The Paleo diet revolves around replicating the eating behaviours of our prehistoric ancestors. Advocates of Palaeolithic methodologies claim eating like a hunter-gatherer is still the most superior diet to avoid disease, increase longevity and improve body composition. Arguments for a Palaeolithic diet derived initially, not from modern science, but from the universal relevance of adaptation.

As the diet tries to mimic that of cavemen, it mainly focuses on the consumption of large quantities of meat (usually grass-fed and unprocessed) and fish, alongside a portion of vegetables. Small quantities of fruit, nuts, seeds and oils can be included. Grains, legumes, potatoes, dairy, processed foods and alcohol are to be avoided [1].

Unlike many fad diets that are targeted towards short-term weight loss results, the Paleo diet is advertised as a lifetime endeavour. The diet does not have strict limitations on meal frequency or caloric intake, and places nearly all its emphasis on ensuring Paleo users do not convert back to eating foods on their “banned list”. Brief instructions such as “restrict or avoid consumption of fruit, nuts and oils” are mentioned for those primarily looking to lose weight, but no specifications on nutrient requirements are advised.

Based on the list of foods you can eat, Paleo followers tend to consume a high protein, high fat, high saturated fat, high cholesterol, low carbohydrate diet.

The Benefits

Refraining from processed foods and added sugar

 The movements push to refrain from eating processed food and refined sugars is definitely a message that can never be said enough. A 2016 survey notes ultra-processed foods could be comprising an average of 57.9% of our total energy intake, and contributed 89.7% of the energy intake from added sugars [2]. Sugar content in highly processed foods is approximately 5 times more than that found in unprocessed or minimally processed foods.

Excess sugar intake can increase hepatic uptake and the metabolism of fructose which can lead to liver lipid accumulation, increased cholesterol and decreased insulin sensitivity. In addition, epidemiological studies show that excess sugar consumption is associated with body weight gain, mainly due to sugars inability to decrease hunger levels and therefore lead to increased caloric intakes [3].

Restricting sugar intake, alongside the high protein and fiber intake (provided a lot of vegetables are eaten), is a great combination for increasing satiety levels and triggering weight loss. No surprise this is a common occurrence when starting this diet. However, it is worth noting that the literature clearly shows fructose intakes below ~50 grams per day have no significant effects on fasting triacylglycerol, plasma glucose concentrations, or body weight, with some studies seeing no negative effects up to 100 grams per day [4][5].

This evidence shows that moderation is key for fructose, with the devil being in the dose, and total elimination may be an unnecessary dietary protocol (especially if it is making you avoid fruit!).

 

The Cons

Prehistoric diets should contain starch-based foods

 Paleo advocates fail to realise that starch-based foods were a staple of our prehistoric ancestors diets. Carbohydrate consumption, especially in the form of starch (plant root tubers, potatoes), have continuously shown to have contributed significantly towards the acceleration of brain growth over the last 3 million years, alongside our ability to heat and cook food [6].

Evidence also conveys the genes that code for the enzymes needed to digest starch evolved about 1 million years ago, in the midst of the Palaeolithic era [7].

A true Paleo diet would include starch-based foods, not avoid them.

The only time in history humans may not have consumed starch-based foods is during a time of severe famine, such as in a widespread flood or ice age, and reliance solely upon animal hunting was key to survive. However, it would be hard to provide evidence that a diet only represented in very short-time periods thousands of years ago due to extreme circumstances have any relevance to optimal health in the modern world.

Avoiding grains and legumes is not supported by science, and is counter intuitive

vegan diet

 

The recurring claim that gluten in grains causes intestinal issues in humans, said by Paleo supporters, is highly exaggerated.

Current estimates of gluten allergy prevalence are below 1% of the population, with gluten intolerance or non-celiac gluten sensitivity prevalence estimated at 0.5% [8]. To assume grains negatively impact on health when only a very small minority of humans notice digestive issues raises suspicion of Paleo’s legitimacy.

To make it worse, half of the “major food allergens” designated by the Food Allergen Labelling and Consumer Protection Act are Paleo-approved. In addition, a recent meta-analysis reviewing 45 studies concluded that whole-grain consumption (~90 grams per day) is associated with a reduced risk of coronary heart disease, cardiovascular disease, total cancer, mortality from all causes, respiratory diseases, infectious diseases, diabetes, and all non-cardiovascular, non-cancer causes [9]. Limiting whole-grains can also lead you deficient in Folate, Magnesium, Fiber, Vitamin E, Potassium, Flavonoids, Selenium, Lignans are Phytosterols [10].

Paleo advocates also claim legumes cause detrimental effects in the human body due to high toxicity levels. However, scientific literature (in both observational and controlled studies) on the health benefits of legumes consumption is substantial. Legumes are fundamental components of some of the healthiest populations in the world.

Beans, including fava, black, soy, and lentils, are the cornerstone of most centenarian diets [11]. The toxicity claims, centred around lectin content in beans, are also false as the heat during cooking completely denatures lectins. Cooked legumes are not only completely safe but their residual lectin levels fight cancer and various types of infection [12].

Promoting large quantities of red meat intake raises diet legitimacy issues

Red meat, although better than processed red meat, has shown in a wide range of studies to contain a magnitude of unique properties than can damage health (especially in excess quantities such as promoted within Paleo).

Red meat contains high amounts high amounts of methionine, which increases mitochondrial superoxide generation and the rate of oxidation leading to protein damage and age acceleration [13]. Methionine, when mixed with glucose, creates gaseous sulphur-containing compounds such as methanethiol and hydrogen sulphide. The diffusion of these compounds increases tumour proliferation rates, and is associated with cancer [14].

Musclefood steak

Heterocyclic amines, a meat mutagen, and heme iron within red meat are also shown to have a carcinogenic nature. A heterocyclic amine, PhIP, has shown to induce prostate tumors and dietary levels induce a rapid and transient increase in phosphorylation of the mitogen-activated protein kinase extracellular signal-related kinase pathway in the prostate cell line PC-3 [15].

This pathway is associated with the promotion and progression of neoplastic properties (abnormal tissue growth). Heme iron can also create N-nitroso compounds that may act as alkylating agents and generate DNA damage such as G>A transitions [16]. These are some of the key reasons why the World Health Organisation list unprocessed red meat as a type 2A carcinogen, labelled as “probably causing cancer”, only second to processed red meat, a type 1 carcinogen, labelled as “causing cancer” [17].

Who should run this diet?

The paleo diet is ideal for someone with a goal to improve their body composition and transition to better eating habits compared to a typical Western or American diet containing mostly processed foods. The diet can be useful at fighting habitual cravings for processed sugar and other ‘junk’ treats and transition to more ‘natural’ dietary choices.

This diet is not ideal for someone who is looking to optimize their health and lose weight in the most appropriate manner. Anyone with this goal should look to more flexible eating plans that do not place a great degree of emphasis on red meat consumption and/or limiting fruit and grain intake.


References

1) Paleo Diet Food List. (2015). Available: https://ultimatepaleoguide.com/paleo-diet-food-list/#

2) Steele EM et al. (2016). Ultra-processed foods and added sugars in the US diet: evidence from a nationally representative cross-sectional study. BMJ.

3) Stanhope KL. (2016). Sugar consumption, metabolic disease and obesity: The state of the controversy. Crit Rev Clin Lab Sci.

4) Livesey G, Taylor R. (2008). Fructose consumption and consequences for glycation, plasma triacylglycerol, and body weight: meta-analyses and meta-regression models of intervention studies. Am J Clin Nutr.

5) Sánchez-Lozada LG et al. (2008). How safe is fructose for persons with or without diabetes?. Am J Clin Nutr.

6) Carbs Needed to Evolve Big Brains. (2015). Available: http://neurosciencenews.com/brain-evolution-carbs-2388/

7) Hardy K. (2015). PALEO DIET: Big Brains Needed Carbs – The importance of dietary carbohydrate in human evolution. The Quarterly Review of Biology

9) Aune D, Keum N, Giovannucci E, Fadnes LT, Boffetta P, Greenwood DC, Tonstad S et al. (2016). 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

10) Higdon J et al. (2003). Whole Grains. Oregon State University

11) Eating To Break 100: Longevity Diet Tips From The Blue Zones. (2015). Available from:  http://www.npr.org/sections/thesalt/2015/04/11/398325030/eating-to-break-100-longevity-diet-tips-from-the-blue-zones

12) Xia L. (2006). A hemagglutinin with mitogenic activity from dark red kidney beans. J Chromatogr B Analyt Technol Biomed Life Sci

13) McCarty MF, Barroso-Aranda J, Contreras F. (2009). The low-methionine content of vegan diets may make methionine restriction feasible as a life extension strategy. Med Hypotheses

14) Yamagishi K, Onuma K, Chiba Y, Yagi S et al. (2012). Generation of gaseous sulfur-containing compounds in tumour tissue and suppression of gas diffusion as an antitumour treatment. Gut

15) Bylsma LC, Alexander DD. (2015). A review and meta-analysis of prospective studies of red and processed meat, meat cooking methods, heme iron, heterocyclic amines and prostate cancer. Biomed Central

16) Bernstein AM, Song M, Zhang X, Pan A, Wang M, Fuchs CS et al. (2015). Processed and Unprocessed Red Meat and Risk of Colorectal Cancer: Analysis by Tumor Location and Modification by Time. PLOS ONE

17) Processed meats do cause cancer – WHO. (2015). Available from – http://www.bbc.co.uk/news/health-34615621