Monday, March 17, 2014

Paleolithic Diet Trials: Part 3


Participants and Diets 

70 reasonably healthy, non-smoking, post-menopausal women with a BMI ≥ 27 were randomised to one of two diets: a Paleolithic diet (PD) or a diet that followed the Nordic Nutrition Recommendations (NNR).  The groups were similar at baseline, except for higher HDL-C in the PD group 

The macronutrient recommendations were: 

 
Protein (%)
Fat (%)
Carbohydrate (%)
PD
30
40
30
NNR
15
25-30
55-60

In addition, the PD group was advised to have a high intake of MUFA and PUFA, base the diet on “lean meat, fish, eggs, vegetables, fruits, berries and nuts”, with additional fat sources from avocado, rapeseed oil and olive oil and avoid “dairy products, cereals, added salt and refined fats and sugar”.  The advice to the NNR group also emphasised on “low fat dairy products and high-fibre products”.  “Both diets were consumed ad libitum” 

Results 

The only dietary information we are given is the macronutrients: 

 
 
Energy (kcal)
Protein (%)
Fat (%)
Carb (%)
PD
Target
-
30.0
40.0
30.0
Baseline
2000
17.1
33.4
46.2
6 Months
1625
23.4
43.4
29.3
24 Months
1599
21.9
40.4
33.5
NNR
Target
-
15.0
20.0-25.0
55.0-60.0
Baseline
2019
17.2
34.6
45.3
6 Months
1660
18.8
32.3
44.2
24 Months
1758
17.4
34.9
43.3

Other dietary data besides P:F:C include: 
 
  • Both groups (especially the PD group) increased MUFA and omega 3
  • The PD group decreased SFA and increased dietary cholesterol
  • Both groups (especially the PD group) increased omega 6 at 6 months, but both groups roughly halved their omega 6 at 24 months
  • There wasn’t any difference in fibre or sugar intake 

Compliance at least to macronutrients was quite poor.  In particular the PD group increased protein at 6 months, but not at 24 months and only less than 50% of the protein target (by %)*.  Also the NNR group didn’t decrease fat or increase carbohydrate and fibre, and actually reduced the absolute amount of carbohydrate at both 6 and 24 months 

At 6 months body weight, fat mass, waist circumference and sagittal diameter (of abdomen) (depth) decreased significantly more in the PD group than the NNR group.  However, at 24 months the differences weren’t significant as between 6-24 months there was some regain in the PD group and some further weight loss in the NNR group. 


Several biomarkers were measured (glucose, insulin, SBP, DBP, HR, hsCRP, tPA, PAI-1, cholesterol, HDL-C, LDL-C and triglycerides).  There were no significant differences in the changes in these biomarkers at 24 months except triglycerides, which decreased significantly more in the PD group.  Generally though the PD group had non-significantly greater improvements, but I hesitate to say that because those p values were nowhere near 0.05. 

In conclusion, for weight loss the PD group did slightly better at 6 months, but there was no significant difference at 24 months.  Adherence to both diet plans was quite a problem and was probably the cause of the modest regain in the PD group 

I can understand why many in the Paleo community are keen to promote these RCTs, particularly with the (mostly) unfounded criticisms over the last year, although I don't think this trial is exciting enough to be considered ‘long term scientific verification of the Paleo diet’.  If verification means 'is safe/healthy long term' you shouldn't need a study to see whether a diet based on meat, fruit and vegetables is safe and healthy; or if verification means 'better than', then this trial doesn't deliver.  Also, while the advice to the NNR group was a low fat, high carb diet, they didn’t actually change their macronutrient intake, so the Paleo diet wasn’t really being compared to a low fat diet (although that depends on how you define low fat I guess)*** 

* Urinary nitrogen wasn’t significantly different at 6 months or at 24 months, even though both absolute and relative protein intake was higher at both time points.  Perhaps the women in the PD group over reported their protein intake.  (As an aside, I hear how getting women to eat more protein or meat is often challenging.  They say things like ‘I couldn’t eat meat for lunch, it’s so filling’, but isn’t that the point if you’re trying to lose weight?) 

** In table 2 the baseline energy intake is lower than total energy expenditure in both groups.  Suggesting either that they were on a weight loss diet before the trial or that this is another example of the classic under reporting of food and/or over reporting of exercise that you hear so much about 

*** The Nordic Nutrition Recommendations have since been updated (which isn’t low fat, high carb), but would have occurred after the trial started 

**** The study is pay per view but I hear you can request access here

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