Why Fast Weight Loss Makes You Fat

Look, we’ve all been in the checkout aisle silently cursing the person in front of us getting out all of their coupons and then proceeding to pay with a check. So since we’re gonna be there for a while, we start to look around. Oh snap, Kim Kardashian lost 25 lbs in just 2 weeks! Holy crap, Jennifer Love-Hewitt dropped 4 dress sizes (I don’t really know what that means, but I’m guessing its a lot) in just 30 days! Oh, and look over there it’s everyone’s favorite TV guru, er I mean look, it’s Dr. Oz. He says that by taking raspberry ketones via enema 6 times a day and then gargling lemon juice, the reaction between the two will help you lose 5 lbs a day!

Luckily you are all smart enough to know that the claims are bogus. Obviously losing weight that fast isn’t realistic. But one thing that is actually correct on those tabloid magazine covers is their use of the word “weight”. We all talk about weight loss, but what we really mean is FAT loss. Dropping weight very rapidly will cause you to lose fat, but it will also pull from your skeletal muscle as well leaving you weaker overall and decreasing your total BMR, or resting metabolic rate. But that’s kind of old news as I’m sure I’ve discussed this phenomenon in previous posts. Today though I’d like to discuss other physiological reasons why losing weight very quickly through a very low calorie diet (VLCD) is a short lived thing and basically the worst way to lose weight. Aside from the extreme hunger, lethargy, and irritability one will undoubtedly encounter, it turns out there’s a bunch of stuff going on at the cellular level too.

Note: A VLCD will vary from person to person, but for practical purposes, I’m referring to the 800-1,000 kcal range or so.

There is a theory out there that we have a set point in terms of body weight and composition (fat:muscle). In other words, our bodies are content at a certain weight and body fat percentage. It’s likely that this is simply genetics because hey, we’re all unique! So the issue is that when we lose a bunch of weight really fast, it sends off a cascade of alarms within the body. You’ve likely heard of this as our bodies going into “starvation mode” or “survival mode”. But those are blanket terms. What are they actually referring to? Below is a list of the changes going on in the body on a VLCD:

  • Thyroid hormone activity decreases. Your thyroid is a very metabolically active gland and it makes up a substantial proportion of your basal metabolic rate. So obviously having this slow down means that you expend fewer calories at rest.
  • Exercise-induced thermogenesis decreases. When we exercise (and I’d include activities of daily living in this category as well) we lose energy in the form of calories. Since energy cannot be created or destroyed, we lose those calories in the form of heat dissipation. Remember that a calorie is simply the energy required to heat 1 kg of water 1 degree Celsius. The obvious conclusion here is that we don’t burn through as many calories when we workout when on a VLCD.
  • Thermic effect of food decreases. Quite simply, it takes energy to break down the foods and beverages we take in. When the body senses a low energy intake, it becomes more efficient in this process, thereby decreasing the amount of energy it takes to do this. Starting to see a trend here?
  • Non-exercise activity thermogenesis decreases. Also known as NEAT, this phenomena is in reference to all of the calories burned during times except for sleeping, eating, and during exercise. This might include showering, getting the kids ready in the morning, and other daily activities. You once again are becoming more efficient. And for fat loss, that’s not a good thing.
  • Fat oxidation decreases. The burning of your fat stores goes down. You hold on to more fat because who knows how long this low energy intake will last?
  • Mitochondrial efficiency increases. The mitochondria are the energy factories located within the cytoplasm of our cells. They are able to take carbohydrates, fats, and to a lesser extent, proteins, and use them to make ATP (energy). The more efficient these processes become, the fewer calories are burned. Waaah waaah…..
  • Fat gene expression changes. This one really goes both ways. Basically, the expression of genes that cause you to store fat increase while the expression of genes responsible for burning fat decrease. Still want to lose 20 lbs in a week?
  • Ghrelin and Leptin are altered. Ghrelin is a hormone that says, “Yo, feed me!”. You know leptin from Thanksgiving dinner. It signals that we are full or satiated. I won’t even extrapolate on what happens to these two because you already know.
  • Adipocyte production increases. An adipocyte is just a fancy word for fat cell. Yep, that’s right. In an extended energy deficit (VLCD), we actually produce more fat cells. This is likely so that when food becomes available again, we are able to store more fat (energy) in case this whole low calorie thing ever rears it’s ugly head again.

So there you have it. I’m willing to bet that this is just a short list of what all is actually going on, but i think it will suffice for now. I wanted to end this with something like “Based on this research, I feel the absolute best weight loss should be done at a rate of 0.1-0.5 lbs per week” or something like that. But I feel the best conclusions are the ones drawn by oneself. Hell, I could be way off. I might be missing something. In fact, I likely am. And I’m OK with that. I’ll just keep trying to get better.


No One Makes it by Themselves


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1 Comment

  1. Avatar


    Thank You Very Much!!!
    Burning 0.1-0.5lb of fat per week wow! ( I thought I read it wrong and went back to double check it). I feel so relieved now, since I thought I was burning fat at a painfully low rate of 0.5lb per week, or 1lb of fat per month. (I have Tanita scale) eating an average net calories of 1750. Trying to go lower but for whatever reason always ending at this level. Now I am actually happy.
    I knew about the starvation mode but I never had a clue about making more fat cells being in calorie deficit, hard to believe but I bet is is true.

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