Have you ever known someone who maintains a trim, fit physique seemingly without effort, while others face chronic struggles with maintaining a healthy weight? While it’s true that in simplest terms a calorie deficit leads to weight loss, the reality is that different people have different nutritional needs pertaining to weight loss and weight management.

Here’s a closer look at how two factors, genes and environment, impact an individual’s weight, along with why a nutrition strategy that takes these factors into account can lead to optimal health and wellness.

The human body is made up of 46 chromosomes, each containing anywhere from hundreds to thousands of segments of deoxyribonucleic acid (DNA), AKA “genes.” From eye color and earlobe attachment to dimples and handedness, a person’s genetic makeup determines many human characteristics known as “traits.” As researchers have continued to learn more about biology, they’ve also become increasingly aware of the relationship between genes and body weight, along with the degree to which the former may influence the latter.

Take research from UCLA, for example, indicating that genes may play a direct role in deciding a person’s metabolic response to food. Specifically, the research suggests that while some people may see no increase in body fat following the switch to a high-fat, high-sugar diet, others may have body fat increases in excess of 600 percent! The reason for the difference, say scientists? “Fat genes.” Simply put: Some people may be genetically predisposed to gaining more weight than others.

Not only that, but there are many ways heredity can contribute to weight gain and obesity. In fact, we are currently aware of 14 genetic variations associated with weight and BMI. These relate to many different mechanisms pertaining to controlling body weight, including everything from energy expenditure to appetite regulation. Genes can also affect how a person’s body responds to vitamins, carbs, fat, caffeine, salt, and alcohol.

Environment and the Weight Loss Equation

This doesn’t mean that you’re destined for obesity if you’ve inherited so-called fat genes, however. While it’s true that you can’t change your genes, it’s also true that you can change how these genes manifest as traits. Genes don’t exist in a vacuum; but in the context of the environment. Therefore, the importance of environment cannot be underestimated or overstated in this process.

In investigating the significant obesity problem in Samoa, where more than 80 percent of the population is overweight, researchers from Brown University discovered that nearly half of the population had a gene which increased their risk of obesity. How does that gene work, exactly? Dubbed the CREB R.F., this gene stores extra fat into tissue every time a person with the gene eats food. While this initially developed as a defense against starvation, it’s become a cause of overweightness in modern times.

At the same time, however, the presence of that gene led to a comparatively small two percent difference in BMI among Samoans. Other factors were also very much in play — including diet, exercise and other environmental impacts. So Diet and exercise matter, but the degree to which differs from person to person.

Still, with genetics accounting for 60 percent of a person’s overall obesity risk, dismissing its role would be a mistake, insists Auckland University professor Peter Shepherd. Echoes Irma Silva-Zolezzi, of the Nestlé Research Center, “Nutrition, exercise and other environmental factors are just part of the puzzle that affects an individual’s risk to develop particular conditions or disease.”

The Personal Nutrition Imperative

This knowledge of the degree to which genetics and the environment mutually impact weight and BMI has opened new doors to understanding the value of targeted intervention strategies for weight loss and overall health. After all, no two people are the same in terms of either genetic makeup or environment. Nor does the environment impact everyone’s genes the same way. So why would we expect all people to have success with one-size-fits-all diets? Rather, it follows that in order to ascertain an individual’s “ideal” dietary strategy for wellness, we must acknowledge his/her unique combination of genes and environment.

Enter epigenetics and nutrigenomics. Scientific American defines epigenetics as “the study of how different biological and environmental signals affect gene expression.” In other words, epigenetics isn’t about changing a person’s genetics, but rather about how to turn certain genes on and off in order to lead to certain desired outcomes.”

Is your DNA the weight loss key you’ve been looking for?

Diet, in particular, is heralded as one of the most pivotal factors in epigenetics, and scientists now propose that what we eat can play a paramount role in modifying gene expression and influencing health. So, while genes do determine function, what we eat determines the extent to which these genes are expressed.

The takeaway? While we have long wrestled with the question of whether a person’s weight is a question of nature versus nurture, the reality may be that it’s actually both — more specifically, that it’s about how the integration of the two plays out from person to person. Even better? This information can now be harnessed to support wellness. The more we understand about how an individual’s genes uniquely interact with the foods he/she eat, the more effectively we can use this analysis to create customized eating plans aimed at minimizing disease and maximizing health.

Many people spend their lives chasing fad after fad in search of the “secret” to weight loss. However, modern science tells us that they’ve been searching in the wrong places. Rather than embracing every fad and trend that comes along in the hopes of stumbling upon one that will finally work, people can now use enhanced understanding of nutrigenomics — and their own distinct genetic compositions and environmental stressors — to harness the largely untapped power of personalized nutrition.