Currently a professor at the Human Nutrition Biochemistry Laboratory at Institut Agro / INSERM in Rennes, a former ANSES expert and a member of the French Academy of Agriculture, Professor Philippe Legrand has just published Je mange donc je vis, comprendre la nutrition vers un nouvel omnivore (“I Eat, Therefore I Live: Understanding Nutrition Towards a New Omnivore”) with Caradine Editions.
A reflection on the science of nutrition, an introduction to the concept of the “new omnivore,” a return to the fundamentals of food, popularization, consumer understanding, the Nutri-Score, the risks of eliminating entire food groups, public health, and the new US dietary guidelines: in this interview, the expert offers a wide-ranging overview of the ideas at the heart of his new book.
The European Scientist: You have just published Je mange donc je vis, a title that nods to Cartesian philosophy. Are you calling for more rationality in nutrition? Has this science lost its reason?
Philippe Legrand: Science is losing ground in society: there is declining interest in the hard sciences, with physics struggling while psychology and sport are on the rise; fears and anxiety are amplified by social media, self-proclaimed experts and certain NGOs that promote their ideologies while presenting themselves as scientific authorities. On top of that, there is systematic suspicion toward official experts, such as those at ANSES, where I served, with links being confused with conflicts of interest, while NGOs are placed above suspicion.
In nutrition, it is even worse, because everyone has an opinion on it: it concerns each of us every single day. For example, if you say “delta-6 desaturase has low activity,” no one reacts. But if you say “the conversion of omega-3s into DHA is low,” people immediately object — “we can do without fish” — even though the two statements are scientifically equivalent.
The book offers a simple answer: if the scientific route seems too difficult, come in through common sense. Everyone can experience the effects of eating too much fibre or consuming too many calories. Nutrition is an applied, universal science, born out of the history of deficiencies, with millions of deaths avoided thanks to the discovery of essential nutrients such as vitamins and fatty acids. Now that undernutrition has almost disappeared from our well-fed countries, we indulge in endless introspection and pointless debates.
Today, we know how to feed a human being, an infant or an elderly person without leaving out anything essential. The problem is not a lack of data, but a lack of common sense and an overload of anxiety-inducing messages.
Too many laboratories are content with statistical correlations produced through modelling, which the media then turn into causal relationships, generating “nutri-anxiety” without solid foundations. Nutrition suffers particularly from this ambient irrationality.
TES: You define the “new omnivore” as a central concept in the book. What is it?
P.L.: Human beings have always been omnivores, as shown by the work of Marylène Patou-Mathis at the CNRS on the Paleolithic, by studies of the Middle Ages, and above all by the last three centuries of nutritional science, during which we have gradually identified and completed the list of essential nutrients. This is a scientifically established reality.
Yet omnivorism is now under attack for ideological reasons, whether linked to animal welfare or ecology. The “new omnivore” I propose incorporates the idea of evolution. Unlike rigid diets — vegetarian, vegan and so on — which impose a restrictive list and display a certain arrogance, as if to say “this is what you must eat and nothing else,” the omnivore has no closed list. The omnivore is open, adaptable and constantly questioning.
My formula is simple: “To be sure of missing nothing, you must eat everything.”
The new omnivore addresses legitimate questions. Can omnivorism be reconciled with ecology? And with animal welfare? Yes, by exploring greater diversity — seaweed, seeds, insects, reasoned plant-based eating — by making targeted reductions, for example in high-carbon-footprint beef, and by respecting the “social contract” with animals described by Francis Wolff. But it does so without dogma. It adapts, broadens its food spectrum, and seeks to correct the real deficiencies of the current French omnivore, including omega-3s, vitamin D and iron, which is lacking in one woman out of two.
The omnivore is the only scientifically open, and therefore adaptable, diet. Historically, it has helped us avoid pitfalls: cod liver oil, for example, helped prevent rickets while also correcting omega-3 deficiencies. Today, the goal is no longer revolutionary discoveries — miracle vitamins, as it were — but fine-tuned balances, such as dairy fatty acids that promote omega-3 conversion, and above all bringing life expectancy into closer alignment with healthy life expectancy, something the Japanese do better than we do.
Finally, it also incorporates evolutionary risk-taking: millennia-old adaptations, such as Asian women living without dairy or vegetarian Hindus, which arise from culture and selection, should not be confused with modern, abrupt ideological choices.
Philosophically, the new omnivore embodies openness, exploration and adaptation — the keys to keeping pace with evolution, preserving health and building a sustainable future.
TES: Your book reads almost like a novel while covering the fundamentals of nutrition: energy rhythms and expenditure, the digestive tract, macro- and micronutrients, mineral salts and more. Are you aiming to provide a complete overview of the science of food?
P.L.: It is more a book about the physiology of nutrition than about food science, but the key word remains “science.” The basic principles of physiology are essential: the body functions according to immutable realities. Essential nutrients matter, and energy takes priority over everything else. Take a child with protein deficiency: the body will prioritize energy for the heart at the expense of the muscles. If the child is poorly nourished, they waste away.
I approach these questions through nutrients — energy, carbohydrates, lipids, proteins, vitamins and minerals — in order to show both their completeness and their necessary interactions. The cell needs a little of everything, all at once, and it adapts remarkably well. A pregnant woman who lacks meat, for example, may develop specific cravings; in rats, the animal instinctively chooses the diet that supplies the amino acid it is missing. Physiology is powerful, but also highly adaptable.
The book is structured very simply. The first chapters deal with the omnivore and the new omnivore, then come energy, which is the basis of everything, the physiology of eating behaviour, with all the human biases that go with it — culture, taboos and so on — and finally cellular needs, broken down nutrient by nutrient. It is a bit like “Physiology for Dummies.”
The approach may seem professorial, but it is anchored in current debates and written with some humour. Each chapter incorporates the controversies of our time: animal versus plant proteins, the rehabilitation of fats, antioxidants, the concept of the food matrix and so on. The goal is to show the positive, solid reality of nutrition as a means of preventing disease and deficiency, far removed from fashions and approximations.
TES: You have an extraordinary ability to make science accessible. But do the metaphors you use ever make you fear some loss of precision?
P.L.: Yes, that is a very good question, and as old as the world, if I may say so. Anyone who popularizes simplifies, and anyone who simplifies introduces some degree of distortion. Right at the beginning of the book, I reflect on the ethics of popularization.
The challenge is to educate without boring, to simplify without distorting, to persuade without seducing, and to spark interest without overstimulating.
That is how I constructed the chapters: hard science first, then pedagogy to make it easier to understand, then an account of the debates, of what is poorly received or misunderstood, and finally each chapter ends by setting out the risks of moving away from the recommendations, now that the reader fully understands them.
TES: Unlike those who reduce food to colour codes, labels and prohibitions, you begin with complexity so that the reader can understand the underlying logic. Can we trust the intelligence of a well-informed individual to make the right choices? Is there any risk in doing so?
P.L.: I very clearly make that bet. Imposing constraints, as with the Nutri-Score, can be useful, just as a red traffic light is useful for safety, but it remains limited. It explains nothing about how the body works and does not cultivate biological understanding. It is a restrictive approach, often ideological or simplistic, far removed from the kind of exciting education that transmits real culture, in the same way that one might explain a painting or Victor Hugo.
A red light is necessary, but it teaches you nothing about asphalt, wheels or engines. Similarly, the Nutri-Score provides a relative qualitative indication, from green to red, but fails to convey the essential quantitative message: moderation, and quantity above all else. You can gain weight by converting carbohydrates into fat without eating any fat at all. Initially, its designers were trying to communicate effectively in a very small space: colour codes work better than abstract images of “stacks” or moderation. But this caricatures the message and neglects quantitative self-education, which is fortunately still handled by health professionals.
There is no risk in placing our trust in intelligence and knowledge. Faced with ideology and obscurantism, common sense — allied with science — reasserts itself. Everyone is both an eater and a patient. With chocolate, for instance, we all know when too much is too much; there is no need for a guilt-inducing colour code. This book is a step toward the general public through scientific explanation: “Listen to yourself, eat everything in moderation.” Everything is allowed, including the Nutri-Score, but it misses the quantitative dimension. Here, popularization meets common sense. You do not need studies to understand moderation and variety. I remain optimistic: informing people strengthens autonomy, far from purely restrictive or medicinal logics.
TES: The key message of your book seems to be: “Eat everything, and avoid elimination like the plague.” Can you explain this philosophy?
P.L.: “Eat everything” is not a fixed principle. It is an open-ended, ongoing process, synonymous with research and exploration. For the average person, this already means varying one’s diet; for society, it means constantly expanding the range of foods available to us: new seaweeds, molluscs, marine cultivation, insects and more. There is no exhaustive list, because omnivorism is evolutionary by nature.
Elimination, by contrast, should be avoided as much as possible. Allergy is a medical issue, and disgust is understandable, but eliminating entire food groups — no meat, no fish, no dairy products, or even no legumes or cereals — carries a level of risk proportional to the scale of the elimination. A healthy adult can cope with moderate and temporary elimination, such as ovo-lacto-pesco-vegetarianism, but becomes more fragile with age. Over the long term, it is not optimal for health.
This is even more true for the more vulnerable age groups, which still account for 80% of the population: pregnant and breastfeeding women, infants, children, adolescents in growth, very young adults and people over 65. For them, elimination is a very bad choice. They need to be omnivores even more urgently.
Eliminations are dangerous, including because of what we do not yet know. Evolution pushes us to broaden our food spectrum. Anyone who refuses to broaden it is already failing to optimize their health. So if we add further restrictions, for example lacto-ovo-pesco-vegetarianism, we must educate ourselves, monitor ourselves and often turn to supplements. In fact, the heaviest users of supplements are vegetarians.
Even the most conscientious omnivore does not have perfect nutrition, because they too lack what we still do not know.
TES: What public health measures would you recommend to curb the obesity epidemic in Europe? And are the new US dietary guidelines for 2025–2030 moving in the right direction?
P.L.: I am wary of overly directive guidelines, but absolute priority must be given to quantitative messages about energy balance — intake versus expenditure — and not only to qualitative ones such as the Nutri-Score. Obesity and overweight result from imbalance: the total calories consumed versus the total calories expended. Since the body converts carbohydrates, and alcohol as well, into fat, we should not fixate on lipids as the enemy. We should focus on total energy intake, without forgetting alcohol, and insist on a simple message: eat less, move more. The PNNS already says this, but it needs to become a real culture, not just a narrow focus on the idea that “fat is bad.”
The qualitative aspect, including the Nutri-Score, has its place when it comes to composite products, but it must not obscure what matters most: education about quantity and physical activity. That is what really regulates overweight and obesity, upstream of cardiovascular disease. It is too easy to blame only industry, parents, the genome or “the glands.” We must also, and above all, involve the consumer, without stigmatizing them, because with the understanding and support of the patient-consumer, you get much better results, as health professionals know.
As for the US 2025–2030 guidelines, I have not examined them in detail, but in truth we do not really need American recommendations. Our guidelines in France and Europe are far more refined, and have been for a long time. Still, it may be useful if they emphasize that elimination is not the answer, since meat is not demonized there in the way it can be in frameworks such as EAT-Lancet. In that sense, they align with European common sense and with the omnivorous nature of human beings. But they should not encourage greater consumption either.
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