Although intensive interventions with low carbohydrate diets compared with higher carbohydrate diets can reduce HbA1c in people with type 2 diabetes, it is not clear if simple advice to make modest reductions in carbohydrate is effective in clinical practice. Forty-three people with type 2 diabetes and poor control (HbA1c > 7.5%) were randomized to receive 2 short education sessions over 6 months with a non-dietitian researcher on how to reduce carbohydrate intake by about 25% or to 2 control sessions in which the Australian Guide to Healthy Eating was provided. Hba1c and fasting glucose and lipids were measured at baseline and 3 months and 6 months. 33 volunteers attended a baseline visit; 27 completed 3 months and 24 6 months. HbA1c was reduced by 0.6% - 0.7% in the low carbohydrate diet group compared with the control group (P = 0.1). Fasting glucose was reduced by 2.3 mmol/L compared with the control group at 3 months (P < 0.03) only. Changes in HbA1c at 6 months were related to baseline HbA1c in the intervention group only. Although we have obtained suggestive evidence that a low carbohydrate diet can be successfully implemented in normal practice without professional help, our results are limited by low participant numbers and further studies are required.
Intensive intervention with very low carbohydrate diets combined with weight loss could lead to lower HbA1c levels and reduced medication use [
We hypothesized that a relatively flexible, straightforward and sustainable dietary regimen low in carbohydrate (replaced with protein and/or unsaturated fat) offered to poorly controlled type 2 diabetes patients (HbA1c > 7.5%), would significantly reduce HbA1c and fasting glucose over a period of 6 months in the absence of weight loss and without intensive contact compared with usual care.
Men and women aged 18 - 80 years with confirmed type 2 diabetes with an HbA1c of more than 7.5% were recruited from the BakerIDI Diabetes Clinics (a tertiary referral centre) by a direct mail out to individuals who indicated they wished to be involved in research or via public advertisement in the local newspaper. Volunteers could be on no medication or on multiple medications including insulin. Exclusion criteria were bariatric surgery, pregnancy or lactation or following a low carbohydrate diet within the last 3 months
Any changes of medication were at the discretion of the primary treating doctor and not the researchers. Information on medication changes was obtained after the volunteer completed the study. The study was approved by the Alfred Hospital Ethics committee approval number 228/12 and the study was recorded on the Australian and New Zealand Clinical Trial Registry ACTRN12612000676819.
Volunteers were randomized 1:1 by computer generated randomization code to a control diet (The Australian Guide to Healthy Eating) or to a low carbohydrate diet. Diets were pragmatic food based diets with no particular percentage of carbohydrate to be achieved and the amount of change depended on the amount of carbohydrate consumed in the pre-trial diet. They were not weight loss diets and the food substitution strategy was designed to ensure weight neutrality. This was a 6 month translational style study with dietary advice given to the intervention group on only two occasions (baseline and 3 months) in the form of 2 × 30 min consultations with a researcher with take home information sheets. The dietary advice was to omit all salty snacks, sweets, cake and biscuits, pies and pasties and replace them with 2 - 3 pieces fruit/day or low fat dairy (e.g. yoghurts). Breakfast of cereal/toast was to be replaced on 2 mornings per week with lean meat (e.g. steak or fish) and eggs. Lunch was to be lean meat/fish/cheese/egg salad on 3 days per week with no bread/biscuits. Dinner was lean meat- steaks or casserole/lean beef/chicken/fish with unlimited green vegetables and pumpkin. Volunteers had the option of including small amounts of starchy carbohydrate in their main meal (e.g. rice/pasta/potato) for 1 - 2 meals per week. Potentially in a volunteer who consumed 45 g of breakfast cereal each day plus 2 slices of bread for lunch and a medium (250 g) potato each evening−the maximum reduction in carbohydrate would be about 100 g per day or about 350 - 400 g per week if the above scheme was adhered to. This would represent about a 25% reduction in typical carbohydrate intake and more if snack foods were consumed e.g. from a typical 55% of energy as carbohydrate to less than 45%. Food records were not kept as this is not part of routine clinical practice.
Volunteers were seen on 3 occasions at baseline, 3 and 6 months and had fasting blood samples taken for lipids, glucose and HbA1c. Spot urines were also collected on each occasion and sodium, potassium and creatinine measured in order to obtain an index of bread/cereal intake as well as fruit and vegetable intake. The tests were performed at the Alfred Hospital an accredited pathology supplier using standard laboratory tests.
Data was analyses using repeated measures ANOVA and Pearson’s correlations using SPSS 21. Data are shown as Mean and SD. We calculated with an SD of 1% we would be able to see a difference of 1% in HbA1c (P < 0.05, 80% power) with 16 completers in each group. Our primary end points were HbA1c and fasting glucose with secondary end points of lipids and weight. It was hypothesized that the secondary endpoints were not change. Analysis was based on completers only
Forty-three volunteers were randomized but only 33 attended a baseline visit. Of those who completed the baseline visit the medication profile was 20 on metformin, 9 on sulphonylureas, 9 on insulin, 7 on DPPIV inhibitors, 4 on GLP1 analogues and 3 on thiazolidinediones. Nine volunteers took 2 medications, 6 took 3 and one took 4 and one took 5 medications while the remainder took 1 medication. Only 3 volunteers were controlled with diet alone. Baseline characteristics are shown in
16 control volunteers and 11 low carbohydrate diet volunteers attended the 3 month visit. At 6 months there were 15 control (83% of those randomized) and 9 low carbohydrate diet volunteers (56%). Hba1c at 3 months was 8.0% and 7.7% and at 6 months was 8.0% and 7.3% respectively. In the control group 6 volunteers had a decrease in HbA1c and 10 had an increase or no change while the low carbohydrate group had 8 decreases and 3 increases at 3 months. At 6 months there were 7 decreases and 8 increases in HbA1c in the control group and 5 decreases and 4 increases in the intervention group. The changes in HbA1c were not significant overall (
Low Carbohydrate Diet (n = 15) | Control Diet (n = 18) | |
---|---|---|
Gender | 7M, 8F | 11M, 7F |
Age | 59 | 64 |
Weight | 86.3 ± 14.1 (62 - 110.3) | 95.8 ± 23.9 (47 - 139.6) |
BMI | 29 ± 5.0 | 31.8 ± 7.4 |
HbA1c% | 8.1 ± 1.8 (6.0 - 12.2) | 8.3 ± 1.2 (6.5 - 11.1) |
Fasting glucose | 8.7 ± 3.1 (5 - 16) | 8.6 ± 3.9 (5 - 22) |
Medications (total) | 29 | 28 |
Insulin | 4 | 5 |
Diet control | 2 | 1 |
Change at 3 months | Change at 6 months | |||
---|---|---|---|---|
Low Carbohydrate diet (11) | Control diet (16) | Low Carbohydrate diet (9) | Control diet (15) | |
HbA1c | −0.57 ± 1.4 | 0 ± 0.8 | −0.73 ± 1.4 | −0.04 ± 1.0 |
Fasting glucose | −1.4 ± 2.6* | 0.93 ± 2.7 | −0.07 ± 2.1 | 0.47 ± 1.9 |
TC | 0.11 ± 0.57 | −0.03 ± 0.75 | 0.26 ± 0.83 | 0.13 ± 1.0 |
TG | 0.08 ± 0.38 | −0.11 ± 0.43 | 0.08 ± 0.33 | −0.06 ± 0.44 |
HDL | 0.18 ± 0.06 | 0.02 ± 0.12 | −0.03 ± 0.11 | 0.14 ± 0.19 |
Weight | 0.05 ± 3.4 | −0.95 ± 1.6 | −1.6 ± 2.8 | −0.61 ± 1.7 |
*P < 0.03 vs control.
and were not different between diets (P = 0.1) nor were the differences in the number of responders in each group. Only the change in glucose at 3 m was different between diets (P < 0.03). Weight did not change significantly in either group with a decrease of 0.6 kg at 3 months in the control group and a 0.05 kg increase in the low carbohydrate group. Spot urine Na/Cr and N/K ratios did not change with time or between diets (data not shown). There was a modest correlation between baseline HbA1c and changes in HbA1c at 3 months (r = 0.52, P = 0.1) and 6 months (r = 0.76, P < 0.02,
In this study advice to reduce carbohydrate appeared to have been followed by a majority of the group allocated to the diet but low numbers of participants prevented changes in HbA1c from being significant compared to the control group or compared to baseline. However fasting glucose was significantly different from the control diet at 3 months. Although a large number of volunteers expressed initial interest in the study only 43 were randomized and 33 attended a baseline visit with only 24 completing a 6 month visit. Thus although many people express an interest in a low carbohydrate diet the reality of following any kind of diet dramatically reduced the numbers of active participants despite recruitment being open to the study for 2 years and over 3000 patients per year being seen in the clinic. This reflects the reality in clinical practice where most patients with type 2 diabetes on multiple medications find it too difficult to follow lifestyle advice to any significant degree. Mayer et al. [
Although there have been two published low to moderate intensity clinic based dietary interventions in type 2 diabetes [
There have been several meta-analyses examining low and very low carbohydrate diets in type 2 diabetes. One analysis was restricted to 13 studies performed in the USA and Canada and reported that low carbohydrate diets improved HbA1c, fasting glucose and triglyceride but the effect was related to weight loss [
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Although we have obtained suggestive evidence that a low carbohydrate diet can be successfully implemented in normal practice without professional staff and lower fasting glucose and HbA1c, our results are limited by low participant numbers and further studies are required.
Thanks to all the volunteers for their contribution to the study. Baker IDI Heart and Diabetes Institute supported the study with internal funds.
Peter Clifton conceived the study, analyzed the data and wrote the manuscript. Claire Galbraith and Leah Coles designed the volunteer handout material and databases, saw the volunteers and supervised all logistical aspects of the trial.
The authors declare no conflict of interest.
Peter M. Clifton,Leah T. Coles,Clare E. Galbraith, (2016) Low Carbohydrate Diets in Type 2 Diabetes—A Translational Study. Journal of Diabetes Mellitus,06,152-157. doi: 10.4236/jdm.2016.62016