Wednesday, May 25, 2011

Why Low-Carb Diets 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NOTE: This post is outdated.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.

Although it may seem counter-intuitive, a diet low in carbohydrates, which by definition is also higher in fat, may be the most effective way to lose weight.  I remember when I first heard of the Atkins Diet back in high school, when I saw my friend's father take the cheese off of a piece of pizza and throw away the bread.  Surely you can't lose weight by eating fatty cheese and throwing out the low-fat bread!  But while it made little sense to me at the time, low-carbohydrate diets really do work, and the science supporting this concept is just about indisputable.

Firstly, I would like to state that in weight-loss, what most people are concerned about is losing fat, as opposed to just weight in general.  Fat is the enemy, not muscle; we want to keep our muscle.  As a result, I'll be discussing how the fat tissue is regulated in the body.  In order to understand how low-carb diets help you lose fat, it is important to understand the function of two key enzymes that regulate the fat tissue:  lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL).  The activity of both of these enzymes is controlled by the hormone insulin, which is secreted in response to carbohydrate consumption.  I'm going to get into some biochemistry here... I like biochemistry because, since most people don't understand it, I can make it look like I really know what I'm talking about, even though in reality I'm just making up words and hoping I don't get caught.  Seriously though, it's important to understand a little basic biochemistry in order to truly understand how a low-carb diet burns fat like nothing else.

The first enzyme, LPL, is located on the cell membrane of various cells throughout the body, and when it is activated, it pulls fatty acids out of the bloodstream and into that cell.  If LPL is on the surface of a muscle cell, it directs fatty acids into the muscle to be used as fuel.  LPL on fat cells, however, pulls fatty acids in to be stored as body fat.  The trigger to activate LPL on the fat cells?  Insulin.  When insulin levels are high, LPL activity is up-regulated on the fat cells, and the body starts storing fatty acids as body fat.  The more insulin we secrete, the more active the LPL, and the more fat that is diverted into fat cells.  Carbohydrates may even be converted directly to fat if there is no immediate need for them.  Translation:  the more carbohydrates we eat at a meal, the more insulin we secrete and the more fat we store.  Insulin also suppresses LPL activity on muscle cells, and just about every other cell in the body that isn't a fat cell.  This has two important implications.  Firstly, these cells will not be able to take up fatty acids to burn as fuel.  Instead, they must use the carbohydrates in the bloodstream.  The body has no choice but to do this; high blood glucose (carbohydrates are broken down into glucose) is toxic, so it has to lower the amount of glucose in the bloodstream any way that it can.  Carbohydrates get used first for fuel, not because the cells prefer them over fat, but simply because the body needs to do something with all of that glucose.  And secondly, suppression of LPL on every cell except fat cells creates a one way express highway for fatty acids (and some carbohydrates) to be delivered to your fat tissue.  As long as insulin is high, glucose is the preferred fuel, and any fatty acid in the bloodstream is likely to be stored as body fat.

HSL (hormone-sensitive lipase), another enzyme on the surface of fat cells, works in very much the opposite way.  While LPL pulls fatty acids in to a cell, HSL mobilizes fat from the fat cell and releases it into the bloodstream, allowing the body to burn it as fuel.  Insulin suppresses HSL, meaning it prevents fat from leaving your fat cells.  To make things worse, it only takes a little insulin to have this effect, so even if insulin is only slightly elevated, HSL will be down-regulated and fat will be stuck in the fat cells. This is the key to fat loss; your body must be able to access its own body fat and burn it for energy, and in order to create a free-flowing environment where fatty acids are easily released from the fat stores, your carbohydrate intake must be kept in check.

When eating a low-carbohydrate diet, the vast majority of your calories are coming from fat and protein, neither of which trigger a significant insulin release.  Sure, you're eating a lot of fat; your caloric intake may consist of up to 80% fat.  But the significant reduction of carbohydrate intake makes all the difference in the world.  With fewer carbohydrates, and a much smaller insulin release, the body begins to use fat as its main fuel.  The fat you eat, instead of being locked away in fat cells, is now likely to be delivered directly to cells that need energy.  In addition, the fat cells are free to release fatty acids as they please, whenever energy is needed.  The fat loss floodgates are now open!  In fact, since so much body fat is being burned on a low-carb diet, most people find that they experience a reduction in appetite.  The reason is simple:  The body's cells can't tell the difference between fat from the diet and fat from it's own fat stores; all it knows is that it's getting energy, and that's all that matters.  You've now turned your body into a fat burning machine!  And that means that you can let hunger be your guide; you can eat as much as you want to eat.  No more going to bed hungry or replacing lunch with a 100-calorie pack.

Sounds easy right!?  Well, losing weight is never easy.  You can't lose weight without giving up something.  But hey, if all you do is limit carbohydrates, the rest will essentially take care of itself.  There's no calorie counting, no meal timing, and no starving yourself.  Just eat as much as you want of certain foods and don't eat others.  Most importantly, on a low-carb diet you are working with your physiology, not against it like you would do by simply reducing calorie intake.  You can win the battle versus carbohydrates; you'll never win by starving yourself.


  1. Burn, of all the articles, this one has been by far the most enlightening. This is the key to what most folks are missing - the biochemistry. You lay out the physiological processes beautifully and most importantly, in lay mans terms. Well done my friend, I'm sending this to papa

  2. do you have any advice on exercise while in ketosis?

  3. I haven't researched exercise in ketosis too much, but I know Dr. Jeff Volek has done some interesting research showing that performance actually improves on a ketogenic diet.

    I've had no problem exercising in ketosis, I've never felt depleted of energy by any means. I would avoid doing any long-duration intense exercise though, and probably limit glucose-demanding stuff like crossfit. But most importantly just listen to your body, if you're becoming chronically fatigued, either tone down the intensity or eat more carbs.

    Thanks for reading!

  4. I'm curious on how you've changed your thinking about this and the last post. Is it the actual content or how you're describing the biochemistry?

    1. A lot of the information from these two posts came from Gary Taubes' books Good Calories Bad Calories and Why We Get Fat. I've since learned that a lot of his ideas aren't scientifically accurate. This article did a lot to change my mind. In my mind, the real reason low-carb diets work so well is because it's near impossible to overeat on just fat and protein. People on low-carb diets can eat as much as they want and still only end up with like 1500 calories. So I think that's the main reason it works for weight loss.