Why does it seem that some people can eat anything they want and not put on weight? The rate that their bodies burn up food seems very different from people who feel like they gain weight just by looking at a piece of cake or pizza.
Can your metabolism be faster or slower than someone else's? Is it possible to change your metabolism to burn more calories?
Metabolism sustains life. It is the process of converting food into the energy you need to function, which we measure in calories. Even when you're at rest, metabolism powers everything: breathing, thinking, blinking. As you sleep, you're burning calories.
A fast metabolism burns calories quickly. A slow metabolism burns calories slowly.
So yes, metabolism does differ from person to person. And yes, you can take certain steps to boost your metabolism and burn more calories.
A cautionary note
Some people do not need to boost their metabolism. This is something you should discuss with your doctor. For instance, if you are underweight or already at a healthy weight, or if you have certain health conditions such as heart disease, this may not be right for you. Your doctor may not want you to raise your heart rate.
But if you and your doctor agree you should lose some weight, pump up your energy level or work on improving your muscle strength, here are some things you should know.
The heart of it all: your BMR
Everyone has what's called a basal metabolic rate, or BMR. This is the amount of calories you burn at rest just to keep your body alive and functioning. Put another way, it's the amount of energy your body would consume if you slept all day. Your BMR represents 60 to 75 percent of all the calories you burn in a day.
A number of factors determine your basic metabolism. Some are hard or impossible to change. They include body size (bigger people burn more calories); body composition (muscular people burn more calories); gender (men burn more calories because they usually have more muscle); and age (younger people have a faster BMR).
Here are some other things that can affect your metabolism:
- Genetics. Again, this is something you cannot control. You may have been born with a naturally fast or slow metabolism.
- Hormones. Hormones produced by the thyroid gland regulate metabolism. If you have an overactive thyroid, you may have an elevated BMR. If your thyroid is not working properly, you may have a slower metabolism. Other hormones and proteins also can affect how your body burns calories, so the thyroid is not alone in this equation.
- Health conditions. For instance, people with diabetes have different metabolic rates than those without diabetes, due to complications with metabolizing blood sugar produced by the foods we eat. Other health conditions can also affect how you burn calories.
- Level of activity. As we said above, lean muscle naturally burns more calories. Strength-building activities can help build lean muscle.
- The foods you eat. When you control the total calories you consume and burn more than you take in, you are changing your body's energy balance. Your path to losing weight and boosting your metabolism is to burn calories over and above your BMR. Several websites offer a BMR calculator based on your height, weight, age and gender.
These are just some of the things that determine your BMR. Let's take a closer look at a few of these factors.
How age affects metabolism
As we age, we tend to have a lower level of physical activity. Therefore we naturally burn fewer calories. On top of that, according to the American Council on Exercise, our metabolism actually declines as we get older.
The BMR is thought to slow by 1 to 2 percent per decade of life. Experts think this is largely because we have less muscle mass, which is high in metabolic activity. The decline in BMR appears to be fastest in men after 40 and women after 50.
Calories in, calories out
Eating well and exercising to build lean muscle are the best prescription for a healthy metabolism.
Your caloric intake - and output - will be the most important factors. Here are some tips:
- Rethink your portions. Most of us consume more calories than we need. Try downsizing the amount of food on your plate. At ChooseMyPlate.gov, you'll find tips on including more fruits, vegetables and whole grains in every meal. For guidance on what constitutes a proper portion and what to include in a balanced diet, consult the Department of Agriculture's 2010 Dietary Guidelines for Americans.
- Eat breakfast and spread calories throughout the day. But not because they directly affect metabolism. These behaviors keep blood sugars even and hunger under control. So they prevent overeating.
- Include lean protein. Your body burns more calories to digest protein. Strive for a balanced diet, and look for a variety of protein-rich foods such as seafood, beans and peas, nuts, and lean meats, poultry and eggs. Trim fat from meat and chicken. Avoid processed meats that are high in sodium (salt).
- Don't slash your calories. Cutting calories too much can cause your metabolic rate to drop, as though your body is trying to conserve weight. We call this a calorie deficit, or starvation mode. As you cut back your calories dramatically, your weight loss will actually slow down.
What's more, if you restrict calories too much or for too long, you'll lose muscle. Since muscle burns more calories than fat, loss of muscle will reduce your metabolic rate.
- Drink water instead of sugared drinks. Limit alcohol consumption to one drink a day for women and two for men, keeping in mind that mixers can also contain calories. Sugary beverages and alcohol might seem to give you an initial lift, but your body can crash later, leaving you light-headed and unable to enjoy your activities.
- Remember, there is no magic pill. Some studies have found that dietary supplements such as green tea or green tea extract and fish oil capsules may boost your metabolism. But there is no miracle food or pill to help you lose weight. It's all about balance and moderation.
Avoid fad diets that promise overnight weight loss. Instead, set a realistic goal of losing 1 to 2 pounds per week - and keeping them off.
If your doctor approves, your plan should also include:
- Strength training. These are exercises and activities you can work into your daily life. As you're building muscle, you're burning calories. You're also creating muscle tissue that burns more calories than fat tissue. Therefore, having more muscle will increase your metabolic rate. Your body will actually need more calories to function than a person with more body fat.
The key is to go slow. You might start with stretchy resistance bands - they are low-cost and you can use them anywhere. You might progress to hand weights, and eventually join a gym. Increasing your intensity over time is your goal.
Adults should work all major muscle groups (legs, hips, back, abdomen, chest, shoulders and arms) at least two days a week.
Strength training has many benefits. That's especially true as we age and our muscle mass declines. Strength training can fight arthritis, diabetes, osteoporosis, obesity, back pain and depression.
- Aerobic activity. This means getting out of your chair and moving. To get real health benefits, do 150 minutes of moderate-intensity activity each week. Or 75 minutes of vigorous aerobic exercise (exercise that raises your heart rate and makes you breathe harder). These bouts of aerobic activity should last at least 10 minutes. Spread them throughout the week. Working even harder and longer can further increase the health benefits.
- Good hydration. Drinking water not only fills you up, but staying hydrated keeps your metabolism at a steadier rate.
In the end, to manage weight, you need to do the math. Determine the number of calories you eat and the number of calories you burn. Then, to lose weight, strive to burn off more than you take in. To maintain, try to even out the calories consumed and the calories burned.
Over time, you can boost your metabolism by getting leaner and eating smarter.Greg Breining contributed to this report.
Created on 06/10/2008
Updated on 02/08/2013
- Centers for Disease Control and Prevention. How much exercise do adults need?
- American Council on Exercise. Is it true that metabolism decreases with age?
- American Thyroid Association. Thyroid and weight.
- Academy of Nutrition and Dietetics. Metabolism myths and facts.