Why Low-Calorie, Low-Fat Diets Don't Work

NOTE: This post is outdated.  I no longer believe everything I have written in this article.  I'll keep it up regardless, but it does not accurately reflect my current thinking. 

Losing weight isn't easy.  Just ask your neighborhood middle-aged yo-yo dieter.  It's hard to get the weight off, and it's even harder to keep it off.  But the problem, in my opinion, does not lie in a lack of motivation or drive to make a successful lifestyle change.  The problem is that the vast majority of dieters are going about it the wrong way.  The media loves to promote this simple calories in, calories out model of weight loss, and while calories certainly do count for something, there's much more to the story.  What the calories in, calories out concept fails to account for is what your body actually does with the calories it receives, and it turns out that is a vitally important concept in weight loss. 

First off, let's discuss what happens when you try to lose weight by simply eating less (also known as starving yourself).  You start off with all the motivation in the world, probably counting calories and planning out all of your meals.  Let's say you aim to eat 1500 calories a day, and your body wants to burn 2500.  At this rate, according to the simple math of the calories in, calories out model, you should be losing about 2 pounds per week.  And indeed, you'll probably lose a few pounds in the first few weeks on a diet like this.  But you're setting yourself up for failure in the long-term.  Here's why.

Insulin.  Weight loss is all about the hormone insulin, which is responsible for a number of important weight-related processes in the body.  What's important to understand here is that in order to lose weight, your insulin levels must be kept at a low level.  Your body is only capable of removing fat from the fat cells when insulin is low.  So how do you keep insulin low?  Eat fewer carbohydrates.  For example, if you're lowering your calorie intake primarily by reducing the fat you're eating, your insulin levels haven't changed and you're still not utilizing your own body fat for fuel.  If you're losing any weight at all at this stage, it's probably muscle weight, and you want to target fat, not muscle.  Yes girls, even you.  You need muscle to get that "toned" look that you're striving for.  Nobody wants to look skinny-fat.

Your body is not stupid.  So you're consuming 1500 calories, but your body wants to burn 2500, and insulin is still keeping your fat all locked up in your fat cells.  You may be getting some energy from burning up your own muscle protein, but you still need more.  At this point, your hypothalamus and thyroid come into play.  The hypothalamus is the master regulator of metabolism in the body, and when it senses a starvation situation like this one, it down regulates your thyroid, reducing the amount of calories you burn throughout the day.  Now all of a sudden, your body's going to gradually adapt to the amount of food you're taking in until it strikes a balance.  This will obviously stall your weight loss efforts, but there are other consequences as well, and this leads right into my third point.

You will never win a battle between you and your physiology.  Think of your body on a low-calorie diet as similar to a school making budget cuts.  Your body, or the school, doesn't have the resources to continue operating in the manner in which it's accustomed to, so it has to cut out something.  In the human body, instead of cutting the water polo team, you're forced to cut some of the less urgent bodily processes, like maintenance and growth of hair, eyebrows, fingernails, etc, or perhaps your immune function.  In addition, you'll feel tired and lazy, because your body doesn't want you to be active and burn any additional calories, and you'll probably start to sink into a deep, dark depression.  At this point, you may drive by the nearest Haagen Dazs one day on the way home from work and end up binging on three large double-chocolate cups of ice cream with extra caramel and rainbow sprinkles.  Sound familiar?  At least now you can grow fingernails again.  I said it before, and I'll say it again: You cannot win a battle with your own physiology.  You're body will get what it needs one way or another, and it will make you miserable until it does.

So low-calorie, low-fat diets are not your best option when trying to lose weight.  There's clearly more to the story than simply cutting your calories.  In my next blog post, I'll talk about why low-carbohydrate diets do work and discuss some of the basic biochemistry of it.  Thanks for reading!