Is the Paleo diet outdated?

Posted on Thu, 2 Apr 15

The poplar paleo diet is based on the notion that we are have Stone Age bodies and should therefore be eating Stone Age food, but scientists think the foundation of the paleo diet concept is fundamentally wrong.

Few topics in popular nutrition generate as much interest and controversy as the question of “what is the ideal diet for optimal health?” In 1985 Eaton & Konner’s seminal New England Journal of Medicine article “Paleolithic Nutrition: A Consideration of its Nature and Current Implications (1)” bought evolutionary nutrition and the hunter-gatherer diet to the world, but should we all revert to a hundred thousand year old nutritional plan?

Dietary guidelines and recommendations are often the constructs of observational studies blended with contrived policy and generalized for the population (2). And flamboyant individuals who write books telling us what to eat are almost perpetually at the top of New York Times Best Sellers List for advice books (3). This could be why Paleolithic nutrition is so interesting; it offers a rationale template for the optimal human diet that is grounded in history.

The Paleolithic diet concept, the notion that what we ate a millennia ago provides an evolutionary template for what we should and shouldn’t eat today, has gained scientific interest and permeated popular diet books, from low-carbohydrate diets that use evolutionary theory to explain why you are not designed to eat pasta, to books that center primarily on “Paleolithic prescriptions” (4). But while the study of traditional diets is undoubtedly important, there are concerns that the assumption that the optimal human diet was genetically determined in the Paleolithic era may be fundamentally wrong.

Death of the Paleolithic human

In 2006 a provocative editorial entitled “Epigenetics: Death of the Paleolithic human?” was published by Jeff Bland PhD, who proposed that we may need to move beyond the view that our genes only evolve by natural selection and incorporate more recent and rapid epigenetic changes (5). Bland suggested that because diet is known to influence epigenetics within generations, it is probable that a number of metabolic adaptions to agricultural diets have occurred and therefore it is unlikely we are still suited to a 10,000-year-old Paleolithic diet. In other words, we may have adapted to dietary changes much more quickly than previously thought.

 “It may be time to recognize that the Paleolithic human is gone and the metabolism of the 21st century human is adapted to the nutritional and agricultural environment that has prevailed during the past 100 centuries.” - Jeff Bland, PhD

Prophetically it now appears that he was right. There is evidence for a number of post-agricultural, diet-driven shits in gene expression. For example, just one year after his editorial it was found for the first time that there are distinct differences between hunter-gathers and agricultural societies in the human amylase gene, with higher expression in a populations with high-starch diets likely to contribute to improved carbohydrate digestion and dietary adaptation (6).

There is also evidence that our gut microbiota genome is evolving in response to post-stone age dietary changes as well. Lateral transfer of genes acquired from marine bacteria that live on commonly eaten seaweeds into the gut microbial gene pool has enabled Japanese people to digest components of seaweed that would otherwise indigestible (7). The way in which environmental dietary changes have influenced our gut microbiota is still being explored, but likely to have relevance to our nutritional requirements and health.  And it is not simply recent genetic adaptions that question the Paleolithic prescription; there may be no such thing as a genetically predetermined diet in the first place.

No such thing as the Paleo diet?

Central to Paleolithic nutrition is the hypothesis that a characteristic diet that predominated the Paleolithic era is the diet we are best suited to. This hypothesis relies on the notion that there is a universal Paleolithic diet that is distinctly different from agricultural diets. Further, that this Paleolithic diet was not associated with “diseases of civilization” while the latter are. But there are a number of problems with this idea.

A recent review by anthropologists Turner & Thompson challenges a number of Paleolithic presuppositions (8). They propose that it is difficult to clearly define a Paleolithic diet or distinctly separate it from agricultural diets. For example the suggestions that hunter-gatherers did not consume many calories from carbohydrates and that we are maladapted to evolutionary novel cereal grains may not be correct.

Modern hunter-gatherers have a wide range in carbohydrate intakes; a recent analysis found that hunter-gatherers living in grasslands environments consumed as much as 30% of the total energy from carbohydrate. It is also difficult to suggest that a transition from a hunter-gatherer diet automatically resulted in widespread disease when agricultural diets are not necessarily associated with chronic illness, even societies that rely primarily on dietary carbohydrate (including cereals) may be relatively disease free.

"We are not biologically identical to our Paleolithic predecessors, nor do we have access to the foods they ate. And deducing dietary guidelines from modern foraging societies is difficult because they vary so much by geography, season and opportunity." - Feris Jabir, in Scientific American

“A growing body of scholarly data suggests that no such thing as an evolved human diet exists,” write Turner & Thompson “and that popular notions of returning to a diet that is more true to human nature are inconsistent with the ways in which metabolisms and eating habits develop in humans.”

Beyond stone age nutrition

So where does this leave us? There is no question that the study of human ancestral dietary patterns plays an important role in understanding human nutrition however, advising people to adopt a Paleolithic diet may be neglecting evidence that there are recent adaptions to healthful agricultural based diets. As Marlene Zuk, a biology professor at the University of California put it; a modern mismatch between everyday life and our evolutionary past may be nothing more than a “paleofantasy (9).” This does not detract from the benefits of encouraging a minimally-processed, plant-based diet (10), but suggests recent physiological, cultural and environmental dietary adaptations need to be taken into account.

References:

1. Eaton SB, Konner M. Paleolithic nutrition. A consideration of its nature and current implications. N Engl J Med. 1985 Jan 31;312(5):283-9.
2. Chiuve SE, Willett WC. The 2005 Food Guide Pyramid: an opportunity lost? Nat Clin Pract Cardiovasc Med. 2007 Nov;4(11):610-20.
3. Shikany JM, Barash J, Redden DT, Westfall AO, Heimburger DC, Henson CS, Allison DB. Divergence in popular diets relative to diets consumed by Americans,  and implications for diet selection. MedGenMed. 2007 Jul 9;9(3):8.
4. Knight C. "Most people are simply not designed to eat pasta": evolutionary explanations for obesity in the low-carbohydrate diet movement. Public Underst Sci. 2011 Sep;20(5):706-19.
5. Bland, J. Epigenetics: Death of the Paleolithic human? IMCJ. 2006;5(4):10-12.
6. Perry GH, Dominy NJ, Claw KG, Lee AS, Fiegler H, Redon R, Werner J, Villanea FA, Mountain JL, Misra R, Carter NP, Lee C, Stone AC. Diet and the evolution of human amylase gene copy number variation. Nat Genet. 2007 Oct;39(10):1256-60.
7. Hehemann JH, Correc G, Barbeyron T, Helbert W, Czjzek M, Michel G. Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota. Nature. 2010 Apr 8;464(7290):908-12.
8. Turner BL, Thompson AL. Beyond the Paleolithic prescription: incorporating diversity and flexibility in the study of human diet evolution. Nutr Rev. 2013 Aug;71(8):501-10.
9. Zuk, M. The Evolutionary Search for Our Perfect Past. The New York Times. January 19, 2009.
10. Katz DL, Meller S. Can we say what diet is best for health? Annu Rev Public Health. 2014;35:83-103.
11. Jabir, F. How to Really Eat Like a Hunter-Gatherer: Why the Paleo Diet Is Half-Baked. Scientific American. June 3. 2013.