Most of us, particularly if we struggle with our weight goals, have blamed the dreaded “metabolism” monster: “It’s too slow,” we say. We often target it as a common weight-loss enemy without truly knowing the factors that play into metabolism — and whether or not we can change them.
3 major things that determine your metabolism
Metabolism refers to the process of converting the calories you eat into energy to power all of your bodily processes. Your metabolism determines the amount of calories you can eat all day and still maintain your weight. It’s affected by three major things:
- Basal metabolic rate (BMR): Tells you the number of calories needed to maintain your body in a rested, fasting state. It’s affected by your gender, age, size, muscle mass, genetics and health-related factors. Your BMR accounts for 60-70% of the total calories you burn each day.
- Activity level: Tells you the number of calories you use up during exercise. Your activity level accounts for about 20% of the total calories you burn each day.
- Food thermogenesis: Tells you the number of calories you need to digest and absorb your food. It accounts for about 10% of the total calories you burn each day.
Anything that affects the three major things mentioned above would change the amount of calories you need to maintain your body weight. Your basal metabolic rate is adaptable, and it will increase or decrease to provide for your body’s needs. For example:
- Your metabolism dials up and burns more calories during a fever or infection to help you heal.
- Your metabolism dials down and burns fewer calories during a long fast to conserve calories and prevent you from wasting away.
How aging affects metabolism
If you’re a healthy adult, your metabolism is likely a-okay. Instead of blaming thyroid diseases, relatively rare culprits of a slowed metabolism, you should consider how aging slows metabolism—and implement strategies to fight back. Aging happens to everyone, and it’s usually accompanied by a decrease in BMR. Why?
Our BMR is naturally at its highest during childhood and adolescence, mainly because we need the extra calories to grow and mature into adulthood. Once we reach our 20s, this phase is complete and our BMR levels off. The trend here on out is sneaky, steady weight gain over the course of decades. Research published in the New England Journal of Medicine revealed the weight-gain trends of 120,000 participants for up to 20 years. Scientists found that participants gained about 3.4 pounds (1.5 kilograms) each over a four-year period, which translates to a gain of 16.8 pounds (7.6 kilograms) over 20 years.
The biggest issue isn’t so much the weight gain, but the type of weight we tend to gain as we age; most of us tend to lose lean muscle mass and correspondingly replace it with fat. In a typical young adult, lean muscle mass makes up about 50% of total body weight, which declines to about 25% of total body weight when that individual reaches 75-80 years old. Having lower lean muscle mass decreases our BMR since, pound for pound, it takes more energy to maintain muscle compared to fat.
Don’t get me wrong! Having a protective amount of fat is a good thing, especially when we hit an older age, which is why adults aged 65 and older are advised to maintain a BMI between 25 to 27, instead of the 18.5 to 24.9 recommendation for the rest of us. The goal, of course, is to maintain as much lean muscle mass as possible since doing so would…
- Stop your BMR from declining. It has been shown time and again that BMR naturally decreases as we age. But, if you can maintain or build upon the muscle mass that you have, you’ll have a higher BMR (compared to if you took no action).
- Preserve your muscles’ ability to propel you through all of life’s activities. Even if you don’t care about your metabolism, aim to maintain and build muscle because this allows you to live your life to the fullest. Muscles are involved in every movement you make, from playing with your child to carrying a load of groceries.
Ways to combat a slowing metabolism
- Aim to strength train at least 2-3 times per week (hint, hint: This is the most important tip!). Whether you’re a gal or guy, prioritize weight lifting in your exercise plan. Adding muscle mass increases your BMR, allowing you to burn more calories even when you’re not exercising. If you’re a newbie to strength training, check out So You Want to Start…Strength Training.
- Ramp up the intensity of your aerobic exercise (think running, swimming, biking faster). Exercising at higher intensities allows you to reap the benefits of “after burn,” a phenomena where you burn extra calories post-exercise. To benefit from this effect, you should run, jump, dance, swim, bike, etc. at a pace where it’s difficult to talk. If you can push a little harder, then do so.
- Eat enough protein from high-quality sources. High-quality protein sources supply amino acids to your muscles post-exercise so that they can repair and grow. To learn more about how to determine your protein needs, check out this Beginner’s Guide to Protein.
- Stay well hydrated. Water is important because all of the chemical reactions in your body requires water—including the ones that burn calories. To work on drinking more water each day, check out 20 Lifehacks for Drinking More Water.
- Don’t starve yourself in order to lose weight. You need to consume a moderate amount of calories in order to lose weight. If you eat a significantly low amount of calories, you’ll lose weight rapidly but much of it will be from water and muscle loss. Plus, you’ll likely lose hard-earned muscle mass that’s responsible for maintaining a higher BMR.
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