Imagine it’s a cold, snowy day and you’ve been out Christmas shopping and all of sudden hunger overtakes you and you reach for a Christmas cookie and before you know it, 5 or 6 of them are gone in a flash! What if it was more like 9 or 10 of them? How many calories did you just unwittingly consume? How much are you going to have to work out to expedite the usage of excess glucose now swirling around your blood stream while your pancreas faithfully pumps out insulin to combat the surge in blood sugar??
Well, I’m glad you asked. Because, really, life happens, and although I’m sure we’d all like a little more “Silent night, holy night, all is calm, all is bright”, the fact of the matter is, life is incredibly hectic this time of year. Even if you are like me and you’re at least trying to focus on the real meaning of Christmas and not get wrapped up in the American trappings, excess sugar consumption (most often in the form of sucrose) is bound to happen. I would like to mention that there are 3 Luminaries I’m coaching right now who have all made dedicated decisions to avoid all sweets this season – I am very proud of K.S., A.D., & S.C. – but I’m writing this blog post for the readers who might have accidentally eaten a plate of cookies (or maybe it was just your doppelganger…if it was, does that mean those calories don’t count?).
A broad generalization puts a decorated sugar cookie (approximately 2” in diameter, buttercream frosting, and sprinkles of course) at 140 calories, 20 g carbohydrates (12g of those from sugar), 6 g of fat, 2 g of protein. Let’s pretend you ate 6 – please do the math – oh wait, I’ll just do it for you…840 calories, 120 g carbs (72 g from sugar), 36 g fat, 12 g protein. What would you have to do, physical-fitness-wise to burn this off?
Let’s back up for a bit to establish a few facts from what we know of energy metabolism. The body will use ingested carbohydrates as its first source for energy. All throughout the day, your body is making ATP (Adenosine TriPhoshatase). ATP is the “energy currency” of our cells – moving around in any form requires energy “withdrawls”, so to speak, and the body has to make energy “deposits” every 3-5 seconds to make up for the “withdrawls”. This happens metabolically through glycolysis. Glycolysis is the breakdown of glucose (i.e. carbohydrates) into energy from either ingested carbohydrate or through muscle glycogen (the stored form of carbohydrates in either the muscle tissue or the liver). The body can also make energy through the TCA cycle (aka the Krebs cycle or citric acid cycle) or lipolysis (using stored fat for energy). The body prefers to use ingested carbohydrates first for energy, then when the glucose from the ingested carbohydrates in the bloodstream are used up, it will next use the glycogen stored in the muscles and liver for energy. Thankfully, it will also use adipose tissue (a nice term for our stored fat cells) for energy through lipolysis, and the body can even use protein for fuel (but this is less than 5% of energy provision during physical activity). During starvation and when glycogen stores become depleted, protein catabolism may become an increasingly important sources of energy for muscular work. (Reference: Sport Nutrition: An Introduction to Energy Production and Performance by Asker Jeukendrup and Michael Gleeson, 2nd Ed, 2010).
“Burning calories” is a layman’s term for “making energy in your body” to produce movement. The more you move, and the intensity of your movement, causes your body to “burn” more calories and ultimately get to the point where it is using stored fat for the energy it needs to supply you with ATP to accomplish your tasks.
The rate at which a person’s metabolism uses calories and stored fat for energy depends on many, many factors. At the top of the list are your body composition, your activity level, and your food and drink choices. Body composition means your body weight and the percentage of that weight from muscle, bones, fat, and water. I.e. more muscle tissue in your body means you burn more calories throughout the day (even at rest). A higher bodyweight also means you burn more calories than a lower-weight person. Your activity level doesn’t just mean how hard and how long you work out, it also means what V02 Max you perform at, how much you move throughout the day even when not exercising, and also the heartrate levels you had while performing that exercise or (or at rest). Thus, wearing a heartrate monitor is an effective way to accurately gauge how many calories you burned in an exercise session (especially paired with your body composition information).
Here are a few examples from real people I’ve witnessed in the past week (a few details have been changed to protect people’s privacy). This is what would be required, based on simplistic body composition and heart-rate figures, to burn off the 840 hypothetical sugar cookie calories.
1. 125 lb woman, age 40, lower body fat, somewhat high muscle content, works out with moderately-high intensity cardio and strength workout maintaining 80% of her target heart-rate, for 90 minutes. Her exercise consisted of interval running, rowing, and bodyweight exercises like lunges and mountain climbers with no breaks. 840 calories burned over 90 minutes.
2. 225 lb man, age 35, high body fat, low muscle content, works out with moderate-intensity maintaining 80% of his target heart-rate for 60 minutes. His exercise consisted of walking at an incline, rowing, and bodyweight exercises like lunges and mountain climbers, with a few breaks. 840 calories burned over 60 minutes.
3. 185 lb man, age 41, low body fat, extremely high muscle content, works out with high intensity, maintaining 85% of his target heart-rate for 50 minutes. His exercise consisted of running at a fast pace, rowing, and bodyweight exercises like lunges and mountain climbers, with no breaks. 840 calories burned over 50 minutes.
4. 250 lb woman, age 55, high body fat, low muscle content, works out with moderately-low intensity, maintaining 75% of her target heart-rate for 120 minutes. Her exercise consisted of brisk walking with no breaks. 840 calories burned over 120 minutes.
5. 195 lb man, age 37, low body fat, high muscle content, works out with super-high intensity, maintaining 80% of his target heart rate for 50 minutes. His exercise consisted of cycling at a high intensity with no breaks. This athlete has been able to train his body to have a lower heart-rate and high intensity which leads to the ability to do endurance events at the same level of output for a much longer time. It only took 50 minutes to burn 850 calories.
The lower weight woman had to exercise a lot longer (90 minutes) to burn 850 calories than the higher weight (185), higher-muscle content man doing the same work-out (50 minutes in duration). But, no matter what, it is possible to burn this many calories in a work-out session no matter what your current state of physical fitness or body composition, however, it might just take a longer duration for some people.