“What is Paleo? – An edited research review from Dr. Christopher Pitt

The rationale for the Palaeolithic diet, otherwise known as the Stone Age diet or simply as Paleo, stems from the evolutionary discordance hypothesis – that human evolution ceased 10,000 years ago, and our Stone Age genetics are ill-equipped to cope with our modern diet and lifestyle, leading to the ‘diseases of civilization’. Thus, only foods that were available to hunter–gatherer groups are optimal for human health – ‘Could I eat this if I were naked with a sharp stick on the savanna?’. Therefore, meat, fruit, and vegetables are acceptable, but grains and dairy products are not.

Such views have drawn criticism from anthropologists, who argue that there is no blanket prescription of an evolutionarily appropriate diet, but rather that human eating habits are primarily learned through behavioral, social and physiological mechanisms. Others have noted that the claims of the Paleo diet are unsupported by scientific and historical evidence. The Paleo diet’s anthropological validity notwithstanding, is there scientific support for the various health claims made of it? Pragmatically speaking, is a diet without dairy and refined carbohydrates beneficial, even if it is not historically accurate?

The Paleo diet remains controversial because of exaggerated claims for it by wellness bloggers and celebrity chefs (For example, that the Paleo diet could prevent or cure polycystic ovary syndrome, autism, mental illness, dementia, and obesity.), and the evolutionary discordance hypothesis on which it is based. However, a number of underpowered trials have suggested there may be some benefit to the Paleo diet, especially in weight loss and the correction of metabolic dysfunction.

  • Further research is warranted to test these early findings.
  • A clear danger to be considered for those who are on the Paleo diet is the less than adequate calcium intake, especially for those at higher risk of osteoporosis.

Does the research support the vast and extravagant claims made by the Paleo diet’s celebrity proponents? Looking at the studies as a whole, the Paleo diet was often associated with increased satiety, along with improvements in body weight, waist size, blood pressure, and lipid profiles. However, the studies were short, unspecific, and very small. The strongest of the studies was by Mellburg, who showed no long-term differences between participants on the Paleo diet and those on the control at 2 years. You could just eat more vegetables and drink more water, which is probably just as healthy in the long run, but without the weight of celebrity expectations.

In the studies that measured inflammatory markers, there was no significant difference as a result of consuming the Paleo diet. Adherence and desirable options were common issues raised about the Paleo diet. Some studies reported improvements in plasma glucose or other markers of blood sugar control, though some didn’t, including the study of Bligh, which was a high-quality, laboratory-controlled study. It showed no significant difference in glucose and insulin levels for the Paleo diet, compared with their standard meal.

Other factors should be considered when thinking of the Paleo diet. The cost of the Paleo diet is approximately 10% more expensive than an essential diet of similar nutritional value, which may limit the Paleo diet’s usefulness for those on a low income. Calcium deficiency also remains a significant issue with the Paleo diet; the study by Osterdahl in 2008 showed that the calcium intake of the Paleo diet was about 50% of the recommended dietary intake. 

Overall, conclusions about the effectiveness of the Paleo diet should be considered cautiously. Nevertheless, there appears to be enough evidence to warrant further consideration of the Paleo diet as a potential dietary option. Claims that the Paleo diet could treat or prevent conditions such as autism, dementia and mental illness are not supported by clinical research. The Paleo diet is currently over-hyped and under-researched.

The Research

While proponents of the Paleo diet claim that it is evidence-based, there are only a limited number of controlled clinical trials comparing the Paleo diet to accepted diets such as the diabetic or Mediterranean diets.

In 2007, Lindeberg performed a randomized controlled trial of the Paleo versus Mediterranean-like diet in 29 patients with heart disease and impaired glucose metabolism over 12 weeks. Both groups lost approximately the same amount of weight; however, the Paleo group showed a significantly decreased waist size and improved glucose sensitivity. In 2009, Jönsson expanded on the study by Lindeberg . They published a randomized study of 13 patients with type 2 diabetes, randomized to either the Paleo or diabetic-like diet over two consecutive three-month periods. Compared with patients on the diabetic-like diet, patients on the Paleo diet showed improved hemoglobin1Glycated hemoglobin is a form of hemoglobin that is measured primarily to identify the three-month average plasma glucose concentration. The test is limited to a three-month average because the lifespan of a red blood cell is four months.,  blood pressure, lipid profile, weight and waist size, and no significant change in C-reactive protein2C-reactive protein (CRP) is a substance produced by the liver that increases in the presence of inflammation in the body. An elevated C-reactive protein level is identified with blood tests and is considered a non-specific “marker” for disease. (CRP).

Osterdahl and colleagues published a pilot study in 2008, in which 14 healthy volunteers were placed on the Paleo diet over the course of three weeks. Six participants gave a complete dietary assessment. Across all participants, there was an average weight loss of 2.3 kg over the three weeks and an average decrease in waist size by 0.5 cm, and blood pressure improved slightly. The authors noted that the Paleo diet was significantly lower in calcium compared to the subjects’ pre-study diet.

Frassetto performed a metabolically controlled study in 2009 in nine non-obese, sedentary, healthy volunteers, comparing the Paleo diet to their usual diet. The Paleo diet led to significant reductions in blood pressure with improved arterial distensibility, insulin sensitivity, and plasma lipids, all unrelated to body weight.

In 2013, Jönsson studied the satiety of the Paleo diet, compared with the diabetic diet, in a randomized trial of 13 patients with type 2 diabetes. The Paleo diet resulted in greater satiety for energy, energy density, and glycemic load per meal. While the Paleo diet was more satiating per calorie than the diabetic diet, they also noted that it was difficult to adhere to.

In 2014, Boers compared the Paleo diet with healthy control diet in 32 subjects with metabolic syndrome. The Paleo diet resulted in lower blood pressure and improved plasma lipid profile. Body weight decreased in the Paleo group, compared with the other.

Whalen in 2014 used previous data collected between April 1991 and April 1994 to analyze the frequency of colorectal polyps versus the diet history given on a standardized dietary questionnaire. They found that for both the Paleo and Mediterranean diets, there was no significant change in risk.

Mellberg published a longer term trial on the Paleo diet in 2014. Their study was a randomized controlled trial of 70 women who were obese and post-menopausal, and they compared the Paleo diet to a reference diet based on the Nordic Nutrition Recommendations over a two-year period. The Paleo group lost significantly more weight than the group on the other diet at six months, although this was not sustained at the 24-month mark. The Paleo diet group lost more body fat and lean tissue than the reference group. Both groups showed similar improvements in blood pressure, C-reactive protein3C-reactive protein (CRP) is a substance produced by the liver that increases in the presence of inflammation in the body. An elevated C-reactive protein level is identified with blood tests and is considered a non-specific “marker” for disease., and cholesterol, whereas there were no changes in fasting glucose and insulin.

In a double-blind randomized controlled trial of 24 healthy male volunteers in 2015, Bligh compared the acute satiety and gut hormone responses of two Paleo-type meals with a reference meal. There was no significant difference in the response of glucose and insulin between the meals.

Author: Christopher E Pitt MBBS, FRACGP, General Practitioner, Carseldine, QLD.

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See my post on Calcium

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