If you struggle to lose every ounce -- and seem to gain it all back by simply looking at a cheeseburger -- you know the power of a slow metabolism. Your metabolic rate depends on a few factors within your control, such as your activity level, but factors outside your control can play a role, too. You'll most likely experience difficulties with weight management if you have a slow metabolism and, depending on the cause, you might notice other symptoms, as well.
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Metabolism and Weight Loss 101
At its core, metabolism is all about how many calories you burn. Each cell, out of the billions of cells in your body, needs a small amount of energy for survival, and the sum of your cells' energy needs add up to your overall energy consumption -- your calorie burn for the day.
You'll likely see two figures used to describe your metabolic rate -- your basal metabolic rate, or BMR, which is the number of calories you'd burn lying in bed all day, and your TDEE, or total daily energy expenditure, which is the actual calories you burn daily, taking into account your activity level.
Regardless of the speed of your metabolism, eating more than your TDEE will cause weight gain -- roughly one pound per extra 3,500 calories. Conversely, eating less than your TDEE will make you lose weight -- roughly one pound per 3,500-calorie deficit. However, a slow metabolism -- whether it's caused by an underlying health issue, by genetics or by another reason -- means your BMR and TDEE are lower than average, which can affect how easily you lose weight.
Slow to Lose, Quick to Gain
The most obvious sign of a slow metabolism is having difficulty losing weight, or losing weight at a slower rate than you anticipated when you're counting calories, and also gaining weight easily. That's because calorie-burn estimators assume you have an average metabolic rate, not a slow metabolism. Your actual metabolic rate might deviate 5 to 10 percent from the average, according to a study published in Current Opinion in Clinical Nutrition and Metabolic Care in 2004. As a result, an online calculator may overestimate your calorie needs by as much as 10 percent.
That makes a big difference when you're trying to shed pounds. For example, a 40-year-old woman who's 5-foot-5-inches tall, weighs 140 pounds, lives a moderately active lifestyle and has an average metabolism, would burn an estimated 2,354 calories a day. To lose weight, she could reduce her caloric intake to 1,854 calories daily, creating a 500-calorie deficit per day that should result in a one-pound loss each week.
However, a woman of the same height, weight and activity level who has a slow metabolism might only burn 2,119 calories each day. If she followed the 1,854-calorie diet, she would only create a 265-calorie deficit -- or enough to lose a pound about every two weeks. As a result, her slower metabolism will make her lose weight at roughly half the rate of someone who has an average metabolism.
When you have a slow metabolism, calorie calculators also overestimate how many calories you need to maintain your weight. If the same 40-year-old woman with a slow metabolism needs 2,119 to maintain her weight, eats the same number of calories as a woman who has an average metabolism and who needs 2,354 calories, she'll take in an extra 235 calories daily, or enough to gain roughly two pounds per month.
Other Potential Signs and Considerations
If you have a slow metabolism from an underlying medical issue, you might also notice other symptoms. For example, low thyroid activity or hypothyroidism, causes a slow metabolism. That's because thyroid hormones typically control your metabolic rate, and lower-than-normal thyroid hormone levels can make your metabolism slow to a crawl, even if you're not overeating. You might also notice other symptoms, such as dry hair and skin, difficulty concentrating and feeling cold, lethargic or depressed.
A slow metabolism caused by Cushing's syndrome, which is a condition caused by too much of a stress hormone called cortisol, might also cause purple marks similar to stretch marks on your skin. Cushing's syndrome can also cause an excessive growth of body hair or, in women, irregular menstrual periods.
Speeding Up a Slow Metabolism
You can boost your metabolism modestly with lifestyle tweaks. For example, muscle burns more calories each day than fat, so strength training two to three times weekly may increase your metabolism. Include cardiovascular exercise in your fitness routine to burn more calories, and choose higher intensity cardio to keep your metabolism revved for hours after your workout. You'll also burn slightly more calories digesting protein than digesting carbs or fat, so increasing your protein intake can increase your metabolism a bit. Protein can also provide the amino acids you need for muscle growth. You'll need to eat 0.8 grams of protein per pound of body weight. Choose high-quality proteins such as lean poultry, eggs, fish, dairy, quinoa and beans. If you weigh 140 pounds, that works out to 112 grams of protein daily.
Talk to your doctor if you suspect you have a slow metabolism. She can diagnose any underlying medical issues and may be able to offer treatment that can return your metabolism to an average metabolism. A nutrition professional can also help you estimate your calorie burn more accurately, so you'll have greater success when you try to lose weight.