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1. Protein intake- nutritional requirements to maintain tissue and body functions

Protein intake supplies precursors for protein synthesis and different nitrogen compounds, as well as substrates for energy metabolism. Important characteristics of the intake include its quantity, amino acid composition, the presence of bioactive peptides and the availability profiles of these compounds. Various studies have evaluated the impact of these characteristics on the assimilation and nutritional impact of proteins in different situations such as physiological normality, energy restriction leading to tissue loss (Chaston et al.et al. 2007), more general dysfunction (for example digestive defects, being overweight, metabolic syndrome) or in states of catabolic weight loss (inflammation, trauma and surgical intervention) (Biolo, 2013). Of particular interest is the consumption of diets rich or very rich in protein - achieved by a proportionally large intake of animal products- in order to control weight or body composition (Pedersen et al.et al. 2013). Our studies have looked at the impact of dietary protein on intestinal physiology and the composition and activity of the intestinal microbiota, whose state influences the health of the host (Pepper JW and Rosenfeld S. 2012; Lazupone et al. 2012; Costello et al.2012).( We have also investigated protein metabolism, inter-organ exchanges and metabolic conversion pathways (gluco- lipo- and ketogenic) in relation to tissue maintenance (intestine, muscle mass, bone mass), the regulation of energy reserves (adipose tissue, glycogenesis) and body homeostasis.

2. Protein intake- digestive and metabolic dysfunction

Research has also been undertaken by the Unit to determine whether manipulating the protein intake can contribute to bringing about or aggravating digestive and metabolic dysfunctions induced by risky nutritional or physiological conditions (diets rich in sugar and/or lipids, low levels of physical activity, for example). Nutritional guidelines that aim to prevent digestive and metabolic disorders have generally focused on the carbohydrate and fat content of the diet.  Less data is available with respect to protein, including certain amino acids that have roles as signal or active metabolite precursors and what little data wich remains ambiguous. Some data have suggested a preventive effect of the intake of protein or certain amino acids on markers of metabolic syndrome (Westertep-Plantenga et al.et al. 2012; Gannon and Nuttall 2010; Dong et al. 2011). By contrast, other studies have demonstrated the potential toxicity of certain bacterial metabolites at the digestive or whole-body levels (Macfarlane et Macfarlane, 2012; Nyangale et al.et al. 2012; Davila et al., 2013), the effects of certain amino acids (particularly of the branched-chain type) that might induce insulin resistance and diabetes (Tremblay et al. 2007; Zanchi et al. 2012,) and a risk of metabolic pathologies induced by perinatal exposure to elevated levels of protein or certain amino acids (Sarr et al., 2010; Oster et al., 2011; Koletzko et al., 2013; Hallam et al., 2013). The Unit's work focuses on these different phenomena and aims to measure synergistic or antagonistic effects between protein and other nutrients (simple sugars, indigestible or partially-digestible carbohydrates, lipids and certain fatty acids, in particular n-3). In general, polymorphism and other sources of inter-individual variability in response to different diets are also examined and accounted for.

3. Protein intake and the control of food consumption

The control of appetite by molecules acting on satiety is an important issue in the context of weight control strategies (Westertep et al. 2009). The role of protein is of growing interest, although the underlying mechanisms and the presence and persistence of effects in humans remain unclear (Fromentin et al. 2012). One related question concerns the control of protein ingestion and the role of homeostatic and reward mechanisms in controlling food intake and choice (Volkow et al. 2013)(Griffioen-Roose et al. 2012). We have investigated these processes by analysing the type of information transmitted to the brain via neural (the vagus nerve) and circulatory (hormones, nutrients) pathways (Tome et al. 2009 AJCN; Rasoamanana  et al. 2012) and by studying their influence on pathways involved in the homeostatic control of energy intake, as well as those involved in reward systems. This research takes account of the types of proteins, their interactions with other nutrients (such as lipids and fibre) and the structure/texture of foods. Inter-individual differences in sensitivity to weight gain are systematically observed in rats and humans given lipid-rich diets (who can be separated into fat sensitive or resistant individuals), or, as shown recently, in rats given a diet rich in carbohydrate (carbohydrate sensitive or resistant) (Nadkarni et al. 2013). In this context the laboratory also uses human and animal models to analyse differences in the sensitivity to the impact of protein on metabolism and satiety, taking account of differences in predisposition to obesity. Finally, as an extension to this work, we also use consumption to study the relationship between food choice, protein intake (quantity and quality) and compliance with nutritional guidelines