Measuring What We Eat

Food gives us the energy to move, and nutrients to help us grow. Nowadays, many people are interested in what they should eat to prevent disease and live long and healthy lives. But how do we know which foods are healthy? To tell people what they can eat to stay healthy, researchers must first understand what healthy and unhealthy people eat. Currently, we do this by asking people questions about what they eat, how much, and how often they eat various foods. We could ask them what they ate yesterday, or what they normally eat. We can also ask people to write down exactly what they eat, like a food diary. To find out about what people normally eat, we often use a questionnaire with questions like, “How many times do you eat fish in a month?” Collecting information about foods in a person’s diet over a certain period of time is called a dietary assessment [1]. Researchers link this information with food composition tables (which contain information about the types and amounts of nutrients inside a particular food, including carbohydrates, protein, fat, fiber, sugars, salt, vitamins, and minerals) to calculate the amount of energy and nutrients that person gets from his or her diet.

Investigating the Link Between Food and Health

After figuring out what and how much people eat, researchers who study nutritional epidemiology want to know if diet (or a certain food or nutrient in the diet) influences the chances of people getting sick. These researchers are like detectives: they ask the right questions to gather the evidence (data), and they use it to figure out if a food is linked to a crime scene (the disease) (Figure 1). Imagine that you are a researcher given the task of figuring out whether eating fish can help prevent heart attacks. What would you do? First, you might want to gather information from many people, asking them if they eat fish and how often (dietary assessment). Second, you would need to find out whether those people have had heart attacks (health assessment). You may also want to collect information on each person’s age, sex, and job, as this information could give you clues about the people’s health or which foods they tend to choose. You could also collect blood samples to measure early signs of a heart attack, like blood cholesterol levels. Then, you could analyze the data using math to see if there are differences in the health of people who eat a lot of fish and people who eat very little fish. If you do this, you are doing an observational study. Researchers in nutritional epidemiology look at data collected from lots of observational studies to make links between foods and health. The government can then use this information as evidence to help create dietary guidelines, which are a set of recommendations for the public on what they should eat if they want to be healthy.

Mistakes and Missing Information Lead to Confusing Evidence

This may sound like a straightforward path: collect information on what people eat and their health, see if there is a link between what people eat and whether they get a certain disease, and use this information to advise people on what to eat. But unfortunately, it is not so simple. Often the evidence researchers find does not seem to fit together very well, and it is difficult for researchers and the government to decide which type of diet to advise. One reason for this difficulty is that the dietary assessment used in these studies relies on people telling researchers what they ate, which is not always a good strategy. Can you remember exactly what you ate yesterday? How about last month? Sometimes, people simply forget what they ate. Estimating how much they eat can be even more difficult, because different people might have different ideas about what portion sizes of various foods should be. Your idea of one piece of fish may be much larger or smaller than someone else’s! Other times, people may lie about eating certain foods because they feel embarrassed about what they ate. We often underestimate how often we eat junk foods and overestimate how often we eat healthier foods like fruits and vegetables. In all these situations, scientists’ dietary data already contain a lot of mistakes, even before these data are linked to disease data.

Another reason for the confusing evidence about which foods to eat is that researchers actually know very little about what is inside of foods. Each food is made up of many different compounds that are like the building blocks of the food (Figure 2). When we digest food, some of these building blocks are further broken apart into small compounds called metabolites. Currently, food composition tables contain information on about 150 compounds that are important nutrients in the human diet, including carbohydrates, protein, fat, fiber, sugars, salt, vitamins, and minerals [2]. But there are over 26,000 compounds found in foods, and this number is still growing! Researchers also do not know very much about the many metabolites that are generated from the compounds in foods once they are eaten. Each of these compounds and their metabolites can have its own effects on human health.

New Tools That Can Improve Our Understanding of Both Foods and Health

Recently, researchers have discovered some new ways to uncover more clues about how foods affect health. As a group, these are called omics tools (Figure 3A). One of these tools is called metabolomics. Using laboratory equipment, researchers can measures thousands of metabolites from a food at once! Metabolomics can help us to get a better idea of which foods are healthy or unhealthy. Researchers can also use metabolomics to measure metabolites in the human body, such as in the blood, urine, hair, or even toenails! Some of these metabolites can act as biomarkers, which is short for biological markers. Biomarkers are signals in the body that can help researchers understand both food intake and disease. Biomarkers of food intake can be used to help confirm what people ate, and correct mistakes in dietary assessment in our observational studies [1]. Docosapentaenoic acid (DHA) is an example of a food biomarker (Figure 2). It can be found in the fat tissues of people who eat fish [3].

But It Is Complicated

Sometimes, two people could eat the same things, but one person could be healthier than the other. How can this be? Since we are all unique, each person can have a different health response to the same foods. This is partly influenced by a person’s individual genes. Another tool called nutrigenomics can help researchers better understand how diet influences which genes are turned on or off, and also how genes can affect the way a person’s body reacts to foods and nutrients. Foods and genes are constantly playing a poking game—foods that “poke” a person’s genes can change which genes are turned on or off and impact health, while genes can “poke” back to influence the body’s response to a food.

Different people also have different microorganisms living in their bodies. After food is chewed and swallowed, it travels down the digestive tract to the gut. There, the food is greeted by millions of microorganisms that can help to further break down the food. The whole community of microorganisms in the gut is called the gut microbiota. Each person has a unique gut microbiota. Researchers can measure the microbiota (and their genes) using a new tool called metagenomics. Since these microbes break down foods, they can also produce metabolites, which can affect health. The gut microbiota can even affect a person’s risk of getting diseases such as a heart attack [4].

Every person is unique. Our uniqueness is why dietary recommendations for the public sometimes do not work for everybody. By using omics tools in research, researchers can find out how people respond differently to the foods they eat. Then, we can help individuals or groups of people who are at risk for certain diseases, such as heart attacks, by offering them personalized nutrition advice (Figure 3B) [5].

The Future of Food and Health Is Personalized!

It is an exciting time for researchers! We have always known that the human body is unique and complex, and that finding the link between food and health is not simple task. But with new omics tools, we are starting to learn more about the role of various food components, as well as genes, microbiota, and metabolites, for preventing certain diseases. We still have a lot of work to do, especially in regards to how diets should be personalized and making sure that personalized nutrition is available to everyone, but there is a lot of promise. Imagine going into a grocery store in the future, where you can choose foods off the shelves based on your age, body weight, and maybe even your genes or gut microbiota—how cool would that be? The challenge in the future may be finding the right balance, so that we can eat the foods our bodies need to eat to stay healthy, but still have the joy of sharing a meal with our friends and family.

Glossary

Nutritional Epidemiology: ↑ A field of research that studies the relationships between a nutrient, food, or diet and the health of a large population of people.

Metabolites: ↑ Small compounds that are produced when the body breaks down foods or larger compounds in the body. Some metabolites are necessary to provide energy, or to maintain health.

Metabolomics: ↑ An area of study that measures all of the small molecules (metabolites) in our foods and in our body.

Biomarker: ↑ A signal that researchers can measure in the blood or other body fluid or tissue that can tell them more about which foods people ate, and if people’s bodies are working well.

Nutrigenomics: ↑ An area of study that analyzes the relationships between genes, diet, and health.

Gut Microbiota: ↑ The entire community of microorganisms (including bacteria) that live in the gut.

Metagenomics: ↑ An area of study that analyzes all of the genes of the microorganisms from a (bio)sample. Metagenomics can be used to analyze the gut microbiota from a fecal sample.

Personalized Nutrition: ↑ A field of research that aims to find the best diet for each unique person, to keep that person healthy or help him or her prevent, manage, and treat disease.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.