The most robust controlled study to date on the effects of a Paleo diet has just been published in the prestigious European Journal of Clinical Nutrition. The study is the best quality Paleo trial to date, largely because food composition and consumption was very closely monitored with compliance confirmed by composition analyses of several 24-h urine collections.
The researchers conducting the study were from San Francisco and have previously published another trial showing beneficial metabolic effects from just 7 days consumption of a Paleo diet. But in this study, they sought to make it more robust by providing a control group that consumed a diet based on recommendations by the American Diabetes Association (ADA).
To meet inclusion criteria, each subject had to be a type 2 diabetic between the ages of 50-69 years with a BMI less than 40 kg/m2. In total there were 24 subjects that completed the study with the ADA diet group having ten subjects and the Paleo group fourteen. Most subjects were also on some type of medication for type 2 diabetes or blood pressure control.
Each dietary intervention lasted for 14 days. However, subjects in the Paleo group had a series of 3 ramp diets in the 7 days leading into the study. Each ramp diet featured increasing amounts of fiber and potassium in an attempt to allow for adaptation of the subjects’ intestinal tract and potassium handling systems to adjust to the markedly higher dietary content of the fiber and potassium in the Paleo diet.
As far as the nutritional composition of the two diets was concerned, the Paleo diet was comprised of meat, fish, poultry, eggs, fruit, vegetables, tree nuts, canola oil, mayonnaise and honey. Just as important, the Paleo diet excluded dairy products, legumes, cereals, grains, potatoes and products and products containing potassium chloride.
As for the ADA diet, it contained foods comprising cereal grains, dairy or legumes, with an emphasis on moderate salt intake and low-fat dairy. The researchers were nice enough to devise two daily diet plans for each diet so that participants were not eating the same meals every day. Each diet was divided into three meals and three snacks. What makes this study especially significant is that each diet was prepared by kitchen staff at the research centre. As such the calorie content was very tightly controlled. What’s more the nutrient composition of each diet was verified by independent laboratory composite analysis. Participants were required to eat some meals in the Research Center, with the rest of the meals packed for take-out.
Another important point to make is that neither of the diets were calorie restricted, as the researchers were not trying to induce weight loss in subjects. In fact the researchers went so far as to measure bodyweight every 2 days, and if a deviation of three pounds from the third day’s weight in the study occurred calorie intake was adjusted accordingly. The respective diet compositions are shown below.
Interestingly, the Paleo diet was not low in carbohydrate or high in fat compared with the ADA diet. This may contradict with some peoples definition of a Paleo Diet, which many believe should be low in carbohydrate and high in fat. While the above table shows that each diet did not differ significantly in its macronutrient content, the major differences were the foods that made up each macronutrient. For example, the Paleo group derived their carbohydrates largely from fruits, vegetables and honey, while the ADA diet there from food items like rice, bread and pasta. Another key difference was the higher fiber content of the Paleo diet. Lastly, another important difference was that the Paleo diet was lower in saturated fats and higher in mono- and polyunsaturated fats compared with the ADA diet.
The table below summarises the changes in measured variables throughout the 2 week study. One of the most positive significant changes was the improvement in insulin sensitivity for subjects in the Paleo diet group. Moreover, there was a trend for those who were most insulin resistant at baseline to demonstrate the greatest improvements in insulin sensitivity. This was accompanied by significant favourable changes in HbA1c, fasting plasma glucose and fructosamine (a shorter term marker of glycemic control).
The Paleo group also had statistically significant decreases in total cholesterol, HDL cholesterol and calculated LDL cholesterol. In contrast the ADA group only had a decline in HDL cholesterol but not in total cholesterol and calculated LDL cholesterol. The researchers suspected this was due to the lower saturated fat and high mono- and polyunsaturated fats in the Paleo diet compared with the ADA diet.
As far as blood pressure was concerned there was no significant changes in systolic or mean arterial pressures with either diet. This was an interesting finding especially in light of the increased potassium and lower sodium intake of both diets.
Weight loss was slightly higher in the Paleo group, which most likely was tied to the improved insulin sensitivity as the two are known to be tightly associated. The authors note that there may have seen more weight loss in the Paleo group if the caloric intake of the diets weren’t adjusted to avoid weight loss. The subjects in the Paleo group complained that the volume of food that they had to eat was excessive and without the encouragement of the researchers, they would have likely ate less. This is an interesting observation, which seems to indicate that the Paleo diet was more satiating.
In summary, this study provides the best evidence so far that the nutritional composition of a Paleo diet (i.e. high-fiber, high antioxidants, high mono- and polyunsaturated fats, low sodium and high potassium) may be particularly beneficial for individuals with type 2 diabetes.
Masharani U, et al. Metabolic and physiologic effects from consuming a hunter-gathere (Paleolithic)-type diet in type 2 diabetes. European Journal of Clinical Nutrition. 2015, 1-5.