Do you wish there were a knob you could turn to instantly speed up your metabolism? Who doesn’t, especially after eating a big piece of chocolate cake? Sadly, no such “knob” exists. Still, you hear claims that such and such will boost your metabolism, although it’s a good idea to take those claims with a grain of salt. Is it really possible to change your metabolism, the amount of energy your body burns each day, through exercise and lifestyle?
Breaking Down Metabolism into Its Component Parts
First, be aware that your metabolism is made up of a number of components, the largest being your resting metabolism. Resting metabolism refers to the energy required to run basic bodily functions when you’re in a relaxed state and haven’t just eaten a meal. About 60 to 75% of the energy you burn every day is accounted for by resting metabolism. Unfortunately, resting metabolism slows by about 2.5% per decade during adulthood, partially due to loss of lean body mass.
Next in line is “thermic effect of activity,” the calories you burn when you’re doing purposefully exercising, walking around and when your muscles are contracting for other reasons like fidgeting. As you might expect, this component is variable since some people are couch potatoes and some people are constantly moving their hands and feet fidgeting even when they aren’t working out. Fidgeting burns up to 300 extra calories over the course of a day. Don’t discount it! In general, the thermic effect of activity accounts for between 15 and 30% of total energy expenditure.
You burn more energy when you eat something too. This phenomenon is known as the “thermic effect of food.” How can you explain it? Your body has to put forth some effort to digest and break down what you eat and you get the most thermogenic “bang for the buck” when you eat protein. That’s why it’s sound advice to eat more protein and eat small meals throughout the day. Thermic effect of food accounts for around 10% of daily energy expenditure.
Thyroid Function
When you exercise or eat, you transiently burn more calories, but the metabolic component most people are fixated on is resting metabolism since it compromises the lion’s share of the calories you burn every day. Resting metabolism is highly dependent on thyroid function. Thyroid hormone sets your basal metabolic rate, which is roughly the same as your resting metabolic rate. The only difference is basal metabolic rate is measured in the morning after an overnight fast with no exercise in the past 24 hours, whereas resting metabolic rate can be measured after as little as 15 minutes of rest.
People who have an overactive thyroid usually lose weight, while those with sluggish thyroid function tend to gain but to say thyroid hormone is the sole determiner of how fast your resting metabolism is would be overly simplistic. Your resting metabolic rate is influenced by other hormones, including adrenalin, cortisol, growth hormone, testosterone, and estrogen. Producing more thyroid hormone would likely lead to short-term weight loss, but at a price. Thyroid hormone also increases muscle catabolism, so you’d lose lean body mass along with fat.
Can You Increase Your Resting Metabolic Rate?
Your resting metabolic rate naturally increases when you have a fever and when you’re pregnant. It also is ramped up when you take stimulant medications, including caffeine. A study published in the American Journal of Clinical Nutrition showed caffeine boosts metabolism by between 10 and 30% for up to 3 hours after consuming it. Green tea and hot, spicy foods also modestly boost your metabolism short term. Simply hanging out in a cold environment boosts your metabolic rate as long as you stay in it. You shiver to stay warm, which burns energy – and it doesn’t even have to be freezing cold. Temps under 62 degrees Fahrenheit are enough to induce “non-shivering thermogenesis,” as it’s called. Of course, all of these effects are temporary, unless you decide to live in an environment that’s 62 degrees F. or lower.
What You CAN Do to Boost Your Resting Metabolism
Here’s the good news. Resting metabolic rate is proportional to how much metabolically active tissue you carry on your body – and that means muscle. Hitting the heavy weights and increasing the size of your muscles will give your metabolic rate a boost. Ever wonder why men have a resting metabolic rate 10% higher than a woman? Simple, they have more lean body mass. One thing you can do to boost your resting metabolism is to train with weights or resistance bands to increase the amount of muscle you carry on your frame.
Yes, you burn more calories during steady-state aerobic exercise, but your metabolic rate returns to its resting rate once you stop. If you increase the intensity of your workout with high-intensity interval training, you get an added benefit, a temporary increase in your resting metabolism. High-intensity workouts require your body to work harder, and expend more energy, during the recovery period, what we think of as the after-burn effect. So, high-intensity exercise, both aerobic and resistance, is the key to maximizing your metabolism.
Don’t Focus Too Much on Your Metabolism
Keep in mind that your resting metabolic rate isn’t the “end all” when it comes to controlling your weight. In experimental studies when resting metabolism is slowed by artificial means, such as a drop in body temperature, animals don’t always gain the amount of weight expected. Energy intake enters into the equation too. If you were able to increase your resting metabolic rate, you’ll likely eat more in response.
The Bottom Line
Stop worrying about whether your metabolism is too slow. If you’ve noticed a sudden change in your weight, have your doctor check your thyroid function for peace of mind. Otherwise, focus on resistance and interval training and on getting enough dietary protein.
References:
Med Sci Sports Exerc. 1989 Oct;21(5):515-25.
Am J Clin Nutr. 1980 May;33(5):989-97.
Am J Clin Nutr December 1999 vol. 70 no. 6 1040-1045.
Med Sci Sports Exerc. 2014;46(7):1352-1358.
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Is Muscle Loss the Only Reason Your Metabolism Slows with Age?
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