Precision Nutrition: The Merger of Nutrition and Medicine By Tim Hlavinka, MD

Precision Nutrition:

The Merger of Nutrition and Medicine

By Tim Hlavinka, MD

"Let food be thy medicine, and medicine be thy food."

–Hippocrates

It was the Spring semester of 1979 and I needed another "hard science" class to fulfill medical school application requirements. I’d had enough of Organic and Biochem for one pre-med lifetime, so I perused the class handbook and stopped at Nutrition Science 101. Why not? It qualified and I wanted to learn about nutrition, as my career plan at that time was to become a pediatric surgeon. I thoroughly enjoyed learning about calorie requirements and vitamins and minerals and their physiology and impact on metabolism. Nutritional therapy at that time was directed toward easily phenotyped diseases such as phenylketonuria, or classic deficiency states such as pernicious anemia. It was fortuitous to have that background knowledge in med school as I went through Biochem and Pharmacology. In residency, nutritional advances such as TPN and enteral feedings were being developed and I tackled those with alacrity. Physicians' approach to nutrition seemed to stop at disease states and not approach healthy eating and a healthy lifestyle. I propose that nutritional and dietary advice should be incorporated into all of our therapeutic interventions—this is not the future but the present. The concept of Precision Nutrition has been coined to designate the use of personalized nutritional approaches for prevention and management of disease. The discipline is in its infancy. Much work remains to create an integrated, interdisciplinary framework that in-

corporates clinicians, nutritionists, exercise physiologists, food resource personnel and life coaches, but much has been done.

The bioinformatics pillars of precision nutrition include genetics, dietary habits, food behavior, physical activity, metabolic variance and the gut microbiota. The goal is the design of tailored nutritional recommendations to prevent and treat. Although large design trials have been few in the field, they are not lacking, and much observational research has been collected.

Numerous genetic variants and polymorphisms have been identified to be active in the heterogeneous metabolic response to nutrients and specific diets. With the explosion of at-home genetic screening, many private sector laboratories offer customized dietary recommendations based on genetic markers. While this approach is straightforward, it fails to recognize the complexity of the contributing factors to our variance in metabolism. The individual genome remains a target for personalized approaches to nutrition, but solutions based simply on genetic codes are few. The interplay between genetics and environment is axiomatic.

Dietary habits may seem self-evident, but for the discipline of precision nutrition, it refers to the quantity and variety of nutrients; macro- and micronutrients. Limitations of quantification of intake have perplexed nutritionists for decades. Research instruments are few and cumbersome and face the dilemma of self-reporting bias. Similarly, adherence to dietary measures remains a difficult-to-quantify behavior.

If dietary habits are "what" we eat, then food behavior is "how" we eat. This field looks at frequency, timing and relative proportion of total intake over a given time cycle. It is also known as "food style monitoring." Included in this field is the concept of Circadian rhythms and their impact on metabolism, highlighted by the search for the optimal manner of intermittent fasting.

The role of physical activity in metabolic balance is also axiomatic. Precision nutrition, however, attempts to see beyond the obvious need for increasing the total level of METs. It attempts to arrive at the type and timing of physical activity and its relation to intake to achieve more metabolic bang for the exercise buck. It also explores the phenomenon of epigenetics and the relationship between exercise, diet and the expression of multiple atrisk genes for obesity.

Deep phenotyping is defined as the precise and comprehensive analysis of phenotypic abnormalities in which the individual components of the phenotype are observed and described. Assessment of the impact of a given nutritional intervention requires accurate and well-defined disease stratification. For instance, a trial looking at outcomes measuring only the traditional risk factors of hypertension, dyslipidemia, BMI and inflammatory markers would be better defined if body composition by DEXA, echocardiography, ocular pressures, fundus exam and spirometry were also included.

Metabolic variance has on its surface the obvious reference to how and why individuals vary in their response to the same dietary measures. However, the field goes beyond to include the rapidly emerging arena of metabolites of nutrients and the creation of biomarkers to identify the impact of these metabolites on the body's systems.

From malabsorption syndromes to its impact on the immune system, gut microbiota has seen an explosion in research. The precise interplay between food intake and its effects on enteric microorganisms is further defined by studies that show specific dietary alterations changing the gut microbiome and leading to disease. Therapeutics for these entities have remained elusive.

We live in an obesogenic society and changing diet and lifestyle has proven challenging for most of our patients. The wealth of literature that speaks to vast improvements in outcomes with weight loss is an overwhelming reminder to us that we are our patients' advocates in the journey to health. From Anesthesia to Vascular Surgery, all specialties have literature supporting this intervention. Carry this with you—the loss of a single Kg of weight decreases the relative risk of diabetes by 16%. It is possible to make that intervention with every patient at every visit and not change anything but the course of a human life.

As more is recognized about the benefits of dietary and lifestyle changes, the need for an integrated, comprehensive approach utilizing the multiple stakeholders in the field of nutrition science looms large. We rely on our colleagues in nutrition, food resources, personal training and life coaching to produce the outcomes long sought by a nation suffering from an epidemic of obesity. Let us learn from our colleagues so that we can have the true "stakeholders," our patients, achieve the health outcomes they richly deserve.

Tim Hlavinka, MD is a Urologist in San Antonio, and is Medical Director of Vidamor Medical in Boerne. He is a member of the Bexar County Medical Society.