How Your Genes Affect Your Jean Size

By Molly Galbraith

Note: This article is about the influence of genetics on the structure and shape of your body. It goes without saying (but we'll say it anyway) that clothing sizes, which are typically determined by the designers or manufacturers, are outrageously arbitrary. You could (and probably do) wear a wide range of sizes, and these sizes have nothing to do with your worth and value as a person.

This article is co-authored by Molly Galbraith and exercise physiologist Dr. Krista Rompolski. Krista is an Assistant Professor at Drexel University, where she teaches Exercise Physiology, Anatomy and Physiology, and courses in clinical research.


I am just big-boned. Everyone in my family is big-boned."

"My mom is overweight. My dad is overweight. I'll never be anything but overweight."

"My sister is tall and lean like my dad, and I am short and stocky like my mom. I will never be lean like my sister."

At one point or another, you've probably heard your friends or family members utter these phrases. Heck, you may have even said similar things yourself. For every average-height, average-age woman who can stay pretty lean with very little effort, no matter how much she eats or what she does for exercise, there is another woman of the same height and age, with the same eating habits and activity level, whose body composition is completely different.

What gives? Genetics. That’s what gives.

How Much Do Your Genes Affect Your Weight?

Your genetics, above all else, determine how your body responds and adapts to your food intake and your activity. Whether it’s how much lean mass you hold, how much fat mass you gain or lose, and where on your body you carry these tissues, your body has a blueprint that is, to say the least, difficult to manipulate. We get our genes from our parents, who got them from their parents, and so on. We carry a bit of each of them in our chromosomes.

Ongoing research aims to identify specific genes, or portions of genes called alleles, which increase the risk of obesity. While it is very difficult to isolate a genetic effect from environmental factors. Twin studies and studies of families in which all children are fed the same diet have estimated that genetics account for approximately 60 to 70 percent of our Body Mass Index (BMI)1. This leaves anywhere from 30 to 40 percent of our body weight attributable to our environment, which includes the food available to us, our family and social influences, and our lifestyle choices.

AmandaGraydon-321x356 - flexingThe story doesn’t end with the genes we inherit. While in utero and during our earliest years, our genes can interact with and be influenced by the environment, altering their expression. This is a field known as epigenetics. Examples of early childhood epigenetic influences include what our mothers ate diet while pregnant with us2, whether we are delivered vaginally or via C-section, and whether or not we are breastfed, just to name a few. All of these factors can impact our weight.

A staggering example of the influence of epigenetics comes from studies in women who have had weight-loss surgery, and later had children. In one such study, after women received biliopancreatic diversion, a procedure that significantly reduces the amount of food that one can eat and absorb, they were 52 percent less likely to give birth to overweight babies3. These women may have passed a genetic predisposition to their children to be obese, but the influence of the weight-loss surgery had a greater influence on their offspring.

These relationships can go both ways. You may inherit genes that tend toward leanness, but also experience an epigenetic effect that increases your risk for obesity. For example, if your mother greatly increased her food intake while pregnant with you, you are at an increased risk of being overweight or obese even if you have “lean genes.”

While we do have some control over our body composition, genetics do make a big difference.

Every message in the media, or even among peers, is typically along the lines of “just eat less and move more,” as if it is always that simple and works for every person uniformly. People carrying excess weight are often stigmatized as being overeaters, or lazy. At the same time, we often assume that a very thin person doesn’t eat enough. Some people are simply going to have an easier time than others managing their body weight.

What About Your Body Type?

Although weight gets a lot of attention, body shape is heavily influenced by genetics, and for many women, they struggle to achieve the particular body shape they envision, no matter how much weight they gain or lose. We implore you to take the pressure off of yourself for not having the body you expect or prefer to have. So many of us bemoan genes-jeans-jvb-ivonne-jensinkler-body-types-327x341our bodies and try desperately to change them, but we are all born with a specific genetic makeup that we cannot control. If you look at families as a whole, you’ll see patterns in body type and shape.

There are always exceptions of course, but when we go about our daily lives without putting much serious effort towards changing the way our bodies look, we tend to look a lot like our parents or other family members due to the influence of genetics. Of course, thanks to the randomness of heritability, within a family you can have sibling who is 6’5” and can devour two Thanksgiving dinners with no impact on their weight or body composition, and another one barely who is barely 5 feet tall and feels like she gains weight from simply looking at a slice of pecan pie.

Take, my (Molly’s) personal story, for example: I have broad shoulders and a small waist. I also have large breasts, wide hips, and a tendency to carry excess body fat. I have more of an hourglass shape, so while my belly can be lean enough to show abdominal definition, my thighs still tend to be "thicker" even when my body fat levels are normal or low. Several members of my family have struggled (or currently struggle) with their weight, and I used to struggle with my weight as well. However, now that I know how to eat and exercise properly, I am able to control my level of leanness to some degree. This means that while I may struggle to get extremely lean (more on that later), I am able to alter my lifestyle enough to avoid being overweight or obese, and keep myself healthy.

genes-jeans-ggs-women-beach-walking-body-types-327x341In the medical and scientific communities, bodies are generally classified as one of three body types (also referred to as somatotypes) based on certain physiological characteristics. Those three body types are: ectomorph, mesomorph, and endomorph.

In general, if you are thin, have long limbs and a long neck, and low body-fat levels, you are an ectomorph. If you would describe yourself as an "athletic" build, and it's not hard for you to add body fat or muscle mass to your frame, you are a mesomorph. The mesomorphic body type is more common among men than women. If you have a softer, less athletic build, with larger hips and thighs, and you tend to easily gain weight, you are an endomorph. The endomorphic body type is more common in women than in men.

In addition to these three main body types, there is an association between risk for lifestyle-related diseases and where people carry or store body fat6. If you tend to carry most of your weight in your hips, thighs, and buttocks, you’re at a lower health risk than those who carry fat elsewhere. In fact research suggests that storing fat in your lower body might protect you against cardiovascular disease. People who tend to carry weight in their abdominal area and upper torso are said to be at a greater risk of developing lifestyle-related diseases such as diabetes and heart disease. If you’re somewhere in between, and your weight is a little more evenly distributed, your health risks may be somewhere in the middle.


"Strong" and "Healthy" comes in a variety of shapes and sizes.

While reading through the descriptions above, it's only natural to immediately try to identify under which category you fall. You might have found one that sounds exactly like you and your build. Or maybe it wasn't so clear which one you are. Very few people are one "pure" body type. Usually, we have some characteristics from one or more categories. Hybrid body types are quite common and if you found yourself nodding along to characteristics in two of the different categories, you are likely a hybrid.

Finding your happiest and healthiest body weight is part genetics, part lifestyle, and part body embracement.

Feeling healthy and comfortable in your skin is what’s most important. You only get one body. You might as well embrace it.

What Happens When We Go Too Far?

While we can influence our physical appearance to some degree, ultimately genetics are a big determining factor in many of our physical characteristics. You can't switch from one body type or shape to another. Your bone structure, your height, and the length of your limbs are pretty much set once you're done growing. Lifestyle choices such as your nutrition, physical activity, sleep, and stress management can influence your metabolism, how much muscle mass you have, and how much body fat you carry, and your genes determine to what degree your lifestyle will influence those things.

When you set physique goals that go against your body’s natural tendencies, it can take an extreme amount of work and diligence to get there, and then maintain that state.

Your body may never be comfortable there and will put up resistance in an effort to revert to what feels more comfortable and natural. Taking extreme measures to make physical changes puts your body under a lot of stress. What’s more, if those extreme measures involved prolonged energy restriction, your body will fight back in an effort to stop the restriction, leading to behaviors that encourage your body to regain weight.

A great example of the physical and psychological consequences of severe restrictions was the famous Minnesota starvation study, performed by Ancel Keys during World War II. Men in this study volunteered to undergo months of severe food restriction to examine how starvation influences physical as well as psychological health. This study showed, to say the least, disturbing results. During the study, metabolic rate decreased by an average of 40 percent, and the subjects experienced everything from dizziness, weakness, anxiety, and depression, to a loss of interest in their hobbies and strange rituals and behaviors around food. Participants started doing things such as collecting recipes, obsessing about food, and mixing foods together into unusual combinations. They also felt guilty about resuming normal food intake, yet frequently binged and purged to rid themselves of discomfort. Only when their weight was restored several months later did these symptoms resolve5.

star_magazine_cover - croppedThe results of this study are scary, but even more so when you consider the number of people who spend years trying to manipulate their body weight (often through extreme calorie restriction) in an effort to achieve a certain physical ideal. We live in a time in which bodies are scrutinized on every television show, magazine, and all over social media, so it’s unsurprising that the quest for the perfect body is such a society-wide preoccupation. It seems that, for most people, all this quest is doing is creating more dissatisfaction, shame, and body-image disorders than they would have had, had they not attempted to change their bodies.

As Brown University, a leader in health promotion and healthy weight research, states, “ would probably need to pathologically distort your relationship with food and exercise in order to do it [override your genetics]; you'd have to be willing to divert resources from a lot of other important pastimes (school, work, relationships, hobbies), and you'd have to be able to keep that up for—well, the rest of your life. This is impossible to maintain and would seriously undermine your emotional and physical health.”

(To be clear, this is referring to trying to make an extreme change that overrides your genetics, not making reasonable changes like trying to improve your health by losing a bit of body fat or gaining a bit of muscle).

Yes, it's absolutely possible to totally transform your body. But is it really worth it? Only you can decide. Brown University’s Healthy Weight program suggests that you ask yourself these questions to evaluate your body composition:

  • Do you get feedback from your doctor that suggests that your pulse, blood pressure, and lab work results are healthy for someone of your age and gender?
  • If you have finished growing (and remember, many people will not finish growing until their early 20s), does your weight tend to stay in the same range, without a lot of significant fluctuation, and without any strenuous effort on your part?
  • Do you find that you have plenty of energy throughout the day, and that you are not more likely than your peers to catch colds and flus?
  • Are you getting 30 to 60 minutes of enjoyable physical activity on most days of the week?
  • Do you generally eat only when you are hungry and stop when you are comfortably full?
  • Do you eat a wide variety of foods (covering all the food groups or food group substitutes)? Would you say that most of your choices are high in nutrients and moderate in calories?
  • Do you include lots of high-fiber choices in your meals and snacks?
  • Do you eat a minimum of five servings a day of fruits and vegetables?
  • If you drink alcohol, do you drink it in moderation?
  • Does your body resemble the size and shape of other healthy members of your family?
  • If you are a woman, do you get your periods regularly, and is the flow pretty normal?

How do you know if your lifestyle choices are going too far? If you answer “no” to some of the Healthy Weight questions listed above, you are probably leaving the “healthy lifestyle zone” and venturing into disordered territory.

I (Molly) have learned from experience that I don't want to go to extremes. For me, competing in figure competitions and trying to get extremely lean placed great stress on my body. In fact, the three times that I tried to achieve an extreme level of leanness when I prepped for different figure competitions, I found myself exhausted, depleted, and without a period for months at a time. I have learned to love and embrace my body, and I no longer try to force it to attain uncomfortable levels of leanness. I simply maintain a level of leanness that feels comfortable, but not extreme for me, through proper eating and consistent, intelligent exercise.


The bottom line is that you cannot control your unique genetic makeup, your body type, your bone structure, or your tendency to store fat in certain places instead of others. But you do have some control over how your genes express themselves based on your lifestyle and how well you take care of yourself. Because your lifestyle is what you can control, focusing on that—as opposed to cursing your "bad" genes—is what is most important, not to mention, more productive.

Make the Most of Your Genes

So which lifestyle factors are most important to focus on? Spoiler alert! They probably look a lot like the sane and sustainable recommendations we often make for living a healthier lifestyle: eat whole, minimally processed food most of the time, lift moderate to heavy weights two to four times a week, move your body as often possible in ways that feel enjoyable to you, manage your stress effectively, get seven to nine hours of quality sleep a night, and above all, love yourself.

Yes, on the surface these changes sound simple enough, but if you’ve ever tried to make them on your own, you know it’s harder than it sounds, and sometimes you need a little guidance.

Get in the best shape of your life—for good.

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  • Get stronger
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... or anything else, we’ll help you achieve them. You can experience life-changing results while eating and exercising in a way that actually fits into your life — instead of controlling it.

Throughout our 12-month program, you’ll get a simple, step-by-step plan for developing nutrition, fitness, and mindset habits that will lead the way in reaching your goal.

Your coach is available 5 days a week to answer questions and help you navigate situations — like eating while you’re on vacation, exercise substitutions so you don’t aggravate your knee pain, or planning a workout with limited equipment options — so you always have support when you need it. And together, you'll find the best path toward long-term results in a way that works for you.

You’ll learn how to:

  • Improve your nutrition without giving up the foods you love
  • Exercise safely and effectively so you’re getting maximum results from your workouts without burning yourself out
  • Increase your confidence, love the way your body looks, feels, and performs — and enjoy your life more than you ever thought possible

And you’ll become the happiest, fittest, strongest version of yourself, one step at a time.

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About the author:  Molly Galbraith

Molly Galbraith, CSCS is co-founder and woman-in-charge at Girls Gone Strong, a global movement of 800,000+ folks passionate about women’s health, fitness, and empowerment. She’s also the creator of the The Girls Gone Strong Academy, home of the world’s top certifications for health and fitness pros who want to become a Certified Pre-& Postnatal Coach or a Certified Women’s Coaching Specialist.   The GGS Academy is revolutionizing women’s health and fitness by tackling critical (and often overlooked) topics like body image struggles, disordered eating, menopause, amenorrhea and menstrual cycle struggles, PCOS, endometriosis, osteoporosis, pre- and postnatal exercise, incontinence, diastasis recti, pelvic organ prolapse, postpartum recovery, and much more.   Learn more about Molly on her website and connect with her on Facebook, Instagram, and Twitter.


  1. Textbook of Obesity: Clinical Management. Wiley-Blackwell 2012.
  2. Walley AJ, Asher JE, Froguel P: The genetic contribution to non- syndromic human obesity. Nat Rev Genet 2009, 10:431-42.
  3. Kral JG, Biron S, Simard S, Hould F-S, Lebel S, Marceau S, Marceau P: 
Large maternal weight loss from obesity surgery prevents transmission of obesity to children who were followed for 2 to 18 years. Pediatrics 2006, 118:e1644-9.
  4. Pasquet P, Apfelbaum M: Recovery of initial body weight and composition after long-term massive overfeeding in men. Am J Clin Nutr 1994, 60:861-3.
  5. Kalm, L.M., & Semba, R.D. (2005). They starved so that others be better fed: Remembering Ancel Keys and the Minnesota Experiment. Journal of Nutrition, 135, 1347–1352.
  6. Williams, M.J., Hunter, G.R., Kekes-Szabo, T., Snyder, S., Treuth, M.S. (1997). Regional fat distribution in women and risk of cardiovascular disease. Am J Clin Nutr, Mar;65(3):885-60

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