A break from our usual Holford coverage, to discuss a recent EJCN Short Communication on “Effects of a short-term intervention with a paleolithic diet in healthy volunteers“. The study began with a small sample of 20; however, a high proportion of these dropped out, and the researchers appear to have lost some of the data on many of those remaining in the study. Moreover, a surprising proportion of those involved showed signs of illness, and the study lacked a control group. Frankly – with so much going wrong – I rather felt for the researchers: one could almost conclude that the Paleo diet is somewhat cursed. However, they were blessed in one respect: plenty of positive media coverage, meaning that the NHS felt the need to offer a critical response to the study.
Because of these problems, while the study concludes that the intervention showed some apparently positive effects, the problems with it mean that (as the authors rightly acknowledge) considerably more research is needed before conclusions can be reached. Frankly, we struggled to see much useful information to be gained from this problematic study.
The study began with 20 subjects; of these
One subject did not start, one missed the laboratory test, four broke the study, three because of illness and one could not fulfil the diet
This significantly reduces the power of the study. However, matters were worsened considerably when
Owing to a computer error, food registration data were available for eight subjects regarding normal diet (two men, six women), and seven regarding paleolithic diet (one man, six women); complete data were available for six subjects (one man, five women)
It’s mean to mock – and I know that we all occasionally have computer problems – but to lose so much important data does seem unfortunate.
Next – drop out rate. 14 subjects completed the study, 1 dropped out because they found the diet too hard to fulfil. In other words, 1/15 subjects could not stick to this diet for three weeks, even given the extra motivation provided by being included in the study.
We should also ask what type of illnesses were causing people to drop out. For 3 healthy subjects to become too ill to complete the study – compared to just 14 who did complete – seems notable: of course, the illnesses may have been absolutely nothing to do with the diet, but I would like more detail. Also, the study found that “Two subjects showed elevated CRP, probably virus infection related”. If 3/20 subjects are too ill to complete, and 2/20 seem to have picked up a virus, this does seem to flag up a potential concern.
Moving on, then, to what the study did show. It does show that — if people stick to a restricted diet, which pretty much eliminate ‘junk’ food, for a few weeks — they do tend to lose weight. Eating a diet with lots of fruit and veg, and limited saturated fat and salt intake, correlated in the study to higher vitamin C levels in subjects’ blood, and reduced blood pressure. This is all well and good, but not exactly surprising: as the NHS notes
Low calorie, low salt diets are expected to have an effect on weight and blood pressure in people who are overweight or have high blood pressure
One should also note that – presumably because of the restrictive nature of the Paleo diet – calcium levels were reduced. A final caution is that the write-up the study is not entirely clear as to what foods were allowed, and why: for example, mineral water intake was restricted; while I am all for avoiding bottled water and environmental and financial reasons, I fail to see why tap water is more Paleo than bottled. Moreover, the study write-up does not specify whether or not a number of ‘staple’ foods – eggs, for example – were allowed.
Here at HolfordWatch, we certainly don’t object to diets which are low in ‘junk’ and high in fruit, vegetables, fish etc. However, we would be reluctant to subject ourselves to a diet as restrictive as the Paleo diet without seeing much stronger evidence for its benefits. This study also failed to show whether the Paleo diet is safe for periods longer than three weeks, or whether people find it palatable in the longer term. We would, anyway, emphasise that you should speak to your doctor or dietician before trying anything so radical: a Paleo diet would certainly not be suitable for everyone.