Dietary carbohydrate restriction in type 2 diabetes mellitus and metabolic syndrome: time for a critical appraisal

Carbohydrate restriction (with or without additional dietary cholesterol provided by eggs) reduces insulin resistance and plasma leptin without modifying appetite hormones in adult men

Carbohydrate-restricted diets (CRDs) have been shown to reduce body weight, whereas whole egg intake has been associated with increased satiety. The purpose of this study was to evaluate the effects of additional dietary cholesterol and protein provided by whole eggs while following a CRD on insulin resistance and appetite hormones. Using a randomized blind parallel design, subjects were allocated to an egg (640 mg/d additional dietary cholesterol) or placebo (0 mg/d additional dietary cholesterol) group for 12 weeks while following a CRD. There were significant reductions in fasting insulin (P < .025) and fasting leptin concentrations (P < .01) for both groups, which were correlated with the reductions in body weight and body fat (P < .05 and P < .01, respectively). Both groups reduced insulin resistance as measured by the homeostatic model assessment of insulin resistance (P < .025). There was a significant decrease in serum glucose levels observed after the intervention. We did not observe the expected increases in plasma ghrelin levels associated with weight loss, suggesting a mechanism by which subjects do not increase appetite with CRD. To confirm these results, the subjective measures of satiety using visual analog scale showed that both groups felt more "full" (P < .05), "satisfied" (P < .001), and "wanted to eat less" (P < .001) after the intervention. These results indicate that inclusion of eggs in the diet (additional dietary cholesterol) did not modify the multiple beneficial effects of CRD on insulin resistance and appetite hormones.

Comparative study of the effects of a 1-year dietary intervention of a low-carbohydrate diet versus a low-fat diet on weight and glycemic control in type 2 diabetes

OBJECTIVE

To compare the effects of a 1-year intervention with a low-carbohydrate and a low-fat diet on weight loss and glycemic control in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

This study is a randomized clinical trial of 105 overweight adults with type 2 diabetes. Primary outcomes were weight and A1C. Secondary outcomes included blood pressure and lipids. Outcome measures were obtained at 3, 6, and 12 months.

RESULTS

The greatest reduction in weight and A1C occurred within the first 3 months. Weight loss occurred faster in the low-carbohydrate group than in the low-fat group (P = 0.005), but at 1 year a similar 3.4% weight reduction was seen in both dietary groups. There was no significant change in A1C in either group at 1 year. There was no change in blood pressure, but a greater increase in HDL was observed in the low-carbohydrate group (P = 0.002).

CONCLUSIONS

Among patients with type 2 diabetes, after 1 year a low-carbohydrate diet had effects on weight and A1C similar to those seen with a low-fat diet. There was no significant effect on blood pressure, but the low-carbohydrate diet produced a greater increase in HDL cholesterol.

Effects of a low-carbohydrate diet on glycemic control in outpatients with severe type 2 diabetes

We previously demonstrated that a loosely restricted 45%-carbohydrate diet led to greater reduction in hemoglobin A1c (HbA1c) compared to high-carbohydrate diets in outpatients with mild type 2 diabetes (mean HbA1c level: 7.4%) over 2 years. To determine whether good glycemic control can be achieved with a 30%-carbohydrate diet in severe type 2 diabetes, 33 outpatients (15 males, 18 females, mean age: 59 yrs) with HbA1c levels of 9.0% or above were instructed to follow a low-carbohydrate diet (1852 kcal; %CHO:fat:protein = 30:44:20) for 6 months in an outpatient clinic and were followed to assess their HbA1c levels, body mass index and doses of antidiabetic drugs. HbA1c levels decreased sharply from a baseline of 10.9 ± 1.6% to 7.8 ± 1.5% at 3 months and to 7.4 ± 1.4% at 6 months. Body mass index decreased slightly from baseline (23.8 ± 3.3) to 6 months (23.5 ± 3.4). Only two patients dropped out. No adverse effects were observed except for mild constipation. The number of patients on sulfonylureas decreased from 7 at baseline to 2 at 6 months. No patient required inpatient care or insulin therapy. In summary, the 30%-carbohydrate diet over 6 months led to a remarkable reduction in HbA1c levels, even among outpatients with severe type 2 diabetes, without any insulin therapy, hospital care or increase in sulfonylureas. The effectiveness of the diet may be comparable to that of insulin therapy.

Lifestyle-induced metabolic inflexibility and accelerated ageing syndrome: insulin resistance, friend or foe?

The metabolic syndrome may have its origins in thriftiness, insulin resistance and one of the most ancient of all signalling systems, redox. Thriftiness results from an evolutionarily-driven propensity to minimise energy expenditure. This has to be balanced with the need to resist the oxidative stress from cellular signalling and pathogen resistance, giving rise to something we call 'redox-thriftiness'. This is based on the notion that mitochondria may be able to both amplify membrane-derived redox growth signals as well as negatively regulate them, resulting in an increased ATP/ROS ratio. We suggest that 'redox-thriftiness' leads to insulin resistance, which has the effect of both protecting the individual cell from excessive growth/inflammatory stress, while ensuring energy is channelled to the brain, the immune system, and for storage. We also suggest that fine tuning of redox-thriftiness is achieved by hormetic (mild stress) signals that stimulate mitochondrial biogenesis and resistance to oxidative stress, which improves metabolic flexibility. However, in a non-hormetic environment with excessive calories, the protective nature of this system may lead to escalating insulin resistance and rising oxidative stress due to metabolic inflexibility and mitochondrial overload. Thus, the mitochondrially-associated resistance to oxidative stress (and metabolic flexibility) may determine insulin resistance. Genetically and environmentally determined mitochondrial function may define a 'tipping point' where protective insulin resistance tips over to inflammatory insulin resistance. Many hormetic factors may induce mild mitochondrial stress and biogenesis, including exercise, fasting, temperature extremes, unsaturated fats, polyphenols, alcohol, and even metformin and statins. Without hormesis, a proposed redox-thriftiness tipping point might lead to a feed forward insulin resistance cycle in the presence of excess calories. We therefore suggest that as oxidative stress determines functional longevity, a rather more descriptive term for the metabolic syndrome is the 'lifestyle-induced metabolic inflexibility and accelerated ageing syndrome'. Ultimately, thriftiness is good for us as long as we have hormetic stimuli; unfortunately, mankind is attempting to remove all hormetic (stressful) stimuli from his environment.

Comparison of three commercially available prescription diet regimens on short-term post-prandial serum glucose and insulin concentrations in healthy cats

Dietary therapy is an important treatment component for diabetes mellitus (DM). In this study, the impact of three different commercially available diet regiments (1 general use and 2 aimed for treating obesity and DM) on short-term post-prandial serum glucose and insulin concentrations of five healthy cats to better understand what impact each of these diets may have for diabetic cats. The diet regiments used in this study were as follows: C/D dry (General Use- Low protein, High fat, High carbohydrate, and Low fiber), M/D dry (DM- High protein, High fat, Low carbohydrate, and High Fiber), and W/D dry (DM- Low Protein, Low Fat, High Carbohydrate, and High Fiber). No significant difference in post-prandial serum glucose levels were observed with the C/D (84.6 +/- 1.5 mg/dl) and W/D (83.8 +/- 1.4 mg/dl) dry diets when compared to pre-prandial fasting levels (83.9 +/- 1.4 mg/dl). However, a significant reduction was observed with the M/D diet (78.9 +/- 0.8 mg/dl) which had 50-60% less carbohydrates than either C/D or W/D diet. Unlike what was observed with post-prandial glucose levels, an interesting pattern emerged with post-prandial insulin levels, which were increasing with W/D, C/D, and M/D diets in that order (1.1 +/- 0.2, 1.7 +/- 0.2, and 2.3 +/- 0.2 ng/ml respectively). Most surprising, though, was the fact that the W/D diet did not seem to stimulate insulin secretion as compared to pre-prandial levels (1.1 +/- 0.1 ng/ml) in healthy cats. Interestingly, the W/D diet had high levels of carbohydrate and low levels of protein. Coincidentally, the only diet (M/D) which had a significant reduction in post-prandial glucose also showed the highest increase in post-prandial insulin in healthy cats. Therefore, dietary amounts of carbohydrate, fat, protein and fiber can all have an individual impact on post-prandial glycemia and subsequent insulin requirement levels. Just as concepts regarding dietary management of people with DM are evolving, investigators are reassessing what constitutes the ideal diet for the diabetic feline. As such, having a better understanding for each dietary component, may lead us to better understand how we can synergize certain dietary components to aid in DM management.

Favorable glycemic response of type 2 diabetics to low-calorie cranberry juice

Fruit and vegetable intake is typically low for type 2 diabetics, possibly due to a perceived adverse effect on glycemic control. Cranberry juice (CBJ) may represent an attractive means for increasing fruit intake and simultaneously affording positive health benefits. This single cross-over design compared metabolic responses of type 2 diabetics (n= 12) to unsweetened low-calorie CBJ (LCCBJ; 19 Cal/240 mL), carbohydrate sweetened normal calorie CBJ (NCCBJ; 120 Cal/240 mL), isocaloric low-calorie sugar water control (LCC), and isocaloric normal calorie sugar water control (NCC) interventions. CBJ flavonols and anthocyanins, and proanthocyanidins were quantified with HPLC, LC-MS, and MALDI-TOF that includes an original characterization of several large oligomeric proanthocyanidins. Blood glucose peaked 30 min postingestion after NCCBJ and NCC at 13.3 +/- 0.5 and 12.8 +/- 0.9 (mmol/L), and these responses were significantly greater than the LCCBJ and LCC peaks of 8.1 +/- 0.5 and 8.7 +/- 0.5, respectively. Differences in glycemic response remained significant 60 min, but not 120 min postingestion. Plasma insulin values 60 min postingestion for NCCBJ and NCC interventions were 140 +/- 19 and 151 +/- 18 (pmol/L), respectively, and significantly greater than the LCCBJ and LCC values of 56 +/- 10 and 54 +/- 10; differences were not significant 120 min postingestion. Metabolic responses within the 2 high and 2 low-calorie beverages were virtually identical; however, exposure to potentially beneficial nutrients was greater with CBJ. Relative to conventionally sweetened preparation, LCCBJ provides a favorable metabolic response and should be useful for promoting increased fruit consumption among type 2 diabetics or others wishing to limit carbohydrate intake.

Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet

We recently proposed that the biological markers improved by carbohydrate restriction were precisely those that define the metabolic syndrome (MetS), and that the common thread was regulation of insulin as a control element. We specifically tested the idea with a 12-week study comparing two hypocaloric diets (approximately 1,500 kcal): a carbohydrate-restricted diet (CRD) (%carbohydrate:fat:protein = 12:59:28) and a low-fat diet (LFD) (56:24:20) in 40 subjects with atherogenic dyslipidemia. Both interventions led to improvements in several metabolic markers, but subjects following the CRD had consistently reduced glucose (-12%) and insulin (-50%) concentrations, insulin sensitivity (-55%), weight loss (-10%), decreased adiposity (-14%), and more favorable triacylglycerol (TAG) (-51%), HDL-C (13%) and total cholesterol/HDL-C ratio (-14%) responses. In addition to these markers for MetS, the CRD subjects showed more favorable responses to alternative indicators of cardiovascular risk: postprandial lipemia (-47%), the Apo B/Apo A-1 ratio (-16%), and LDL particle distribution. Despite a threefold higher intake of dietary saturated fat during the CRD, saturated fatty acids in TAG and cholesteryl ester were significantly decreased, as was palmitoleic acid (16:1n-7), an endogenous marker of lipogenesis, compared to subjects consuming the LFD. Serum retinol binding protein 4 has been linked to insulin-resistant states, and only the CRD decreased this marker (-20%). The findings provide support for unifying the disparate markers of MetS and for the proposed intimate connection with dietary carbohydrate. The results support the use of dietary carbohydrate restriction as an effective approach to improve features of MetS and cardiovascular risk.

Nonalcoholic fatty liver disease: the potential role of nutritional management

PURPOSE OF REVIEW

To review available data pertaining to dietary imbalances and metabolic alterations leading to the development of fatty liver disease and nutritional managements.

RECENT FINDINGS

The importance of treating fatty liver disease is now firmly recognized not only because of the risk of progression toward a more aggressive liver disease but also because the fatty liver is an important provider of cardiovascular risks. The ideal diet for nonalcoholic fatty liver disease/nonalcoholic steatohepatitis patients should reduce fat mass and inflammation in the adipose tissue, restore insulin sensitivity, and provide low amounts of substrates for de-novo lipogenesis, but scientific evidence to recommend specific diets is currently lacking. Moderate weight loss, low-calorie diets, reduction in saturated fatty acids intake, together with an increase in monosaturated and n-3 polyunsaturated fatty acids appear to be beneficial. Excessive consumption of high glycemic index carbohydrates appears deleterious, as it favors hyperglycemia and hyperinsulinemia and stimulates de-novo lipogenesis. Physical exercise is an important component of the approach, as it improves insulin sensitivity. Behavioral therapy promotes long-term compliance to lifestyle modifications.

SUMMARY

One panacea is unlikely to be found, the more useful approach is probably multimodal and includes tailored lifestyle modifications. Randomized controlled trials are needed to establish dietary recommendations. While awaiting such trials, reduced consumption of simple sugar, especially sweetened beverages, and incremental increase in physical activity must be encouraged.

Low-carbohydrate diet in type 2 diabetes: stable improvement of bodyweight and glycemic control during 44 months follow-up

Background

Low-carbohydrate diets, due to their potent antihyperglycemic effect, are an intuitively attractive approach to the management of obese patients with type 2 diabetes. We previously reported that a 20% carbohydrate diet was significantly superior to a 55–60% carbohydrate diet with regard to bodyweight and glycemic control in 2 groups of obese diabetes patients observed closely over 6 months (intervention group, n = 16; controls, n = 15) and we reported maintenance of these gains after 22 months. The present study documents the degree to which these changes were preserved in the low-carbohydrate group after 44 months observation time, without close follow-up. In addition, we assessed the performance of the two thirds of control patients from the high-carbohydrate diet group that had changed to a low-carbohydrate diet after the initial 6 month observation period. We report cardiovascular outcome for the low-carbohydrate group as well as the control patients who did not change to a low-carbohydrate diet.

Method

Retrospective follow-up of previously studied subjects on a low carbohydrate diet.

Results

The mean bodyweight at the start of the initial study was 100.6 ± 14.7 kg. At six months it was 89.2 ± 14.3 kg. From 6 to 22 months, mean bodyweight had increased by 2.7 ± 4.2 kg to an average of 92.0 ± 14.0 kg. At 44 months average weight has increased from baseline g to 93.1 ± 14.5 kg. Of the sixteen patients, five have retained or reduced bodyweight since the 22 month point and all but one have lower weight at 44 months than at start. The initial mean HbA1c was 8.0 ± 1.5%. After 6, 12 and 22 months, HbA1c was 6.1 ± 1.0%, 7.0 ± 1.3% and 6.9 ± 1.1% respectively. After 44 months mean HbA1c is 6.8 ± 1.3%.

Of the 23 patients who have used a low-carbohydrate diet and for whom we have long-term data, two have suffered a cardiovascular event while four of the six controls who never changed diet have suffered several cardiovascular events.

Conclusion

Advice to obese patients with type 2 diabetes to follow a 20% carbohydrate diet with some caloric restriction has lasting effects on bodyweight and glycemic control.