Severe Carb Restriction in Type 2 Diabetes

U.K. researchers found major metabolic improvements in obese type 2 diabetics following a very low-carbohydrate diet, compared to a low-fat portion-controlled diet.  The latter is a standard recommendation in the U.S. for overweight type 2 diabetics.

 

This study is an oldie (2005) but a goodie.

 

 

The investigators randomly assigned 102 poorly controlled diabetics to follow one of the two diets for three months.  Participants had average weights of 224 pounds (102 kg),  body mass index 36, age 58, hemoglobin A1c’s of 9%.  Half of them were men.  About 40% of the diabetics in both groups were on unspecified oral diabetic drugs; 20% were on insulin and 40% were using a combination of the two.  Sulfonylurea was mentioned, but not metformin. 

 

Participants were randomly assigned to either a low-fat portion-controlled weight-loss diet or a low-carbohydrate diet.  The goal with the low-carb diet was “up to 70 g of carbohydrate per day,” including at least a half a pint of milk and one piece of fruit.  (Is a UK pint the same as in the US?).  Increased physical activity was recommended to both groups. 

 

Only 79 of the 102 participants made it through the three-month diet intervention.  Drop-out rate was the same for both groups.

 

 

(Differences are statistically significant unless otherwise noted.)

Weight loss for the low-carb group was 3.55 kg (7.8 lb) compared to only 0.92 kg (2 lb) for the low-fat cohort.

 

The total/HDL cholesterol ratio improved for the low-carb group (absolute decrease of 0.48 versus 0.10). 

 

Hemoglobin A1c and systolic blood pressure tended to decrease more for the low-carb group, but did not reach statistical significance.  For instance, HgbA1c dropped 0.55% (in absolute terms) for the low-carb group, and 0.23% for the low-fat group.  Lower HgbA1c indicates improved blood sugar control.

 

Caloric intake was not different between the groups (about 1350 cals/day by diet recall method).

 

The low-carb group reduced carbs to 109 g/day compared to 168 g in the  low-fat cohort.

 

The low-carb group consumed 33% of energy as carbs compared to 45% for the low-fat group.

 

The low-carb group consumed 40% of energy as fat compared to 33% in the low-fat cohort.

 

Protein intake was 26% of energy for the low-carbers compared to 21% for the low-fatters.

 

Absolute saturated fatty acid intake was higher for the low-carbers, but still considered moderate.

 

Insulin dose was reduced in about 85% of the insulin users in the low-carb group but in only 22% of the low-fat group.  Oral diabetic pill use was unchanged in both groups.

 

 

 

The improved total/HDL cholesterol ratio in the low-carbers may reduce risk of heart and vascular disease.  These investigators didn’t look at LDL particle size.  Other studies have found that low-carb eating tends to shift LDL cholesterol (bad stuff) from small dense particles to light fluffy particles, which are thought to be less harmful to arteries.

 

The authors considered reduction of carbs to 109 grams a day to be “severe.”  That compares to 275 grams a day eating by the typical U.S. citizen.  I agree that a reduction of carbs by two-thirds is major restriction.  Dr. Richard Bernstein and I consider severe restriction to be 20–30 grams, or perhaps up to 50 g.

 

I suspect the improved metabolic numbers in the low-carbers would have been even more dramatic if they had reduced carbs well below 100 grams a day.  The Ketogenic Mediterranean Diet reduces digestible carbs to 20–30 grams daily.  Many diabetics start losing control of their blood sugars when daily carbs exceed 60–80 grams.

 

Low-carb diets often yield better weight loss than low-fat calorie-restricted diets, as was seen here.  This is often attributed to lower calorie consumption on the low-carb diets.  These investigators didn’t see that here.

 

Low-carb diets are often criticized as being hard to stick with.  The low-carbers here didn’t have any more drop-outs than the low-fat group.  Granted, it was only a three-month study.

 

Based on what we know today, the reduced need for insulin in these patients was entirely predictable. 

 

The authors had some concern about the higher relative saturated fatty acid consumption in the low-carbers.  In 2011, we know that’s not much, if any, cause for concern.

 

 

 

 

Reference: Daly, M.E., et al.  Short-term effects of severe dietary carbohydrate-restriction advice in Type 2 diabetes—a randomized controlled trial.  Diabetic Medicine, 23 (2006): 15-20.  doi: 10.1111/j.1464-5491.2005.01760.x