Widening the horizons of ‘evidence’: Nutrition and disease in ecological perspective

Nutrition science draws on human, animal and tissue studies. Nutritional epidemiology faces four basic methodological difficulties: (i) the diet is a complex exposure; (ii) dietary intake is difficult to estimate; (iii) the biological impact of diet is often age / stage-dependent (affecting choice of study design and duration); and (iv) reductionist assumptions are often inappropriate - whole diets may be more important than specific nutrients in determining health risk. Beyond these research challenges lies a penumbra of other questions. For example: What health risks result from intensified methods of food production? What are the global and local environmental consequences, and resultant health risks, of the escalating demand for food (driven by population size and changing consumer preference)? Arising from the above are questions about the range and quality of evidence that is appropriate within the broad field of 'nutrition science'. Those issues include consideration of: 1. The health consequences of integrated whole-diets (Mediterranean, 'PolyMeal', low GI diet, etc.) versus seeking classic, atomistic, evidence of risks / benefits from specific nutrients or foods. 2. Life-course dietary data versus short-term controlled-trial dietary interventions. The former provide low-quality but high-relevance data; the latter provide high-quality but often low-relevance (short duration, age / stage-specific) data. 3. Palaeo-anthropological and historical data on the types of diet that have prevailed during long, formative, periods of human biological evolution - e.g. palaeolithic diet v. modern industrial diet. What profile of nutrient intake are we humans best equipped to consume? 4. Evidence of collateral human health risks from modern modes of food production, distribution and availability. For example: extravagant use of antibiotics in commercial high-volume livestock production, resulting in antibiotic-resistant bacteria chemical contamination of factory-farmed foods: pesticides, heavy metals, hormones intensified methods of livestock production, leading to health risks such as human variant Creutzfeldt-Jacob disease (due to 'mad cow' disease, or bovine spongiform encephalopathy), Nipah virus disease and avian influenza diversion of grain as livestock feed, versus availability as food for Third-World populations: a source of food deprivation, malnutrition and its health consequences contribution of forest clearance and livestock production to greenhouse gas emissions, climate change and its adverse health impacts (now and, more so, in the future) adverse health impacts of loss of small-farmer livelihoods as food-producing conglomerates and supermarket chains consolidate 'production units'. (This applies in both high- and low-income countries.) Items 1 and 2 suggest that we can gain useful, integrated, information from a synthesising analysis of whole diets as the determinant of health risks / benefits. Item 3 helps us understand how we have deviated from the nutrient profile of the human ancestral diet. Item 4 underscores the other ecological and socioeconomic risks that we take when we intensify food production and treat food primarily as a (profit-making or foreign exchange-generating) commodity rather than as a life-sustaining dividend from the natural world and its food-producing (and often human-managed) ecosystems.