Sunday, August 17, 2014

Low Carb Diet Trials: Dansinger, et al (2005)

 
Participants and Diets
 
160 participants with BMI between 27-42 and at least 1 metabolic risk factor (high cholesterol, trigs, glucose or blood pressure, or being treated for at least one of them) were randomised to one of four diet groups: Atkins, Zone, Weight Watchers or Ornish.  The groups were similar at baseline although the Zone and Ornish groups had almost significantly higher insulin
 
Diet Group
Diet Advice
Atkins
< 20g carbs, then gradual increase to 50g
Zone
30P:30F:40C
Weight Watchers
Calorie restriction based on points (~1200-1800 kcal)
Ornish
Vegetarian diet and 10% calories from fat
 
“We encouraged all participants to take a nonprescription multivitamin daily, obtain at least 60 minutes of exercise weekly, and avoid commercial support services. To approximate the realistic long-term sustainability of each diet, we asked participants to follow their dietary assignment to the best of their ability until their 2-month assessment, after which time we encouraged them to follow their assigned diet according to their own self-determined interest level.”
 
·         The Atkins group initially reduced carbohydrates from 239g to 68g at 1 month, but returned to 190g at 6 and 12 months.  The Atkins group had the smallest reduction in calories
·         The Ornish group initially reduced fat from 75.5g to 26.5g at 1 month, but returned to 64.0g at 12 months.  Similarly, they increased fibre from 14.0g to 20.5g at 1 month but slid back down to 15.0g at 12 months
·         The Zone and WW groups maintained the largest reduction in calories, which came fairly equally from fat and carbohydrate 

 
For more information see Table 2
 
* Once again the low fibre intake (~15g) in the groups suggests they didn’t eat much whole plant foods, suggesting the overall diet quality was poor
 
Results
 
In the intention to treat analysis:
 
·         All groups lost weight, but there were no differences between the groups
·         All groups lowered their LDL-C except Zone and WW at 6 months and Atkins at all time points
·         All groups increased their HDL-C at 12 months except Ornish
·         All groups lowered the LDL-C:HDL-C ratio
·         Atkins and Zone had significantly lower triglycerides at 1 month, but not at any other timepoint
·         All groups reduced CRP at 12 months except Zone (p = 0.09)
 
See table 3 below.  When missing values (from drop out) were excluded the figures remained pretty similar (see Table 4)
 
 
Adherence was an issue.  Dropout rates were 21% at 2 months, 38% at 6 months and 42% at 1 year.  At 1 year there was an almost significant difference (p = 0.08) between drop out in Atkins (48%) and Ornish (50%) compared to Zone (35%) and WW (35%).  “The most common reasons cited for discontinuation of the study were that the assigned diet was too hard to follow or not yielding enough weight loss”
 
 
Not surprisingly, adherence was associated with weight loss
 
 

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%

Sunday, August 10, 2014

Intro to the Low Carb Diet Trials

Inducing weight gain and glucose intolerance in mice using a high fat diet (for my honours project) has got me interested in the low carb diet trials.  I don’t think fat per se is promotes obesity or glucose intolerance, at least not in humans.  After all, low carb diets are reputed to be equal to if not more effective than low fat diets in clinical trials.  That being said, I also don’t buy into the carbohydrate insulin hypothesis of obesity, nor do I think that carbohydrates are poisonous or toxic (within reason).
 
I searched for low carb diet trials by going through meta-analyses and this Wikipedia page (which was quite thorough).  I was surprised how many of them there were, but many of them were quite small and/or short, which is to be expected.
 
This meta-analysis (published 2012) was particularly helpful.  It included 23 trials based on the following criteria: the low carb diet was defined as ≤45% of energy from carbohydrates*; there being a low fat comparison where ≤30% of energy came from fat; at least 6 months long; random allocation; participants at least 18 years old; and no “differences other than macronutrient and energy intake between the 2 diets”***
 
They arrived at the conclusion that:
 
“Reductions in body weight, waist circumference and other metabolic risk factors were not significantly different between the 2 diets. These findings suggest that low-carbohydrate diets are at least as effective as low-fat diets at reducing weight and improving metabolic risk factors. Low-carbohydrate diets could be recommended to obese persons with abnormal metabolic risk factors for the purpose of weight loss. Studies demonstrating long-term effects of low-carbohydrate diets on cardiovascular events were warranted.”**
 
I want to look at several of the main low carb diet trials more closely.  So after compiling a list I decided to look at trials that had at least 100 participants, lasted at least a year and were proper low carb or very low carb diets (~ ≤25% energy from carbohydrates).  This left me with 9 trials which I’ll look at in the following weeks
 
1.      Stern, et al (2004).  The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial.
2.      Dansinger, et al (2005).  Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial
3.      Gardner, et al (2007).  Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A to Z Weight Loss Study: a randomized trial
4.      Shai, et al (2008).  Weight loss with a low-carbohydrate, Mediterranean, or lowfat diet
5.      Brinkworth, et al (2009).  Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo.
6.      Davis, et al (2009).  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
7.      Foster, et al (2010).  Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: a randomized trial.
8.      Iqbal, et al (2010).  Effects of a low-intensity intervention that prescribed a low-carbohydrate vs. a low-fat diet in obese, diabetic participants.
9.      Lim, et al (2010).  Long-term effects of a low carbohydrate, low fat or high unsaturated fat diet compared to a no-intervention control.
 
* In my opinion 45% of energy from carbohydrates should be considered moderate and ~25% of energy from carbohydrates should be considered low (see here).  That meta-analysis included 8 trials where 30-45% of energy from carbohydrates.  I’m also kind of interested in those because that’s kind of the level I eat, but I suspect there probably won’t be much, if any difference between the groups considering the macronutrient composition is so similar and food quality seems to be far more important than macronutrient ratios
 
** The wording in trials, meta-analysis, reviews, etc suggests that in the authors’ mind low carb, high fat (LCHF) diets are kind of guilty until proven innocent.  This probably goes back to ideas that ‘fat clogs your arteries’ and fat is calorie dense therefore fattening.  But then when LCHF diets don’t worsen the lipid profile and are at least as effective as low fat diets regarding weight loss they still remain hypervigilant, looking for the first warning signs to say ‘I told you so’ or ‘the LCHF diet is unsafe’.  I wouldn’t mind so much if the same approach was also applied to conventional dietary advice (not to mention testing national dietary guidelines in clinical trials), but it isn’t
 
*** Even though this was one of their criteria, many of their included trials didn’t actually meet it as for example, many low carb diet trials include an ad libitum low carb diet and a calorie restricted low fat diet

Monday, July 28, 2014

Comparing Nutrient Density using the USDA Nutrient Database

In an earlier blog post I compared food groups using the NUTTAB nutrient database.  This time I’m going to do the same using the USDA nutrient database.  As usual, the group medians for micronutrients and LCO3 is the amount of a given nutrient in 2000 calories of food divided by the RDI.  This table is arranged by nutrient density (left = most, right = least).  I omitted things like restaurant foods, fast food, snack food and fats and oils as this is a comparison between whole foods

 
 
One of the problems of comparing food groups this way is that NUTTAB and the USDA ND group many types of food in the same category.  This is quite evident in the USDA ND as many of their groups are groups of food products.  So the worse whole food groups may simply have their nutrients more diluted by additives.  Finally, I did the same thing, this time using my old nutrient database which only includes some whole (and raw) foods from the USDA ND
 

While none of these are perfect measures, the rankings are pretty consistent between all three measures (see below) (also see the NUTTAB comparison).  My main internal debate is whether to make a new tier for nuts and put fruit, whole grains and seeds in tier 5 

Tier 1
Offal, shellfish, non-starchy vegetables, immature legumes
Tier 2
Eggs
Tier 3
Meats and fish, mature legumes
Tier 4
Dairy, fruit, whole grains, seeds
Tier 5
Nuts

* In NUTTAB and the USDA ND, the dairy, fruit and grains groups are most likely to be an underestimate as these groups seem to have more processed items (for example: butter, cream, yoghurt and milk with added sugar, refined grains, grain products, fruit juice)

Sunday, July 20, 2014

Nutrient Database (USDA)

I previously used some entries in the USDA nutrient database and organised them in such a way to compare the nutrient density of foods and food groups.  More recently I did a similar thing but used all the entries in the NUTTAB nutrient database (Australia) to form another nutrient database.  This time I used all (8463) the entries in the USDA database

To download the nutrient database click here.  Don't try and read it in the Google drive viewer because you won't be able to see much of it, just download it