Why it works…..temporarily at least
A change in eating from the standard Western diet to a well-executed Paleo diet can be beneficial to health. After all, the Paleolithic Period did not have processed food, fried foods, dairy, isolated oils, sugar or salt, all of which are implicated in our modern health problems. In addition, the plant foods allowed in a Paleo diet would ideally be eaten in their natural states, complete with the health-giving properties of their self-contained fiber, antioxidants, vitamins and minerals. These factors alone offer a massive improvement over the average Western diet. Unfortunately, the emphasis on high meat consumption in a Paleo diet ignores substantial evidence regarding the health risks of eating animal protein.
Surprisingly, a recent comparison among diets illustrates that in most respects a vegan diet is actually closer in nutrients to a true Paleolithic diet than is the modern version of Paleo eating. Amounts of such nutrients as fat and saturated fat, carbohydrates, fiber, calcium, potassium, iron, sodium, Vitamin C, Vitamin E, riboflavin and thiamin are in the same range in both vegan and true Paleolithic diets. Only the higher amounts of protein, Vitamin A and zinc of a modern Paleo diet more closely resemble those of a true Paleolithic diet. The modern Paleo diet contains levels of fat, saturated fat, cholesterol and sodium that are from two to five times higher than those of true Paleolithic diets while the levels of carbohydrates, calcium, fiber and Vitamin C are lower by 30 to 50%. (1)
The Paleo Diet is one of several low-carbohydrate diets. Others are the Ketogenic Diet, the Atkins Diet, the South Beach Diet and the Bulletproof Diet. All of these diets substantially reduce carbohydrate consumption while increasing fat and protein. The exact ratio of macronutrients varies among these diets but they are all low in carbohydrates. The science surrounding any of these diets can apply to a large extent in all of these diet choices.
Before we get to the actual science supporting Paleo eating there are some points to keep in mind. Many of the following studies have drawbacks;
The studies are overwhelmingly short. Most of them are only a few weeks to a few months long.
The studies generally have very small sample sizes.
Some of the studies do not use a control group for comparison.
None of the studies use a whole-food plant-based diet as a comparison. The low fat diets chosen as control diets encompass a wide range of foods, many of which do not promote health.
The studies do not focus on meaningful health outcomes such as prevention and reversal of modern chronic health problems like heart disease, cancer or diabetes. Instead they look at biomarkers like blood pressure, cholesterol or PSA levels which are symptoms of disease rather than causes.
The studies are often funded by the industries that they benefit.
Many studies have been performed in test tubes or on animals. Results from such studies cannot be transferred over to human beings.
STUDIES SUPPORTING A LOW-CARBOHYDRATE DIET
Proponents of the Paleolithic diet site scientific studies to support health claims from its consumption however the actual number of controlled clinical trials that compare human beings eating Paleo to humans eating other diets is limited. The following is an overview of the available science on this topic. Only studies performed on human beings are included.
A 2007 randomized controlled trial in 29 patients compared the Paleo diet with a Mediterranean-like diet for twelve weeks. Both groups lost about the same amount of weight and saw improvement in markers of diabetes such as improved glucose sensitivity. However, the Paleo eaters showed greater improvements in blood sugar levels and larger decreases in waist circumference (2).
In 2008 fourteen healthy volunteers started a Paleolithic diet and were observed over three weeks. Participants experienced an average weight loss of 2.3 kg and a decrease in waist circumference of 0.5 cm. They also experienced a slight drop in systolic blood pressure and a large rise in C-reactive protein (a negative result as this a measure of inflammation). There was no control group in this trial (3).
A 2008 study involved 322 participants and included a follow-up of over two years. This study compared weight loss due to the adoption of one of three diets – a low-fat restricted-calorie diet; a moderate-fat restricted-calorie Mediterranean diet; a low-carbohydrate non-calorie restricted diet. Study results indicate that all three test diets promoted weight loss with the average loss being 4.7 kg for the low-carbohydrate group, 4.4 kg for the Mediterranean-group and 2.9 kg for the low-fat group. A reduction in the ratio of total cholesterol to high-density cholesterol occurred of 20% in the low-carbohydrate group and 12% in the low-fat group. Hold on though! There is a major problem with these results. The so-called low-fat diet is not low in fat at all. It allows 30% of daily calories to come from fat with 10% from saturated fat. These levels are actually very close to those of the notoriously high-fat standard Western diet (4).
A randomized crossover study published in 2009 followed thirteen patients with type-2 diabetes who were randomized to either a Paleo diet or a diabetic diet for three months and then switched to the other diet for the next three months. Compared to eating a standard diabetic diet, those on the Paleo diet showed improved HbA1c, diastolic blood pressure, lipid profile, weight and waist circumference with no statistically significant change in C-reactive protein (5).
In 2009 a study on nine non-obese, sedentary, healthy volunteers compared the effects of eating a Paleo diet to eating their usual diet over ten days. The Paleo diet led to significant reductions in blood pressure, insulin sensitivity and lipid levels which were all unrelated to body weight. There was no control group in this study (6).
A 2013 study compared the satiety of the Paleo diet to that of a diabetic diet through a randomized crossover trial of thirteen patients with type-2 diabetes lasting two periods of three months. The Paleo diet resulted in longer satisfaction after a meal. Researchers noted that the Paleo diet was difficult to stick to (7).
A 2013 study placed 27 women of high BMI (greater than 27) on a modified Paleolithic diet for five weeks. The women lost an average of 4.5 kg and saw reduced waist and hip circumference as well as lower fasting blood sugar, lower diastolic blood pressure and lower lipid levels. Fat amounts in the liver were lowered but fat in the skeletal muscles did not decrease. Insulin sensitivity did not change. There was no control group in this study (8).
In 2014 a comparison of the Paleo diet with a “healthy” control diet recruited thirty two participants with metabolic syndrome and followed them for two weeks. The control diet was based on the Dutch dietary guidelines at the time and recommended vegetables, fruit, whole grains, vegetable oils, fish, low-fat dairy and meat. The Paleo diet produced lower systolic and diastolic blood pressures and improved lipid profiles. Paleo diet eaters also showed a larger decrease in body weight. There was no significant difference found in inflammatory markers (9).
Other data collected in 2014 compared Paleo diet consumption to Mediterranean diet consumption and found no statistical difference in risk of colorectal polyps (10).
A longer trial from 2014 recruited 70 obese, post-menopausal women and, using a randomized controlled format, compared the Paleo diet to a control diet. The control diet followed the 2012 Nordic Nutrition Recommendations and consisted of vegetables and pulses, fruits and berries, fish and seafood, nuts and seeds, low-fat dairy, vegetable oils and limited processed meat and red meat. The Paleo group lost significantly more weight at 6 months with the loss occurring in both body fat and lean tissue. This weight loss was not sustained at 24 months. Both groups were similar for improvements in blood pressure, C-reactive protein and lipid profiles. There was no change in insulin or fasting blood glucose levels (11).
A 2014 study placed 44 healthy adults on a Paleo diet that included lean meat, fish, eggs, nuts, fruits and vegetables and avoided all grains, dairy products, legumes and processed foods. The participants also took part in a high intensity exercise program. After ten weeks LDL cholesterol had increased by 12.5mg/dl and total cholesterol by 10.1 mg/dL. Triglycerides were also increased. There was no control group in this study. (12)
In 2015 a double-blind randomized controlled trial compared the gut hormone responses in 24 health male volunteers eating one of two Paleo-type meals or a reference diet based on World Health Organization guidelines. Both Paleo meals were predominantly plant based but contained some fish. The Paleo first meal contained protein and fat in the range typical of hunter-gatherers and contained no cereal or dairy products. The second Paleo meal consisted of identical plant-based ingredients but its protein and fat ingredients were altered to adhere to World Health Organization recommendations. No significant difference in insulin or glucose blood levels were observed between the consumption of the two meals (13).
In 2015 twenty volunteers with high lipid levels followed a traditional heart-healthy diet (fruits, vegetables, whole grains, nuts, seeds, vegetable oils, lean meat, poultry, fish, eggs, low-fat dairy, limited salt) for four months and then changed to a Paleo diet for four months. The Paleo diet period resulted in lowered total cholesterol, LDL and triglycerides, increased HDL-cholesterol levels (14).
WHAT CONCLUSIONS CAN WE MAKE FROM THESE STUDIES
In these short-term scientific investigations the Paleo diet did show health improvements, especially in body weight, waist circumference, blood pressure, lipid profiles and satiety. Studies that measured inflammatory markers recorded either a steep increase (worsening of inflammation) or no significant change in these markers from the consumption of a Paleo diet (3,5,9,11). Other results were variable among the studies. For example, some reported improvements in insulin or blood glucose levels (2,5,6) while others showed none (8,11,14). One study showed increases in cholesterol and triglyceride levels (12). The two longest studies lasted two years. One of them showed no difference in weight loss between the Paleo diet and the control diet after two years (11). The other one used an unhealthy diet as its control (4).
The Paleo diets used in these studies restricted dairy intake and were conservative in their meat ingestion while being generous in their intake of plant-sourced foods. Today’s Paleo diet recommends a higher meat and fat intake than that used in these studies and includes some dairy. Most importantly, none of these studies compared a Paleo diet to a completely plant-based whole-food diet.
There has been an abundance of research performed over many decades on the consequence of long-term low-carbohydrate diets with results that contrast sharply with those of short-term studies. Watch for “Eating Paleo Part Three” next week on this blog for more on this subject.
2 Lindeberg, S., Jonsson, T., Granfeldt, Y., et al. A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease. Diabetologia 2007; 50:1795–1807.
3 Osterdahl, M., Koctuk, T., Koochek, A., Wandell, P.E. Effects of a short-term intervention with a paleolithic diet in healthy volunteers. Eur J Clin Nutr 2008; 62:682–685
4 Shai, I., Schwarzfuchs, D., Henkin, Y., Shahar, D.R., Witkow, S., Greenberg, I., Golan, R. et al. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med 2008; 359(3);229–241.
5 Jönsson, T., Granfeldt, Y., Ahren, B., et al. Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: A randomized cross-over pilot study. Cardiovasc Diabetol 2009; 8:35.
6 Frassetto, L.A., Schloetter, M., Mietus-Synder, M., Morris, R.C. Jr, Sebastian, A. Metabolic and physiologic improvements from consuming a paleolithic, hunter-gatherer type diet. Eur J Clin Nutr 2009; 63:947–955
7 Jönsson, T., Granfeldt, Y., Lindeberg, S., Hallberg, A.C. Subjective satiety and other experiences of a Paleolithic diet compared to a diabetes diet in patients with type 2 diabetes. Nutr J 2013; 12: 105
8 Ryberg, M., Sandberg, S., Mellberg, C., Stegl,e O., Lindahl, B., Larsson, C., Hauksson, J., Olsson, T. A Palaeolithic-type diet causes strong tissue-specific effects on ectopic fat deposition in obese postmenopausal women. J Intern Med. 2013 Jul; 274(1):67-76.
9 Boers, I., Muskiet, F.A., Berkelaar, E., et al. Favourable effects of consuming a Palaeolithic-type diet on characteristics of the metabolic syndrome: A randomized controlled pilot-study. Lipids Health Dis 2014; 13: 160
10 Whalen, K.A., McCullough, M., Flanders, W.D., Hartman, T.J., Judd, S., Bostick, R.M. Paleolithic and Mediterranean diet pattern scores and risk of incident, sporadic colorectal adenomas. Am J Epidemiol 2014; 180:1088–1097.
11 Mellberg, C., Sandberg, S., Ryberg, M., et al. Long-term effects of a Palaeolithic-type diet in obese postmenopausal women: A 2-year randomized trial. Eur J Clin Nutr 2014; 68:350–357
12 Smith, M.M., Trexler, E.T., Sommer, A.J., Starkoff, B.E., Devor, S.T. Unrestricted Paleolithic diet is associated with unfavorable changes to blood lipids in healthy subjects. Int J Exerc Sci. 2014; 7: 128-139.
13 Bligh, H.F., Godsland, I.F., Frost, G., et al. Plant-rich mixed meals based on Palaeolithic diet principles have a dramatic impact on incretin, peptide YY and satiety response, but show little effect on glucose and insulin homeostasis: An acute-effects randomised study. Br J Nutr 2015; 113:574–584.
14 Pastore, L., Brooks, J.T., Carbone, W. Paleolithic nutrition improves plasma lipid concentrations of hypercholesterolemic adults to a greater extent than traditional heart-healthy dietary recommendations. Nutrition Research June, 2015; 35 (6): 474-479.