The impact of dietary protein and carbohydrates on gene expression in a generalist insect herbivore

ABSTRACTNutrition fuels all of the physiological processes that animals rely on for survival and reproduction. Of all the nutrients that are required, dietary protein (p) and carbohydrates (c) have a primary role. Insect herbivores are capable of detecting amino acid and sugar concentrations in plant tissue via chemoreception and regulate their intake of these two macronutrients to reach an optimal protein:carbohydrate, or p:c, ratio, termed an intake target. A multitude of studies have shown that the two nutritional factors that have the strongest impact on insect survival and performance are dietary p:c ratio and total macronutrient content, which is the proportion of the diet made up by p and c and a proxy for energy content. Variations in these two dietary traits have strong unique and interactive effects on many insect life history traits, yet the mechanisms that mediate these effects are not well understood. While many studies have documented the effect of host plant usage on gene expression, differences in plant secondary compounds between plant species and tissue types have confounded efforts to understand nutritional contributions to transcriptional changes. This study is the first to document the transcriptional effects of dietary p:c ratio and total macronutrient content in a phytophagous insect, the polyphagous moth species Helicoverpa zea. Our results show that changes in dietary p:c ratio produced a rather limited transcriptional response, while total macronutrient content had more dramatic effects on gene expression. The invariable expression of many metabolic genes across diets also suggests that H. zea larvae employ a strategy of constitutive expression to deal with nutritional imbalances rather than diet-associated changes in expression. We also observed many similarities in the transcriptional response to diets that varied from the intake target diet in different ways (c-biased, p-biased, increased energy content). This indicates that similar mechanisms are used to deal with nutritional imbalances regardless of the direction of the imbalance, and further supports the importance of nutrient regulation.HIGHLIGHTSVariations in plant macronutrients can have strong impacts on herbivore fitnessDespite a wealth of studies documenting the physiological effects of macronutrient nutrition, underlying mechanisms are still ambiguousDiet protein-to-carbohydrate ratio had an unexpectedly small impact on overall transcription, while total macronutrient content had a stronger effectThe transcriptional response to dietary variations away from an optimal diet was similar across diets that varied in different ways (carbohydrate-biased, protein-biased, more concentrated)Maintaining consistent consumption and constitutive expression of digestive enzymes across diets that varied in macronutrient profiles led to compensation for the most limiting dietary macronutrient

Developing food-based dietary guidelines for 1–5 year old children: a protocol for use in population health globally

Early childhood is a well-established critical period for growth and development, potentially impacting on life-long health. Healthy dietary habits formed during the transition from a predominantly milk-based to a food-based diet track into later life. Globally, there is no established process for developing food-based dietary guidelines (FBDG) for 1–5 year old children. This study aims to establish a protocol for developing FBDG for 1–5 year old children for use in population health globally.Foods consumed by > 10% of consumers aged 1–5 years (at each eating occasion) were identified by secondary analysis of the Irish National Pre-School Nutrition Survey (NPNS; 2012). Consultations were held with registered dietitians to update the NPNS data and reflect current dietary habits. Dietary modelling, based on healthy eating principles, was conducted on boys (n30) and girls (n30) at five percentiles on the World Health Organisation (WHO) growth charts (0.4th; 25th; 50th; 75th; 99.6th) and at six age time-points (1y; 1.5y; 2y; 3y; 4y and 5y). Intake targets were identified for energy, macronutrients and 6 key micronutrients. For those with inadequate nutrient intakes, key contributing foods were identified and used in the modelling.Dietary modelling yielded 640 four-day food intake patterns. For 1–3 year olds, especially those < 25th growth percentile, iron was identified as an at-risk nutrient as the intake target was not achieved. For all 1–5 year olds, vitamin D was identified as an at-risk nutrient. Red meat and iron-fortified cereal (> 12mg/100g) were identified as key contributors to iron intake. A combination of red meat (30 g, 3 days/week) and iron-fortified cereal (30 g, 5 days/week) resolved inadequate iron intakes for 1–3 year olds, except those < 25th growth percentile. For those children, the additional inclusion of 4 mg iron from use of iron-fortified milk (1.2mg/100mL) or a low-dose iron supplement (7 mg, 4 days/week) resulted in adequate iron intakes. For all children aged 1–5 years, vitamin D intakes improved by including a daily 5μg vitamin D supplement, but still did not reach the intake target.Worldwide, significant resources are invested in assessing growth and development of 1–5 year olds. This study provides a protocol for developing FBDG to meet nutritional needs of 1–5 year olds at various growth parameters (age and percentiles), using WHO charts. This enables the provision of practical food-based interventions to nutritionally vulnerable children. Using national dietary data, this approach can be applied for developing FBDG specific to a country's needs.

Beyond Nutrients

This chapter demonstrates that the conventional categorization of food components into “macronutrient,” “micronutrient,” “toxin,” “medicine,” and so on works well from a distance, but on greater magnification, the boundaries between these categories blur. When viewed through a geometric lens, however, a new structure falls into focus, which emphasizes not the chemical identity of the food component but the target-like perspective of optimal intakes. The chapter structures its argument around three interlinked themes: (1) the distinction between “nutrient” and “toxin” is fuzzy and sometimes imaginary; (2) the phenomenon of “self-medication” in nonhuman animals can involve compounds that are conventionally classified either as nutrients or natural “medicines”; and (3) even when a compelling case can be made for distinguishing a “toxin” from a “nutrient,” the biological impacts of the toxin depend on the levels of nutrients in the food relative to the intake target for those nutrients.

The Geometry of Human Nutrition

This chapter explores the methods of nutritional geometry on the modern human diet, applying the geometric approach to an analysis of a key aspect of human nutrition: the topical subject of human obesity. This analysis leads to three conclusions. First, the available evidence suggests that humans can regulate macronutrient intake, but that the intake target contains a built-in component for fat storage. Failure to use this stored fat promotes obesity. Second, when humans are faced with imbalanced diets, protein intake is prioritized. When the ratio of protein to carbohydrate in the diet is lower than optimal, it is easier to gain the required amount of protein—and hence overconsume fat and carbohydrate—when foods are high in energy density, present in great variety, and easily available throughout the day. Lastly, the regulation of nutrient intake in humans has evolved “assuming” a higher level of energetic expenditure than is usual today.

Integrative models of nutrient balancing: application to insects and vertebrates

We present and apply to data for insects, chickens and rats a conceptual and experimental framework for studying nutrition as a multi-dimensional phenomenon. The framework enables the unification within a single geometrical model of several nutritionally relevant measures, including: the optimal balance and amounts of nutrients required by an animal in a given time (the intake target), the animal's current state in relation to these requirements, available foods, the amounts of ingested nutrients which are retained and eliminated, and animal performance. Animals given a nutritionally balanced food, or two or more imbalanced but complementary foods, can satisfy their nutrient requirements, and hence optimize performance. However, animals eating noncomplementary imbalanced foods must decide on a suitable compromise between overingesting some nutrients and underingesting others. The geometrical models provide a means of measuring nutritional targets and rules of compromise, and comparing these among different animals and within similar animals at different developmental stages or in different environments. They also provide a framework for designing and interpreting experiments on the regulatory and metabolic mechanisms underlying nutritional homeostasis.