Sunday, September 29, 2013

Thoughts on the Paleolithic Diet Trials

Trial 1
A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease (2007) [1]
A paleolithic diet is more satiating per calorie than a mediterranean-like diet in individuals with ischemic heart disease (2010) [2]

Trial 2
Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: a randomized cross-over pilot study (2009) [3]
Subjective satiety and other experiences of a Paleolithic diet compared to a diabetes diet in patients with type 2 diabetes (2013) [4]

Diet Wars

I’m mainly going to concentrate on the two trials I just blogged about (part 1, part 2) because they are the only Paleo diet trials that have a control group (which is important to minimise the placebo effect and effects from other confounders).  In both trials the ‘control group’ was either the Mediterranean diet or a Diabetes diet, both of which represents fairly conventional dietary advice for weight loss and health.  This design allows one to compare the efficacy of the Paleo diet to the other approaches and see which one is more successful.
First up though, it’s not like any of the diets were unsuccessful.  Many people feel like they have to restrict calories and stay hungry in order to lose weight, and that being on a diet is a pretty miserable existence.  Even without deliberate calorie restriction, the Mediterranean diet, the Diabetes diet and the Paleo diet decreased mean BMI and waist circumference and generally improved other health markers.  What’s more is that the participants mostly had good things to say about the Paleo diet and the Diabetes diet.  If anything, this should be empowering for people who want to lose weight.

The Paleolithic diet was more successful, it:

  • Led to more weight loss [1] [3] 
  • Improved glucose tolerance whereas the Mediterranean diet did not [1] 
  • Was more satiating per calorie [2] [4] 
  • Improved CVD risk factors such as HDL-C, triglycerides, diastolic blood pressure and several markers of glucose tolerance whereas the Diabetes diet did not [3]

The key differences between the diets were essentially that the Paleolithic diet was:

  • Higher in fruit, vegetables and meat, but lower in grains and dairy 
  • Higher in protein, but lower in calories, carbohydrate and saturated fat 
  • More nutrient dense per calorie, except for calcium and sodium

With the implication being that at least one of the key differences between the diets explains why the Paleolithic diet was more successful
 
* I suspect someone (in the CICO is everything camp) will point out that ‘the Paleolithic diet caused greater weight loss and improved XYZ because it had fewer calories’.  That’s obvious, particularly for the fewer calories >> weight loss connection.  But why did the participants eat fewer calories on an ad libitum Paleolithic diet than an ad libitum Mediterranean/Diabetes diet?  This will likely be met with ‘the Paleolithic diet was more satiating because it had more fibre, water and protein, but lower energy density’, and yet the researchers didn’t find any correlations between these and satiety per calorie.  Weight loss must obviously be a result of negative energy balance.  Instead of telling people to simply eat less and go a bit hungry, which is generally unsustainable, how about looking for strategies that promote a spontaneous reduction in calories and support the neuronal control of appetite.
 
Fruit

The Paleolithic groups in both trials had a relatively high fruit intake, averaging 513g in the first trial and 451g in the second.  This was almost twice the amount of fruit as the other group and 6-7x higher than the median intake among Swedish men.  This may sound like a lot of fruit, but it’s only equivalent to about 4 bananas, 2.5 oranges or 3 apples (just a piece of fruit at the end of each meal)
 
Many people in the Paleo community and elsewhere avoid fruit because fruit contains fructose and they hold to the belief that fructose is a poison, is fattening and promotes insulin resistance (see here for some counter-arguments).  These two trials provide evidence that a dietary pattern with a ‘high’ intake of fruit can cause spontaneous weight loss and improve CV risk factors like IR, HDL-C, triglycerides, and blood pressure.  The first study also found a high fruit intake “was not associated with change in AUC Glucose0–120 or AUC Insulin0–120 and “was associated with larger waist loss”.  “Thus, our study lends no support to the notion that fruit intake should be restricted in patients with diabetes or glucose intolerance.”
 
What Conclusions can we Draw?
 
Since there are only two trials with a control group, with a total of 42 participants (39 of whom were men) it’s difficult to draw too many conclusions.  Also, since there were several differences between the diets, you can’t simply ignore the differences except one and draw conclusions along the lines of ‘this proves grains are bad’ (this is kind why of I stressed to not make conclusions from the correlations)*.
 
These trials provide some evidence for the Paleolithic diet being more effective than conventional approaches for weight loss/satiety, IR/T2D and to improve CVD risk factors.  I would like to see further studies and am surprised these results haven’t attracted enough interest from the NIH/etc because they are essentially saying ‘the Paleolithic diet is better than the one which is currently recommended’
 
* Sometimes these trials have been misrepresented to promote an agenda.  This [1] study has been described as a ‘very low carb diet’, but the carbs provided about 40% of total calories.  It’s what I would call a ‘lower, but moderate carb diet’.
 
** No doubt someone is out there thinking: ‘without long term epidemiological studies and further RCTs, how will we know whether a diet of meat, fruit and vegetables is safe?’

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