Claire Gaudichon: Stable isotopes to track dietary proteins in the body

Claire Gaudichon is a professor in Human Nutrition and leads the “Nutrition and Health” specialism for the Nutrition and Food Science Master’s at Université Paris-Saclay. She is also the director of the Physiologie de la nutrition et du comportement alimentaire (Nutritional Physiology and Eating Behaviour) laboratory - PNCA (Université Paris-Saclay, AgroParisTech, INRAE). For almost thirty years, she has concentrated her research on the issues of protein digestion, protein-energy metabolism and the quality of protein intake in humans through the use of stable isotope biomarkers in particular.

In 2018, after more than 15 years in managerial positions (team leader, deputy unit manager), Claire Gaudichon became the director of the PNCA laboratory. The laboratory’s work focuses on the consequences of fluctuations in protein intake on health. “I’ve been lucky enough within this laboratory to work around some of the key issues surrounding nutrition in my research. After having worked for nearly ten years on high-protein diets, I am now concentrating on exploring the quality of proteins (particularly plant proteins) within the context of sustainable nutrition, as well as on the methodological research required for this subject.” 

The manipulation of stable isotopes as a common thread

Although Claire Gaudichon graduated in 1990 as an agricultural engineer with a specialisation in animal science from the “Institut national agronomique de Paris-Grignon” (National Agronomic Institute of Paris-Grignon), she decided to embark on a CIFRE thesis on the digestibility of milk and yoghurt proteins in humans. “It was during this period that I discovered the use of stable isotopes as biomarkers for dietary proteins, which I went on to develop and which has become a common thread throughout my career,” recalls the researcher. Her career could have taken a completely different trajectory when, after completing her thesis, she joined the company Danone. “I accepted the position at Danone as I didn’t manage to start a post-doc in England as initially planned. I wanted to return to the academic world, but this experience in the private sector proved to be very enriching for me.” A year later, an opportunity arose to take up a contract teaching position within the Department of Human Nutrition at AgroParisTech, which Claire Gaudichon immediately accepted. “After having passed the competitive examination which allowed me to secure my teaching position, I was able to join the laboratory which would become the PNCA laboratory in 2002, and which I now manage.”

The issue of high-protein diets

In this unit, the aim of the research is to assess how variations in protein intake affect physiology, metabolism and dietary behaviour, and what the implications are for health. Since 1997, Claire Gaudichon has been focusing on the issue of high-protein diets which are currently an area of growing interest. She is particularly interested in the link between protein intake, metabolic adaptations and satiety in humans. She carries out a large proportion of her research on animal models. “Thanks to the rodent facility which the laboratory acquired when it moved to AgroParisTech, we have been able to study the long-term effects of a high-protein diet on rats - something which would have been difficult to do with humans,” she explains. This research has allowed her team to pinpoint certain beneficial effects of these diets on food intake and metabolism which do not have adverse effects on the major functions of the body. “However, we realised that, when applied to humans, these beneficial effects were not so important and that, in a context where protein is a resource to be preserved, it was not useful to over-consume it.” 

The shift to sustainable nutrition

The issue of the preservation of resources as regards nutrition started to emerge at the end of the year 2000 through calls for tenders focusing on sustainable nutrition. “At the time, I remember we were wondering how to integrate our research into these areas of sustainable nutrition, whereas today such issues dominate the laboratory’s work.” Claire Gaudichon gradually shifted her focus to addressing the quality of different sources of protein in humans. “I returned to my isotope tracers and intestinal probes in humans and refocused my efforts on the quality of animal/plant proteins.” This is illustrated by the fact that between 2012 and 2015, she worked on the digestibility of meat proteins according to how they are cooked as part of a sustainable food project funded by the French National Research Agency (ANR).  

Supporting protein transition

The question of plant-based proteins as a substitute for animal protein sources has become a major societal concern, both for environmental and ethical reasons. “After 2015, there was a growing trend towards dietary changes, diets which excluded certain types of food and, above all, the transition to a more plant-based diet. We therefore needed to acquire a lot of data on these subjects.” Since 2016, Claire Gaudichon has been coordinating a research project, again financed by the ANR, on the value of oilseed crops (sunflowers, rape, flax) as regards human consumption. “The laboratory is seeking to assess how far we can go in this transition. Personally, I’m not advocating the elimination of meat and animal products. I’m wary of any form of restraint on these highly complex issues for which it is important to have objective data on the impact on the health of individuals and populations.” 

The need for methodological innovation

“As research progresses, methods for assessing protein quality must also evolve,” points out Claire Gaudichon. This is for good reason. A few years ago researchers were content to measure the overall digestion of the protein, whereas today it is the digestibility of each amino acid which they are seeking to quantify. This is methodologically more complex and requires material to be recovered directly from the small intestine. On the recommendation of the Food and Agriculture Organization (FAO), techniques to measure stable isotopes in blood amino acids from a blood sample have been developed. The unit has invested in these analytical developments and is currently one of the few to master isotopic analyses of carbon-13, deuterium and nitrogen-15 in amino acids. “As a laboratory, we are the only ones to master both probe sampling of the ileum and this less invasive isotopic method, so we are working on its validation. This is all the more important as traditional methods, which are far too invasive, are unthinkable for vulnerable populations, people suffering from digestive disorders or the bariatric surgery patients I am currently interested in. I am therefore fully aware of the need to make progress on this methodological aspect as well,” she concludes.