OK, before you go any further, let me inform you that this is yet another fitness myth. Read on to find out why.
Let’s say that you hear about a new great diet that claims you can lose 10 pounds in one week. You want to lose weight so you imagine this could be the diet for you! Before you consider trying something similar to this scenario, let’s figure out if it’s in your best interest and if it will work right for you. What does it take to lose 10 pounds of fat in one week?
1. We know that 1 pound of fat is approximately 3500 Calories.
2. We know that to lose one pound of fat, you must actually use it. This goes back to high school physics. The second law of thermal dynamics states that mass is neither created nor destroyed. So, in order to get rid of fat off your body, you must use that stored energy to do work.
3. Burning Calories (“work”) can be accomplished in several ways:
a) RMR – short for the Resting Metabolic Rate. This is the minimum amount of calories needed to sustain the vital functions of the body during a relaxed, reclined, and waking state Things like breathing, heart beating, digesting food and even thinking all require calories. Most people have a RMR that falls into a range of 1200 – 2500 Calories per day. Also note that things like aging, muscle mass, hormone activity, and starvation (often AKA “dieting”) influence our BMR. The best thing to do to increase your BMR is to exercise (aerobic and strength train) and eat enough. When we eat less than around 1200 Calories per day our RMR actually slows down.
b) TEF – short for the Thermic Effect of Food. Different foods require different amounts of Calories to digest. For example, meats take longer to digest than crackers. TEF is responsible for approximately 5% (give or take) of your total daily caloric expenditure.
c) TEE – short for the Thermic Effect of Exercise. Any activity we partake in requires energy to accomplish. Driving takes fewer Calories than running. TEE can add a few hundred to a few thousand extra Calories towards your total daily expenditure. Various forms of physical activity require more work (and thus more energy) than others; additionally the way in which you perform physical activity can have an impact on how much your metabolism is increased after your workout, but that is a topic for another day.
4. Weight loss occurs only when the Calories you expend each day are more than you consume (eat).
5. We can approximate how much weight loss would occur if we find your Calorie balance HERE
a) Calculate your Resting Metabolic Rate (you can find various formulas or calculators online, or use one ). Let’s say that your RMR is 1800 Calories per day.
b) Calculate the amount of Calories you burn during your daily activities. This will depend on many activities – your occupation and other activities during your average day. Let’s pretend that you burn an extra 500 Calories doing these things.
c) Calculate the amount of Calories you burn doing structured workouts or other exercises during your average day. This is easier for some activities (such as running, if you know how far and long you ran) than others, but additional calculators can be found online to provide estimates. Let’s say that you burn an average 200 extra Calories per day through exercise.
d) Calculate the number of Calories you eat. Let’s pretend you eat 2000 Calories per day.
1800 (RMR) + 500 (Activity Level) + 200 (Exercise) = 2500 Calories per day.
Calorie Balance (Calories in minus Calories out):
2000 – 2500 = -500 Calories. You are in a calorie deficit of 500 Calories.
e) If 1 pound of fat is equal to 3500 Calories, it would take you 7 days (1 week) to lose 1 pound of body fat.
BOTTOM LINE: If someone lost 10 pounds of fat in one week, they would have to expend an extra 35,000 Calories that week, or be in a caloric deficit of 5,000 Calories per day. To achieve that in the example above, you would have to burn and extra 2500 Calories per day, and that’s if your diet consisted of eating NOTHING! Therefore, if someone really lost 10 pounds, they lost something other than fat.