Height and Body Mass: The Role of Genetics and Environment

Height and body mass are what geneticists call “complex traits.” That means there’s no single gene that determines your size or shape.

In this research review, we’ll explore two important studies:

1. A 2021 study that reviewed decades of research on the genetics of obesity.

2. A 2024 study examining the heritability of height and BMI, offering a clear picture of their genetic and environmental influences.

Study #1: The Heritability of Body Size and Body-Fat Distribution

If a trait is highly heritable, offspring often reflect that trait. For instance, we might expect children of highly athletic or intelligent parents to inherit those traits. However, it doesn’t always work that way. Twin studies provide valuable insights into heritability by comparing identical twins (who share nearly all their genes) with fraternal twins and non-twin siblings (who share about 50% of their genes).

For BMI, heritability shows interesting patterns:

• In identical twins, BMI differences averaged 12 percentile points.

• For same-sex fraternal twins, the difference was 16 percentile points.

• For opposite-sex twins and non-twin siblings, the difference widened to 29 percentile points.

Shared environments (like meals and routines) partly explain these differences. Identical twins often grow up in nearly identical circumstances, while opposite-sex siblings tend to have more diverse experiences.

BMI heritability is strongest during childhood when caregivers have the most influence over meals and activities. As we age and make our own choices, environmental factors and lifestyle decisions play a bigger role. Interestingly, heritability is much higher for those with higher BMIs, as genetic predispositions have stronger effects in these cases.

Study #2: The Genetics of Height and BMI

Height was once thought to be controlled by a single gene, but researchers have now identified over 10,000 genes associated with it. By contrast, fewer than 1,000 genes are linked to BMI.

The 2024 study found height to be 76% heritable and BMI 55% heritable. However, heritability varies:

• For individuals with “normal” BMI, genetic influence is around 30%.

• For those with the highest levels of obesity, it can range from 60% to 80%.

This variability underscores that while genetics play a significant role, environment and lifestyle are also critical.

What This Means for You

1. Heredity is not destiny.

While our genes influence traits like height and BMI, they don’t dictate our outcomes entirely. The relationship between genotype (our genes) and phenotype (how those genes are expressed) is complex, with environmental factors often playing a decisive role.

For example, someone genetically predisposed to be tall might end up shorter due to illness or poor nutrition. Similarly, genetic predispositions for obesity or chronic conditions like diabetes can be mitigated through lifestyle changes.

This is where coaching comes in. By helping you modify your environment, activity level, and habits, we can minimize the expression of genes that contribute to less favorable outcomes. Your choices matter—a lot.

2. Don’t blame yourself for what you can’t control.

While we have influence over our lifestyle, we don’t have total control. Genetics can create significant challenges, especially for those predisposed to higher BMIs. This doesn’t mean efforts are futile, but rather that progress should be measured by what’s realistic and sustainable for you.

As a coach, I’m here to guide you in focusing on the aspects you can control, such as developing healthy habits and fostering a growth mindset. Together, we’ll work toward being as healthy as possible at a weight that’s achievable for you.

Closing Thoughts

Understanding the interplay between genetics and environment is empowering. It reminds us that while heredity sets the stage, our daily actions shape the outcome. My role as a coach is to help you navigate this balance, focusing on progress, not perfection. Let’s work together to optimize your health, regardless of the genetic hand you’ve been dealt. Remember, your choices today can create a healthier and happier tomorrow.

Michael Beiter

Personal Trainer

Nutrition, Sleep, Stress Management, and Recovery Coach

References

1. Bouchard, Claude. 2021. Genetics of Obesity: What We Have Learned over Decades of Research._ Obesity (Silver Spring, Md.)_ 29 (5): 802–20.

2. Sidorenko, Julia, Baptiste Couvy-Duchesne, Kathryn E. Kemper, Gunn-Helen Moen, Laxmi Bhatta, Bjørn Olav Åsvold, Reedik Mägi, et al. 2024. Genetic Architecture Reconciles Linkage and Association Studies of Complex Traits. Nature Genetics, October, 1–9.

3. Price, Joseph, and Jeffrey Swigert. 2012. Within-Family Variation in Obesity. Economics and Human Biology 10 (4): 333–39.

4. Pulit, Sara L., Charli Stoneman, Andrew P. Morris, Andrew R. Wood, Craig A. Glastonbury, Jessica Tyrrell, Loïc Yengo, et al. 2019. Meta-Analysis of Genome-Wide Association Studies for Body Fat Distribution in 694 649 Individuals of European Ancestry. Human Molecular Genetics 28 (1): 166–74.