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On a recent lecture tour through Northern Italy, I enjoyed the delicious Mediterranean diet in its many regional variations, from the Alto Adige region in the Dolomites, to Parma and Piacenza in the Emilia Romagna and to Riva del Garda in the Trento region. As always I was impressed by the simplicity and delicious taste of the dishes, embedded in the unique Italian lifestyle of close social interactions, and regular physical activity. On this trip, the idea of personalization of the optimal diet did not come to mind “in the real world” except during a session at the Italian Nutrition Society in Piacenza at which I gave a talk on this topic.

Humans in different regions of the world have adhered to diets followed for thousands of years without a perceived need for individualizations. Many factors such as food availability, agricultural practices, religious belief systems, and longstanding cultural traditions and genetic adaptations have resulted in stable, generally accepted diets for many regions in the world, such as the Mediterranean basin (as described in my recent cookbook, Interconnected Plates) Asia and Africa and in indigenous populations. With the emergence of chronic diseases, personalized diets developed as adjuvant therapies for different metabolic and genetic diseases, including celiac disease, type I diabetes or chronic kidney disease. Personalization in these cases meant to adapt the diet to a specific disease- related factors, and not to interindividual differences in the response to food.

“Traditional nutritional guidelines have attempted to address this challenge with population-wide recommendations for ‘healthy’ versus ‘unhealthy’ foods.”

The epidemic of chronic non-contagious diseases which has been unfolding progressively over the past 75 years, including type II diabetes, cardiovascular disease and neurodegenerative disorders, has created a new challenge to the field of human nutrition. Traditional nutritional guidelines have attempted to address this challenge with population-wide recommendations for ‘healthy’ versus ‘unhealthy’ foods. These often failed for various reasons, as seen by the continued global increase in the prevalence of obesity and the associated chronic non-contagious disease epidemic. As a response, the overall goal of personalized nutrition is to preserve or increase health by using genetic, phenotypic, medical, nutritional, and other relevant information about individuals. By using this approach, personalized medicine aims to deliver more specific healthy eating guidance  and other nutritional products and services.

Recent scientific advances, in particular in the field of microbiome science and bioinformatics approaches have led to the hypothesis that there may be no single, one- size-fits- all diet for a given population, and that differential human responses to dietary inputs may rather be driven by unique and quantifiable host and microbiome features. This trend towards dietary personalization is the result of four important developments: 1) Nutrition research that provides a better understanding of how diet affects health. 2) New technologies that enable better and continuous measurements of markers of individual health and fitness. 3)New analytical tools that interpret the massive amount of collected data and transform it into actionable information. 4) Personal nutrition integrates with the change in bioscience and public health programs towards prevention of disease.

“Microbiota-based nutrition is beginning to be utilized…”

Based on this hypothesis, it has been suggested that the integration of these person- specific host and microbiome readouts into actionable modules by machine learning approaches may complement traditional food measurement in devising diets that are of benefit to the individual. Microbiota-based nutrition is beginning to be utilized to predict variable clinical phenotypes or to guide personalized therapies in type II diabetes and metabolic syndrome as well as gastrointestinal disorders. Recent efforts in the development of personalized diets regulating blood sugar levels provide hope for further advancements in the control and treatment of disease. Even though the majority of data to date has come from correlational human, or from preclinical studies, a growing number of human studies suggest that personalized dietary programs may benefit healthy individuals as a means of disease prevention and weight regulation.

Initial attempts have focused on developing personalized nutritional approaches to patients with type II diabetes, a rapidly increasing component of the chronic disease epidemic. In a landmark study from the research team at the Weizmann Institute in Tel Aviv under the leadership of Eran Elinav, Ory Ben Yacov and co-investigator published a paper in the journal Diabetes Care in 2021 comparing postprandial blood sugar responses to a personalized dietary program (PDP), developed by integrating several parameters such as dietary habits, physical activity, and gut microbiota, with responses to a Mediterranean diet in a 800 person cohort. They reported that using personal and microbiome features was able to accurately predict the postprandial glucose response, a predictor of type 2 diabetes, and based on their findings concluded that personal dietary interventions successfully lowered post-prandial glucose levels.

“The gut microbiota composition remained person-specific throughout this trial and was generally resilient to the dietary intervention.”

In an earlier paper, published in Cell Metabolism in 2017, Korem and co-investigators from the same Israeli research group reported findings from a randomized crossover trial of two 1-week-long dietary interventions comprising consumption of either traditionally made sourdough-leavened whole-grain bread or industrially made white bread. The gut microbiota composition remained person-specific throughout this trial and was generally resilient to the dietary intervention. However, they found a statistically significant interpersonal variability in the glycemic response to different bread types. The type of bread that induced the lower glycemic response in each person could be predicted based solely on microbiome data prior to the intervention. Both interventions reduced the daily time with glucose levels >140 mg/dL and HbA1c levels, but reductions were significantly greater in the personalized diet group compared with Mediterranean diet group. No significant differences were noted between the groups in an oral glucose tolerance test performed with a continuous glucose monitoring device. Importantly, the significant group differences were maintained at 12-month follow-up. The observation of marked personalization in both bread metabolism and the gut microbiome, suggested to the investigators that understanding dietary effects requires integration of person-specific factors.

“The intervention resulted in greater reductions in TG concentration, weight, waist circumference and HbA1c, but not LDL-C.”

In the most recent publication on the effectiveness of a personalized nutrition program, by a group of investigators under the leadership Kate M. Bermingham and published in Nature Medicine in 2024, 347 participants, aged 41–70 years and generally representative of the average US population, were randomized in equal numbers to the PDP and a control diet. The PDP used food characteristics, individual postprandial glucose and triglyceride responses to foods, microbiomes and health history. The intervention resulted in greater reductions in TG concentration, weight, waist circumference and HbA1c (secondary endpoints), but not LDL-C. Other parameters, including blood pressure, insulin, glucose, C-peptide, apolipoprotein A1 and B, and postprandial TGs did not differ between groups. However, the PDP shifted the gut microbiome composition, as well as subjective feelings of hunger, energy and mood. Based on their findings, the authors concluded that a dietary program focused on personalized advice is more effective in reducing central adiposity and TG concentrations than standard dietary advice in generally healthy individuals.

In summary, scientific and analytical progress in nutrition and microbiome science has made it possible to design highly personalized diets, incorporating a large amount of objective and subjective personal data. However, the clinical benefit, cost effectiveness, practicability and compliance of these new approaches remains to be established. Despite the impressive progress, the most cost-effective approach to identify optimal diets for healthy people, for now is based on the concept of an individually adjusted Mediterranean-style diet, taking into consideration food allergies, intolerances and accessibility. In my opinion, this approach is supported by a large amount of scientific evidence and will remain the gold standard for an optimal diet for a while.