Do you wish you had a faster metabolism so you could eat more without gaining weight? Many people are convinced their metabolism is too slow, and it makes it harder for them to lose weight. Each person has a metabolic rate that’s affected by a number of factors. Some of these factors can be altered, while others can’t be so easily changed. Have you ever wondered what makes your metabolic rate fast or slow?
First, a definition. Metabolic rate is simply the amount of energy expended over a given period of time. This energy is released as heat. You can measure your metabolic rate at a single point in time using different methods, but the rate will vary throughout the day based on a variety of factors including activity level. Here are some factors that affect metabolism.
Factors That Determine Your Metabolic Rate
According to a study published in Obesity Research, black women have a resting metabolic rate that’s about 5% slower than white women.
Men have a metabolic rate that’s 10 to 25% higher than women. This is at least partially due to greater muscle mass since muscle is more metabolically active than fat tissue. You can’t control your sex, but women can increase their lean body mass through exercise.
Resting metabolic rate drops by as much as 2% each year after the age of 20. Both men and women also lose muscle mass as they age, which accounts for some of this decline. You can’t control the aging process, but you can do strength training to increase how much muscle you have.
Larger people have higher metabolic rates because they have greater total mass. You can’t determine your height or the size of your frame, but you can alter your body composition and how much mass you carry to some degree through diet and exercise.
Genetics play a role in determining metabolic rate too. Most people know someone who can eat anything they want without gaining a pound. Unfortunately, it catches up with them as they age, and their metabolism starts to slow down. Some people aren’t able to adapt to their changing metabolism and gain significant amounts of weight as they grow older. You’ve probably heard formerly thin people say, “I was as skinny as you when I was younger.” They probably were.
The primary hormone responsible for regulating metabolic rate is thyroid hormone, but sex hormones such as estrogen, progesterone and testosterone play a role too. This may be due to their effects on lean body mass. Most women experience a steeper decline in metabolic rate after menopause, but accelerated loss of muscle mass also contributes to this slow down. Growth hormone and other fat-burning hormones likely plays a role in regulating metabolism, and growth hormone levels decline with age.
Other Factors That Affect Your Metabolic Rate
Factors such as ambient temperature affect metabolic rate. Colder temperatures boost metabolic rate by causing shivering, which produces more heat. Turning down the temperature in your home can subtly boost your metabolism.
If you’re anxious or have a fever, you have a faster metabolic rate and produce more heat. Some medications can alter it too. Thyroid hormone, nicotine and caffeine raise it, and some medications such as anti-psychotic drugs lower metabolism.
High-intensity exercise that uses the anaerobic energy system such as heavy weight-lifting and sprinting boost metabolism for hours to days afterwards, and when you build lean body mass you burn more calories. Moderate-intensity endurance exercise has less of an effect on metabolic rate.
What and how you eat plays a role too. Restrict calories too much and your metabolism slows down to protect you against starvation.
What You Can Do to Boost Your Metabolism
Certain factors such as genetics, sex, race and age you can’t control. But you can boost your metabolism by doing high-intensity exercise and resistance training to increase lean body mass. If you restrict calories, never go below 1200 calories a day to avoid slowing down your metabolism. Focus on eating smaller meals more frequently that contain small amounts of lean protein. Drinking caffeinated beverages and green tea may also subtly increase metabolism.
Ann Intern Med. 1995 Nov 1;123(9):673-5.
Obesity Research (2002) 10, 726-732.