Myth Busted: The 500 Calorie Deficit
Raise your hand if you’ve heard the following: “Eat 500 calories less per day to lose a pound a week!”
Now that I’ve walked away and silently screamed into my pillow, let’s talk about why this is NOT the case!
One pound does not necessarily equal 3,500 calories
So, the general theme above states that if you have a 500-calorie deficit per day x7 for the week, you would have a net deficit of 3,500 per week. If one calories equals… well you get the rest.
The 3,500 calorie per pound standardization comes from some seriously old research (hello, 1958) and has been readily adopted because, well, it’s an easy number to wrap our brains around. For those of you that don’t want to read the fine print, here’s what it said:
One pound equals 454 grams.
Pure fat contains 8.7–9.5 calories per gram.
Body fat tissue is 87% fat.
On average, nutritionists also choose to round that fat calorie number down to 9. So, if you see 4 grams of fat on a nutrition label, it’s generally assumed that there are 36 calories from fat (9 calories x 4g) in that item. But, if there could be more or less fat, that could noticeably change your macros. We use 9 calories simply because it’s an easy round number.
The same can be said about the fat percentage in a pound of body fat tissue. The average body fat tissue is 87% but that doesn’t mean that all tissue is that percentages! Some studies have shown that body fat tissue could be as low as 72% fat! That makes a huge difference.
Even so, using the above values, one pound equals 454 grams. 454 x .87 = ~395 grams are fat. This gets us somewhere between 3,436 calories to 3,752.
So…anyone seeing a problem here? If I thought that by creating a 500-calorie deficit per day, I would get to this magical 3,500 calorie number I could be under OR over. Let’s say I was shooting under, consistently. Each “pound” I thought I was losing, was really not quite. At the end of the year, I’m 13,000 calories short - which, based on our above equation, is almost four pounds.
The body’s response to DIET
Another thing that this myth fails to address is the body’s physiological response to changes in its composition and your diet. I’ve mentioned this numerous times again, but when you eat less, your body responds in kind. If, by creating a caloric deficit, you get too close to your body’s basal metabolic rate (BMR), your body will respond by burning fewer calories. Essentially, your body doesn’t truly know if you’re starving or strategically trying to fit into a skimpy bikini this weekend. So, less food = less calories burned. Your body, essentially, becomes less efficient.
As your body shifts to this “starvation mode,” it’s also quite possible that you start burning muscle mass, even before you burn fat. Here’s how: Your body uses available carbohydrates (glycogen) for immediate energy. At any given time, there’s a substantial amount floating around in our system to burn for energy. After that, your body will turn to muscle tissue for amino acids and fat tissue for triglycerides for energy.
Burning muscle first likely comes from an evolutionary survival response. If your body is in starvation mode, the largest calories stores on the body belong in the fat cells. If your body is starving, it is going to do everything possible to maintain those stores, for as long as possible. Muscle, on the other hand, is expendable since it also requires more calories to maintain. Therefore, it’s in your body’s better interest to shed the muscle and keep the fat stores. Since amino acids are not stored in fat tissue, the breakdown of muscle tissue is also the only way for the body to receive essential amino acids to continue hormonal processes within the body.
So, if you’re having issues with fat loss, it’s likely that you’re eating too few calories.
The body’s response to composition
This antiquated “500-calorie deficit” myth also assumes that weight loss is linear. It does not take into consideration that as you lose weight, you’re potentially also changing your body composition. Are you strength training more? If so, you’re gaining lean muscle mass. As I talked about in a previous myth busting post, (read: Myth Busted: Lifting Weights Makes Women Bulky) one pound of lean mass burns up to 2-3x as many calories as the same of fat! If you’re shifting your body composition, your daily needs change and therefore, so does your macronutrient requirement. If we continue to eat the same way as our body shifts, we risk running into the plateau effect that so many fear. Your body will simply adjust to the current way that you are eating and the weight loss will stop. You have continually tweak your macro ratios to make sure that you are eating enough to compensate for this change in muscle mass and body composition!
Also, let’s discuss body composition as it pertains to males vs. females. The idea that “just be in a 500-calorie deficit” is a laughable “one-size-fits-all” concept. A male, weighing upwards of 160 pounds, will require a much different caloric intake than a female weighing 130 pounds. A 500-calorie deficit for a female is much more restrictive than her male counterpart. If you are listening to this advice and consistently under eating or entering “starvation mode,” it will lead to the body breaking down muscle tissue for fuel. Losing muscle mass means fewer calories burned at rest, which continues to put you farther away from your goals! And no one wants that.
What the Hell, Ashley?
I’m not saying that eating fewer calories per day doesn’t lead to weight loss. It does. But, only in the short term. If you want to lose weight, consistently and permanently, you have to continue to adjust your diet. This is one of the main reasons that fad diets are a terrible idea and one size does not fit all!