What is metabolism? The truth about metabolism and weight

• Metabolism is the process of converting food and drinks into energy for all bodily functions.
• A fast or slow metabolism doesn't necessarily mean someone will lose more or gain more weight.
• You may be able to slightly boost your metabolism by building muscle, eating protein, and hydrating.

Metabolism refers to the process by which your body converts what you eat and drink into energy. However, today the term is often used in reference to weight. For example, many think a fast metabolism equates to weight loss, but that's not necessarily the case.

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In fact, overweight people often have faster metabolisms than thinner people because larger bodies require more energy to perform necessary functions like pumping blood and breathing.

All that said, certain lifestyle changes may help to boost your metabolism so that your body can burn more calories and possibly lose more weight. Here's what to know about the factors that can affect your metabolism, and what you can do to speed yours up.

What is metabolism?

Metabolism involves all the bodily functions that keep us alive, and can be broken down into three metabolic processes:

• Basal metabolic rate (BMR), which is the total number of calories you need at rest to perform basic life-sustaining functions like pumping blood, breathing, and repairing damaged cells.
• Food processing, which is how much energy it takes to digest food.
• Physical activity, which is how many calories you burn through movement like walking or lifting weights.

Weight gain occurs when you consume more calories than your metabolism burns a day. So, whether you're trying to gain, lose, or maintain weight, calculating your BMR can be helpful because it can help you determine your baseline caloric needs.

The Mifflin St. Jeor formula - which is based on your age, weight, and height - tends to be the most accurate for calculating your BMR, according to Charlotte Hodges, MD, an advanced laparoscopic general and bariatric surgeon at City Hospital at White Rock. You can also get your BMR tested at a lab, which will give you a more precise estimate.

Factors that affect your metabolism

Some people have a faster BMR, and thus faster metabolism, than others, says Hodges. Below are some factors that impact the speed of your metabolic rate.

• Genetics: The speed of your metabolism is mostly determined by your genes.
• Age: Studies have found metabolism tends to naturally slow as you age. That's why people over the age of 50 typically need fewer calories than they did in their 20s, 30s, and 40s.
• Body composition: Since muscle burns more calories at rest compared to fat, the more muscle mass you have, the higher your metabolism.
• Sex: A 2018 study of adults with prediabetes found men lose weight more quickly than women. This is likely due to men typically having more muscle mass.
• Physical activity level: Research has repeatedly found that you can help your body burn more calories, even at rest, through regular exercise, mostly due to increased muscle mass.
• Hormonal disorders: Conditions that affect your hormone levels, like hypothyroidism and Cushing syndrome, can interfere with your metabolism, thus predisposing you to weight gain or loss.
• Medications: Certain medications can interfere with your metabolism and sometimes slow it down. These include some beta-blockers, as well as antihypertensives, antidepressants, steroids, and antipsychotics.
• Stress levels: Stress-related hormones, like cortisol and epinephrine, may increase your appetite while also causing your body to store more fat. In fact, a small 2014 study of middle-aged women found that participants who reported being stressed during the 24 hours prior to having a high-fat meal burned 104 fewer calories in the seven hours after eating than the women who were not stressed.

Metabolism and weight loss

Having a slow metabolism is rare, and it's often not the culprit behind weight gain or obesity.

In fact, a 2016 review found that adults with low BMRs did not gain more weight than adults with high BMRs. Researchers suggested this may be due to differences in physical activity and food intake, which is why eating right and exercising regularly are crucial components of weight management.

However, if you're looking to lose weight and therefore decrease your calorie intake, it's important to avoid extreme calorie restriction, which can slow your metabolism.

"This is called adaptive thermogenesis," says Kayla Girgen, a registered dietitian at CentraCare and founder of Nutrition Untapped. "When calories are decreased, the metabolism slows to conserve energy."

In the long run, extreme calorie restriction leads to the loss of lean muscle, which can decrease your BMR, thus making it even more difficult to lose weight.

How to boost metabolism

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While it's impossible to significantly boost your metabolism, you can at least burn more calories in a day by adopting the following habits:

Exercise regularly

Strength training and building muscle may be the most effective way to boost your metabolism. A 2009 study found that when overweight young adults - who were previously sedentary - participated in 11 minutes of resistance training three times a week, their BMR increased by 7.4%. This resulted in an additional 125 calories burned daily.

Research has also indicated that the more intense your workout, the more calories your body burns afterward to return to its resting state. This "afterburn" effect can last up to 38 hours post-workout. High-intensity interval training (HIIT) is a great example of this.

Eat enough protein

Protein has a higher "thermic effect" meaning it requires more energy to digest. In fact, eating protein can increase your metabolic rate by 15% to 30%, which is significantly higher than carb's 5% to 10% and fat's 0% to 3%.

In fact, a small 2021 study of healthy, normal-weight adults found that those who ate a prescribed 32-hour diet with a higher proportion of protein and lower proportion of carbs experienced more calorie burning and fat breakdown than those who ate a diet with a higher proportion of carbs and lower proportion of protein.

Stay hydrated

A small 2013 study found that when overweight girls drank 2 cups of water half an hour before meals without any other changes to their diet, they lost weight, reduced their BMI, and improved their body composition. Researchers theorized this is because water promotes thermogenesis, the process by which your body generates heat and energy from digesting food.

Get plenty of sleep

A 2010 study found sleep deprivation can alter the way you break down sugar and your hormone levels. Hormones are involved in regulating your metabolism as well as your appetite and your body's fat storage.

Drink caffeinated beverages

The caffeine in beverages like coffee, black tea, and green tea may rev your metabolism as it stimulates thermogenesis.

In fact, a small 2007 study found that when healthy young men took just 50 milligrams of caffeine - half the amount in a typical cup of coffee - their BMR increased by 6%.

Important: Excess caffeine may interfere with sleep, and getting adequate sleep is crucial for keeping your metabolism functioning properly.

Insider's takeaway

The speed of your metabolism is mostly out of your control since it's largely driven by genetics, age, sex, and other unchangeable factors.

However, certain lifestyle changes may increase the number of calories your body burns. These include engaging in more strength training and high-intensity aerobic exercise, drinking more water, consuming more protein, and improving your sleep habits.

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