Definitions and recommendations
Response to carbohydrate restriction shows both continuous, graded outcomes [
17,
18] as well as a threshold effects. LDL particle size, e.g. appears to depend linearly on the level of dietary carbohydrate[
36,
37]. On the other hand, many studies show maximum benefit for very low carbohydrate intake; the early phases of popular low carbohydrate diets target such very low levels [
6,
15,
21,
59,
60]. The principle rests on the concept of a catalytic or threshold effect for insulin in shifting the body from an anabolic state to fat oxidation. The tipping point is empirically taken as the onset of ketonuria, also used as an indicator of compliance with a very low carbohydrate ketogenic diet (VLCKD). The threshold carbohydrate reduction for ketonuria varies among individuals, but a rough estimate is 50 g of carbohydrate per day or, approximately 10% of energy on a nominal 2000 kcal diet, (a target of 30 g/d is common in the early phases of popular VLCKD diets)[
15,
21,
60].
We suggest the following definitions:
The ADA designates low carbohydrate diets as less than 130 g/d or 26% of a nominal 2000 kcal diet and we consider this a reasonable cutoff for the definition of a low-carbohydrate diet. Carbohydrate consumption before the epidemic of obesity averaged 43%, and we suggest 26% to 45% as the range for moderate-carbohydrate diets. The intake of less than 30 g/d, as noted above should be referred to as a very low carbohydrate ketogenic diet (VLCKD). The term Ketogenic Diet should be reserved for the therapeutic approach to epilepsy. These diets do not independently specify the level of carbohydrate, but rather the sum of carbohydrate and protein.
In practice, many low carbohydrate dieters do not add additional fat. First shown by LaRosa, [
61] it has now been observed by many other investigators. [
8,
62,
63] A reduced carbohydrate diet may show significant per cent increase in fat, but there may be no change in the absolute amount consumed. Not everybody on a low carbohydrate diet follows this pattern, but a recommendation based on this behavior would seem more appropriate than unqualified rejection of low-carbohydrate diets.
While some proponents of carbohydrate restriction for the management of diabetes favor sustained adherence to very low levels of carbohydrate intake [
6], all options may be considered and therapeutic choices can be determined by individual physicians and their patients
The term low-carbohydrate diet is frequently taken as synonymous with the popular Atkins diet[
60] which remains highly controversial. Carbohydrate control, however, has many implementations and the severity of the epidemic of diabetes makes it appropriate to go beyond historical controversy and analyze dietary interventions as they are actually implemented.
There is reluctance to make recommendations for low carbohydrate diets on the grounds that people will not follow them but compliance and efficacy of dietary recommendations are separate phenomena. In fact, all recommendations are specifically intended to be different from average consumption[
1] and it is sensibly the purpose of health agencies to encourage conformance to the best therapies.
It is time to re-appraise the role of carbohydrate restriction. Although pessimism exists in the medical community on the efficacy of any diet in the treatment of diabetes 2 and MetS, the success of carbohydrate restriction for many practitioners and individual patients[
64] mandates that we should determine how this approach can be consistently and effectively employed.
Finally, while no systematic study of clinical practice has been done, anecdotal evidence suggests that carbohydrate restriction is a common clinical recommendation for diabetes. We believe that there is a need to codify these recommendations in light of current evidence.
Basic biochemistry, clinical experience and an evolving understanding of metabolic syndrome support the need for evaluation of the efficacy and safety of carbohydrate-restricted diets for the treatment of type 2 diabetes. The fact that carbohydrate restriction improves markers of cardiovascular health, even in the absence of weight loss, sensibly removes historical objections to the dangers of this approach. A critical re-appraisal could form the basis for an alternative for those patients for whom current recommendations are not successful.