Lifestyle vs. Genetics: What Determines Your Weight Fate?

weight fate
Written by Amanda Capritto

You know those people: The ones who eat non-stop but never seem to gain an ounce. Maybe you’re one of them. Or maybe you’re one of the many people who find it nearly impossible to shed weight.

Some people seem to lose weight easily and others don’t — and balancing the tightrope between nature and nurture can be tricky. This is because obesity, as it turns out, isn’t just a matter of eating too much — it’s a result of intricate interactions between biology, behavior and environment.

Obesity is a major public health issue that affects more than one-third of adults in the United States, with the national rate exceeding 35 percent in seven states as of 2018. Obesity rates have nearly tripled since the Centers for Disease Control first began tracking them in 1960. Just since 1990, rates have doubled. Nearly one in six young people — ages 10 to 17 — is considered obese, according to the latest National Survey of Children’s Health.

The sharp upturn coincides with lifestyle changes people are familiar with today: overly processed and pre-packaged foods, fast-food restaurants and vending machines, food-related advertising, a change in the means of transportation and advances in technology. People are besieged every day by highly palatable, convenient and inexpensive foods. Most of these foods are high in fat and sugar, and, consequently, high in calories.

Meanwhile, the physical demands of our society have also changed, creating a massive imbalance in most people’s energy intake and expenditure. Millions of people spend the majority of their days at desks, hardly taking breaks to move around or simply stand. Not only does sitting induce bad posture and musculoskeletal imbalances, it promotes high blood sugar and fat deposition around organs — also known as visceral fat, the kind that can lead to heart disease.

So we’re eating more and moving less. That alone is a recipe for weight gain. Combine that with our bodies’ ancestral mechanisms and you have the blueprint for obesity.

How We Evolved to Hang Onto Fat

Consider the thermostat in a house. A temperature is set, and then the HVAC system kicks on and off to sustain the set temperature.

The same concept applies to people and their body weight. Every person has a genetically predetermined set point, which can be described as your body’s “happy weight.” Bodies tend to defend the weight that is their set point, but once the body gains weight, it tends to defend the higher weight.

Human physiology lends itself toward weight gain rather than weight loss. The hormonal mechanisms contributing to that phenomenon are part of humankind’s survival system: the very mechanisms that kept our ancestors alive when they went days without proper nourishment. Being able to store extra fat helped people survive during famine, and your body still lives with the notion that there might be famine in your future.

The two main hunger hormones are leptin and ghrelin. Leptin — known as the satiety hormone — signals the brain when you’re full. It’s secreted by fat cells, so when fat cells shrink or disappear, they produce less leptin and your brain doesn’t get the message that you’re satisfied.

Ghrelin comes from the stomach and tells the brain it’s time to eat. During weight loss, leptin levels decrease and ghrelin levels increase. A person’s brain is then left thinking one thing: Refuel.

Additionally, humans have a complex system called metabolic compensation, which means that a thinner body burns fewer calories during activity than a heavier body. For example: If you weigh 150 pounds and run one mile, you might burn around 120 calories. If you lose 20 pounds and run a mile at the same pace, you might only burn around 105 calories.

Where Genetics Come into Play

Research suggests that for most people, between 40 and 70 percent of body weight comes from the genes they inherit from their parents; however, the genetic effect for each person may vary from as little as 1 percent to as much as 99 percent. This means that it is not guaranteed that our body shape or fitness level will mirror that of our parents.

Studies of similarities and differences among twins and adoptees offer evidence that at least some variation in weight among adults is due to genetic factors. But considering obesity rates started rising in 1980 despite no change in the human genome, it’s unlikely genetics are the only driving force. We can’t just blame “bad genes” when we put on pounds.

“Moving from genetic predisposition to obesity itself generally requires some change in diet, lifestyle or other environmental factors,” according to researchers at the Harvard University School of Public Health. The bottom line? Don’t give up just yet on the battle against those extra pounds.

How to Fight Your Physiology

The genes we inherited may mean that we just have to work harder to keep extra weight off.

At a minimum, everyone should follow the government’s Physical Activity Guidelines for Americans, which advise 150 minutes of moderate to vigorous exercise each week, or 20-30 minutes of physical activity each day. Brisk walking is a good example of moderately intense activity, while slow jogging reaches the vigorous level. But anything that gets you moving is a good place to start.

Parents can help their children fight the burden of extra weight by setting healthy household standards early on.

While scientists search for answers to the obesity epidemic, there are always two proven methods for controlling weight: keep an eye on your calories and make sure to keep moving throughout the day. Those two seemingly small habits add up to quite a few pounds over the years, which reinforces the importance of including a healthy routine into your everyday lifestyle.

If your parents are overweight, it may mean it’s easier for you to gain weight, but it certainly doesn’t mean that you are doomed to be overweight. Even if you’re predisposed to weight gain, persistent efforts can help even the most susceptible person lose weight and keep it off.

About the author

Amanda Capritto

Amanda Capritto is a certified personal trainer and integrative nutrition
health coach who writes about nutrition, fitness and healthcare. A
journalism alumna of Louisiana State University, Amanda embraces a
balanced lifestyle and strives for mind-body wellness. Her favorite forms
of exercise are endurance running and CrossFit.

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