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Breaking Down Metabolism

by Meaghan posted June 3, 2010

As I mentioned last week, I went back up to Massachusetts for Memorial Day Weekend. (I guess our server was down for a bit though, so you can check out that post here if you missed it.)

Round-trip bus ticket: $120

Time spent en route: 14 hours

Waking up surrounded by family and friends, 15 minutes away from this:


Nope, no oil spill on Cape Cod; just a lot of rocks and seaweed…But hey, I’ll take it to wake up to a sunrise on the beach.

As expected, most of the weekend festivities revolved around food. Unfortunately, my beefalo didn’t arrive in time. But it has since been pre-ordered, so I’ll be making a couple more trips back before summer is over! This time, however, I had to settle for a grass-fed beef burger and a WICKED GOOD LOBSTAH ROLL!

Sans mayo and hold the fries please…

As usual, I received several comments about the amount of food (albeit, healthy food) I seem to be able to eat without putting on appreciable weight. The fam always likes to chalk it up to my being blessed with a “fast metabolism.” But we have the same genes, so I really don’t think luck has a whole lot to do with it… The more I discuss this issue with them and with others, the more I realize that most people don’t really understand what metabolism actually is.

In simplest terms, metabolism represents all the physical and chemical changes your body undergoes to use energy. It involves two processes: Anabolism (i.e., building up) occurs when you eat too much and the extra energy gets stored as either fat or glycogen, or used to repair and build muscle; and catabolism (i.e., breaking down) occurs when you don’t eat enough and your body pulls energy from stored fat, glycogen or muscle tissue to meet its needs. You fluctuate between anabolism and catabolism throughout the day, depending on when, what and how much you last ate in relation to the amount of energy your body requires. If you spend more total time in anabolism, you gain weight. Similarly, more time spent in catabolism means you’ll lose weight.

There are three components to metabolism:

1. Basal Metabolic Rate (BMR). This is the energy your body uses to sustain basic life functions (breathing, heart rate, respiration, etc.) at rest. It represents the largest component of metabolism (60-75%), but it may vary greatly depending on body mass and composition (larger individuals have an increased BMR, as do those with a greater percentage of muscle mass), as well as age and sex (women have a 10-15% lower BMR than men and it declines with age in both sexes).

2. Thermic Effect of Food (TEF). This number represents the rise in metabolism that occurs after a meal due to the energy needed to digest, absorb, transport and store the food consumed. It is highest about one hour after eating and may remain elevated for up to four hours. It is most affected by the caloric content of the meal (the more calories, the higher the TEF), but is also somewhat dependent upon the macronutrients consumed (protein elicits a TEF of 20-30%, while carbs yield a 5-10% increase and fats have a TEF of less than 5%).

3. Thermic Effect of Exercise (TEE). This is the most variable component of metabolism, accounting for anywhere from 15-30% or more of daily energy expenditure, depending on your activity level. Exercise not only requires energy to perform, it also elevates resting metabolism during the 24-hr. recovery period (what we in the fitness world refer to as EPOC, or the “afterburn”). The most significant energy expenditure occurs with rhythmic movements involving large muscle groups, and the extent to which the metabolism is elevated during recovery is largely dependent on the INTENSITY of the exercise.

The answers to the following questions should now be pretty clear, but I’ll spell them out just in case you skipped over the first half of the post and scrolled straight to the picture of Serena Williams…

What RAISES metabolism?

1. GAINING WEIGHT, particularly muscle. The aim obviously isn’t to get fatter, but increasing body mass will significantly raise BMR. (NOTE: Although gains in lean mass alone will raise metabolic rate SLIGHTLY, the increase is not nearly as much as people think. In fact, a 1-lb. gain in muscle tissue barely amounts to 7 extra calories per day.)

2. EATING FOOD. The more food you eat, the greater the TEF.

3. EATING PROTEIN. As mentioned, protein elicits the greatest TEF of all macronutrients.

4. EXERCISE, especially high-intensity exercise that uses large muscle groups.

5. Non-Exercise Activity Thermogenesis (NEAT). This includes any additional unstructured physical activity throughout your day (e.g., running all over Manhattan with a computer, exercise equipment and a 10-lb. cooler filled with food in your bag…).

So, what LOWERS metabolism?

1. LOSING WEIGHT, particularly muscle. Decreased body mass (and lean mass) lower BMR.

2. NOT EATING. This is probably the fastest way to destroy metabolism. Aside from a negligible TEF, your body naturally adapts by altering hormones to conserve fat stores and slow resting metabolic rate. This is what’s meant by the term “starvation mode.”

3. NOT MOVING. No movement means no NEAT and definitely no TEE.

And that’s metabolism in a nutshell. I hope things are starting to make more sense to those members of my family reading right now, and to anyone who may have been confused about the matter by the likes of Jillian Michaels.

Filed under: exercise Q&A, fat loss, nutrition

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2 responses to “Breaking Down Metabolism”

  1. UJ says:

    Meaghan, for neophytes like me, this helps…Did you jog to the beach or take a bike? Nice photo! Next time you’ll have to get my butt out of bed to join you.

  2. Meaghan says:

    Happy to help! We actually drove to the beach so the DOG could run… Good thing I made it to your class! Thank Colleen again for me; nice to see someone else running a SAFE “bootcamp.” See ya on the 4th!

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