Wednesday, August 13, 2014

Low Carb Diet Trials: Stern, et al (2004)

A low-carbohydrate as compared with a low-fat diet in severe obesity [1]
The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial [2]
 
Participants and Diets
 
132 people with BMI ≥ 35 and without a major comorbidity were randomised to either a low carbohydrate diet (LCD) or low fat diet (LFD)
 
“The subjects assigned to the low-carbohydrate diet were instructed to restrict carbohydrate intake to 30 g per day or less. No instruction on restricting total fat intake was provided. Vegetables and fruits with high ratios of fiber to carbohydrate were recommended.” [1]
 
“The subjects assigned to the low-fat diet received instruction in accordance with the obesity-management guidelines of the National Heart, Lung, and Blood Institute, including caloric restriction sufficient to create a deficit of 500 calories per day, with 30 percent or less of total calories derived from fat.” [1]
 
The groups were pretty similar at baseline, except the LCD group had slightly higher rates of hypertension which was not significant (p = 0.082) [2]
 
The LFD group seemed to make minimal changes to their diet in the long term.  Despite being asked to maintain a 500 calorie deficit and eat ≤ 30% fat they only managed to eat 97 fewer calories at 1 year and reduce their fat intake from 34.7% to 34.1%.  Whereas the LCD group were eating 510 fewer calories even though they weren’t asked to, which came from roughly a halving in carbs (but still nowhere near the 30g target) without much increase in fat (22g).  The LCD also reduced fibre by 5g, which is generally expected with a reduction in carbohydrates, but they were only eating 7g of fibre at 1 year which isn’t much.  The LFD group didn’t do much better as they were eating 12g at 1 year.  These intakes of fibre suggest quite a lack of whole plant foods in both groups (such as fruits, vegetables, whole grains, legumes).  Also, sodium intake slightly increased in the LFD group, but slightly decreased in the LCD group [2].  See table 2 below and table 3 in [1] for 6 month (there isn’t much difference between 6 months and 1 year, except the calorie intake in the LFD group)
 
[2]
 
Results
 
The LCD group lost significantly more weight in the first 6 months, but didn’t keep losing, while to LFD group did.  So at 1 year the difference in weight loss wasn’t significant [1] [2]
 
Weight Loss (kg)
6 Months
1 Year
Low Carb
5.8 ± 8.6
5.1 ± 8.7
Low Fat
1.9 ± 4.2
3.1 ± 8.4

[2]
 
This is unexpected given the reported calorie intake over time [1] [2].  One explanation is that the LCD group may have been substantially underreporting their calorie intake at 1 year.  It’s also interesting that the standard deviation is so large for both the weight loss and the calorie deficit during the trial, perhaps suggesting many participants in both groups didn’t create a calorie deficit and actually gained weight during the trial
 
Calories Compared to Baseline
6 Months
1 Year
Low Carb
-460 ± 902
-510 ± 1187
Low Fat
-271 ± 1260
-97 ± 1067
 
Below are significant differences in metabolic markers between the groups.  The LCD group has significant improvements in triglycerides, HDL-C and HbA1c in diabetics relative to the LFD group, but their blood urea nitrogen level worsened.  Total cholesterol, HDL-C, blood glucose, plasma insulin, insulin sensitivity, serum creatine, uric acid level, systolic blood pressure and diastolic blood pressure weren’t significant [2].  However, insulin sensitivity and insulin and glucose in diabetics improved in the LCD group relative to the LFD group at 6 months [1]
 
 
 
Baseline
1 Year
Change
Triglycerides
(mmol/L)
Low Carb
2.27
1.63
-0.65
Low Fat
1.83
1.88
0.05
HDL Cholesterol
(mmol/L)
Low Carb
1.06
1.04
-0.03
Low Fat
1.06
0.93
-0.13
HbA1c in people with diabetes
(%)
Low Carb
7.4
6.6
-0.7
Low Fat
7.3
7.2
-0.1
Blood urea nitrogen level
(mmol/L)
Low Carb
5.7
6.1
0.4
Low Fat
5.4
5
-0.5
 
Compliance seems to be pretty similar between the groups.  Interestingly those who dropped out of the LCD group were less likely to lose weight, whereas those in the LFD group lost a similar amount of weight whether or not they remained in the study [2].
 
 
Low Carb Diet
Low Fat Diet
Participants who completed the study
44
43
Participants who dropped out of the study
20
25
Total
64
68
% Completed
69%
63%

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