The DRI (Dietary Reference Intake) is 0.8 grams of protein per kilogram of body weight, or 0.36 grams per pound. This amounts to:
* 56 grams per day for the average sedentary man.
* 46 grams per day for the average sedentary woman.
As I noted in a prior post (Overfeeding Studies) minimum protein requirements are determined by nitrogen studies which typically give standard diets with adjusted protein contents until excess nitrogen is produced in the urine. This indicates that the person is in a positive protein intake since the excess protein is being expelled as urea (nitrogen).
The problem is the standard diet is used for the baseline which includes carbohydrates. In the standard diet glucose needs are completely met from carbohydrates. In a Low Carb diet glucose needs come from fat and protein in the diet (via GNG).
It is important to determine if the Dietary Recommended Intake (DRI) for protein is adequate for people on a Low Carb Diet (Protein Intake – How Much Protein Should You Eat Per Day?).
So how should we determine if those are adequate levels for a person on a low carb diet? Protein Sparing Modified Fasts (PSMF) are low carb diets which also are low fat. They are typically higher levels of protein with the intent of preserving Lean Body Mass (LBM) in the face of a high caloric deficit. There is a study which determined the Protein needs via nitrogen balance on the PSMF diet (Bruce R Bistrian, George L Blackburn, Jean-Pierre Flatt, Jack Sizer, Nevin S Scrimshaw, Mindy Sherman. Nitrogen Metabolism and Insulin Requirements in Obese Diabetic Adults on a Protein-Sparing Modified Fast. Diabetes Jun 1976, 25 (6) 494-504).
In the three patients who had extensive nitrogen-balance studies, balance could be maintained chronically by 1.3 gm. protein per kilogram IBW, despite the gross caloric inadequacy of the diet.
This seems like a reasonable approximation for the minimal protein needs on a Low Carbohydrate Diet. The number 1.3g/kg of body weight is significantly more than 0.8g/kg of body weight. A 200 lb (100kg) person would need to eat a minimum of 130g of protein a day.
Here is a similar view from Dr Donald Layman (Donald K. Layman; The Role of Leucine in Weight Loss Diets and Glucose Homeostasis, The Journal of Nutrition, Volume 133, Issue 1, 1 January 2003, Pages 261S–267S).
More recently, the overall contribution of dietary amino acids to glucose homeostasis received further support on the basis of quantitative evaluations of hepatic glucose production. Jungas et al. provided an elegant argument that amino acids serve as a primary fuel for the liver and the primary carbon source for hepatic GNG. Other investigators extended this thinking with the findings that endogenous glucose production in the liver is a critical factor in maintenance of blood glucose. After an overnight fast, GNG provides 70% of hepatic glucose release, with amino acids serving as the principal carbon source. These studies provide further evidence for a linkage between dietary protein and glucose homeostasis.
…a diet with low carbohydrates and increased protein would reduce the role of insulin in managing acute changes in blood glucose and maximize the liver’s role in regulating blood glucose through hepatic GNG.
We need additional protein in a low carb diet to provide the substrate for GNG.