- The Paleo Diet is rich in meat, poultry, seafood, fruits, vegetables, with no grains, refined white flour or sugar and low in sodium.
- A true Paleolithic diet is impossible to mimic since wild game is not readily available, most modern plant food is cultivated rather than wild, and meats are domesticated.
- A problem with the Paleo Diet is consumption of excessive red meat (and elimination of grains) has been associated with cancer and cardiovascular death and other diseases.
Our Paleolithic ancestors
The popular Paleolithic diet centers on the idea that eating like our Paleolithic ancestors must be nutritionally superior to our current Western diet since our Paleolithic ancestors did not suffer from many of the chronic diseases such as diabetes and heart diseases so common in the western world today. Moreover, Paleo advocates note that the increase in many chronic diseases corresponds with the agricultural revolution which added grains, legumes and dairy to meals. The Paleo diet has appeal among the general public and is by its nature low in carbohydrates (22-40% of calories) and encourages fruits and vegetables, restricts processed foods, sucrose as well as grains and legumes.
The belief that Paleo diets and animal based diets offer unique health advantages is unfortunately not supported by the evidence. For one thing it is likely that our Paleolithic ancestors did not suffer the the ravages of 21st century living: diabetes and hardening of the arteries since paleolithic skeletons estimate the average life-expectancy was only 30-35 years -and likely did not live long enough to develop the diseases of modern society. Secondly, the Paleolithic diet of about 10,000 years ago was not a “one-size” fits all since our Paleolithic ancestors ate a great variety of foods based on geography and season.
Red meat and chronic disease
The recent National Heart, Lung and Blood Institute (NHLBI) funded observational study by researchers at the Harvard School of Public Health (HSPH) reported on over 37,000 men from the Health Professionals Follow-up Study and over 83,000 women from the Nurses’ Health Study and showed that those who consumed the highest levels of red meat had the highest risk of all-cause of mortality, cancer mortality and cardiovascular disease mortality. The lack of whole grains and diary are among the more controversial aspects of going Paleo. Low calcium is another concern since dairy products are one of the greatest sources of calcium -essential for heart, muscle, nerve and bone health. The risks of processed red meats may be related more to the sodium, nitrates and other preservatives.
It is true that the associations of chronic diseases related to red meat, not to mention, saturated fat have been challenging at best and we know association does not imply causation. Many of the classic nutrition studies have been observational and “associations” do not confirm cause and effect so a deeper look at the evidence is important.
- Many of the studies initially linking red meat and saturated fat to an increased risk for diabetes and heart attacks suffered from poor study design. We now realize the issue of what was substituted for red meat in many earlier studies was a major study design flaw muddying the water in the red meat-saturated fat controversy. Certainly replacing red meat with refined carbohydrates and sugar can have negative health effects including increased risk of diabetes and heart disease. Many more observational studies on meat suffered from other biases as well. For instance, meat eaters are more likely to also take in more calories and less calories from fruits, vegetables, fish and grains. Meat eaters were also more likely to be current smokers and more likely to be overweight. Thus, contributing poor health to red meat and saturated fat intake in isolation has been unclear. A deeper look into the red meat story and new science is enlightening.
We now appreciate that there are a number of plausible factors to explain the mounting associations of red meat with adverse health risks. Some factors under intense study to explain this association include: association with sodium (especially with processed meats), carnitine (an amino acid derivative), heme-iron (that’s part of myoglobin -the protein that makes red meat red), high cooking temperature, and carcinogenic chemicals.
More to the story on heart health
Unrelated to saturated fats is the fact that red meat is a rich source of carnitine, which may alter the population of our gut bacteria (adults whose diets are rich in red meat consume on average around 60-180 mg of carnitine per day, compared to only 10-12 mg per day among vegans). New research points to red meat’s association to heart risk (atherosclerosis) as a result of it’s ability to alter our gut’s bacterial community (our microbiome). The alteration of our microbiome is manifested by an overgrowth of a specific L-carnitine eating type of bacteria. The metabolic byproduct produced by these carnitine (or choline) loving bacteria is a compound called TMA (trimethylamine). The body can then metabolize TMA to a new and cardiotoxic chemical called TMAO (trimethylamine N-oxide).
- Higher levels of TMAO are associated with increased cardiovascular risk –a finding recently reported by researchers at the Cleveland Clinic that has caused great interest about how our microbiome intersects with nutrition and health. People who regularly eat red meat may have an increased colonization of a population of intestinal bacteria that break down the carnitine in red meat into a metabolite that may promote hardening of the arteries (atherosclerosis). Of note L-carnitine (D-carnitine is not biologically active) can be found not only in meat but in some energy drinks and many dietary supplements marketed for exercise, weight loss and healthy aging –look for more MedChefs reporting on this evolving subject in the near future.
Other issues related to red meat and disease include: heme-iron -considered a powerful pro-oxidant and pro-inflammatory risk factor for both diabetes and heart attacks. Heme-iron is the form of iron we have in blood and muscle and is name given to the form of iron found in red meat. Non-heme iron, on the other hand, is found in plants and is less well absorbed. Plant sources of iron (think spinach) are loaded with non-heme iron. Higher amounts of heme-iron can be toxic and contribute to the oxidation of LDL-cholesterol, a process that promotes the formation of artery-clogging plaque (a strong pro-oxidant may increase free radical formation in the body, which can damage proteins, fats, and DNA in body cells). Oxidation and inflammation are important at all stages of “hardening” of the artery disease (atherosclerosis) from initiation through progression and, ultimately, to the occurrence of heart attacks. This is a field of active research.
High cooking temperatures and carcinogens (cancer-causing chemicals) are other plausible issues related to the association of cancer risk with increased meat consumption. High temperature commercial cooking or frying, commonly used in preparing processed meats, can introduce potentially harmful chemicals (heterocyclic amines, nitroso-amines and polycyclic aromatic hydrocarbons), which could increase risk of both heart disease, diabetes and cancer. In fact, in 2015 the International Advisory Committee of the World Health Organization (WHO) labeled processed meats as “carcinogenic to humans” which means “can cause cancer” based on reviews of more than 800 studies. Processed meats are now in the same category as such causes of cancer such as tobacco smoking and asbestos (IARC Group 1, carcinogenic to humans). This group considered red meat as “possibly” carcinogenic.
The International Advisory Committee of the World Health Organization classifications describe the strength of the scientific evidence about an agent being a cause of cancer, rather than assessing the level of risk. To put the risk of processed meats in perspective: the strongest cancer link of was with colorectal cancer -the third most common cancer in men and the second in women worldwide. The life-time risk for this cancer for an average individual is 5% and with daily ingestion of processed meat this risk could jump to 6%. Processed meats include hot dogs, ham, bacon, sausage and some deli meats including turkey and chicken sausage and bacon.
To quote Oscar Wilde, “Everything in moderation, including moderation.” The focus of healthy nutrition should not be on miracle foods or evil foods that are going to prevent or promote disease. Avoiding processed meats, in favor of occasional non-processed red meat is reasonable -avoiding excessive red meat consumption is supported by the science. Processed deli meats, for example, includes: bologna, salami as well processed chicken, and turkey. We must strive for a healthy “eating pattern” that can be individualized to the way we like to eat.
Micha, R et al. Unprocessed red and processed meats and risk of coronary artery disease and type 2 diabetes–an updated review of the evidence. Curr Atheroscler Rep. 2012 December;14(6):515–524
Tang, WH et al. The contributory role of gut microbiota in cardiovascular disease J Clin Invest. 2014 Oct 1; 124(10):4204–4211
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