Share this post
A critical review of the evidence
One of the most controversial diets in recent times is the Paleolithic (“Paleo”) diet, also known as the Stone Age diet. The Paleo diet seeks to address 21st century ills by revisiting the way humans ate during the Paleolithic era, more than 2 million years ago. As a nutritionist, I’m intrigued by this diet and by claims that it may reduce many of the chronic diseases that afflict society today.
Paleo proponents believe that because our genetics and anatomy have changed very little since the Stone Age, we should eat foods similar to those available during that time to promote good health. Stone Age people hunted, fished, and gathered wild plants for food, and had a high level of physical activity. If they lived long enough, they were believed to experience less modern-day diseases like heart disease. Although living beyond the age of 40 was rare according to Paleolithic records,, studies of hunter-gatherer tribes show they are largely free of the cardiovascular diseases common in industrialized societies.
Foods generally permitted as a part of the Paleo diet include fresh lean meats, fish, shellfish, eggs, nuts, seeds, fruits, vegetables, olive oil, coconut oil, and small amounts of honey. Proponents emphasize choosing fruits and vegetables with a low glycemic index (i.e., foods that cause a lower and slower rise in blood glucose). Foods generally not allowed on the diet include dairy products, grains (whole or refined), legumes (peanuts, beans, lentils), sugar, salt, refined vegetable oils such as canola, and most processed foods in general, along with alcohol and coffee.
The Paleo diet has many advocates, but it has been criticized due to exaggerated claims made by some of its proponents. In this article we’ll review the evidence for and against the Paleo diet.
What are the benefits of a Paleo diet?
Some aspects of the Paleo diet are highly desirable, including the elimination of processed foods and sugars, and an increased consumption of vegetables and fruits. There is overwhelming evidence that consuming refined grains and added sugars (especially in drinks) increases the risk of obesity, diabetes, and cardiovascular disease.,,, A strong case can be made that refined sugar should be avoided altogether. In contrast, non-starchy vegetables, whole fruits, legumes, and whole kernel grains may help protect against chronic diseases.
Vegetable consumption is universally recommended across evidence-based healthy diets. Vegetables have a low glycemic index and are rich in fiber and a variety of important micronutrients, including vitamins, minerals, and antioxidants. Higher vegetable consumption is correlated with a lower risk of hypertension, type 2 diabetes mellitus, and cardiovascular disease.,, Whole fruits are similarly recommended across a variety of heart-healthy diets due to their antioxidant and anti-inflammatory effects, generally low glycemic index, and high satiety profile.
Both the Paleo and control groups lost weight, but there was no difference in weight loss between the groups at the two-year mark.
As of this writing, a limited number of controlled clinical trials have studied the effects of the Paleo diet. A 2019 meta-analysis of 11 trials showed an average weight loss of approximately 3.5 kg in individuals consuming Paleo diets. While 11 trials may sound impressive, one of the studies enrolled only seven subjects on the Paleo diet, and six subjects on the control diet, which is hardly a convincing sample size. Consistent with the small size of the 11 studies, not one of them was given an “A” grade for evidence quality: four studies received a “B”, and seven studies were graded “C” by the authors. Also, most of the studies had durations of six months or less. In a longer-term study that was not included in the meta-analysis, 35 obese postmenopausal women were placed on the Paleo diet for two years, while a control group consumed the Nordic Nutrition diet (a healthy diet that emphasizes fatty fish, berries, root vegetables, nuts, legumes, low-fat dairy, and whole grains). Both the Paleo and control groups lost weight, but there was no difference in weight loss between the groups at the two-year mark.
Some studies suggest that the Paleo diet may lower blood cholesterol, triglycerides, and other metabolic disease markers,,, while one study observed an increase in these parameters in healthy subjects. Meta-analyses, again involving very small numbers of subjects, suggest that a Paleo diet may improve some blood markers more effectively than control diets., However, some of the control diets had excessively high levels of carbohydrates. Critics have pointed out that high-carb, low-fat diets should not be considered as controls, because they are not heart-healthy., Larger clinical studies, using a more relevant control such as the Mediterranean diet, are needed.
Are there risks associated with a Paleo diet?
Omitting whole grains, dairy, and legumes can lead to suboptimal intake of important nutrients.
Advocates of the Paleo diet have not shown whether eliminating dairy, legumes, and whole grains is good for your health. Moreover, omitting whole grains, dairy, and legumes can lead to suboptimal intake of important nutrients. One study showed that the dietary intake of thiamine, folate, magnesium, calcium, iron, and iodine decreased significantly in individuals adopting Paleo or Atkins-style (high-protein) diets.
Dairy products are a major source of calcium and vitamin D, and much larger clinical studies and meta-analyses have shown that the inclusion of dairy in the diet is one factor that may decrease the risk of osteoporosis., Dairy consumption was associated with lower risk of mortality and major cardiovascular disease events in a diverse multinational cohort. Although some plant foods contain calcium, it can be difficult for Paleo followers (or vegans) to meet recommended daily calcium intakes unless supplements are included in their diets.,, Bone broth is commonly advocated as part of the Paleo diet, but a single serving provides less than 5% of the daily recommended calcium intake for adults.
Modern lifestyles limit our exposure to sunlight, and the incidence of vitamin D deficiency has been surging.
Vitamin D is another nutrient of concern. In hunter-gatherers, vitamin D was mainly obtained via the body’s synthesis of this hormone from ultraviolet irradiation (sunlight exposure) of the skin. Modern lifestyles limit our exposure to sunlight, and the incidence of vitamin D deficiency has been surging., Vitamin D3 (cholecalciferol) supplements seem to be the best way to ensure adequate vitamin D status for individuals who do not consume dairy or other vitamin D-fortified foods.,
The elimination of salt in the Paleo diet also increases one’s risk for iodine deficiency., In a 2-year prospective randomized trial of healthy postmenopausal overweight or obese women who consumed a Paleo diet, there was a 50% decrease in the average urinary iodine concentration after 6 months. Thus, iodine supplementation may be advisable for Paleo followers.
Paleo diets exclude whole grains and legumes, even though epidemiological studies have shown that such foods can help protect against many chronic diseases. Legumes offer a sustainable source of protein and fiber, promote weight loss due to their low calorie and high nutrient density, and are associated with a reduction in cardiovascular disease and all-cause mortality. Whole wheat, brown rice, barley, and oats are important sources of dietary fiber, minerals (including iron and magnesium), and essential B vitamins., Whole grain intake also has been associated with lower risks of cardiovascular disease, cancer, and all-cause mortality.
Long-term Paleo diet followers experienced a massive reduction in Bifidobacterium, a bacterial genus that plays a critical role in gut health and immune function.
Finally, although the Paleo diet is often promoted for gut health, the exclusion of whole grains and legumes reduces the intake of prebiotic fibers that promote a healthy microbiota.,,, A 2019 study raised red flags when it showed that long-term Paleo diet followers experienced a massive reduction in Bifidobacterium, a bacterial genus that plays a critical role in gut health and immune function. Owing to their beneficial effects, bifidobacterial species such as B. lactis are frequently included in probiotic formulations. Importantly, low levels of bifidobacteria are associated with inflammation.
The same 2019 study showed an increased abundance of Hungatella, a bacterial genus that spits out trimethylamine (TMA), resulting in higher serum levels of trimethylamine-N-oxide (TMAO) in Paleo followers. TMAO is associated with an increased risk of cardiovascular disease, although recent studies suggest that TMA itself may be the culprit. Higher grain consumption was associated with lower TMAO levels. Although scientists are still sorting out the various dietary influences on TMAO, preliminary evidence suggests that whole grains and other dietary fiber sources may be required to reduce levels of this compound and maintain gut and cardiovascular health. The authors state, “Taken together with the greater observed serum TMAO concentrations, it cannot be concluded that the Paleoithic diet is associated with improved gut health and a reduction in risk of cardiovascular disease as promoted.”
Benefits of a hunter-gatherer lifestyle
Many Paleo proponents are focused on the diet, but hunter-gatherer lifestyles also feature a high level of physical activity. Archaeological evidence shows that our skeletons have become lighter and more fragile since Paleo times, a result of our increasingly sedentary lifestyles., Further evidence suggests that 80% of U.S. adults and adolescents are not sufficiently active. Sedentary lifestyles are associated with an increased risk of cardiovascular disease, diabetes, and many cancers.,,, “Contemporary humans live in a cultural and technological milieu incompatible with our evolutionary adaptations,” said Dr. Colin Shaw from the University of Cambridge. “There’s seven million years of hominid evolution geared towards action and physical activity for survival, but it’s only in the last say 50 to 100 years that we’ve been so sedentary — dangerously so.”
At this time, it cannot be concluded that the Paleo diet per se is associated with a reduction in cardiovascular disease risk as is often promoted. Preliminary studies suggest that Paleo diets may help reduce body weight and improve blood cholesterol levels, at least over the short term, but may have harmful effects on other cardiovascular risk markers such as TMAO over the long term. The high level of physical activity associated with Paleolithic life inevitably is a factor, oft neglected, that contributes to weight management and overall health. Because the exclusion of whole grains, legumes, and dairy can reduce valuable bifidobacteria populations in the gut and increase the risk for micronutrient deficiencies, a probiotic supplement that includes Bifidobacterium spp. and a high-quality multivitamin and mineral supplement that includes calcium, iodine, and vitamin D3 may be advisable to protect Paleo diet followers from these potential adverse effects.Click here to see References
 Berggren T, et al. Nutrition and Health Info Sheet: The Paleo Diet. Davis (CA): University of California; 2018 [cited 18 Sep 2019]. Available at: https://nutrition.ucdavis.edu/outreach/nutr-health-info-sheets/pro-paleo-diet
 Trinkaus E. Late Pleistocene adult mortality patterns and modern human establishment. Proc Natl Acad Sci U S A. 2011 Jan 25;108(4):1267-71.
 Coolidge FL, Wynn T. Psychology Today. The truth about the caveman diet [Internet]. New York: Sussex Publishers; 2013 (cited 18 Sep 2019). Available at: https://www.psychologytoday.com/us/blog/how-think-neandertal/201311/the-truth-about-the-caveman-diet
 Eaton SB, et al. Stone agers in the fast lane: chronic degenerative diseases in evolutionary perspective. Am J Med. 1988 Apr;84(4):739-49.
 Ludwig DS, et al. Dietary carbohydrates: role of quality and quantity in chronic disease. BMJ. 2018 Jun 13;361:k2340.
 Malik VS, Hu FB. Sugar-sweetened beverages and cardiometabolic health: an update of the evidence. Nutrients. 2019 Aug 8;11(8):1840.
 Yang Q, et al. Added sugar intake and cardiovascular diseases mortality among US adults. JAMA Intern Med. 2014 Apr;174(4):516-24.
 Hu FB. Resolved: there is sufficient scientific evidence that decreasing sugar-sweetened beverage consumption will reduce the prevalence of obesity and obesity-related diseases. Obes Rev. 2013 Aug;14(8):606-19.
 Pallazola VA, et al. A clinician’s guide to healthy eating for cardiovascular disease prevention. Mayo Clin Proc Innov Qual Outcomes. 2019 Aug 1;3(3):251-67.
 U.S. Department of Health and Human Services and the U.S. Department of Agriculture Dietary Guidelines for Americans 2015-2020, 8th edition [Internet]. Bethesda (MD): National Institutes of Health; 2015 (cited 18 Sep 2019). Available from: https://health.gov/dietaryguidelines/2015/guidelines/
 Slavin JL, Lloyd B. Health benefits of fruits and vegetables. Adv Nutr. 2012 Jul 1;3(4):506-16.
 Li M, et al. Fruit and vegetable intake and risk of type 2 diabetes mellitus: meta-analysis of prospective cohort studies. BMJ Open. 2014 Nov 5;4(11):e005497.
 Micha R, et al. Etiologic effects and optimal intakes of foods and nutrients for risk of cardiovascular diseases and diabetes: systematic reviews and meta-analyses from the Nutrition and Chronic Diseases Expert Group (NutriCoDE). PLoS One. 2017 Apr 27;12(4):e0175149.
 Moore LV, Thompson FE. Adults meeting fruit and vegetable intake recommendations – United States, 2013. MMWR Morb Mortal Wkly Rep. 2015 Jul 10;64(26):709-13.
 De Menezes EVA, et al. Influence of Paleolithic diet on anthropometric markers in chronic diseases: systematic review and meta-analysis. Nutr J. 2019 Jul 23;18(1):41.
 Mellberg C, et al. Long-term effects of a Palaeolithic-type diet in obese postmenopausal women: a 2-year randomized trial. Eur J Clin Nutr. 2014 Mar;68(3):350-7.
 Pastore RL, et al. Paleolithic nutrition improves plasma lipid concentrations of hypercholesterolemic adults to a greater extent than traditional heart-healthy dietary recommendations. Nutr Res. 2015 Jun;35(6):474-9.
 Boers I, 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 Oct 11;13:160.
 Smith MM, et al. Unrestricted Paleolithic diet is associated with unfavorable changes to blood lipids in healthy subjects. Int J Exercise Sci. 2014 Apr 1;7(2):128-39.
 Manheimer EW, et al. Paleolithic nutrition for metabolic syndrome: systematic review and meta-analysis. Am J Clin Nutr. 2015 Oct;102(4):922-32.
 Ghaedi E, et al. Effects of a Paleolithic diet on cardiovascular disease risk factors: a systematic review and meta-analysis of randomized controlled trials. Adv Nutr. 2019 Jul 1;10(4):634-46.
 Fenton TR, Fenton CJ. Paleo diet still lacks evidence. Am J Clin Nutr. 2016 Sep;104(3):844.
 Hyde PN, et al. Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss. JCI Insight. 2019 Jun 20;4(12):e128308.
 Sacks FM, et al. Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association. Circulation. 2017 Jul 18;136(3):e1-23.
 Churuangsuk C, et al. Impacts of carbohydrate-restricted diets on micronutrient intakes and status: a systematic review. Obes Rev. 2019 Aug;20(8):1132-47.
 Iguacel I, et al. Veganism, vegetarianism, bone mineral density, and fracture risk: a systematic review and meta-analysis. Nutr Rev. 2019 Jan 1;77(1):1-18.
 Sahni S, et al. Dairy intake is protective against bone loss in older vitamin D supplement users: the Framingham Study. J Nutr. 2017 Apr;147(4):645-52.
 Dehghan M, et al. Association of dairy intake with cardiovascular disease and mortality in 21 countries from five continents (PURE): a prospective cohort study. Lancet. 2018 Nov 24;392(10161):2288-97.
 Pitt CE. Cutting through the Paleo hype: the evidence for the Palaeolithic diet. Aust Fam Physician. 2016 Jan-Feb;45(1):35-8.
 Osterdahl M, et al. Effects of a short-term intervention with a paleolithic diet in healthy volunteers. Eur J Clin Nutr. 2008 May;62(5):682-5.
 Weaver CM, et al. Choices for achieving adequate dietary calcium with a vegetarian diet. Am J Clin Nutr. 1999 Sep;70(3 Suppl):543S-8S.
 Hsu DJ, et al. Essential and toxic metals in animal bone broths. Food Nutr Res. 2017 Jul 18;61(1):1347478.
 Luxwolda MF, et al. Vitamin D status indicators in indigenous populations in East Africa. Eur J Nutr. 2013 Apr;52(3):1115-25.
 Hochberg Z, Hochberg I. Evolutionary perspective in rickets and vitamin D. Front Endocrinol (Lausanne). 2019 May 15;10:306.
 Liu X, et al. Vitamin D deficiency and insufficiency among US adults: prevalence, predictors and clinical implications. Br J Nutr. 2018 Apr;119(8):928-36.
 Schmid A, Walther B. Natural vitamin D content in animal products. Adv Nutr. 2013 Jul 1;4(4):453-62.
 National Institutes of Health, Office of Dietary Supplements. Vitamin D fact sheet for health professionals [Internet]. Bethesda (MD): US Department of Health and Human Services; 2018 [cited 2018 Jul 13]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
 Manousou S, et al. A Paleolithic-type diet results in iodine deficiency: a 2-year randomized trial in postmenopausal obese women. Eur J Clin Nutr. 2018 Jan;72(1):124-9.
 Kim SJ, et al. Effects of dietary pulse consumption on body weight: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. 2016 May;103(5):1213-23.
 O’Neil CE, et al. Whole-grain consumption is associated with diet quality and nutrient intake in adults: the National Health and Nutrition Examination Survey, 1999-2004. J Am Diet Assoc. 2010 Oct;110(10):1461-8.
 Papanikolaou Y, Fulgoni VL. Grain foods are contributors of nutrient density for American adults and help close nutrient recommendation gaps: data from the National Health and Nutrition Examination Survey, 2009-2012. Nutrients. 2017 Aug 14;9(8):873.
 Aune D, et al. Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies. BMJ. 2016 Jun 14;353:i2716.
 Keenan MJ, et al. Role of resistant starch in improving gut health, adiposity, and insulin resistance. Adv Nutr. 2015 Mar 13;6(2):198-205.
 Yang X, et al. Resistant starch regulates gut microbiota: structure, biochemistry and cell signalling. Cell Physiol Biochem. 2017;42(1):306-18.
 Gopalsamy G, et al. Resistant starch is actively fermented by infant faecal microbiota and increases microbial diversity. Nutrients. 2019 Jun 14;11(6):1345.
 Simpson HL, Campbell BJ. Review article: dietary fibre-microbiota interactions. Aliment Pharmacol Ther. 2015 Jul;42(2):158-79.
 Genoni A, et al. Long-term Paleolithic diet is associated with lower resistant starch intake, different gut microbiota composition and increased serum TMAO concentrations. Eur J Nutr. 2019 Jul 5:1-14.
 Hills RD Jr, et al. Gut microbiome: profound implications for diet and disease. Nutrients. 2019 Jul 16;11(7):1613.
 Sarkar A, Mandal S. Bifidobacteria – insight into clinical outcomes and mechanisms of its probiotic action. Microbiol Res. 2016 Nov;192:159-71.
 Qi J, et al. Circulating trimethylamine N-oxide and the risk of cardiovascular diseases: a systematic review and meta-analysis of 11 prospective cohort studies. J Cell Mol Med. 2018 Jan;22(1):185-94.
 Jaworska K, et al. TMA, a forgotten uremic toxin, but not TMAO, is involved in cardiovascular pathology. Toxins (Basel). 2019 Aug 26;11(9):490.
 Li Q, et al. Soluble dietary fiber reduces trimethylamine metabolism via gut microbiota and co-regulates host AMPK Pathways. Mol Nutr Food Res. 2017 Dec;61(12): 1700473.
 Ryan TM, Shaw CN. Gracility of the modern Homo sapiens skeleton is the result of decreased biomechanical loading. Proc Natl Acad Sci U S A. 2015 Jan 13;112(2):372-7.
 Chirchir H, et al. Recent origin of low trabecular bone density in modern humans. Proc Natl Acad Sci U S A. 2015 Jan 13;112(2):366-71.
 Piercy KL, et al. The physical activity guidelines for Americans. JAMA. 2018 Nov 20;320(19):2020-8.
 Moore SC, et al. Association of leisure-time physical activity with risk of 26 types of cancer in 1.44 million adults. JAMA Intern Med. 2016 Jun 1;176(6):816-25.
 Gallardo-Alfaro L, et al. Leisure-time physical activity and metabolic syndrome in older adults. Int J Environ Res Public Health. 2019 Sep 11;16(18):3358.
 Lear SA, et al. The effect of physical activity on mortality and cardiovascular disease in 130 000 people from 17 high-income, middle-income, and low-income countries: the PURE study. Lancet. 2017 Dec 16;390(10113):2643-54.
 Aune D, et al. Physical activity and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis. Eur J Epidemiol. 2015 Jul;30(7):529-42.
 University of Cambridge. Hunter-gatherer past shows our fragile bones result from inactivity since invention of farming [Internet]. Rockville (MD): Science Daily; 2014 [cited 18 Sep 2019]. Available from: https://www.sciencedaily.com/releases/2014/12/141222165033.htm
Share this post
Marina MacDonald, MS, PhD
Say Yes to NO: Nitric Oxide
Support for heart health, sexual performance, and beyond Nitric oxide (NO) is a tiny gas molecule produced in the blood vessels, nerves, and immune cells. Best known for its role in maintaining blood pressure, NO also mediates penile erections, supports healthy blood flow to the brain, enhances muscle oxygen use during exercise, and helps…
Nrf2, Antioxidant Superhero
Fighting oxidative stress and inflammation with natural substances If you cut up an apple and leave it on the counter, you may notice its white flesh turn to brown. A similar effect happens to our own cells when they’re exposed to unstable molecules known as free radicals. This “rusting,” or “browning” process is called…
Fighting Fatty Liver, Part 1 of 2
How the gut, microbes, inflammation, and diet affect the liver, and what to do about it The fatty liver epidemic Sedentary lifestyles, nutrient-poor diets, chemical exposures, and an excess of sugar and refined foods are wreaking havoc on and in our bodies more than ever before. And the effects aren’t just cosmetic – beyond…
Is the Mediterranean Diet is Really Good For You?
A literature review on this increasingly popular diet What exactly is the Mediterranean diet? The Mediterranean diet (MD) is one of the better known and well-studied dietary patterns that has consistently been shown to have a beneficial influence on health and longevity.,,, It is recognized by the World Health Organization as a healthy and…
Missing Out on the Keto Craze?
Should you hop on the bandwagon? One of the latest diet trends is the “keto” (ketogenic) diet, which has eclipsed Paleo as the hottest diet trend around. Keto diets are touted as helping you lose weight, improve your memory, and live longer. And a slew of businesses are lining up to capitalize on the…
B Vitamins for Brain Health
Simple-yet-powerful nutrients to fight depression, dementia, and more B vitamins are required for just about every major function in the body, from red blood cell production, to metabolism, to brain health. There are eight different B vitamins – B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate) and…