Monday, January 27, 2014

Low carb, super low carb, ultra low carb, what does it all MEAN?

Ordinary words can seem so clear.  "Low carbohydrate" sounds precise, right?  But it really isn't. No standard definition can be found for "low carbohydrate diets."

The "Standard American Diet" (or SAD for short; the irony should not be lost on us) has somewhere around 250-350 grams of carbohydrate according to USDA recommendations, with the "bare minimum for women" being 130 gm. Remember that there are about 4 Kcal (kilocalories, also called a Calorie with capital C) per gram of carbohydrate, so that recommendation comes to 1000-1400 Calories per day from carbohydrates. From this article, 130 gm/day would be "low carb."

Take down your copy of The New Atkins for a New You.  In the initial, induction phase, the authors recommend 20 grams/day of carbohydrate.  20 grams is only 80 calories!  Now that's low carb!

Other people say 50 gm/day, 75 gm/day, etc.  All call their diets "low carbohydrate." 

It's all a bit confusing.  Let's look at a couple of physiologic facts to gain some perspective.

Our brains are real energy hogs. The three pounds of brain, 1-3% of our body weight, burns 400-600 Calories/day.  If our brains really burned only glucose, as legend says (like the legend I learned at Mr. Duke's Medical School) then we would need 100-150 gm of glucose/carbohydrate per day just to stay alive. How on earth can we live on only 20 grams of carbohydrate per day, like I've been doing many days for a year and a half?  (I'm going to cheat. The answer is, Ketone Bodies!  Our brains love them. When your body learns to burn fat instead of carbohydrate, your brain burns ketones like beta hydroxybutyrate.)

Another fact for perspective. A high-normal blood sugar is 100 mg/dl (milligrams per deciliter.)  That is 1000 mg, or 1 gm/ per liter of blood. Most of us walking around have about 5 liters of blood volume, and so our total circulating glucose at any point in time is about 5 grams. 5 grams. If that doubles, we have a toxic blood sugar of 200 mg/dl and are considred diabetic. And yet 5 grams of glucose is almost nothing at all. In fact it is just over two teaspoons of table sugar (which is half glucose and half fructose.)

Another confusing concept is "net carbohydrates" or net carbs. When you look on a label, you'll see total carbohydrate and fiber. Fiber is just another name for a complex chain of simple sugars that our bodies don't have enzymes to break down. Many in the low carb world think you should count "net carbs" instead of total carbs. For example, a cup of broccoli contains about 4 "net carbs" plus 2 grams of "fiber" for a total carb count of 6 gm.

As you read about low carbohydrate diets, remember to ask the question about just how much carbohydrate is really in the diet? Also keep in mind your diet needs--if you are a 5'7 buff 59 year old 155 pound powerhouse of ripped muscle like me, you might need 2500 calories a day to stay huge while a little slip of someone with a totally sedentary job might only need 1600 Cal/day.

Maybe next time we'll take on an even more emotional topic: What is a low fat, moderate fat, or high fat diet???


  1. Hi Jim, great to see you are still Paleo and doing great! I heard about your blog so wanted to check in and read some of your articles. Keep up the good work! Eric Wong

  2. Hey Jim - you've really summed up quite nicely several of the points that can be most confusing for people who address the topic of low carb diets.

    I like the subtle levels of snarkyness - anybody who finds themselves evangelizing the low-carb lifestyle probably needs a bit of an outlet sooner than later :D