Reasons for Weight Gain: Genes, Lifestyle, or Both?

Learn about the biological and lifestyle factors behind weight gain and how to address them.

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Andrew J. Funk, DC, DACNB
— Signos
Health & Science Writer
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Updated by

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Science-based and reviewed

July 24, 2024
December 28, 2021
— Updated:

Table of Contents

Weight gain and obesity are serious problems in today’s modern society. In fact, 25 percent of U.S. children are overweight and about 50 percent of adults are either obese or overweight in several countries<sup>1</sup>. 

The World Health Organization (WHO) says that being overweight and obese is a significant health concern that’s only getting worse. Obesity carries the risk of high blood pressure, stroke, heart disease, certain cancers, and diabetes—and that’s not a complete list<sup>2</sup>.

Signos has responded to this issue by getting “on a quest to tackle the obesity epidemic.” They help people lose weight and adopt healthier lifestyles.

You may have been wondering, “why am I gaining weight?” If so, this article will help you answer that question and tackle weight gain by covering the following:

The biological factors behind weight gain: 

  1. Appetite
  2. Satiety (the sense of fullness)
  3. Metabolism
  4. Food cravings
  5. Body-fat distribution

The lifestyle factors behind weight gain:

  1. Diet 
  2. Consuming caffeine, cigarettes, alcohol, and sugar 
  3. Stress 
  4. Lack of sleep 
  5. Dehydration

Simple steps you can take to address weight gain

Biological Factors Linked to Weight Gain

These factors revolve around hunger, the feeling of fullness, how people burn calories, food cravings, and body-fat distribution. One—or all—of them can be reasons for weight gain.

Research shows that genetic factors play an important part in weight gain<sup>3</sup>. More specifically, scientists have found mutations in several genes that regulate appetite, fullness, metabolism, and cravings<sup>3</sup>.

Even though some biological factors are genetic and beyond our control, there are lifestyle factors behind weight gain that we can influence.


Many people report feeling hungry all the time. Why is this?

The answer may relate to appetite-regulating hormones. These chemicals, specifically cortisol and peptide YY, are responsible for controlling the feelings of hunger and fullness<sup>4</sup>.

Cortisol makes us feel hungry and peptide YY decreases appetite<sup>5</sup>.

<p class="pro-tip"><strong>Learn about </strong><a href="/blog/how-to-manage-stress">managing cortisol and stress levels</a></p>

Interestingly, a study involving obese and lean subjects showed that obese people have low levels of peptide YY, suggesting that not having enough of this chemical leads to weight gain<sup>5</sup>.

It’s frustrating, but when a person already struggles with weight gain, that gnawing feeling of hunger can lead to further weight gain.

Satiety (Sense of Fullness)

It’s common for people to report that they never feel full throughout the day. The feeling of fullness does not magically happen. Hormones in the body control satiety. 

Peptide YY links the feeling of hunger and the sense of fullness. Just as we discussed that peptide YY decreases the feeling of hunger, it also makes us feel full<sup>6</sup>.

A lack of peptide YY can keep you feeling hungry all the time, as well as never feeling full.


What is metabolism?

Metabolism pertains to all the chemical reactions that happen in your body to keep you alive. It’s commonly considered the amount of calories your body burns in order to function<sup>7</sup>.

Not everyone’s metabolism runs the same. In fact, there are differences in metabolism from person to person that can lead to weight gain<sup>8</sup>. 

In a study of 37 normal subjects, researchers found a stark difference in how some people responded to high-carbohydrate eating<sup>9</sup>. Some people in the study increased their metabolism when they ate a high-carb meal, while other people showed a slowing of their metabolism. These differences may be due to genetics<sup>9</sup>.

Food Cravings

You may be wondering what causes food cravings. That wouldn’t be surprising since food cravings are common and associated with weight gain<sup>10</sup>. 

One study found that food cravings are associated with a certain hormone called ghrelin. The more ghrelin a person had in their body, the greater their number of food cravings<sup>10</sup>.

If you’re wondering how to stop food cravings, keep reading to see which lifestyle factors contribute to hunger. 

Body-fat Distribution

Where we accumulate fat on the body matters—some places where we carry extra weight are linked with a higher rate of health issues.

One study of women and men showed that abdominal fat is associated with high blood pressure, while another showed that abdominal fat is linked to insulin resistance<sup>11, 12</sup>.

A study of children found that higher cortisol levels correlated with more abdominal body-fat distribution. There are certain genetic variants that can lead to chronically high cortisol levels<sup>13</sup>.

Lifestyle Factors Linked to Weight Gain

Although we may not notice it, there are many reasons for weight gain that revolve around what we eat, how we handle stress, our water intake, and our sleep habits.

Even though we may not be able to control our genetics, we can learn about certain lifestyle factors associated with weight gain and make gradual improvements in these areas. 



The food we eat really matters. Many people want to eat healthy, but don’t always know what to eat.

It’s overwhelming to see the diet wars rage around us. All the different diets promoted—low-carb, keto, vegan, plant-based, low-fat, high-protein—can confuse the public and many stop trusting nutrition science<sup>14</sup>  

However, although many of these diets may be at odds with one another, they often agree on one thing: stay away from ultra-processed foods<sup>14</sup>.

Ultra-processed foods are often high in calories, sugar, salt, and fat<sup>15</sup>. Eating these can lead to disordered eating behavior, according to a study involving undergraduate students and Amazon workers<sup>16</sup>. In a study of adults of stable weight, ultra-processed foods were highly linked to weight gain<sup>14</sup>.

Brazil’s national food guidelines go so far as to tell their citizens to avoid ultra-processed foods due to the risk of obesity<sup>17</sup>. 

So what are some examples of ultra-processed foods to avoid? 

<ul role="list"><li>Sweet or savory packaged snacks</li><li>Sugar-sweetened beverages</li><li>Candy</li><li>Industrial bread</li><li>Industrial breakfast cereal</li><li>Ready-to-heat pasta and pizza</li><li>Reconstituted meat products<sup>18</sup></li></ul>

Consuming Caffeine, Cigarettes, Alcohol, and Sugar

All four of these substances can increase cortisol, a stress hormone made in the body.

A study of healthy participants concluded that frequent caffeine intake throughout the day increased cortisol levels in both men and women<sup>19</sup>.

Nicotine, the addictive chemical found in cigarettes, increased cortisol in the body of regular male smokers<sup>20</sup>.

Alcohol also increased cortisol, based on the amount of alcohol drunk in a week, in a study of both men and women<sup>21</sup>. 

A study of healthy, young subjects showed that eating sugar before an acute stressful event increased the cortisol response in their bodies<sup>22</sup>.

So, what does cortisol have to do with weight gain?

When cortisol levels get too high in the body, appetite gets stimulated. That’s why the jump in cortisol from caffeine, cigarettes, alcohol, or sugar could drive us to want to eat more<sup>23</sup> and potentially gain weight. 

Also, any physical or mental stress can also bump up our cortisol levels, making us hungry and craving processed foods (4). However, everyone is going to respond differently to a cortisol spike—and it does depend heavily on differences like gender and personal attitude around food<sup>24</sup>. 

Add a little stress to consumption of caffeine, cigarettes, alcohol, or sugar, and that can make us feel really hungry—especially for our go-to comfort foods.

One way to stop excessive hunger and cortisol weight gain is to cut back on any of these four substances.

<p class="pro-tip"><strong>Learn about </strong><a href="/blog/alcohol-weight-gain">how alcohol contributes to weight gain</a></p>


Stress levels matter when it comes to weight gain. In both the U.S. and Europe, mental stress is linked to obesity rates, especially regarding abdominal fat. Stress seems to add to abdominal obesity in people of all ages. Stress can come in many forms, such as with struggles in your personal life or with your job. But stress is really subjective, and it depends a lot on your own interpretation<sup>25</sup>. 

The bottom line is that you can perceive anything as stressful, which can lead to increased cortisol and potential weight gain. This isn’t to scare you, but it’s important to be aware that stress management can make a huge difference when it comes to weight gain.

Stress also has a strong effect on a developing fetus in the womb. It hinders their ability to cope with stress later in life. This stress exposure sets them up to have a higher body mass index (BMI) during the course of their lives<sup>25</sup>.

One study of obese Greek women showed that an 8-week stress management plan can possibly help people lose weight<sup>26</sup>. So, it’s important to limit stress if you want to keep the pounds off.

Lastly, a pilot study of obese African-American women found that a weight loss program with added stress management techniques helped them lose weight—more so than the weight loss program alone<sup>27</sup>.

Lack of Sleep

Does not sleeping cause you to gain weight?

Sleep is closely tied to our hormones and metabolism. If you get too little sleep, this can greatly impair your metabolism. Lack of sleep is linked to increased cortisol, disrupted hormones, and insulin resistance—all of which can give us excessive appetites that can lead to overeating and weight gain<sup>28</sup>.

Sleep is so important to good metabolism that just one night of too little sleep will disrupt your metabolism, according to a study done on healthy young men. This happens because even after one night of poor sleep, cortisol levels get too high, skewing metabolism<sup>29</sup>.

Another study showed that healthy participants who slept less than 5.5 hours per night ended up eating more calories from snacks—even though the extra snacking didn’t lead to them to burn any more calories<sup>30</sup>.

Can sleep apnea lead to weight gain?

Apart from lack of sleep, sleep disorders like obstructive sleep apnea can disrupt metabolism and lead to weight gain, according to a study of obese males with apnea compared with normal-weight males with apnea<sup>31</sup>.

The bottom line is that lack of sleep—or disrupted sleep—has the potential to lead to weight gain.

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Will you gain weight if you don’t drink enough water?

Many people may not connect the dots when it comes to water intake and weight gain.

However, a study showed that when mixed martial arts fighters dehydrate themselves, they see a gain in their weight just prior to their competition. The fighters gained an average of 4.4 percent of their body weight in the 22-hour period before the fight<sup>32</sup>.

There appears to be a possible link between water intake and weight. In fact, increasing water intake may lead to weight loss<sup>33</sup>.

One study of 71 subjects showed that drinking water as opposed to diet beverages decreased their BMI and improved their resistance to insulin<sup>34</sup>.

Another study found that overweight dieting females who drank more than 1 liter of water per day lost weight. How does this much water intake help people lose weight? The study investigators suspected that this level of water intake makes people burn more calories by increasing the amount of energy expended<sup>35</sup>. 

Drinking water also likely speeds up the rate of burning fatty acids. All these factors seem to drive the weight loss seen in the study<sup>35</sup>.

The study was careful to report that these women did lose some weight because they drank less calories in their beverages. However, increasing water intake alone—and not their specific diet—was linked to significant weight loss in this study<sup>35</sup>.

Action Steps to Address Weight Gain

A complex combination of genetics and lifestyle factors contribute to weight gain. 

It can be confusing, but here are some simple action steps you can take today to deal with weight gain:

  • Refuse to dwell on any genetic aspects about weight gain that you may not be able to control.
  • Choose to dwell on the small lifestyle changes you can make.
  • Pick one aspect from the lifestyle factors to work on. Whether it’s sleep, water intake, stress management, or diet, pick one area to make weekly progress on and focus on that until it becomes second nature. Once that becomes a habit, pick another aspect to focus on the next week, and so on.


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About the author

Dr. Andrew Funk has held board certification in neurology with the American Chiropractic Neurology Board since 2015.

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Please note: The Signos team is committed to sharing insightful and actionable health articles that are backed by scientific research, supported by expert reviews, and vetted by experienced health editors. The Signos blog is not intended to diagnose, treat, cure or prevent any disease. If you have or suspect you have a medical problem, promptly contact your professional healthcare provider. Read more about our editorial process and content philosophy here.

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