By Dr. Atli Arnarson
Your metabolism is the chemical engine that keeps you alive.
The speed at which it runs varies by individual. Those with a slow metabolism tend to have more leftover fuel (calories), which gets stored as fat.
On the other hand, those with a fast metabolism burn more calories and are less likely to accumulate a lot of fat.
This is a review of why some people have a fast metabolism and how you can speed up your metabolism to burn more calories.
What Is Metabolism?
Metabolism is a term that collectively refers to all the chemical processes in your body. The faster your metabolism, the more calories your body needs.
This is the reason some people can eat a lot without gaining weight, while others seem to need less to accumulate fat.
The “speed of metabolism” is commonly known as metabolic rate. It’s the number of calories you burn in a given amount of time, also known as calorie expenditure.
Metabolic rate can be divided into several categories:
- Basal metabolic rate (BMR): Your metabolic rate when you are asleep or at deep rest. It is the minimum metabolic rate needed to keep your body warm, lungs breathing, heart pumping and brain ticking.
- Resting metabolic rate (RMR): The minimum metabolic rate required to keep you alive and functioning while at rest. On average, it accounts for up to 50–75% of total calorie expenditure (1).
- Thermic effect of food (TEF): The number of calories burned when your body is digesting and processing food. The rise in metabolic rate after meals usually represents about 10% of total energy expenditure (2).
- Thermic effect of exercise (TEE): The number of calories burned during exercise.
- Non-exercise activity thermogenesis (NEAT): The number of calories burned during activities other than exercise. This includes fidgeting, changing posture, standing and walking around (3).
Summary: Metabolic rate is also known as calorie expenditure. It is the number of calories used by the body in a given amount of time.
What Factors Affect Metabolic Rate?
Numerous factors affect your metabolic rate. To name a few, these include:
- Age: The older you get, the slower your metabolic rate becomes. This is one of the reasons people tend to gain weight as they age (4).
- Muscle mass: The greater your muscle mass, the more calories you burn (5).
- Body size: The bigger you are, the more calories you burn (6).
- Environmental temperature: When your body is exposed to cold, it needs to burn more calories to prevent your body temperature from falling (7).
- Physical activity: All body movements require calories. The more active you are, the more calories you’ll burn. Your metabolism will speed up accordingly (8).
- Hormone disorders: Cushing’s syndrome and hypothyroidism slow down metabolic rate and increase the risk of weight gain (9).
Summary: Multiple factors affect metabolic rate, or the number of calories burned. These include age, muscle mass, body size and physical activity.
Are Some People Born With a Fast Metabolism?
Metabolic rates vary between people, even when they are newborns.
In other words, some people are born with a faster metabolism than others.
Although genetics may contribute to these differences, scientists don’t agree on the extent to which they affect metabolic rate, weight gain and obesity (10, 11).
Interestingly, most studies show that obese people have a higher total and resting metabolic rate, compared to normal-weight individuals (12, 13, 14, 15).
Researchers have pointed out that this is because obese people have greater amounts of muscle to help support the extra weight (15, 16, 17).
Yet, studies indicate that obese people have higher metabolic rates, irrespective of the amount of muscle mass they have (18, 19).
In contrast, other studies show that formerly obese people have a 3–8% lower metabolic rate, on average, than those who have never been obese (10, 20).
One thing is clear — not everyone is created equal when it comes to metabolic rate.
Most of this variation is due to people’s age, as well as their environment and behavior. However, the role of genetics in these individual differences needs to be studied further.
Summary: Metabolic rates vary by individual, even among infants. However, it is unclear how much of this variation is due to genetics.
Metabolic adaptation, also known as adaptive thermogenesis or “starvation mode,” may also play an important role in the development of obesity.
Starvation mode is the body’s response to a calorie deficit. When your body doesn’t get enough food, it tries to compensate by reducing its metabolic rate and the number of calories it burns.
The extent to which metabolic rate decreases during calorie restriction and weight loss is highly variable between individuals (21, 22, 23, 24).
This metabolic slowdown is more pronounced in some people, especially those who are obese. The greater the slowdown, the more difficult it is to lose weight by dieting or fasting (21, 25, 26).
Starvation mode is probably partly affected by genetics, but previous weight loss attempts or physical fitness could also play a role (27, 28).
Summary: Metabolic adaptation or starvation mode is when metabolic rate slows down during a calorie-reduced diet or a fast. It varies between people and tends to be more pronounced among obese individuals.
Can You Speed up Your Metabolism to Lose Weight?
Weight loss isn’t only about eating fewer calories. Effective weight loss programs also include strategies to speed up metabolism.
Fortunately, there are multiple ways you can do this. Below are eight simple methods.
1. Move Your Body
All body movement burns calories. The more active you are, the higher your metabolic rate becomes.
Even very basic activity, such as standing up regularly, walking around or doing household tasks, makes a major difference in the long run.
This boost in metabolic rate is technically known as non-exercise activity thermogenesis (NEAT).
In severely obese individuals, NEAT may account for a significant portion of the daily calorie expenditure due to the extra burden they have to carry around (3, 29).
There are several ways in which you can boost your NEAT. If you spend a lot of time sitting, here are a few strategies:
- Stand up regularly and walk around
- Take the stairs whenever possible
- Do household tasks
- Fidget, such as bouncing your legs or tapping your fingers
- Chew calorie-free gum (30)
- Use a standing desk (31)
If you have a desk job, using a standing desk may increase the number of calories you burn by 16% (32).
Another study showed that spending one afternoon standing burned an extra 174 calories, compared to sitting (33).
Even seemingly insignificant activities like typing may increase your metabolic rate by 8%, compared to doing nothing (32).
In the same way, fidgeting can make a significant difference (34).
One study found people who sat motionless for 20 minutes temporarily increased their calorie expenditure by 4%, compared to when they lay motionless. In contrast, fidgeting while seated increased calorie expenditure by a whopping 54% (35).
Regular exercise is highly recommended for anyone who wants to lose weight or improve their health. But even light activities like walking around, doing household tasks or fidgeting, can give you an advantage in the long run.
Summary: The more you move your body, the greater your metabolic rate becomes. If you have a desk job, you can improve your metabolic rate by walking around regularly, chewing gum or using a standing desk.
2. Do High-Intensity Workouts
One of the most effective forms of exercise is high-intensity workouts, also known as high-intensity interval training (HIIT).
HIIT is when exercise involves quick and very intense bouts of activity, such as sprints or fast push-ups.
It really speeds up your metabolism, even after the workout has finished — an effect dubbed the “after burn” (36, 37, 38).
Summary: High-intensity interval training is one of the most effective ways to boost your metabolic rate and burn more calories.
3. Strength Train
Another excellent way to speed up your metabolic rate is to strength train (39, 40).
In addition to the direct effect of the exercise itself, strength exercises promote the growth of muscle mass.
The amount of muscle you have is directly associated with your metabolic rate. Unlike fat mass, muscle mass significantly increases the number of calories you burn at rest (5, 41).
One study showed that doing strength exercises for 11 minutes a day, three times per week, resulted in an average increase of 7.4% in resting metabolic rate after half a year. This translated into an additional 125 calories burned per day (40).
Older age is generally associated with muscle loss and drops in metabolic rate, but regular strength exercise can partially counteract this adverse effect (42, 43).
Similarly, a calorie-reduced, weight loss diet often results in the loss of muscle mass and decreases metabolic rate. Again, strength training may help prevent this decline (44, 45).
In fact, a study in overweight women showed doing strength exercises on a low-calorie diet of 800 calories daily prevented decreases in muscle mass and metabolic rate, compared to those who didn’t exercise or only did aerobic exercise (46).
Summary: Strength training can increase metabolic rate by promoting the growth of muscle mass. It may even counteract the drop in metabolic rate associated with aging and low-calorie diets.
4. Eat Protein
Eating adequate amounts of protein is essential if you want to build or maintain your muscle mass. But dietary protein also has other important qualities.
All food leads to a temporary increase in metabolic rate, known as the thermic effect of food (TEF). However, this effect is much stronger after eating protein than after eating carbs or fat (47).
In fact, protein increases metabolic rate by 20–30%, whereas carbs and fat cause a 3–10% increase or less (48).
This boost in calorie expenditure may help promote weight loss or prevent weight regain after a weight loss diet (49, 50, 51).
The TEF is highest in the morning, or during the first few hours after you wake up. For this reason, eating a large proportion of your daily calories early in the day can maximize the effect (52, 53).
Eating high amounts of protein can also help counteract the loss of muscle mass and slowdown of metabolic rate associated with weight loss (54, 55, 56).
Summary: Eating adequate amounts of protein is essential to increasing or maintaining your muscle mass and metabolic rate.
5. Don’t Starve Yourself
While eating less is a key weight loss method, eating too little is usually counterproductive in the long term.
The thing is, calorie restriction causes a decrease in your metabolic rate, or the number of calories burned.
This effect is known as the “starvation response” or metabolic adaptation. It is the body’s way of warding off potential starvation and death.
Research shows that consistently eating less than 1,000 calories daily leads to a significant drop in metabolic rate that’s sustained after the weight loss diet is over (57, 58, 59).
Studies in obese people suggest that the starvation response may significantly reduce the number of calories burned. For instance, one study suggests this slowdown in metabolic rate spares up to 504 calories per day (60, 61).
Interestingly, intermittent fasting seems to minimize this effect (62, 63).
Summary: Sustained calorie restriction slows down your metabolic rate. This effect has been dubbed the “starvation response.”
6. Drink Water
Temporarily boosting your metabolic rate doesn’t have to be complicated. It’s as simple as going for a walk or drinking a glass of cold water.
Many studies show that drinking water leads to an increase in the number of calories burned, an effect known as water-induced thermogenesis (64, 65, 66).
Drinking cold water has an even greater effect than warm water, as this requires the body to warm it up to body temperature.
Studies on this phenomenon have provided varying results. About 16 ounces (half a liter) of cold water may cause anywhere between a 5–30% increase in the number of calories burned for 60–90 minutes afterward (64, 66, 67, 68).
It seems that increasing your water consumption is also beneficial for your waistline. Several studies show that drinking 34–50 ounces (1–1.5 liters) of water daily may lead to significant weight loss over time (64, 69).
You can maximize the benefits by drinking water before meals, as it also fills you up and reduces calorie intake (70).
Summary: Drinking more water improves your metabolic rate and may even cause weight loss over time. Cold water is the most effective.
7. Drink Caffeinated Beverages
Although plain water is good on its own, caffeinated, low-calorie beverages, such as coffee or green tea, are useful as well.
Controlled studies show that drinking caffeinated beverages can temporarily speed up your metabolic rate by 3–11% (71, 72, 73, 74).
However, this effect is smaller in obese people, as well as the elderly. Additionally, seasoned coffee drinkers might have built up a resistance to its effects (75, 76).
For weight loss purposes, sugar-free beverages like plain black coffee are best. Like water, cold coffee may be even more advantageous.
Summary: Drinking caffeinated beverages may temporarily increase your metabolic rate.
8. Get Good Sleep
Getting inadequate sleep is not only bad for your general health, it may also slow down your metabolic rate and increase your risk of gaining weight (77, 78).
One study showed that metabolic rate decreased by 2.6% when healthy adults slept for only four hours per night for five days in a row (77).
Another five-week study found that sustained sleep disruption, along with irregular sleeping times, reduced resting metabolic rate by 8%, on average (78).
Accordingly, lack of sleep has been associated with an increased risk of weight gain and obesity (79, 80, 81, 82).
Summary: Lack of sleep and poor sleep quality may suppress your metabolic rate. For a healthy metabolism, you should aim to get enough high-quality sleep.
Take Home Message
Although your basal metabolic rate is largely beyond your control, there are various ways to increase the number of calories you burn.
The strategies mentioned in this article can give you a significant advantage in your battle against the bulge.