Why doesn't everyone gain weight in the same way

Weight loss
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At first glance, the process behind weight gain seems simple: consuming more calories than we expend, leading to the storage of these calories as fat throughout the body. But then, why doesn't everyone gain weight in the same way? Here is an overview of some factors that play a role in how people gain weight:

1. Genetics

Currently, there are approximately 400 genes in humans that influence weight gain. These genes can impact metabolism, hunger and satiety signals, distribution of fat cells, and more. For example, specific genetic factors may cause an accumulation of fat cells in the thighs for some individuals, while others may have a genetic predisposition for fat accumulation in the abdominal area. Additionally, genes can also influence how easily a person gains weight.

2. Age and Gender

Biological differences between women and men, as well as age, impact body composition and fat distribution, resulting in different patterns of weight gain. Genetics and hormonal factors play a role here as well. For example, it is often observed that women tend to gain weight in the hips, buttocks, and thighs, while men tend to accumulate more weight in the abdominal region. However, with age, the distribution of fat in women may change and become more similar to that of men, due in part to the decrease in production of female hormones during perimenopause or menopause.

3. Health Status

Certain medical conditions or medication use can contribute to weight gain. For instance, Cushing's syndrome typically leads to weight gain in the upper body, particularly in the neck and face. Antidepressants can also cause weight gain, although the reasons behind this weight gain may vary, including increased appetite as a possible factor.

4. Diet and Type of Physical Activity

While weight gain is commonly associated with the accumulation of fat in adipose cells, it can also result from the development of another tissue: muscles. If a person engages in resistance training and maintains a diet rich in protein, along with adequate percentages of fat and carbohydrates, weight gain may be due to an increase in muscle mass rather than fat mass.


Centers for Disease Control and Prevention. (August 17, 2020). Other Factors in Weight Gain. Retrieved November 29, 2020, from https://www.cdc.gov/healthyweight/calories/other_factors.html

Harvard Health Publishing. (June 24, 2019). Why people become overweight. Retrieved November 29, 2020, from https://www.health.harvard.edu/staying-healthy/why-people-become-overwe…

Karastergiou, K., Smith, S. R., Greenberg, A. S., & Fried, S. K. (2012). Sex differences in human adipose tissues – the biology of pear shape. Biology of Sex Differences, 3(13). doi: 10.1186/2042-6410-3-13

Manuel Merck. (May 2019). Hypothyroidism. Retrieved November 29, 2020, from https://www.merckmanuals.com/professional/endocrine-and-metabolic-disor…

MedlinePlus. (n.d.). Aging changes in body shape. Retrieved November 29, 2020, from https://medlineplus.gov/ency/article/003998.htm

Nelms, M., Sucher, K. P., & Lacey, K. (2016). Nutrition Therapy and Pathophysiology. (3rd ed.). Cengage Learning.

Passeport Santé. (July 2016). Syndrome de Cushing. Retrieved November 29, 2020, from https://www.passeportsante.net/fr/Maux/Problemes/Fiche.aspx?doc=syndrom…

Québec Pharmacie. (September 2010). Existe-t-il des antidépresseurs plus susceptibles d'entraîner un gain de poids? Retrieved November 29, 2020

San-Cristobal, R., Navas-Carretero, S., Martinez-Gonzalez, M. A., Ordovas, J. M., & Martinez, J. A. (2020). Contribution of macronutrients to obesity: implications for precision nutrition. Nature Reviews Endocrinology, 16, 305-320. https://doi.org/10.1038/s41574-020-0346-8

Silverthorn, D. U. (2013). Human Physiology: An Integrated Approach. (6th ed.). Pearson Education, Inc.

Registered Dietitian Nutritionist