Canibais e Reis

Na MEDPAG-Today li hoje esta notícia, Fatty Diet Linked to Pancreatic Cancer, mais uma notícia a apresentar extrapolações de causalidade com base em meras associações epidemiológicas. Convém nunca esquecer que correlação epidemiológica não significa necessariamente causalidade. Confundir as duas coisas ou é ignorância ou é então ciência selectiva. Para se demonstrar causalidade serão necessários estudos de intervenção e, convenhamos, isso será mesmo muito difícil de demonstrar, pela simples razão de que alimentos tradicionais, consumidos em doses tradicionais e em contextos de vida tradicionais, jamais serão a causa de doenças modernas.

O Dr. Michael Eades tem uma série de artigos em que analisa estas falácias epidemiológicas das campanhas anti-proteínas animais. Esses artigos são os seguintes:

Meat and mortality
Colon cancer and red meat
Addendum to the colon cancer and red meat post
More on red meat and colon cancer

Acerca destes estudos anti-consumo de carne (e anti-gorduras animais), por sinal a nossa fonte proteica de excelência nos últimos 2.4 milhões de anos, sugiro a leitura do Protein Debate, com o Dr. Loren Cordain e o Dr. Colin Campbell. Tal como o Dr. Cordain explica, as carnes consumidas pelos nossos antepassados do paleolítico eram frescas e obtidas no contexto de uma dieta rica em antioxidantes (muitos vegetais de baixo IG e alguma fruta). Muitas das carnes hoje mais consumidas são altamente processadas e salgadas, os peixes preservados com produtos químicos em latas, etc. Por isso, as dietas hiperproteicas dos humanos que nos antecederam, sendo na maioria ricas em proteínas/gorduras animais, eram consumidas num contexto natural, substancialmente diferente do contexto industrial da actual civilização.

Fonte: Protein Debate, Cordain vs Campbell.

Mas isto não significa que você deva embarcar nas falácias do lóbie vegetariano, abandonar o consumo de proteínas animais e com isso degradar a sua saúde. Repare bem que não existe no mundo nenhum povo saudável a viver estritamente vegetariano, e mesmo os vegetarianos/veganos convictos apenas o são por alguns meses ou poucos anos, retornando depois à carnivoragem. Portanto, certifique-se de que está a consumir carnes/peixe/ovos frescos, preferencialmente de produção biológica e, sim, assegurando-se que os animais que você come tiveram direito a uma existência digna e tão natural quanto possível.

PROTEIN DEBATE
Dietary Protein and Cancer

 

Observational epidemiological studies frequently (119), but not always (120) show that high animal protein diets may increase the risk for a variety of cancers, particularly colorectal cancer (121). Consequently, it might be expected that non-meat eating vegetarians would have a lower risk for these cancers. Paradoxically, this effect has not been consistently demonstrated (119). A proposed mechanism of action for the carcinogenic effect of meat consumption is the formation of toxic N-nitroso compounds (NOC) in the gut from heme iron in meat (122, 123). Short term human studies are in agreement that increased meat consumption increases NOC formation both in the lower (122) and upper (123) gastrointestinal tract. However, whether this situation translates into increased cancer risk is not known because to date, no randomized controlled trials of increased meat consumption in humans, using cancer diagnosis as an end point, have been conducted. The meats and fish consumed by pre-agricultural humans were almost always fresh, whereas current western diets contain significant quantities of processed, salted meats and fish preserved with nitrites and nitrates. Processed meats contains 10 times more NOC (5.5 µmol/kg) than fresh meat (0.5 µmol/kg) (124). Pre-agricultural humans consumed their fresh meats along with high intakes of fresh fruits and vegetables estimated to be between 35-45 % of total energy (14) compared to 8.1 % of total energy in the current U.S. diet (125). Increased fruit and vegetable consumption increases the fecal transit rate so that NOC have less contact time with the colonic mucosa and therefore may reduce the carcinogenic risk (126). Hence, the context under which high meat consumption occurred in hunter-gatherers varied significantly from what occurs in westernized populations. Animal based foods were almost always consumed fresh in conjunction with copious quantities of fresh fruits and vegetables. Even when vegetable intake was low or absent in these peoples, there is little evidence for an association of high protein, animal based diets with colorectal cancer. Prior to western acculturation, the Inuit may have consumed more than 95 % of their daily energy from animal and seafood (15), yet a comprehensive review examining virtually all historical and ethnographic data of these people prior to westernization was unable to document a single case of colorectal cancer (126). Should a high protein meat based diet initiate or promote colorectal cancer, then one might expect obligate carnivores such as cats to demonstrate high incidences of these malignancies. In, fact the opposite is true, and the rate of gastrointestinal tract cancers is quite low in domestic cats (128). In summary the case for animal based, high protein diets causing colorectal cancer, within the context of pre-agricultural diets, is weak.

 

Fonte: Protein Debate, Cordain vs Campbell.