Five Questions Nutrition Science Still Can't Answer

Nutrition advice often sounds straightforward. Eat more vegetables. Get enough protein. Watch your sugar. Choose whole foods. But human biology is anything but straightforward.

Nutrition science has given us important guidance about how food affects health. But the closer researchers look, the more they see how much depends on the individual. The same meal can affect two people differently. Nutritional needs can change across the lifespan. And advice that works well for one person may not work as well for another.

At the UNC Nutrition Research Institute, we study those differences. Our researchers want to understand not simply what is healthy, but what works for whom, when, and why.

Here are five big questions nutrition science is still trying to answer and how NRI researchers are helping move us closer to the answers.

1. Why can two people eat the same food and respond differently?

Imagine two friends sitting down for dinner. On their plates are the same protein, carbohydrate, and vegetable. They eat the exact same meal at the exact same time.

One finishes the meal and feels perfectly fine, maybe even energized enough to head out for an evening walk. The other feels sleepy, bloated, uncomfortable, or hungry again surprisingly soon.

The meal was the same, but their bodies were not.

One person may experience a larger rise in blood sugar. Another may process fat differently. Their gut bacteria may respond differently to the meal. Genetics, age, sleep, physical activity, medications, hormones, and dozens of other factors can influence what happens after that first bite.

That variability drives NRI scientists to study nutrition at the individual level.

As NRI research specialist Walter Friday explains, “Two people can eat the same food, and one might get healthier while the other develops diabetes. Why? Because nutrition depends on your genes, your environment, your lifestyle, and your biology.”

Through clinical studies, metabolic measurements, genetic analysis, and other tools, NRI researchers examine why people respond differently to the same foods and behaviors. They aim to identify biological clues that could eventually help predict those responses rather than leaving people to discover them through trial and error.

2. How much of a nutrient does your body actually need?

Walk down the vitamin aisle, and the labels make nutrition look remarkably precise. A certain number of milligrams. A recommended daily value. A neat percentage telling you how much you should get. However, those numbers guide populations. Your body may not use a nutrient exactly the same way someone else's does.

Consider nutrients such as choline and folate. Genetic differences can affect the enzymes that help the body process and use them. As a result, two people who consume the same amount may not achieve the same nutritional status.

NRI researchers are working to understand why.

“Essential nutrients like choline participate in several critical pathways in the body, but requirements change across the life course and differ between individuals,” said NRI Assistant Professor of Nutrition Isis Trujillo-Gonzalez, PhD. “Choline is a good example of how nutrition science is beginning to move beyond general recommendations toward more precise guidance.”

Trujillo-Gonzalez searches for measurable biological markers that could help researchers determine whether someone actually consumes enough choline rather than relying solely on what that person reports eating.

Other NRI researchers approach the question through genetics. Natalia Krupenko, PhD, associate professor of nutrition, studies how genetic differences change the way the body processes folate.

“Science shows us that ‘more of a good thing’ is not always better,” Krupenko said. “When we recommend the same vitamin intake for everyone, we may overlook people whose enzymes process nutrients differently.”

Together, research like this could someday help move nutrition guidance from “Most adults need this much” toward something much closer to “This is what your body needs.”

3. What is happening inside your gut after you eat?

You eat a bowl of blueberries. To you, that may be the end of the story. Inside your digestive system, however, an enormous community of microorganisms gets to work.

Trillions of bacteria and other microbes live in the human gut, and they interact with the foods we eat in ways scientists are still working to understand. They help break down compounds in food, produce metabolites, interact with the immune system, and may influence how the body responds to a meal or dietary pattern.

And no two microbiomes are exactly alike.

NRI faculty member Katie Meyer, ScD, MPH, studies connections among diet, health behaviors, and the gut microbiome. Her research explores whether microbes living in our digestive system may help explain some of the benefits associated with healthy eating and physical activity.

“These health behaviors have been associated with gut microbial features,” Meyer said, “and it is possible that protective effects of diet may, in part, operate through the gut microbiota.”

NRI researchers examine biological samples alongside dietary, metabolic, genetic, and health data to connect what a person eats with what happens inside the body afterward.

The larger question is not simply, “Which bacteria are there?” It is, “Which differences matter, and can we use that information to improve health?”

4. Does the same food matter differently at various life stages?

Think about how dramatically the body changes over a lifetime.

Before birth, the brain and organs form at remarkable speed. During childhood and adolescence, the body grows and develops. In adulthood, metabolism, hormones, activity, and health status continue to change. Later in life, maintaining muscle, mobility, cognition, and metabolic health becomes increasingly important.

So, it makes sense that nutrition may not have the same effect at every stage.

A nutrient that plays an especially important role during fetal brain development may serve a different purpose decades later. A dietary intervention that works well for a younger adult may produce a different response in an older one.

NRI scientists study these questions across several research programs, including maternal and fetal nutrition, childhood brain development, metabolism, chronic disease, cognition, and healthy aging.

NRI research on choline offers one example. Nutrient requirements can differ not only from person to person, but also across the life course, with particularly important windows during pregnancy and brain development.

Other NRI studies examine how combinations of diet and physical activity may support cognitive health as people age. Researchers are investigating blueberries, exercise, the gut microbiome, and age-related memory decline to better understand how these factors may work together.

The question is not simply what people need, but when nutrition matters most and whether the right intervention at the right stage of life can change someone's long-term health trajectory.

5. If scientists know what helps, how do we make it work in real life?

Knowing that exercise is good for you is one thing. Getting up and doing it after a long workday is another.

The same is true of nutrition. A perfectly designed eating plan does little good if it costs too much, requires too much time, remains difficult to access, or simply cannot fit alongside work, family, travel, stress, and everything else that fills a normal week.

That is why modern nutrition science cannot stop at identifying which foods or nutrients influence health. Researchers also have to understand human behavior.

NRI faculty member Rachel Goode, PhD, MPH, LCSW, studies eating behavior and develops interventions designed to work within people's actual lives.

“Emotional eating is rarely about willpower,” Goode explains. “Precision nutrition helps us understand not only what people eat, but why.”

That distinction matters. Stress, culture, access, environment, habits, and the demands of everyday life all shape nutrition choices.

Other NRI researchers explore how technology can provide support at precisely the right time. Digital tools, wearable devices, personalized messages, and adaptive interventions can help researchers learn not only what works, but what works for a particular person in a particular moment.

NRI Director Deborah Tate, PhD, explains, “Information is key, but it’s not sufficient. Structured programs with personalized recommendations and just in time support outperform information alone.”

Because one of the biggest unanswered questions in nutrition may ultimately be one of the most human:

How do we make the healthy choice work in someone's actual life?

We may not have every answer yet. That is the work. The unanswered questions in nutrition do not mean the science has failed. They point us toward the next discoveries.

At the NRI, scientists use genetics, clinical research, metabolomics, behavioral science, microbiome research, technology, and other approaches to understand why nutrition affects each of us differently.

The goal is not to throw out everything we already know about healthy eating. It is to make that knowledge better. More precise. More personal. And, ultimately, more useful to the person sitting down at the dinner table.