Master Your Metabolism (Part 1)

What’s happened to my metabolism? This is the question countless women ask me after complaining about how their metabolism is no longer what it used to be in their teens or even early twenties. I typically nod my head in agreement but then cringe a little inside and think to myself “it doesn’t have to be this way.”

Let me explain.

For the most part, the biological process of aging has really little to do with a reduced metabolic rate as you get older.

Instead, it’s the lifestyle changes that we often take on with age that leads to the demise of our metabolism. 

In fact, one study compared the resting metabolic rate of three groups of people: ages 20–34, 60–74 and ages over 90. Compared to the youngest group, people between 60–74 years burned about 122 fewer calories, while the 90 plus group burned around 422 fewer calories. However, after controlling for gender, muscle and fat mass, researchers found that people aged 60–74 burned only 24 fewer calories, while those over 90 burned 53 fewer calories on average daily. 

This serves as one example that age has little to do with a sluggish metabolism but instead it’s our change in weight and body composition as we age that play a larger role.

First off, why is it that most people put on weight as they age? That’s a loaded question but largely it comes down to increasing responsibility (e.g., climbing the corporate ladder, having children, caring for an aging family member) which increases stress and often leads to little time to devote to self-care like sleep, exercise or having the time to prepare healthy meals.

Collectively, these factors contribute to a slow weight gain but more importantly an unfavorable body composition (i.e. increased body fat). 

So this is where we are. Now, what can we do to remedy the problem?

Well, first off we have to focus on what is within our control. We are all born with a certain genetic make-up and some of us may have a propensity toward being slimmer whereas others may be naturally larger in stature or ‘big-boned’ as they like to say. 

That said, first set realistic expectations about what changes your body is capable of. Then, nourish your body with a high quality diet, adequate exercise and sleep, and manage stress to keep your metabolism and overall health in an optimal state. 

Each of these factors play a role in how your metabolism is operating at this very moment. That said, in this guide to mastering your metabolism – I’ll be touching on each but focusing more on how food, movement, and even specific nutrients impact your metabolism.

So let’s get to it. 

You can think of metabolism as a sum of all of the chemical processes occurring in your body to support its function. The chemical processes include both anabolic processes (e.g. storage of energy, building up of muscles) and catabolic processes (e.g. converting food into energy, breaking down cells). All of these processes require energy to be either expended or stored.

For the purpose of today’s discussion, I’m going to be talking more about the energy expenditure (i.e., the catabolic component) as this is what most people think of when they refer to a ‘increasing metabolism.’

However, I’ll also be touching on anabolic metabolism when we talk about the role of building muscles/lean mass in relation to metabolism.

The first component is known as your resting metabolic rate (RMR). This is the energy expended to keep our bodies alive at rest. In other words, if you were to be a total couch potato for a day your body would still be using a ton of energy to keep your heart beating, kidneys filtering, liver detoxifying, brain functioning, and so forth.

Your RMR contributes approximately 60-75% of your total energy expenditure per day, making it the largest component of your metabolism.

The second component of TEE and also the most variable component is Physical Activity(PA). Physical activity as you might, expect is any purposeful activity like participating in a spin class, swimming, lifting weights, or even walking the dog.

The energy that is used up during PA largely depends on the type of activity, the duration you are performing it, and the level of exertion or intensity, and finally your size and body composition (more on that later).

In addition to purposeful PA, there is another form of activity called Non-Exercise Activity Thermogenesis (NEAT). NEAT is considered to be spontaneous or unintentional activity which accounts for energy expended during daily activities like walking to the kitchen for a snack, pacing back and forth while you talk on the phone, or unconsciously tapping your foot as you wait in line at the grocery store.

If you are the type that ‘can’t sit still’ chances are you might burn more calories from NEAT compared to more “calm” individuals. 

Together, PA and NEAT make-up between 15-30% of the TEE pie. 

The final component of total energy expenditure is called the Thermic Effect of Food (TEF). TEF accounts for the energy used to digest, absorb, or metabolize food.

TEF is believed to make up about 10% of total energy expenditure. The amount of energy used to process foods is influenced by not only the form of the food but the macronutrient composition.

Beginning with the first and largest component of your metabolism (resting metabolic rate) is it even possible to raise?

It’s 100% possible.

Your RMR is a function of your weight, height, sex and your body composition. Starting with weight and height, generally the taller or heavier you are the higher your metabolic rate.

So contrary to popular belief, having a bigger body doesn’t mean you have a slow metabolism. In fact, if you lose weight (body mass) your RMR will usually decrease in proportion to your new body weight. While this might sound discouraging to the person wanting to lose weight there are some things you can do to preserve a higher RMR. 

Before we get into that, let’s talk about the role of gender on your RMR. As you might guess, men typically have a higher RMR because they typically have greater muscle mass whereas women have more fat mass. This key difference in body composition explains why men have significantly higher RMRs and consequently seem like they eat twice as much as women. I know, I hate it too!

Some still believe your RMR is connected to age, but as we learned early on this post, your actual age has less to do with your RMR than the body composition you possess at a particular age. 

You may have heard ‘muscle burns more calories than fat.’ This is true but to what extent?

According to researchers, muscle is approximately three times as ‘metabolically active’ as fat. In other words, 1 pound of muscle burns 6 calories whereas 1 pound of fat burns only 2 calories.

To put this into perspective, if you are comparing a body of someone with 20 pounds of muscle versus 20 pounds of fat (despite both individuals weighing the same), the person with the 20 pounds of muscle would burn about 80 more calories per day.

While this might not seem like much, over time this small difference adds up. In fact, by the end of the week the leaner person with 20 pounds of muscle would theoretically burn 560 extra calories!

One of the best ways to increase your muscle mass and therefore your RMR is through physical activity (yes, the other main metabolism component). Regular resistance-training can help counteract lean body mass losses during weight-loss thereby preventing a reduction in RMR often seen with weight-loss. 

Some studies have indicated that after several weeks of resistance training, individuals can increase RMR by approximately 7% while also losing body fat!

If you are new to resistance training or feeling intimidated by the idea of picking-up a barbell (I’ve been there, too!), consider working with a personal trainer to understand the basics of resistance training. Also, check out the following article by ACE which explains the various components of an effective strength training program (i.e., compound movements, movement volume, and movement intensity)

Ideally, a weight-loss program should include both weight training for its muscle-building capabilities/potential to elevate RMR and some form of cardio for its ability to efficiently burn calories.

High-intensity interval training (HIIT), is a form of exercise that includes repeated bouts of high-intensity exercise followed by equal periods of rest. HIIT may be more effective at burning calories than any other form of exercise performed for the same length of time.

One study compared the number of calories burned by men during a treadmill, spin, weight-lifting or HIIT session; results showed men burned approximately 12 calories per minute during HIIT whereas other forms of exercise only afforded a calorie burn between 8-9 calories per minute. Extrapolate this to a 30-minute workout session, and that means participants of HIIT would burn 360 calories whereas 30 minutes of other activity would amount to 240-290 calories burned.

In addition, both HIIT and strength training promote a physiological phenomenon known as Excess Post-Exercise Oxygen Consumption or EPOC which is known to increase calorie expenditure up to 24-hours after exercise ends!

You can think of EPOC as basically the energy that is used after a workout to get your body back into homeostasis (or a neutral state).

For example, your body continues to work to bring your body temperature back down after an intense workout causing you to sweat; it replenishes your glycogen store (the energy you just used up) when you feed it; and it repairs the muscle you have broken down. All of these processes cost energy.

And while EPOC is technically not considered a primary component of TEE, it still can play a role in increasing your calories burned and helping with weight-loss. 

What if I don’t like weight training or HIIT? 

I admit, I’m a huge advocate of HIIT and weight-training. Nonetheless, there are plenty of other activities that allow you to burn energy and put you closer to an energy deficit.

Ultimately, you want to find an activity you ENJOY doing. “Consistently doing an activity that you enjoy is more important than inconsistently doing something you dislike."

Okay, now that we’ve talked about the various components of energy expenditure (i.e. metabolism) how does food or specifically calorie intake play into metabolism?

Anytime we eat food (calories) we increase energy expenditure. You can think of your body as a furnace and anytime the furnace receives coals (aka calories) the furnace generates more heat. 

Have you ever noticed larger people generally run ‘hot’ whereas smaller people run ‘cold’? This is because larger people are generating more heat whether from immediate energy consumption or extra stored energy (fat tissue). Whereas smaller people may not have a significant energy surplus therefore their internal thermostat operates on the cooler side.

All of this is to say, there is an energy exchange that occurs when you eat food. When you consume more energy, you burn more energy and the furnace roars. When you consume less energy, you burn less energy and the furnace cools down.

When it comes to weight-loss ideally you want to consume enough calories to keep your furnace burning at a steady state but also not too many that you exceed the number of calories you are capable of burning.

Most women should consume no fewer than 1200 calories during weight-loss to avoid having your RMR plummet.

Your body is smart. And when you limit your calories too much its survival mechanisms kick into high gear to prevent what it feels like a looming famine ahead.

When your body detects less energy coming in it will do whatever it can to hang on to its energy stores (adipose tissue).

Signs you may be under-eating for weight-loss include:

• feeling cold
• slowed pulse rate
• constipation
• fatigue
• hair loss
• menstruation changes

That said, to avoid having your RMR plummet ensure that you are feeding your body enough calories to meet its basal requirements in addition to fueling your physical activity.

Of course you still need to be in a calorie deficit to encourage weight-loss but it’s best to slowly reduce your calories when pursuing weight-loss. Typically, I recommend my clients track their food intake for at least a week to establish their ‘average baseline’ calorie intake and then reduce their intake by 250-500 calories from their maintenance level.

A reduced metabolism with age is not due to the aging process itself but more largely due to a change in body composition, specifically a reduction in lean body mass (i.e muscle) and increase in fat mass. There are 3 components that make up Total Energy Expenditure– Thermic Effect of Food, Activity, and Resting Metabolic Rate.

Your RMR makes up the majority of the calories we burn each day. The best way to keep your RMR elevated as you age is to participate in activities that build muscle and burn fat – strength training and HIIT are great for this.

Lastly, while the name of the game in weight-loss is ‘be in a calorie deficit,’ a larger deficit isn’t necessarily better. Most women should eat at least 1200 calories during weight-loss to keep their metabolism from slowing too much.

I hope you enjoyed Part 1 of Master your Metabolism!

Stay tuned for Part 2, where I share more insight on how to take advantage of TEF for weight-loss, what foods can ‘rev’ up your metabolism, and ways to fit more exercise into your daily life.