We all know people who follow calorie-restricted diets without losing weight or others who always have room for dessert but never gain an ounce. When scientists finished mapping the human genome, many felt that genes held the answers to this conundrum. Researchers identified the first gene variant linked with obesity in 1997; subsequently they discovered more than 50 additional variants impacting weight.

Unsurprisingly, diets based on eating for your genes looked promising. Put to the test, however, they didn’t measure up. While genes influence how your body utilizes food, research shows that genes explain only 5 to 10 percent of your risk for developing any chronic illness, including obesity. Other factors are more significant, including a part of your body known as the epigenome.

Genes Are the Starting Point

Your epigenome and its related phenomenon gene expression are central to personalized nutrition. Researchers have long tracked biomarkers like blood pressure and blood glucose to predict disease development. Now, genetic variations (SNPs) can be added to the mix.

Here’s how it works: Your genes are not static. They react to impacts like nutrition and lifestyle by changing their expression. These deviations affect various bodily processes, including how you utilize calories.

Nip Potential Problems in the Bud

Your genes are ground zero for gene expression and knowing your DNA can help to prevent conditions before they develop. For instance, studies show that if you are genetically predisposed to developing obesity, a sedentary lifestyle and high intake of ultra-processed foods are more likely to tip you over the edge.

Restore Healthy Gene Expression

Nutri-epigenomics, the study of how nutrients affect gene expression, is an emerging science. Researchers are actively investigating "epiregulators," components of food that promote healthy patterns of gene expression.

Aberrant patterns of gene expression are linked with numerous chronic diseases. You can inherit them from your parents and grandparents or they can develop over time in response to an unhealthy lifestyle. The good news is these "epigenetic modifications" can be revamped by positive improvements like exercise and a nutritious diet.

Nutrients Support Gene Expression

Thanks to epidemiological studies we’ve known for decades that nutritious foods help to prevent disease. One example is the connection between high intakes of cruciferous vegetables and lower rates of certain types of cancer. Now scientists are identifying biological mechanisms responsible for these results. For instance, sulforaphane, a component of cruciferous vegetables, has been shown to support healthy epigenetic patterns in certain genes linked with cancer development.

Sulforaphane is just one of many health-promoting chemicals found in foods. Numerous nutrients also interact with genes to support positive patterns of gene expression. Knowing your genetic variants can help you to choose foods that will benefit you most.

One Size Doesn’t Fit Everyone

As noted, high blood sugar is a long-standing biomarker linked with a multitude of diseases. One reason is its potential to disrupt the expression of numerous genes.

For many years, we’ve been using a tool known as the glycemic index (GI) to measure the impact of food on blood glucose levels. Certain foods apparently cause them to rapidly spike, increasing the risk for diseases like diabetes. Traditional wisdom suggests that avoiding these foods is a good strategy for maintaining metabolic health.

However, scientists at Israel’s Weizmann Institute of Science found that the GI may be a poor predictor of whether a food will jump-start blood sugar. Their research showed that even when people ate identical foods their blood sugar rose at very different rates. They also found that some low GI foods—for instance tomatoes—could spark a blood sugar surge in some, while high GI foods like sugary treats didn’t stimulate a similar response in others.

Gut Bacteria Pull Metabolic Strings

While these scientists linked some of these differences to lifestyle, their research also suggested that the subjects’ gut bacteria (microbiome) played a role.

Environmental factors like diet and lifestyle are major factors in shaping your microbiome. (Research shows that people who eat more than 30 different plant foods a week have healthier microbiomes than those who consume 10 or less.) However, genes seed the microbial landscape and genetic variants can influence which bacteria will flourish. Among their many functions, gut bacteria interact with each other, your genes, your diet and your lifestyle to shape your metabolism.

Your Microbiome Influences Your Response to Food

The microbiome is the focus of the PREDICT study, an international research project investigating how food affects disease development. More than half of the participants were identical twins. While they share the same genes, the twins had less than half (37%) of the same microbes. When their glucose, insulin and blood fat responses were measured, the subjects demonstrated very different responses to eating identical foods. Their levels of inflammation also differed dramatically.

Healthy Diet, Healthy Gut, Positive Gene Expression

Inflammation is a key marker for disease development and a healthy gut helps to tamp it down. Diets high in ultra-processed foods promote inflammation in part by killing off beneficial gut bacteria. On the other hand, plant-forward dietary approaches like the Mediterranean Diet (whole grains, fruits, vegetables, legumes and nuts, plus healthy fats obtained mainly from fish and olive oil) support favorable ratios of beneficial bacteria, helping to keep inflammation low. Some friendly bacteria also produce anti-inflammatory substances like short chain fatty acids, which work their magic, in part, by improving gene expression.

Track Your Data to Maximize Your Health

DNA tracking is still an emerging science and genes are not a silver bullet. However, if you’re serious about being proactive about your health, knowing your genetic blueprint is a helpful tool. Along with other biosensors like regular blood work it provides body-specific data, which can help with customizing your diet. Lower-carb may work best for you and higher-fat may be just the ticket for me, but existing knowledge is very clear: We can both benefit from ditching ultra-processed foods and consuming more nutrient-dense plant foods.

Judith Finlayson is the author of "You Are What Your Grandparents Ate: What You Need to Know About Nutrition, Experience, Epigenetics, and the Origins of Chronic Disease." Visit her at www.judithfinlayson.com.

Selected Resources
* Patron, J. Assessing the performance of genome-wide association studies for predicting disease risk. PlosOne 2019

* Tobi, Elmar W. et a. DNA Methylation Signatures Link Prenatal Famine Exposure to Growth and Metabolism Nature Communications 2015.

* Li, Y. et al. Temporal Efficacy of a Sulforaphane-Based Broccoli Sprout Diet in Prevention of Breast Cancer through Modulation of Epigenetic Mechanisms. Cancer Prevention Research 2018.

* Franzago, M. Genes and Diet in the Prevention of Chronic Diseases in Future Generations. International Journal of Molecular Sciences 2020.

Helanza, Y. Gene-Diet Interaction and Precision Nutrition in Obesity. International Journal of Molecular Sciences 2017.

* Zeevi, D. et al. Personalized Nutrition by Prediction of Glycemic Response. Cell 2015

Grieneisen, L et al. Gut microbiome heritability is nearly universal but environmentally contingent. Science, 2021

* Wu, J. et al. Dietary nutrients shape gut microbes and intestinal mucosa via epigenetic modifications. Critical Reviews in Food Science and Nutrition 2020.

* Berry, S. et al. Human postprandial responses to food and potential for precision nutrition. Nature Medicine 2020.