Reasons Calorie Deficit Diets Fail
While a negative calorie balance is required to lose weight, it can also cause unwanted side effects.
You Lose Muscle
At the start of a calorie deficit diet, you almost always lose weight. Though it’s possible that most of that weight is muscle.
The reason is that muscle requires a lot of energy to maintain. So your body eliminates muscle when there’s not enough energy to support it.
To illustrate, researchers from Stanford University put active men on a 40% calorie deficit diet1. Then tracked their weight, lean mass (muscle), and body fat for 3 weeks.
Adapted from Friedlander, et al.
As a result of the diet, participants lost an average of 8.4 pounds in 21 days. Sounds great, right?
Well, in this case, over half of the weight lost was lean mass.
Maybe you don’t care that much about being muscular. But the bigger problem is that muscle loss has a negative effect on metabolism.
Your Metabolism Slows Down
When you lose lean mass your metabolism slows down so your body can survive on less energy. Which sounds efficient, but it comes at a cost.
Like tossing gold out your car window to get better gas mileage… you go further on less fuel, but you lose a valuable resource.
In the previous study, researchers also tracked the participants’ metabolic rates. And they found that metabolism dropped by as much as 230 calories.
Adapted from Friedlander, et al.
Admittedly, 230 calories doesn’t sound like much. Over the course of 3 months, however, that’s enough energy to burn an additional 5 to 6 lbs of fat.
Also, the calorie deficit doesn’t have to be large to lose muscle. A similar study reported metabolism decreases after 19 days of a 20% calorie deficit2.
The point is, a slower metabolism means you don’t burn as many calories. So the calorie deficit goes away and you stop losing weight.
You Stop Losing Weight
As an example, let’s say you eat 2,500 calories per day to maintain your weight. In order to lose weight, you decide to create a 500 calorie deficit by eating 2,000 calories per day.
500 / 2,500 = 0.2 (20% deficit)
After several weeks, your metabolism slows down to 2,000 calories. This is when you stop losing weight and hit a plateau.
Common sense tells you to cut another 400 calories per day to continue losing weight. So now you’re eating just 1,600 calories.
400/ 2,000 = 0.2 (20% deficit)
And for a few weeks, it works. But then you hit a second plateau.
At this point, you’re hungry all the time. Worse yet, you don’t look or feel the way you thought you would after losing weight.
Frustrated, you give up and go back to eating 2,500 calories per day. Sound familiar?
Don’t feel bad. This outcome is almost inevitable in the situation described. Unfortunately, it’s also a formula for rapid weight gain.
You Lose Motivation & Regain the Weight
After the calorie deficit diet, your metabolism stays low. So when you go back to eating more food you’re now in a large calorie surplus. And you regain a lot of weight (that scary red bar).
In many cases, you regain more weight than you lost. Even worse, the majority of the weight gained is body fat!
Over time, your metabolism will gradually increase again. But the damage has already been done.
By now it should be clear that a prolonged calorie deficit isn’t the answer. The good news is, with a few easy changes you can lose weight & keep it off.