The Personalized Diet Prescription: New science ends era of universal dietary guidelines

What is a healthy diet?

It’s hard to imagine a more basic question. For a sophisticated species that has been eating for a long time, we keep getting it wrong. A google search for “diets” yields over a billion hits. Usually the number of opinions on an issue is inversely proportional to the level of understanding. Recent research now promises an answer to this perennial question, specifically tailored to the individual asking.

The first thing one notices when studying traditional approaches to eating is how humans thrived on wildly different diets. East African pastoralists ate milk, meat and blood. Quechua living in the High Andes favored tubers. The !Kung in southern Africa used mongongo nuts as their staple. Seal provided the central ingredient for the Inuit of northern Alaska.

These diets are anything but balanced. Their success proves that there are no essential foods, only essential nutrients. However, the focus on macronutrients has also failed to solve the healthy diet riddle. Vigorous debate continues between the proponents of high/low carb, fat and protein regimens.

Groundbreaking experiments now suggest that the era of universal dietary recommendations will soon be a thing of the past. The key to a healthy diet appears to be defined by each individual’s unique microbiome, the bacterial community inhabiting our gut.

There are many more bacterial cells living in our gut than the total number of our own cells in our entire body. We are, so to speak, colonized. These gut microbes play a leading role in our physiology.

A growing body of evidence indicates that these bugs influence a wide range of things, from appetite and satiety to brain chemistry and longevity. Specific microbiomes are associated with inflammatory bowel disease, metabolic syndrome (prediabetes), asthma, depression, anxiety and obesity.[1 Manipulation of gut bacterial populations provides a novel therapeutic approach.

Gastric bypass has proven a very effective (and tremendously invasive and expensive) intervention for severe obesity and Type 2 diabetes. Until recently it was thought that the procedure was therapeutic because it caused a mechanical restriction of the gut and impaired calorie absorption. We now know that the operation alters the basic physiology of energy balance and metabolism in large part by changing the gut bacteria. In an extraordinary series of experiments, Lee Kaplan at Harvard University and Peter Turnbaugh at Massachusetts General Hospital demonstrated that transplanting bacteria had the same effect as the surgery.

Your microbiome is determined by age, genetics, geography, medication, stress and perhaps most importantly, diet. We never dine alone. When we feed ourselves, we are also serving the bacterial colonists in our gut. What they are fed defines which strains of bacteria thrive. This provides an unexpected variable in the diet — health connection.

We are just beginning to appreciate the health consequences of specific microbiome profiles. The propensity for obesity and its complications, type 2 diabetes, hyperlipidemia (high cholesterol or triglycerides) and insulin resistance, have been associated with identifiable bacterial populations.

Elevated blood sugar levels after meals represent one of the most pressing global health problems. Even glucose readings in the high normal range have been associated with inflammation, cardiovascular disease, dementia and future diabetes. Present dietary strategies focus on foods (calories/carbohydrate content), not individuals.

This approach has been of limited efficacy. Beyond very basic guidelines, the eat-this-not-that approach has not worked.

The assumption that if people follow standard recommendations they will lose weight and develop fewer chronic diseases is unfounded. Different people respond to the same foods very differently. This has been demonstrated most powerfully in identical twins.

In a recent study, foods that spiked blood sugar or fat levels in one twin did not in the other. While identical twins share nearly identical genomes, their microbiomes have only 37% in common. The overlap is 35% in unrelated individuals. This inter-individual variability necessitates the practice of personalized nutrition.

In a remarkable series of experiments involving 800 subjects and 46,898 meals, researchers found high variability between individuals in response to identical meals. The investigators analyzed the data and devised an algorithm integrating blood testing, dietary habits, body composition, physical activity and the microbiome. Their algorithm accurately predicted personalized glycemic response (rise in blood sugar levels after eating) to real-life meals.

More importantly, the algorithm provided dietary recommendations that significantly lowered blood sugar levels after eating. The new diet also resulted in consistent changes in the microbiome. Their findings suggest that personalized diets can prevent the spike in blood sugar that is associated with our epidemic of metabolic problems (inflammation, obesity, diabetes, cardiovascular disease) by identifying individual-specific dietary regimens.

In the not too distant future, analyzing one’s gut bacteria with shotgun metagenomics to predict the effect of specific foods and thereby design precision diets will be common practice.

The human gastrointestinal tract is one of the most densely populated ecosystems on our planet. In the same way that we appreciate the need to protect natural balances in the external environment, we must do the same with our internal biosphere.

Let the personal environmentalism movement begin.