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Science Forum Index » Medicine - Nutrition Forum » The case for low carbohydrate diets in diabetes management
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http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1188071
The case for low carbohydrate diets in diabetes management
Surender K Arora1 and Samy I McFarlane1
1Division of Endocrinology, Diabetes and Hypertension, SUNY Downstate
Medical Center, and Kings County Hospital Center, Brooklyn, NY 11203
NY 11203, USA
Corresponding author.
Surender K Arora: surenderkarora@yahoo.com; Samy I McFarlane:
Samy.McFarlane@downstate.edu
Received March 1, 2005; Accepted July 14, 2005.
This is an Open Access article distributed under the terms of the
Creative Commons Attribution License (http://creativecommons.org/
licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly
cited.
This article has been cited by other articles in PMC.
Abstract
A low fat, high carbohydrate diet in combination with regular exercise
is the traditional recommendation for treating diabetes. Compliance
with these lifestyle modifications is less than satisfactory, however,
and a high carbohydrate diet raises postprandial plasma glucose and
insulin secretion, thereby increasing risk of CVD, hypertension,
dyslipidemia, obesity and diabetes. Moreover, the current epidemic of
diabetes and obesity has been, over the past three decades,
accompanied by a significant decrease in fat consumption and an
increase in carbohydrate consumption. This apparent failure of the
traditional diet, from a public health point of view, indicates that
alternative dietary approaches are needed. Because carbohydrate is the
major secretagogue of insulin, some form of carbohydrate restriction
is a prima facie candidate for dietary control of diabetes. Evidence
from various randomized controlled trials in recent years has
convinced us that such diets are safe and effective, at least in short-
term. These data show low carbohydrate diets to be comparable or
better than traditional low fat high carbohydrate diets for weight
reduction, improvement in the dyslipidemia of diabetes and metabolic
syndrome as well as control of blood pressure, postprandial glycemia
and insulin secretion. Furthermore, the ability of low carbohydrate
diets to reduce triglycerides and to increase HDL is of particular
importance. Resistance to such strategies has been due, in part, to
equating it with the popular Atkins diet. However, there are many
variations and room for individual physician planning. Some form of
low carbohydrate diet, in combination with exercise, is a viable
option for patients with diabetes. However, the extreme reduction of
carbohydrate of popular diets (<30 g/day) cannot be recommended for a
diabetic population at this time without further study. On the other
hand, the dire objections continually raised in the literature appear
to have very little scientific basis. Whereas it is traditional to say
that more work needs to be done, the same is true of the assumed
standard low fat diets which have an ambiguous record at best. We see
current trends in the national dietary recommendations as a positive
sign and an appropriate move in the right direction.
The case for low carbohydrate diets in diabetes management
The epidemic of obesity and diabetes in our society over the past
three decades has been accompanied by a decline in fat consumption and
an apparent attempt to adopt the traditionally recommended low fat
diet [1,2]. According to the USDA Continuing Survey of Food Intakes by
Individuals (CSFII) [2], the absolute amount of fat and saturated fat
consumed has decreased during the obesity epidemic although there is
slight increase for women from 1994 to 1995. This apparent failure of
low fat diets in curbing the obesity pandemic calls into question the
effectiveness and long-term usefulness of such dietary recommendation
and has led to renewed interest in alternative dietary interventions,
notably those recommending reduced carbohydrate intake. Low fat diets
are generally associated with high carbohydrate intake which in turn
is associated with several metabolic abnormalities [3,4]. These
metabolic abnormalities are more pronounced in the diabetic
population, leading to worsening glycemic control, dyslipidemia and
increased inflammation to name a few. In this review, we discuss the
current evidence for a low carbohydrate diet versus a low fat diet in
the management of people with diabetes, highlighting the potential
role of low carbohydrate diet in ameliorating various metabolic
abnormalities associated with diabetes.
Carbohydrate restriction
It is important to understand that there is no clear cut definition of
a low carbohydrate diet in the literature. Various popular versions
recommend carbohydrates intake < 20% of caloric intake with absolute
amounts < 50–60 gm/day, sometime as low as ≤ 20–30 gm/day at least for
short periods. We distinguish between moderate but significant
reduction in carbohydrates (LoCHO diet) and very low carbohydrate
ketogenic diets (VLCKD) with extreme reductions (< 20 or 30 g/day) as
in the early phase of the various popular diets [5-7]. The caloric
deficit due to carbohydrate restriction may be balanced with increased
intake of proteins and fats although the distribution is not always
clear in the application of popular diets and, in at least two
studies, no increase in dietary intake of proteins or fats was
observed presumably due to effect of LoCHO diet on appetite and
satiety [9,12] It is interesting that despite advocating ad libitum
fat and protein intake, a LoCHO diet may be hypocaloric either by
design or by spontaneous reduction of intake [8-12].
Low carbohydrate diets and weight loss
Data from various studies demonstrate that even a modest loss of 5–10%
of initial body weight may significantly improve glycemic control,
hyperinsulinemia and other metabolic abnormalities [13,14]. In the
Diabetes Prevention Program (DPP) and the Finnish trials, lifestyle
intervention including modest weight loss was effective in preventing
the development of diabetes in a high risk population [15,16]. Weight
control, per se, is thus a critical component for achieving glycemic
control, improving insulin resistance and modifying CVD risk in
patients with diabetes and insulin resistance as well as for diabetes
prevention [14,17].
Traditionally, increased fat intake has been considered as the main
cause for excess energy intake and obesity but the trends in food
intake during the obesity epidemic do not support this notion [2,18].
While fat intake has decreased, carbohydrate intake has increased
simultaneously. This rise in dietary intake of carbohydrates, and
especially highly refined carbohydrate, is a likely culprit in
promoting weight gain and obesity [19].
Weight change is governed by two factors: caloric balance and
macronutrient composition. The first has general agreement and the
expectation is that any hypocaloric diet, should be effective in
achieving weight loss [20]. As noted above, LoCHO or VLCKD are
frequently intentionally or spontaneously low calorie. The second
consideration, macronutrient composition, is more controversial.
Comparisons of isocaloric diets of different macronutrient composition
frequently show no difference in effectiveness but there are several
examples where distinct advantages accrue to one of the diets, usually
the low carbohydrate arm [21-25].
In a recent study [21], for example, significantly greater weight loss
was demonstrated with low carbohydrate intervention (< 10% calories
from carbohydrates) despite higher caloric intake (1855 kcal/day)
compared to high carbohydrate (60% calories from carbohydrates) with
lower caloric intake (1562 kcal/day). There are several other reports
indicating metabolic advantage in low carbohydrate diets over short
term (3–6 months) [8,10,11,26-28]. Significant reductions in fat mass
including truncal fat, which is a marker for visceral obesity, have
been demonstrated in many studies [9,11,26,29]. A recent report [30]
indicates that the effect will be seen primarily in subjects with
insulin resistance. The association of insulin resistance with
diabetes makes this of great importance.
Although the exact mechanism for this metabolic advantage is unknown,
it is has been attributed to greater thermogenic effect of proteins in
the face of increased demand for gluconeogenesis, increased futile
cycling and increase in mitochondrial uncoupling [21,22,24]. Despite
evidence suggesting more weight loss with isocaloric low carbohydrate
diets, the issue of metabolic inefficiency with low carbohydrate
dietary interventions is controversial and still not universally
accepted.
The data for long term effectiveness of LoCHO diet is limited to
studies with small sample size, poor adherence to dietary assignment
in all dietary groups and inability to control the dietary
carbohydrate amount over longer duration, making it difficult to
demonstrate an appreciable difference between the dietary
interventions. It is important to stress, however, that the same
disclaimer must be made for low fat diets. Whereas calorie reduction
by any means will lead to weight loss, the only comparisons of low fat
diets are exactly the ones with low carbohydrate diets and few
researchers would maintain that low fat diets have great compliance or
long term effects that can be attributed to the particular regimen
[31]. Two of the low carbohydrate-low fat comparisons were continued
for 1 year [8,27]. It is frequently cited that the difference in
weight loss between the LoCHO diet and low fat diet was not
statistically significant after one year but it should be pointed out
that in these studies, participants had the freedom to increase the
carbohydrate content of the diet over longer duration and it is
reasonable to say that as carbohydrate is added back to the diet, its
effectiveness wanes. For example, in the study by Foster et al. [8],
there was no significant difference in the urinary ketone levels
between the two study groups after 3 months, suggesting inadequate
carbohydrate restriction during the later part of the study which
would contribute to the similarity in various parameters between the
groups. In addition, the authors of these studies included subjects
who had dropped out of the study. This method, justified under the
name "intention to treat analysis" obscures the information in the
study and has the effect of making the more effective diet look worse.
In another recent study [32] comparing the effects of four popular
diets including LoCHO diet and low fat diet, there were no significant
differences in weight loss in the different groups at the end of 1
year. However, this study also had the shortcomings of the above
studies, including small sample size (40 subjects in each group) and
poor adherence in all the groups (30–60% dropouts). The LoCHO diet
group also failed to reach carbohydrate reduction goal with
carbohydrate intake of 190 gm/day at 6 months and 12 months as
compared to baseline of 239 gm/day. Hence, it is not surprising that
weight loss was not significantly different in LoCHO diet group. What
is encouraging is that despite such marginal carbohydrate restriction
in the LoCHO group, this group was able to achieve a modest weight
loss that was comparable to the other diet groups, while maintaining a
greater improvement in lipid profile suggesting that even minimal
carbohydrate restriction may have beneficial effects in term of weight
loss and might be offered to those at high risk who fail to lose
weight with traditional low fat diet.
Low carbohydrate diet and glycemic control
Diets containing 50–60% calories from carbohydrates have been the
standard recommendation for patients with type 2 diabetes and
metabolic syndrome [33-35]. However, evidence from several
epidemiological studies such as the Nurses Health Study [36] and
Health Professional Follow-Up Study [37] has linked dietary
carbohydrate intake (measured as glycemic load) with risk of type 2
diabetes and CVD. In the Framingham Offspring Study [38], high
glycemic index and glycemic loads were positively associated with
metabolic syndrome. Prospective cohort studies have also linked
carbohydrates with development of diabetes [39,40]. Compelling
evidence from clinical and metabolic studies demonstrate worsening of
glycemic control and dyslipidemia in diabetics with high carbohydrate
diet [3,4,41,42] whereas low carbohydrate diet may reverse these
serious metabolic abnormalities [10,27,43-46]
Carbohydrates are the major insulin secretagogues [47] and glycemic
control in diabetic subjects is greatly influenced by dietary
carbohydrate content. In fact, before the discovery of insulin,
dietary carbohydrate restriction was the recommended treatment for
diabetes management [48]. While subjects with type 1 diabetes are
generally counseled to count dietary carbohydrates and adjust insulin
dose accordingly [35], the concept of carbohydrate restriction in type
2 diabetes is not adequately emphasized. High carbohydrate intake is
generally recommended, resulting in suboptimal glycemic control and
lipoprotein profile, gradually increasing insulin and/or oral
hypoglycemic medication requirement and weight gain. On the other
hand, restriction of dietary carbohydrates is associated with
improvement in glycemic control and other parameters of insulin
resistance including body mass and lipid profile[8-10,43,45].
In the analysis of effects of macronutrient composition of diet on
glycemic control, it is essential to differentiate the effect of
carbohydrate restriction from that of weight loss so as to determine
if the diet has beneficial effect on glycemic control independent of
weight loss. This has been clarified by short term study in weight
stable diabetic patients where carbohydrate restriction resulted in
significant decrease (8.1% to 7.3%, p < 0.05) in glycosylated
hemoglobin (HbA1c) compared to a high carbohydrate control diet [46].
In another study by the same group [45] in 8 diabetic men in a
randomized 5-week cross over design with a 5-week wash out period,
even larger beneficial effects on glycemic control were observed with
low carbohydrate intervention (carbohydrate 20%, protein 30% and fat
50%) compared to control diet (carbohydrate 55%, protein 15% and fat
30%). The low carbohydrate diet had lower HbA1c (7.6 % ± 0.3), glucose
levels and insulin levels compared to high carbohydrate group (HbA1c
9.8 % ± 0.5) despite similar weight loss with both diets. These data
demonstrate that the benefits of low carbohydrate diet on glycemic
control are independent of weight loss and are primarily due to
carbohydrate reduction.
In a recent study [43] on obese diabetic subjects, a LoCHO diet (20%
carbohydrates) was associated with a significant reduction in body
weight, BMI, fasting blood glucose and HbA1C at 6 months compared to
the high carbohydrate group (60% carbohydrates). Significant decreases
in insulin and hypoglycemic medication requirement were also observed
in the low carbohydrate diet group. Similar improvements in glycemic
control were also reported by Boden et al. [9]. The study of Samaha et
al. [10] also reported a decrease in mean fasting plasma glucose (FPG)
levels in diabetic subjects with low carbohydrate diet compared to low
fat diet group. The decrease in FPG correlated with the weight loss in
this study though the one year data did not show any significant
difference, likely due to inability to achieve target carbohydrate
intake in the LoCHO diet group and to the significant number of
dropouts affecting the power of the study to measure a statistically
significant difference.
To summarize, the effect of LoCHO diet on glycemic control was
significantly greater and occurred independent of weight loss in those
studies that were able to achieve and maintain adequate carbohydrate
restriction. In other studies, the effect on glycemic control was
modest and proportional to the weight loss, and at least comparable to
that seen with low fat diet.
In conclusion, low carbohydrate diet is associated with significant
improvement in glycemic control and has the potential for reduction in
need for exogenous insulin or oral hypoglycemic medications. Increased
monounsaturated fatty acid (MUFA) intake and reduction of saturated
fat intake may further improve the insulin sensitivity and glycemic
control with low carbohydrate diet.
Low carbohydrate diet and postprandial hyperglycemia
Postprandial hyperglycemia is a risk factor for CVD, particularly in
diabetic patients [49-51]. Many studies including the Nurses Health
Study [36] have suggested a link between dietary carbohydrates
(measured in terms of glycemic load) and CVD risk. Furthermore,
control of postprandial hyperglycemia has been shown to provide
cardiovascular benefits, and to contribute to the overall decrease of
hemoglobin A1c, something that has been clearly shown to reduce
microvascular disease in both type 1 and type 2 diabetes [52,53].
Dietary carbohydrates are the major determinants of postprandial
glucose levels [17,47,54] and LoCHO diets have been reported to lower
postprandial glucose levels directly and indirectly by way of weight
loss and may have beneficial effects on CVD risk factors [4,14].
Significant reductions in postprandial plasma glucose and plasma
insulin levels with LoCHO diet have been demonstrated in many studies
[4,9,42,55]. Furthermore, control of postprandial hyperglycemia with
acarbose, an α-glucosidase inhibitor, has been demonstrated to
significantly decrease the risk of diabetes in patients with impaired
glucose tolerance [56,57].
Low Carbohydrate diet and Dyslipidemia
Type 2 diabetes and metabolic syndrome are commonly associated with
atherogenic dyslipidemia, characterized by elevated triglycerides (TG)
levels and low HDL levels [17,58]. Additionally, qualitative changes
in LDL cholesterol may be present in the form of small, dense LDL
particles which are more atherogenic and may be associated with higher
risk of CVD [58-60]. Evidence from various studies has confirmed that
LDL, HDL and triglycerides are independent predictors of CVD
[17,61-63]. Since nearly 75 % of diabetics die of heart disease,
control of diabetic dyslipidemia is an important strategy in the
primary prevention of CVD and a low fat high carbohydrate diet has
been the standard recommendation from various health organizations to
achieve this target [33-35]. A mounting body of evidence however, has
demonstrated that the traditional low fat high carbohydrate diet is
associated with elevated triglyceride and low HDL cholesterol levels
and may worsen the dyslipidemia of type 2 diabetes and metabolic
syndrome [3,10,25,27,28]. Reduction in dietary intake of fat is
frequently associated with increased intake of carbohydrates and leads
to carbohydrate induced hypertriglyceridemia (HPTG) [64-69]. This
phenomenon has been observed in subjects consuming high carbohydrate
low fat diets for as few as 5 days, with replacement of as little as
10% fat with carbohydrate and with dietary fat intake of as much as
30% of energy [64,65]. Decreasing fat without increasing carbohydrate
does not appear to elevate triglycerides, thereby suggesting that
addition of carbohydrates and not reduction in fat is responsible for
this HPTG seen with high carbohydrate low fat diets. Though the exact
mechanism for carbohydrate induced HPTG has not been clearly
elucidated, both increase in TG synthesis and decrease in fractional
TG clearance have been demonstrated [64-66] with a possible
contribution from increased hepatic de novo fatty acid synthesis
[64,67]. A number of factors influence the occurrence of carbohydrate
induced HPTG and these include high BMI (>28 kg/m2), insulin
resistance, post menopausal state, and genetic factors [64,65].
Diabetic, insulin resistant and obese subjects are thus at even higher
risk. In addition, type and form of carbohydrates, particularly high
sugar/starch ratio also contribute to carbohydrate induced HPTG [64].
Conversely, LoCHO diets have been consistently demonstrated to lower
triglycerides and increase HDL [8-11,26-28]. Even the studies which
failed to show significant differences in weight loss between LoCHO
diet and low fat diets after one year [8,27] demonstrated significant
reduction in TG and an increase in HDL with the LoCHO diet despite
inability of subjects to achieve target carbohydrate intake. This
result suggests that the improvement in TG is not only independent of
weight loss but, again, even modest reduction in carbohydrate intake
may have significant benefits on lipids. Significant clinical
implications comes from the VA-HIT study [61], where a modest
reduction in TG and elevation of HDL cholesterol were associated with
notable improvement in CVD mortality.
Though weight loss per se, in combination with increased physical
activity, is usually associated with an increase in HDL cholesterol
and decreases in triglyceride and LDL cholesterol concentration, the
beneficial effects on lipids of the caloric reduction in LoCHO diets
appear to be secondary or additive to carbohydrate restriction and are
seen even after adjusting for amount of weight loss[27].
A low fat diet, in the presence of weight loss is effective in
lowering serum LDL cholesterol. On the other hand, such a regimen
decreases HDL cholesterol without a significant increase in LDL size
to less atherogenic form [70]. Emerging evidence suggests that LoCHO
diets may actually have beneficial effects on LDL cholesterol by
decreasing LDL particle concentration and increasing LDL size to less
atherogenic form [25,28,70-73].
In summary, a low carbohydrate diet may be more effective than a low
fat diet at improving the characteristic dyslipidemia associated with
diabetes, namely high TG, low HDL and increased small dense LDL
particles [70].
Low carbohydrate diet and insulin resistance
LoCHO diets have been reported to have beneficial effect on
hyperinsulinemia seen in type 2 diabetes and insulin resistance
[8-10,45]. The data is, however, limited by few studies with small
number of diabetic subjects and differences in method of measuring
insulin sensitivity in various studies. Boden et al. demonstrated
significant improvement in insulin sensitivity, up to 75%, with a low
carbohydrate diet as measured by euglycemic hyperinsulinemic clamp
method [9]. In another study [29], significant decreases in insulin to
glucose ratio were seen in the LoCHO group suggesting improved insulin
sensitivity, especially in subjects with insulin resistance and higher
baseline insulin levels. Similar improvement in insulin sensitivity
was reported by Gannon, et al [45]. In the studies by Samaha et al.
[10] and by Foster et al [8], carbohydrate restriction was associated
with a significant increase in insulin sensitivity at 6 months
(measured only in non-diabetic subjects) although the difference
between the low fat and low carbohydrate groups was not statistically
significant at 1 year [27]. Notably, again, these studies allowed
increasing carbohydrate in the LoCHO group with time thereby reducing
the effectiveness of this group. Reduction in visceral obesity and
omental fat may be important since LoCHO diets have been reported to
reduce fat mass including truncal fat over long term in many studies
[11,21,26,29]. Finally, a recent study showed that effectiveness of
low carbohydrate diets was more visible in a group that was insulin-
resistant [30].
Low carbohydrate diet and hypertension
Hypertension is a common co-morbidity in type 2 diabetes affecting 20–
60% of the diabetic population[74] and contributes significantly to
CVD risk. Hypertension is a major predictor of increased macrovascular
and microvascular complications of diabetes [17,52,53,75].
Hypertension in diabetes is usually a component of metabolic syndrome
and is related to carotid wall atherosclerotic lesions and angina
[17]. A number of studies in animals [76] and one in humans [77] have
linked sugar intake with hypertension. Direct correlation between
plasma insulin levels and blood pressure levels has been demonstrated
and there is evidence to suggest a causal relationship between insulin
resistance with resultant hyperinsulinemia and hypertension [17]. The
proposed mechanisms include renal sodium retention, vascular smooth
muscle proliferation, sympathetic stimulation and vascular
hyperreactivity [17].
The role of macronutrient composition of diet on blood pressure has
not been adequately studied, though any dietary intervention effective
for improving insulin resistance should also have beneficial effects
on hypertension. The relationship between hypertension and weight loss
is well documented [13,74] and weight loss of 1 kilogram has been
reported to decrease mean arterial blood pressure by approximately 1
mm Hg. Low carbohydrate diets have been reported to lower blood
pressure by causing weight loss and improving the insulin sensitivity,
though the magnitude of effect on blood pressure has been small (1–10
mm Hg) in most studies [8,10,29] and comparable to that seen with low
fat diet.
Low carbohydrate diet and inflammation
Insulin resistance is the predominant mechanism associated with type 2
diabetes and is also central to the pathogenesis of metabolic syndrome
[17]. Abnormal levels of inflammatory markers such as C-reactive
protein and prothrombotic markers like plasminogen activator
inhibitor-1 (PAI-1) have been reported in insulin resistant subjects
[17] and may contribute to the increased CVD events in this population
in combination with dyslipidemia and hypertension [17]. High
carbohydrate diets, by increasing the insulin secretion, may worsen
insulin resistance in diabetic patients and increase the inflammatory
and prothrombotic tendencies in this patient population. The effect of
low carbohydrate diet on various inflammatory and pro-coagulant
markers is not well studied although these markers have been shown to
improve with weight loss in general [13,78-80]. Therefore, any diet
that causes effective weight loss should be able to cause a decrease
in these inflammatory markers and such decreases in CRP [32,70] and
PAI-1 levels [29] have been demonstrated with low carbohydrate diet.
However, these data are limited, and long term studies are needed to
confirm these findings and to determine the impact of these parameters
on the CVD end points with low carbohydrate diet.
The case for a low carbohydrate diet
Despite the growing popularity of LoCHO diets and emerging evidence
for its effectiveness, there is reluctance among physicians to
prescribe it, even in high risk populations who have failed to benefit
from traditional low fat diets. The possible explanation is that
although carbohydrate restriction can be implemented in any number of
ways, it is generally identified with the popular Atkins diet for
which health organizations have great hostility, focusing on a literal
interpretation of permission for unlimited fat intake. Health
organizations have been slow to adapt carbohydrate restricted diets
even in the face clear evidence for the adverse effects of high
carbohydrate intake exacerbating the metabolic abnormalities in
diabetes and insulin resistant states. Similarly, we have previously
pointed out the general tendency to downplay the beneficial effects of
LoCHO diets by individual researchers [81]. Weight loss associated
with LoCHO diets has been continually attributed to alteration in body
water [82,83]. Numerous studies have shown that, although initial
alteration in body water with carbohydrate restriction is possible,
the new equilibrium state is achieved in 2–3 weeks, followed by active
loss of fat mass [8,20,21,26,29,73]. In fact, a recent study [9]
showed mean energy intake decreased from 3111 kcal/day to 2164 kcal/
day on a low carbohydrate diet with mean energy deficit of 1027 kcal/
day. The weight loss was proportional to mean energy deficit and was
explained by loss of fat mass, not water loss.
Another concern that has been voiced is unlimited fat intake as part
of low carbohydrate diet may cause weight gain and obesity over the
long term. [34,47]. Again, this is not substantiated with evidence and
the objection is not valid for the many reasons. Firstly, there is
evidence that type of fat is much more important than total fat intake
[84]. Whereas saturated fats have been linked with increased CVD risk,
the use MUFA and PUFA have been inversely associated with CVD risk
[84]. Therefore, if carbohydrate restriction is used with increase in
unsaturated fats, the benefits may be even more and indeed,
improvement in glycemic control, insulin sensitivity and dyslipidemia
including reduction in LDL cholesterol has been demonstrated with such
dietary intervention in several clinical and metabolic
studies[3,41,85].
Another major reason for lack of enthusiasm for LoCHO diet is
misinterpretation of data provided by studies up to 1 year duration.
The general view is that the LoCHO diet are not more effective than
low fat high carbohydrate diet in terms of weight loss in studies up
to 1 year duration despite impressive short term weight loss
[8,27,32]. However, as we mentioned earlier, considering that the data
is already biased in favor of low fat diet, the lack of significance
between the diet groups at 12 months still proves the superiority of
LoCHO diet as it was able to achieve similar or better weight loss
despite less than desired carbohydrate restriction. Again, even a
marginal decrease in carbohydrate intake may be beneficial in terms of
weight loss and lipid benefits. The overall dietary compliance was a
major problem in all these studies but was generally comparable
between the two diet groups. A lot has been said about nutritional
inadequacy due to mineral, electrolytes and vitamin deficiencies and
the adverse health effects of LoCHO diets on renal and skeletal mass
[34]. On the other hand, there is evidence that increasing sugar
intake adds empty calories by displacement of whole foods and has been
associated with a linear decrease in intake of many essential
nutrients as demonstrated by Bogalusa Heart Study [86]. Since
carbohydrate restriction may limit some micronutrient and fiber
intake, the popular versions of LoCHO diets recommend mandatory intake
of multivitamins including calcium, fish oil and fiber supplements.
The renal and skeletal effects remain theoretical concerns not
substantiated with evidence. Studies up to 1 year have not shown any
adverse effects on renal function or skeletal mass. Also, adequate
intake of calcium and vitamin D supplements as routinely recommended
with LoCHO diet should help preserve skeletal mass along with
prescription of increased physical activity which should be offered to
all irrespective of the dietary macronutrient composition. There have
been some reports of increase blood urea nitrogen without any decrease
in glomerular filtration which are related to increase in protein
intake and do not represent renal insufficiency. A theoretically
increased risk of renal stones has been claimed with LoCHO diet but
again, there is no evidence for such claims and nothing that adequate
hydration could not correct. However, in the absence of definite
evidence, recommendations must be based on professional judgment.
Although proponents of LoCHO diets recommend ad libitum fat intake, we
do not endorse this and instead favor use of MUFA and PUFA which have
been demonstrated in various studies to reduce the risk of CVD
[3,4,41,84]. A final irony is the report that physicians frequently
choose LoCHO diets for themselves while recommending low fat for their
patients[87].
Based on our examination of current evidence, we find concerns about
LoCHO diets to be unsubstantiated and we see no problem in
recommending them, at least as a means of caloric reduction. Of
course, reducing calories by removing fat is universally agreed on as
beneficial but the real question is which should be the priority. We
believe from the evidence presented here that replacing fat with
carbohydrate is deleterious and caloric restriction should be carried
out by removing carbohydrate in preference to removing fat. Although
calorie counting is not recommended by various popular LoCHO diets, we
routinely remind our patients to avoid excess calorie intake. Also,
because restriction of carbohydrates may limit intake of certain
vitamins and minerals, supplementation with multivitamin supplements
including calcium is a usual recommendation with LoCHO diets. Since
high fiber intake has been inversely associated with CVD [37,88],
patients should be encouraged to increase fiber intake and should
receive fiber supplements if necessary.
As for VLCKD where carbohydrate restriction is targeted to 20–30 gm/
day at least for two weeks, we consider this an extreme change for
most people and therefore we would not recommend it without
substantial evidence from clinical trials is provided as to the
benefits of this extreme dietary intervention.
Low Carbohydrate diet and the current guidelines for diabetes
management
Traditionally, a low fat high carbohydrate diet containing 55–70 %
carbohydrates, 15–20% proteins and 20–30% fats has been recommended by
various health organizations [33-35] for subjects at high risk of CVD
including those with diabetes and metabolic syndrome. Despite
accumulating evidence suggesting deleterious effects of high
carbohydrate diet and potential benefits of carbohydrate restriction,
LoCHO diet have met with increased resistance and have not been
accorded its deserved place in various treatment guidelines.
The current position statement of the American Diabetes Association
(ADA), however, recognizes the importance of amount of dietary
carbohydrates: "With regard to the glycemic effects of carbohydrates,
the total amount of carbohydrate in meals or snacks is more important
than the source or the type". This organization also agrees with role
of carbohydrate restriction as stated "In weight maintaining diets for
type 2 diabetes, replacing carbohydrates with monounsaturated fats
reduces post prandial glycemia and triglyceridemia" and recommends
that "carbohydrates and monounsaturated fat together should provide 60–
70% of the energy intake and the relative contributions of
carbohydrate and monounsaturated fats to energy intake should be
individualized". This can be considered as a nod of approval for
carbohydrate restriction though no specific recommendation has been
made. Furthermore, the ADA's recommendation of individualization
according to patient's risk may provide the much needed flexibility
for adjusting the carbohydrate content according to the patient's
requirement [47]. This gradual adoption of carbohydrate restriction is
also reflected by a recent statement from ADA limiting dietary
carbohydrate intake to provide 45–65% of the calories [47] which is
less than previously recommended.
Low carbohydrate diet compares more favorably, at least over the short
term, to traditional low fat for improving glycemic control, insulin
sensitivity and dyslipidemia of diabetes with reduction in
triglycerides, increase in HDL cholesterol and modification of LDL to
less atherogenic form. The need of the hour is to accept the benefits
of carbohydrate restriction with reservation and to establish
guidelines for its use, especially emphasizing use of mono and
polyunsaturated fats as the way to achieve caloric balance since these
have been inversely linked with CVD risk in various studies. In the
mean time, clinical trials need to be conducted using graded levels of
carbohydrate restriction and fat intake, with special emphasis on
unsaturated fats, to examine their effects of on weight loss, glycemic
control, insulin resistance and CVD risk. This is to resolve the
present controversy about optimal dietary option for patients with
diabetes.
Top Competing interests
The author(s) declare that they have no competing interests
*****
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