A recent study compared effects of a low-carb versus low-fat diet in overweight diabetics (mostly blacks). After one year, the only major difference they found was lower HDL cholesterol in the low-carb eaters. The low-carb diet was more effective measured at three months into the study. Study participants were overwhelmingly black women, so the findings may not apply to you.
The authors note at the outset that:
Optimal weight loss strategies in patients with type 2 diabetes continue to be debated, and the best dietary strategy to achieve both weight loss and glycemic control . . . is unclear.
They also note that in short-term randomized studies, low-carb diets help improve glucose control in type 2 diabetics.
Participants (105) were randomized to either:
- a low-fat diet in the fashion of the Diabetes Prevention Program, with a fat gram goal of 25% of energy needs, or . . .
- the Atkins diet, including the 2-week induction phase and gradually increasing carb grams weekly, etc.
The adult partipants were black (64%), Hispanic (16%), white (15%), or other. Women were 80% of the group. Average age 54. Average weight 215 pounds (98 kg). Average BMI 36. Most of them were taking metformin, half were taking a sulfonylurea, 30% were on insulin. Thiazolidinedione drugs were discontinued since they cause weight gain as a side effect. Short-acting insulins were changed to glargine (Lantus) to help avoid hypoglycemia. For the low-carb group initially, insulin dosages were reduce by half and sulfonylureas were stopped (again, to minimize hypoglycemia). For the low-fat group, insulin was reduced by 25% and sulfonylurea by 50%. Metformin was not adjusted. Subjects were instructed to keep daily food diaries. Goal rate of weight loss was one pound per week.
The drop-out rate by the end of 12 months was the same in both groups – 20%. The low-carbers lost weight faster (3.7 lb/month) in the first three months, but by month twelve each group had the same 3.4% reduction of weight (6.8 lb or 3 kg). As measured at 3 months, low-carbers were down 11.4 lb (5.2 kg) and low-fat dieters were down 7 lb (3.2 kg). Maximum weight loss was at 3 months, then they started gaining it back. At 12 months, low-carb subjects using insulin were on 10 less units, while low-fat dieters were using 4 more units (not statistically significant). Hemoglobin A1c measured at 3 months was down 0.64 in the low-carb group and down0.26 in the low-fat. By 12 months, HgbA1c’s were back up to baseline levels for both groups. Blood lipids were the same for both groups at 12 months except HDL was about 12% higher in the low-carb dieters.
At baseline, subjects derived 43% of calories from carbohydrates, 36% from fats, 23% from proteins. At three months, the low-carb group ate 24% of calories as carbohydrates (estimated at 77 grams of carb daily) and 49% from fat. The low-fat group at 3 months derived 53% of calories from carbohydrate (199 grams/day) and 25% from fat. Diet compliance deteriorated as time passed thereafter.
Study Author Conclusions
After one year, the low-carb and low-fat groups had similar weight reductions. The low-carb dieters raised their HDL cholesterol levels significantly [which may protect against heart disease].
Lasting weight loss is difficult! Down only 6.8 pounds for a year of effort.
These study participants needed to lose a lot more than 6.8 pounds. They needed to lose 50. Both groups were woefully noncompliant with diet recommendations by the end of the study year. They were eating more carbs or other calories than they were assigned. But their results weren’t much different than other groups studied for an entire year.
How do we keep people fired up about maintaining their weight-loss efforts? The solution to that problem will win someone a Nobel Prize.
The Atkins diet was superior – for weight loss and glycemic control – when measured at three months, when compliance by both groups was still probably fairly good.
Results of this study may apply only to black women. There weren’t enough men and other ethnic groups to make meaningful comparisons.
Steve Parker, M.D.
Reference: Davis, Nichola, et al. 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. Diabetes Care, 32 (2009): 1,147-1,152.