Metabolic rate, how fast we burn calories, is the bugaboo of dieting but also the engine of living. If we can set metabolic rate just right we can enjoy high energy, good health and a comfortable body weight. Here’s how we can bring it under our control.
This is a long blog: if you want to jump to the practical advice, skip forward to the last section of this blog.
Metabolic Rate in its Essence
Nola sometimes says to me, “You know, if it wasn’t for that darn gravity, I would weigh less.” And metabolic rate is much the same as gravity – a necessary natural force, and one over which we have little control.
Our bodies subsist by burning fuel: we consume food and “burn” it, that is, combine it with oxygen. These metabolic chemical reactions liberate usable energy, generate waste heat, and exhaust carbon dioxide. Metabolic rate can be measured by several means: by the caloric (heat) energy of foods that our body consumes; by the heat radiated by our bodies; by the oxygen consumed as we metabolize our food; by the carbon dioxide exhaled as a waste product of our food.
Suppose that you wanted to understand a gasoline-burning engine so as to design newer and better engines. You would want to know how it performs in every possible situation: idling, accelerating, at constant speed, under varying torque demands such as going uphill or downhill, with different fuel and oxidizer mixtures. There would be no way to capture the subtleties of engine performance with just a few numbers.
In the same way, metabolic rate is a complicated variable that depends on many factors. To make measurements, physiologists have defined some ideal situations that are special cases, corresponding to an idling vehicle engine:
– Basal Metabolic Rate (BMR) is the minimum energy expenditure needed to keep you alive – the energy to keep you breathing, your heart beating, your body temperature normal. You would achieve this metabolic rate in a vegetative state, which is not the state we want to live in and is therefore of not much practical interest.
– Resting Metabolic Rate (RMR) is the energy you expend when you are awake but resting. You are not moving around, you are not agitated or anxious, you are just zenning out. Again, not too practical for everyday life, but something that can be measured in the laboratory.
– Metabolic Rate alone, without the extra adjectives, is simply the rate at which we burn calories as we live life.
We don’t want too low a metabolic rate: that leads to depression, feeling tired and extreme grumpiness. In other words, the state we put ourselves in when we go onto a crash diet. Because a diet that delivers less than about a thousand calories a day announces to our body systems that food is scarce and must be conserved. As a result our bodies shift to a low engine speed to conserve fuel and rather than losing weight, we just become insufferable to everyone around us.
Too high a metabolic rate would also be a problem, however. One reason that cancer causes wasting of the body (cachexia) is that it accelerates metabolic rate to an uncontrollable degree. If uncontrolled weight gain is bad, so is its opposite.
Components of Metabolic Rate
Normal metabolic rate, the rate at which we expend the energy we derive from food, has three components:
– 60% to 75% of our total energy use comes from Resting Metabolic Rate, the fuel consumed when our body’s engine is idling;
– 5% to 10% of our energy is consumed by the work entailed in digesting the food we eat; and
– 20% to 30% of energy expended results from our daily physical and mental activities.
In the U.S. we have a weight problem – no, worse, an obesity problem. Despite the existence of poverty and hunger in our nation, on average most Americans have no trouble in obtaining many more food calories than they really need, and as a result more than one-third of our adults are officially classified as obese. Diet solutions sell their products by playing on our vanity, our desire for good health and our need to escape the medical problems aggravated by excess weight.
Since weight gain arises from eating more food than our bodies can burn up, advice for controlling weight either advise us to eat less (or differently), or raise our metabolic rate to burn up more of the treats that we can’t push away. Eating less means calorie counting; we all know how to do that, and it’s not much fun. So here we will focus on advice to raise metabolic rate, to work the other side of the energy equation. And you will see that the ways that experts advise raising metabolic rate each reflect the three categories mentioned above:
– The “idling” energy consumption of our bodies, resting metabolic rate;
– The digestive process (“thermic effect of food“); and
– Physical activity (“thermic effect of activity”).
Let’s review the recommended ways to raise metabolic rate and see which ones make scientific sense and which are unproven or likely untrue. Rather than repeating a number of links, when I provide a name in parentheses it credits one of the articles listed at the end of this blog.
Metabolic Rate: Immovables
Getting Older (Hills, ABC Health). The older we are, the slower our metabolism. Considering the alternative, we’re not ready to give up getting older, but many of us would like to slow the process. Slower pulse rate seems to predict greater longevity. This is association, not causation, however it does help support claims that aging, perhaps including metabolic decline, can be slowed by exercise.
Being Female (Topham, Hills, McGregor, ABC Health). Gender is a strong determinant of metabolic rate, with women generally doomed to burn fewer calories than men of the same age.
Genetic Factors (McGregor, Topham, ABC Health). Would that we could choose our parents as easily as we choose our friends! Some ingredients in a high or low metabolic rate are genetic, and may partially explain why there is an inherited tendency toward obesity.
Bigness (McGregor, ABC Health). A big or tall body has more cells to maintain and larger internal organs that use up energy. Big people also have more skin surface constantly radiating heat, so their bodies have to burn more calories to maintain a normal temperature. A bigger body means larger and stronger muscles needed to move it around, and those muscles burn fuel even when they are resting. So you can raise your metabolic rate just by gaining weight, but of course this is not the direction most of us want to head.
Homeostasis (Thomas). Homeostasis is the tendency of biological systems to operate within a normal range. Our bodies get used to having a certain body weight and a particular metabolic rate, and resist our efforts to change either of those. This is seen when people adopt exercise programs in hopes of losing weight: they generally increase their food intake so that they end up losing less weight than they had expected.
Addictions (Miranda). Addictions are inherently difficult to control, and many of them affect metabolic rate as well as damaging health in other ways. Some increase your weight, some decrease it, but all of them upset your bodily systems:
– Addictive drugs upset the metabolism and lead to increased risk of diabetes, cardiovascular problems and obesity. Opiates such as cocaine depress the central nervous system and interfere with fat storage, paradoxically leading to both weight loss and a lower metabolic rate. Marijuana increases cravings for sweets and fatty foods, but does not increase metabolic rate; as a result, frequent marijuana smokers tend to gain weight.
– Alcohol is toxic, and for that reason the liver processes it first before performing other functions such as controlling blood glucose level. This is not so much a change in metabolic rate as a disruption of metabolic processes. As a result, alcoholics can experience an unhealthy loss of weight.
– Tobacco (Audrain-McGovern). Nicotine increases the resting metabolic rate; this would normally make the smoker want to eat more, but smoking blunts the appetite and also keeps the hands and mouth busy. Despite the risk of cancer and emphysema, smoking is sometimes consciously adopted as a weight control measure, especially by girls and young women.
Metabolic Rate: Nonstarters
Before we dig into the things that really work, let’s dispose of a few “nonstarters.” These are bits of advice that are often given, and repeated, but for which I can find no convincing scientific evidence:
– Ice in Your Drink. It’s true that consuming ice burns a few calories, because your body has to warm it up to room temperature. But despite recommendations that ice in your beverage can help you lose weight (Fitwatch), the amount of calorie burn is miniscule: 8 calories for each cup of cold water you consume (Livestrong 2).
– Miscellaneous Vitamin, Supplement and Food Advice. Various folks suggest taking calcium, magnesium, vitamin D and iron (Hills); vitamin C and chromium (Fitwatch); iodine (Topham, BUPA, ABC Health); iron (Hills); eating more carbohydrates (Topham); not eating too much cauliflower and broccoli (Fowkes, commenting in Hills); avoiding pesticides in food (Hills). It’s true that having a nutrient deficiency can wreak havoc on your metabolic rate, but that doesn’t mean that an excess of nutrients will help boost metabolism or control weight. I can’t find scientific evidence that says you can raise your metabolic rate by taking more of these than a normal healthy diet provides.
Metabolic Rate: Things That Work
Fortunately, science gives support to not just one or two, but a large number of things we can do if we want to boost our metabolic rate. This section of the blog groups together bits of advice that seem unrelated, but which to my mind work together as a whole. The following, final, section extracts particular behaviors to derive some practical guidance.
Exercise and Physical Activity
When we eat, a portion of the food is immediately converted to energy for digestion and other bodily processes. The rest of the food is stored in the body as glycogen and fatty acids for future use. When we exercise, our metabolic rate increases as our bodies convert this stored food to energy.
This conversion consumes oxygen and releases carbon dioxide. Our bodies have considerable oxygen stored in the blood and in the muscles. As this is used up, our bodies demand more, which is why we breathe more heavily when exercising in respond to immediate needs, and after exercising to replenish the body’s stores. Whenever you are puffing to catch your breath, your metabolic rate is revved up. Scientists determine metabolic rate by measuring both the oxygen we consume and the carbon dioxide we exhale.
Every expert gives different advice for using physical activity to raise metabolic rate: intense exercise (Blahd, Peloquin), aerobics (Blahd), weight lifting (ABC Health, Blahd, BUPA, Hills, Topham) and interval training (Baumgardner) get lots of votes, but also recommended are walking (Topham), fidgeting (Topham, McGregor) and simply arranging your activities so that you are physically active throughout the day (McCargar).
All these things cause you to burn energy and thereby increase your metabolic rate. However, by how much? A typical research study (Knab et al) had volunteers perform 45 minutes of intense exercise that burned 519 calories. Following the exercise, the participants burned up an additional 190 calories while their muscles rebuilt their glycogen stores and their bodies gradually came back to normal metabolism.
The 519 calories were burned up by some very hard work. If you were to follow this exercise with a Starbucks venti Mocha Frappucino (520 calories) or a large order of fries at McDonalds (510 calories) you would wind up losing, uh…not much weight.
You might say, oh, I can exercise but I don’t have to splurge afterwards. Yes, perhaps that’s true for you, but it’s not true for most people who exercise. A 2012 study (Thomas et al) found that exercise caused almost no change in resting metabolic rate. Moreover, exercisers lost much less weight than they had hoped for, because they increased the amount of food they ate. Not surprisingly, exercise made them hungry!
On balance, experts advise that weight loss by exercise requires very high intensity activity (McCargar) and produces only a modest effect on metabolic rate and weight loss (Reynolds). For those reasons, exercise works best when it’s part of your total life style. If you are a marathoner, frequent cycler, or regular body builder and keep a lid on your caloric input, you will not (I predict) be overweight. However, don’t go overboard: pushing your pulse rate to its maximum every day increases your risk of heart problems.
If an obsessive dedication to exercise doesn’t feel right to you, there’s another approach: simply be the opposite of a couch potato. See the last section for specific advice.
Concerning composition: we noted above that the work of digestion itself consumes between 5% and 10% of the total energy in our food. This is known as the thermic effect of food. Fats and carbs are easily digested, with 85% to 95% of their calories available to our bodies for activity or for adding fat. However, protein is much harder to digest, so only 65% to 80% of consumed calories are left over after digestion.
The digestion of protein not only consumes more energy, it also takes longer. The smooth, steady elevation of blood sugar that results quenches the appetite; thus protein is more satisfying than other kinds of calories.
Food with higher fiber content, such as whole grains, fruits and vegetables, also takes longer to digest. The fiber itself adds zero calories but the slower digestion of your food is likely to make you feel satisfied with total calories in your meal.
How about scheduling of our meals? Cho et al quote two relevant studies:
– Moderately obese women lost more weight by consuming 70% of their calories before noon;
– Lean people lost weight when consuming a 2000-calorie meal at breakfast, but gained weight when consuming the same calories at dinnertime.
They go on to show that there is a significant association between eating breakfast and obesity. I analyzed their data in light of American average weight (166.2 and 195.5 pounds respectively for women and men). Their result show that people who eat cooked cereal (or rice) for breakfast are 6 to 7 pounds lighter than the median, while those who skip breakfast or eat “meat and eggs” or cheese for breakfast are 4 to 5 pounds heavier than the median. All other breakfast types are somewhere in between.
This is association, not causation. The researchers offer the following conclusions based on their work as well as previous studies:
– …skipping breakfast does not lead to attaining or maintaining a healthy weight.
– …it is the eating of a fairly “organized” breakfast that is associated with appropriate body mass regulation. Ready-to-eat cereals, cooked cereals and quick breads such as pancakes are typically eaten at home and represent an attempt to have a “conventional” breakfast.
– …“dysregulated” eating patterns are associated with obesity, instead of or in addition to total energy intake per se.
The last point, calling for regular and steady eating patterns, is reinforced by those writers (Baumgardner, Blahd, Fitwatch) who advise eating 5 or 6 small meals per day rather than 2 or 3 large meals.
A related point is this: drastic dieting causes the metabolic rate to plummet. As a result, you can still gain weight even when you are eating very few calories! These two ways of dieting have been shown to be counterproductive: (1) cramming all your food into one meal per day in hopes of cutting total calories (Topham); and (2) reducing total calorie input below 1000 calories per day (McCargar).
Here’s a point that’s worth remembering: exercising in chunks (“interval training”) is an effective way to exercise; however, eating in chunks (a few large meals) confuses your metabolism and leads to weight gain. We will return to “well regulated body habits” in the last section.
You’ll see many claims that stimulants increase metabolic rate and thereby burn up calories. The stimulants most often touted are caffeinated beverages (coffee and teas) and a large number of spices, especially chiles. From our discussion we’ll omit prescription drugs sometimes taken by athletes to boost their metabolism.
When I look at the research studies, it turns out that stimulants do indeed pump your metabolic rate. Coffee and tea are easy: caffeine is a stimulant that increases metabolic rate by 3 to 11%, with most of that increase coming from burning fat (Gunnars). Studies seem to show that in addition to caffeine, other chemicals in coffee and tea boost the metabolism (Dulloo, Rumpler). Gunnars advising cycling coffee two weeks on, then two weeks off to prevent a buildup of tolerance; logic suggests that you might instead switch between coffee and tea to keep them both effective.
The evidence for spices is more scattered and uncertain. However, I have found research studies supporting metabolism enhancement from chili peppers (Henry et al), garlic (Chang et al), mustard (Henry et al) and turmeric (an ingredient of curry powder) (Meydani et al). In addition, cinnamon (Livestrong 1) and ginger (Mansour) help metabolize food and thereby contribute to burning calories.
Metabolic Rate and Weight: Practical Tips
Physical Activity. Keep active throughout the waking day:
– Bounce your knees or fidget.
– Get up from your chair several times an hour and walk around the room.
– Use a cordless phone and whenever you take a call, walk as you talk.
– Every day, do something that’s more active than usual for you: a long walk, quickly climb several flights of stairs, take a jog, lift some weights (BUPA).
– Give your body some extra work to perform by turning down the thermostat in your home (ABC Health, Lee et al, McGregor, Topham).
The combination of these activities notifies your body that it needs to rev up the metabolic furnace. Because you are varying your exercise throughout the day, your body does not acclimate and responds better to the activity: it’s the same principle as interval training.
Eating Patterns. Keep your diet steady and front-loaded:
– Take your time to eat a healthy breakfast.
– Try to consume most of your calories early in the day, when you are active and your metabolic rate is at its highest. There is scientific support for the adage eat breakfast like a king, lunch like a prince and dinner like a pauper.
– Eat smaller meals, and have healthy snacks between times.
– Eat plenty of fiber and adequate amounts of protein.
– To lose weight, do two things at once: reduce your calories somewhat, while increasing your exercise level to keep your metabolic rate from dropping.
– Drink tea or coffee; if possible swap from one to the other every few weeks to surprise your body.
– Use spices generously, especially chili peppers, garlic, curry powder, cinnamon and ginger.
Well Regulated Body Habits. Apart from exercise, you want to present your body with a predictable schedule of activities:
– When you get up in the morning, set your circadian clock: turn on the lights – sunlight is especially helpful early in the day (Greenfield, Fitwatch, Spencer, Weller). Then drink tea or coffee and eat breakfast.
– When you fly to a new time zone, set your clock the same way in the morning in your new time zone (Hills).
– Avoid large meals, and feel free to have healthy snacks between meals.
– De-stress (Baumgardner).
– Get enough sleep (Hills).
– Drink plenty of water, because dehydration can depress your metabolic rate (Baumgardner, Blahd, Hills, Livestrong, Pulsipher).
Weight control is one of those life tasks that seems never done – like attaining true happiness, or perfect health, or spiritual transcendence. Ignore the hucksters who promise you the silver bullet, because it simply does not exist. But the factors summarized above can help you weave the solution that works best for you.
Comment added 2/17/2018: Jen Reviews has a good article with many additional ideas for weight loss: 11 Best Ways to Lose Weight, According to Science (+12 Delicious Weight Loss Recipes). The article gives references to research and it appears to have been published in 2014. However, its contents are still up to date.
Food, exercise and metabolic rate all contribute to weight. Have you ever dieted with a combination of both diet and exercise?
Drawing Credits: (all from openclipart.org)
“Golden Off Balance Scale” by GDJ
“combustion engine” by samukunai
“wall 2” by jarda on openclipart.org
“Architetto – medizina dottore” by Francesco_rollandin
“Dumbbell” by Eggib on openclipart.org
“Food Bacon” and “Food Fried Eggs” by glitch
“A cup of hot tea” by sheikh_tuhin
“Cayenne red chili pepper” by iolco51
“Small Wrench” by LindsayBradford
News Media Sources: (quick to read, but often just repeated hearsay)
ABC Health, 10 Factors that Affect Your Metabolism
Baumgardner, Metabolism/ Popular Myths And 9 EASY Ways To Rev It Up!
Blahd, 10 Ways to Speed Up Your Metabolism
BUPA, Exercise And Metabolism – Tips to increase your BMR
Fitwatch, 7 Ways to Boost Your Metabolism — And Burn Fat Fast
Greenfield, 8 Surprising Ways You’re Slowing Your Metabolism
Gunnars, Can Coffee Increase Your Metabolism and Help You Burn Fat?
Hills, Top 10 Factors that Affect your Metabolism
Livestrong 1, Does Cinnamon Increase Metabolism?
Livestrong 2, Is Ice Water Good for Metabolism?
McGregor, 9 Factors That Affect Metabolic Rate
Miranda, Drug Use and Your Metabolism
Peloquin, How Exercise Affects Your Metabolism
Pulsipher, Vegan Metabolism/ 13 Ways to Boost Yours on Plant-Based Food
Reynolds, Dieting vs. Exercise for Weight Loss
Spencer, Keep slim by going out in the sun: Exposure to UV rays releases chemical which helps metabolism
Topham, Forget dieting: Speeding up your metabolism is the key to slimness
Weller, Could the sun be good for your heart?
Research Publications: (highly technical, dense reading)
Audrain-McGovern, Cigarette Smoking, Nicotine, and Body Weight
Chang et al, Effect of garlic on carbohydrate metabolism and lipid synthesis in rats
Cho, The effect of breakfast type on total daily energy intake and body mass index: results from the Third National Health and Nutrition Examination Survey (NHANES III)
Dulloo et al, Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans
Ejaz et al, Curcumin inhibits adipogenesis in 3T3-L1 adipocytes and angiogenesis and obesity in C57/BL mice
Knab et al, A 45-minute vigorous exercise bout increases metabolic rate for 14 hours
Lee et al, Temperature-acclimated brown adipose tissue modulates insulin sensitivity in humans
Mansour et al, Ginger consumption enhances the thermic effect of food and promotes feelings of satiety without affecting metabolic and hormonal parameters in overweight men/ A pilot study
McCargar, Can Diet and Exercise Really Change Metabolism? (an excellent article and still accurate, despite its 1996 publication date)
Rumpler et al, Oolong Tea Increases Metabolic Rate and Fat Oxidation in Men
Thomas et al, Why do individuals not lose more weight from an exercise intervention at a defined dose? An energy balance analysis