This is the low-carb year, not week. At the start of this year the American Diabetes Association finally gave its limited endorsement to a low-carb lifestyle. It’s good for weight loss for up to a year, they maintain.
Going low-carb for a week just won’t cut it. But you might feel weak when you start.
When I started very low-carbing last year, I didn’t ever feel weak. But I had been on a rather low-carb diet for a couple of years, ever since starting on Byetta — when certainly did feel weak for a couple of weeks.
At the time I was concerned enough to ask my doctor, Jeffry Gerber, about it.
“Don’t worry,” Dr. Jeff told me. “You will work through it soon.”
I did. But I still wondered why I experienced it.
Since then, I have heard of several people with a similar initial reaction to a very low-carb diet. My friend Jeff R. told me a couple of months ago that he felt weak when he switched to a very low-carb diet. Jeff is a powerful athlete who was regularly running 10 miles every morning, until the switch stopped him in his tracks.
The weakness passed in a couple of weeks for him, as it did for me. But I decided to see if I could find out what was going on and asked several experts.
The most detailed response came from Professor Loren Cordain, Ph.D., of the department of health and exercise science at Colorado State University in Fort Collins. Professor Cordain maintains a website and is best known as the author The Paleo Diet and The Paleo Diet for Athletes.
The Paleo Diet generally doesn’t restrict carbohydrates as much as very low-carb diets like Jeff and I follow. “With the Paleo Diet,” Professor Cordain tells me, “we advise people to get all of their carbohydrates from fruits and vegetables and to restrict grains, sugars, legumes, and processed foods.”
He says that because fruits and vegetables contain so much fiber and water, it is difficult to consume more than about 30 percent of the daily energy from these foods, and that most people don’t experience weakness or lethargy when they adopt the Paleo Diet.
But on a very low-carb diet you may not be getting enough calories to feel good. Almost everyone will feel weak when they are “in a hypocaloric state,” that is, when they don’t take in enough calories, Professor Cordain says.
On a very low-carb diet people may also be restricting their carbohydrates more than on the Paleo Diet. Even if they are getting enough calories, they can still initially feel weak if they restrict their carbs to less than 100 grams a day, he says.
That’s “because their muscle and liver glycogen stores will become depleted,” Professor Cordain says. “They must rely upon beta oxidation — the metabolism of triglyceride — as their primary substrate source.”
But in addition, he says that we need to bear in mind that the brain can only use glucose as an energy source. On a very low-carb diet “hepatic gluconeogenesis,” which is the synthesis of glucose from either protein or fat in the liver, becomes the primary glucose source.
The problem is that gluconeogenesis is inefficient. It can only supply small quantities of glucose. “All of these metabolic adaptations — beta oxidation, hepatic gluconeogenesis and ketosis, which is a byproduct of carbohydrate restriction and beta oxidation — upset homeostatic mechanisms shaped by a lifetime of high-carb intakes for the average westerner.”
So the body doesn’t immediately adjust to a very low-carb diet. Some people probably just give up when they feel weak. It’s important to be patient and hang in there for several weeks.
HealthCentral published an earlier version of this article.