue, difficulty concentrating, moodiness, decreased immunity, and reduced muscle tissue resulting from the body breaking it down to create energy.

Additionally, eating an unhealthy diet and too many calories can lead to other metabolic issues. Having a large waistline, high triglycerides, low HDL cholesterol, high blood pressure, and/or high fasting blood sugar can lead to metabolic syndrome. The National Heart, Lung and Blood Institute states that metabolic syndrome not only disrupts the normal biochemical processes in the body, but also increases the risk for heart disease and other health problems such as diabetes and stroke.

Maintaining a Healthy Metabolism

In order to stay healthy and keep the metabolism, or body processes, functioning like a well-oiled machine, it is important to eat a nutritious diet and exercise.

A healthy diet with balanced calories to meet the RMR, while avoiding overeating, provides adequate energy and nutrition to fuel and repair the body effectively.

Exercise not only helps the body burn extra calories during the day, but if muscle is added, will help increase the RMR. Aerobic exercise is the best way to burn calories, while strength training increases muscle mass.

How Fast is Your Metabolism?

There are various ways to measure RMR, including prediction equations and indirect calorimetry. To find out what your balance of calories should be, talk with a dietitian or doctor.


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Mandy Seay is a bilingual registered and licensed dietitian who holds both a bachelor's degree in nutrition and in journalism. After gaining 30 pounds while living abroad, Mandy worked to lose the weight and regain her health. It was here that she discovered her passion for nutrition and went on to pursue a career as a dietitian. Mandy currently works as a nutrition consultant and freelance writer in Austin, Texas, where she specializes in diabetes, weight management and general and preventive nutrition. She recently published her first book, Your Best Health, a personalized program to losing weight and gaining a healthy lifestyle. Please visit Mandy's website at

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