Reader Question: Low Calorie Intake and Metabolic Slow-Down
If you’ve ever been on a fat loss diet, you know that there is one major requirement to have success – a low calorie intake. Unless you are creating a calorie deficit for the day, you aren’t going to lose weight. Simple as that. Weight loss really isn’t rocket science, it’s a simple mathematical equation that you need to tilt in your favour.
Now that said, with weight loss, there is such a thing as too much. I recently got a question from a reader regarding this topic and I felt it was something important to address.
Let’s have a closer look at low calorie diets and metabolic slow-down.
Question:
Let’s say I’m going to create a calorie deficit of 3500 calories a day, causing me to lose 6 pounds a week, will my metabolism slow down? And if it does, will it be permanent? I only plan to do this for 10 days with diet and exercise and after that maintain a 500 calorie deficit through exercise.
For people who have damaged their metabolisms, how do they fix this?
Answer:
Okay, there are a number of things going on here.
First, let’s talk about the 3500 calorie deficit each day. This, in my opinion, will be virtually impossible. Unless you plan to exercise for 6+ hours a day while eating virtually nothing, you aren’t going to create this large of a deficit.
Second, what would concern me more than the slow metabolism, is that even if you came close to that size of a deficit (let’s say 2000 calories, which is still pretty much impossible), you’re likely not going to be losing fat; you’re going to be losing lean muscle mass.
When you lose muscle mass, yes your metabolism will slow down. This is due to the fact that muscle is one of the more metabolically active tissues in the body, so when it’s lost, you won’t burn as many calories just sitting around doing nothing.
Can this be fixed? Yes, by building new muscle tissue. This, however, is an incredibly long process.
In addition to the lean muscle mass loss on such an extreme diet/exercise program, the metabolism itself may slow down somewhat, but over a ten day period, the chances aren’t all that high.
Any degree it does slow down will be ‘repaired’ once you start eating a normal diet again.
Individuals who have gone for months eating at a too low calorie intake and have damaged their metabolisms often have to take full diet breaks, where they basically bring their calories up to a maintenance value (15 cals/lb of body weight) and take in at least 150 grams of carbs a day (to normalize the thyroid hormones).
This diet break can take anywhere from one week to a few months depending on how bad the situation was.
So to summarize my answer to this question, I firmly don’t believe you will be able to lose that much weight over such a short period of time (unfortunately, which is probably not what you wanted to hear), unless you are losing a combination of water and muscle mass – which again, I would strongly recommend against.
There are just some cases where you can take a diet a little too far and this would be one of them. There are fast weight loss systems out there – the best one I’ve ever seen is Lyle McDonald’s Rapid Fat Loss Handbook, but if attempting to lose weight asap, you really need to be careful you’re doing it the right way.
Creating a 3500 calorie deficit a day – or attempting to, is not the right way.
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