Last updated on April 14th, 2017

Calculating “Net Carbs”

In following my low-carb, high-fat (LCHF) diet, I’ve always been guided by the concept of “net carbs.”

This is the notion that carbohydrates from fiber don’’t get used by the body to raise blood glucose levels, so therefore fiber content can be subtracted from total carbs.

What’’s left, the net carbs, are what the LCHF dieter counts and pays attention to.

Or so I have believed.

I’ve lost weight by keeping my net carb intake to around 30 – 35 grams per day. For instance, for the past five weeks, I’ve averaged a daily intake of 45 grams of total carbs, including 15 grams of fiber. That’s 30 net carbs per day.

I’ve lost weight eating that way — a little over a pound a week on average in that 5-week span. And I’ve done it without feeling hungry, “hangry,” or deprived.

Along Comes “Keto Clarity”

The net-carbs concept seemed clear, logical and uncontroversial to me, so I was surprised when I read a contrary opinion by a respected physician, author and researcher — Dr. Eric C. Westman of Duke University — in Keto Clarity, a book he co-wrote with well-know blogger and podcaster Jimmy Moore.

Let me say first that it’s an excellent book. Moore appears to have written most of it in his trademarked enthusiastic and personable style.

Westman contributes numerous “Doctor’s Note” sidebars. I read the book this past winter, and it had a lot to do with my low-carb diet reboot — and with the reboot of this blog.

I found Keto Clarity to be an inspiration and an eye-opener. The focus, as the title suggests, is on achieving and maintaining a state of nutritional ketosis, in which your body mostly uses ketones for fuel (as opposed to glucose).

Without getting into all the technical details here, when you achieve ketosis, your body is best able to burn its own fat reserves. That’s a very good thing when trying to lose weight. (Note: nutritional ketosis should not be confused — but frequently is — with “diabetic ketoacidosis,” a dangerous condition that that sometimes happens in insulin-dependent diabetics.)

I stress the book’s focus on ketosis because it has a lot to do with the advice that the authors give to forget about net-carbs and just pay attention to total carb intake. Their goal isn’t simply to count and restrict carbs, thus bringing about weight loss. Rather, their goal is to bring about ketosis, which they see as a necessary step in consistent weight loss/ management and long-term healthy living.

To get to ketosis, most people have to eat a very low-carb diet, restricting total carbs to as few as 20 grams per day.

Is Net Carbs a Risky Concept?

Moore and Westman see relying on net carbs as risky for the achievement of ketosis. In Chapter 14, which discusses common problems in reaching ketosis, Moore notes that eating packaged goods that claim to be low in net carbs can lead to getting “extra carbohydrates that you didn’t think you needed to count. . . .”

The point is then taken up by Westman, who says that the concept of net carbs “works well for those who are not very metabolically sick or who don’t have much weight to lose.” However, if your goal is to become ketogenic, then you need to recognize that “some of the fiber is absorbed as glucose.” Therefore, the “more prudent approach” is to count total grams of carbs, and not to calculate net carbs.

Elsewhere in the book, Moore repeats the advice to rely on total carbs, not net carbs.

Had I Been Wrong for Years?

While I understand now that the advice is coming out of a particular context, and that it’s qualified and nuanced, upon first reading I was shaken. The low-carb ground shifted beneath my feet. Had I been wrong to use the concept of net carbs all these years?

The net carb approach has a distinguished pedigree. Dr. Robert Atkins, the god-father of low-carb eating, in his Dr. Atkins’ New Diet Revolution (1992 – 2002) refers to net carbs as “digestible carbs,” which he also calls “the carbs that count.”

He advocates eating plenty of fiber-rich foods, both for the numerous health benefits of fiber and to extend the total carbs available on his diet.

Not So Risky, After All?

More recently, three highly regarded researchers — one being Dr. Westman himself, and the other two Drs. Stephen Phinney and Jeff Volek — writing in their 2010 book The New Atkins for a New You, tell readers flat-out to “focus on net carbs” and that “this means that you count only the grams of carbohydrate that impact your blood sugar level.” Fiber gets a pass.

It could be that the authors are toeing the company line. The concept of net carbs is part of the official Atkins Diet, after all, as well as a key selling point for the packaged foods that bear the Atkins name.

However, I do not believe for a second that these three men would endorse a concept that they viewed as scientifically invalid. Putting together Westman’s statements in the two books, it appears that he believes many dieters can use the net carbs approach to good effect, but that some need to be wary of it.

That’s reasonable, though it leaves me wondering what group I’m in.

It’s important to mention that sometimes more than just fiber grams are subtracted when calculating net carbs.

On the FitDay website, Registered Dietitian Kari Hartel explains that low-carb food manufacturers often subtract “incompletely-digested carbohydrates–including sugar alcohols, fiber and glycerine–from the total carbohydrates (grams) because not all of the calories from those carbohydrates are completely absorbed by the body”  (“What are Net Carbs?”).

However, she warns that this practice is “inaccurate” because a portion of the subtracted elements is absorbed. She recommends that when a food item contains more than five grams of sugar alcohols, only half of the grams be subtracted to calculate net carbs.

Can’t Trust the Labels

That lines up with what Jimmy Moore writes in Keto Clarity: you can’t trust the packaged food labels to give you accurate net carb numbers. Personally, I don’t eat many low-carb packaged foods. In fact, I haven’t eaten any since the earliest days of my low-carb lifestyle. While hardly a food saint, I can live without fake candy, cookies, and treat bars.

Or else, I’ll make low-carb versions myself, with quality ingredients, and know exactly what I’m getting.

I can’t say for sure that I’ve ever achieved nutritional ketosis. I suspect I have, but the only way to know is to measure the ketones in your blood. I haven’t had the equipment to do that, but a ketone-meter is on its way. When I get it, I’ll do some N=1 tests. Maybe I’ll get a clearer picture in my case of the relation of carbs and ketosis.

(Update: my Ketonix has arrived! It confirms that I have achieved ketosis, and I did it while using the concept of net carbs.)

Bragging Rights

I see achieving ketosis as more of an technical question than a pressing issue. Other than for bragging rights, I’m not especially concerned about being in ketosis, not as long as I keep feeling good and losing weight. A pound or two lost a week on average is fine with me.

As long as the concept of net carbs keeps working for me, I’ll keep using it.