I've searched the forum but haven't come across the answer to this question. If this is a topic discussed before and I missed it, then if someone would just point me to that thread I'll go away.

Anyway, does anyone know how 60g carbs per day was chosen as the limit on a low carb diet? It just seems to me that this would be an approximation that would vary greatly depending on a person's gender, metabolism, height, weight, body-fat, and exercise level. I would think some people are unnecessarily restricting the carbs each day and could have more while others would have to only take in 40g or 50g carbs per day.

Can anyone enlighten me as to the science behind the 60g per day limit?

I'm not too sure on where I've heard this but I think anything under 60 is what induces ketosis.

I'm sure others will know better than I.

I think that 60 carbs is what is in the Atkins book as the suggested level to go to for ongoing weight loss, however is some of the other plans here that are not classified as low carb but rather, controlled carb the level is higher. Sometimes up to 150-180 a day depending on the person and the plan. With the ongoing weight loss in Atkins a person is supposed to gradually increase their carbs to find out what level they can eat at and continue to lose.

Edit - and those levels are more left up to the individual to realize for themselves rather than a set number, which I think is what you wanted to know. A lot of people are starting to find out they can go into ketosis at over 100 carbs a day even though their plan does not require them to be in ketosis.

As far as I know, there is no 60 gram "limit". I believe that Dr. Atkins did state that this seemed to be about the average amount of carbs that many of his patients could consume per day on maintainence unless they were either a) young or b) very active or both. Nevertheless, low carbers need to find their own individual level for maintainence by gradually increasing their daily carb levels until they are neither gaining nor losing.
There are those that need to maintain at a lower level and those that can maintain at a much higher level and many variables influence that including age, gender, activity level, degree of insulin resistance/carb intolerance, etc...

"Life without Bread" suggests 72 grams as the maximum. This was what the doctor found to work with his patients. And yes a 6'6" male could probally eat more carbs than a 4'8" female, but the plans try to keep it simple. Under Atkins, the carb intake in maintenance is customized for each person.

Hi Mithridate:

I'm not sure if this directly answers your question, but Lyle McDonald's book "The Ketogenic Diet", states the numbers differently; 100 grams of glucose is required for the brain until ketosis is achieved, after which the requirements lower to 40 grams. Anything over this amount wouldn't be ketogenic.