Body Mass Index
What we eat, digest and absorb impacts our body mass index, which in turn can impact our hormonal system, our neurotransmitters, our levels of inflammation, and therefore our mental health.Hryhorczuk, C., Sharma, S., and Fulton, S. (2013). Metabolic disturbances connecting obesity and depression. [online] Frontiers in Neuroscience, 7 (1), p. 177. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3791387/ [accessed 24 Aug. 2017]. Andrews, Z. and Abizaid, A. (2014). Neuroendocrine Mechanisms That Connect Feeding Behaviour and Stress. [online] Frontiers in Neuroscience 8 (1), p. 312. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4181285/ [accessed 24 Aug. 2017].
Your body mass index (BMI) has an impact on your mental health. Not just because of how you might feel about yourself and your body image, but also it has a knock-on biochemical effect. Amen, D. (2013). Unleash The Power Of The Female Brain. New York: Harmony Books, p. 73. Talbott, S. (2007). The Cortisol Connection. Alameda, CA: Hunter House, p. 102..
You can calculate your BMI using a tool provided by the National Institute of Health here. BMI under 18.5 is considered low; between 18.5 and 24.9 is considered normal; 25 to 29.9 is considered overweight; above 30 is considered obese.
Being overweight or obese results from an imbalance between food intake and energy expenditure which leads to an excessive accumulation of fat.
Being overweight or obese has been shown to negatively impact brain health, and people with high fat stores tend to be at greater risk of mental health issues.Talbott, S. (2007). The Cortisol Connection. Alameda, CA: Hunter House, p. 102.
High BMI correlates with:
Reduced cognitive function
- Being overweight or obese correlates with less brain mass and lower brain activity, which impacts cognitive health and doubles the risk of Alzheimer’s Amen, D. (2013). Unleash The Power Of The Female Brain. New York: Harmony Books, p. 73.
- Being overweight or obese doubles the risk of depression Amen, D. (2013). Unleash The Power Of The Female Brain. New York: Harmony Books, p. 73.
- Fat cells produce inflammatory chemicals and store toxic chemicals in the body which can further increase inflammation which can lead to mental health issues Amen, D. (2013). Unleash The Power Of The Female Brain. New York: Harmony Books, p. 73.
- A 5% reduction in weight can normalize your hormone levels Gottfried, S. (2013). The Hormone Cure. New York, NY: Scribner, p. 226.
- High body fat can impact stress hormones
- Abdominal fat, and generally higher total body fat, correlates with increased levels of the stress hormone cortisol which is released by fat cells
- Obesity dysregulates the HSD enzyme in fat tissue, which leads to chronically high cortisol levels in fat cells
- Equally, fat tissues, the liver and the brain show the highest levels of HSD activity, which may explain why chronic stress and cortisol overexposure are so detrimental for obesity (adipose fat tissue), diabetes (the liver) and memory (the brain)
- High cortisol levels correlate with anxiety and depression
Talbott, S. (2007). The Cortisol Connection. Alameda, CA: Hunter House, p. 17, p. 52, p. 55, p. 58, p. 117.
- High body fat can impact sex hormones
- In women, high fat stores, especially abdominal, can increase estrogen and testosterone. Obesity can result in anovulation (lack of ovulation) due to high male hormones, which results in reduced progesterone Carlson, M., Thiel, K., Yang, S. and Leslie, K. (2012). Catch it before it kills: progesterone, obesity, and the prevention of endometrial cancer. [online] Discovery Medicine, 14 (76), pp. 215-22. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3964851/ [accessed 24 Aug. 2017].
- In men, high fat stores can reduce testosterone and increase estrogen Liedtke, S., Schmidt, M., Vrieling, A., Lukanova, A., Becker, S., Kaaks, R., Zaineddin, A., Buck, K., Benner, A., Chang‐Claude, J. and Steindorf, K. (2012). Postmenopausal sex hormones in relation to body fat distribution. [online] Obesity, 20 (5), pp. 1088–1095. Available at: http://onlinelibrary.wiley.com/doi/10.1038/oby.2011.383/abstract [accessed 24 Aug. 2017].
- High body fat can impact the metabolic hormone insulin
- High body fat can cause insulin resistance, which in turn can cause blood sugar imbalances
- Obesity is closely associated with increased risk of metabolic diseases such as insulin resistance. Insulin resistance is a major predictor for the development of type 2 diabetes
- Obesity induced insulin resistance is caused by a number of factors: high body fat causes the secretion of inflammatory markers called “cytokines”. Inflammation contributes to insulin resistance Jung, U. and Choi, M. (2014). Obesity and its metabolic complications: the role of adipokines and the relationship between obesity, inflammation, insulin resistance, dyslipidemia and nonalcoholic fatty liver disease. [online] International Journal of Molecular Sciences, 15 (4), pp. 6184–223. Available at: https://www.ncbi.nlm.nih.gov/pubmed/24733068 [accessed 24 Aug. 2017].
Being underweight can also be disruptive to mental health.Mond, J., Rodgers, B., Hay, P. and Owen, C. (2011). Mental health impairment in underweight women: do body dissatisfaction and eating-disordered behavior play a role? [online] BMC Public Health, 11(1), p. 547. Available at: https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-11-547 [accessed 24 Aug. 2017].
Low BMI can:
Affect your hormones
- Many of our key hormones are stored in body fat, and made from fat. Lowering fat stores can negatively impact our hormonal balance
- Women who suffer from anorexia nervosa or bulimia, or high performance athletes can suffer from imbalanced hormones due to low BMI. Anorexia affects many hormonal systems in the body:
- Causes an increase in growth hormones in an attempt to maintain blood glucose by increasing fat breakdown
- Causes increased cortisol
- Correlated with lower insulin and glucose levels
- Causes a decrease in estrogen and other sex hormones Misra, M. and Klibanski, A. (2014). Endocrine consequences of anorexia nervosa. [online] The Lancet Diabetes & Endocrinology, 2 (7), pp. 581–592. Available at: https://www.ncbi.nlm.nih.gov/pubmed/24731664 [accessed 24 Aug. 2017].
Lower your sex hormones
- Such as estrogen (especially estradiol) and progesterone
- When a woman’s body fat is lower than 21% of total body mass, the hormonal control centres in her brain keep her from making enough estrogen to ovulate or to build up her uterine wall Gottfried, S. (2013). The Hormone Cure. New York, NY: Scribner, p. 185.
- This can result in the dysregulation of menstrual periods as seen in patients with anorexia nervosa Ziomkiewicz, A., Ellison, P., Lipson, S., Thune, I. and Jasienska, G. (2008). Body fat, energy balance and estradiol levels: a study based on hormonal profiles from complete menstrual cycles. [online] Human Reproduction, 23 (11), pp. 2555-2563. Available at: https://www.ncbi.nlm.nih.gov/pubmed/18641044 [accessed 24 Aug. 2017]., Misra, M. and Klibanski, A. (2014). Endocrine consequences of anorexia nervosa. [online] The Lancet Diabetes & Endocrinology, 2 (7), pp. 581–592. Available at: https://www.ncbi.nlm.nih.gov/pubmed/24731664 [accessed 24 Aug. 2017].
- The lowering of sex hormones can have a knock-on effect of lowering key neurotransmitters such as mood, sleep and appetite regulating serotonin (linked with low estrogen) and calming GABA (linked with low progesterone)
Affect your stress hormones
- Low BMI is associated with high cortisol in adults and adolescents
- This is consistent with a mechanism designed to maintain a normal blood glucose, when available energy stores are low Misra, M. and Klibanski, A. (2014). Endocrine consequences of anorexia nervosa. [online] The Lancet Diabetes & Endocrinology, 2 (7), pp. 581–592. Available at: https://www.ncbi.nlm.nih.gov/pubmed/24731664 [accessed 24 Aug. 2017].
Cause nutritional deficiencies
- If low BMI is the result of either not getting enough, or not getting the right macro and micro nutrients, this could be detrimental to your mental health
- High quality and sufficient quantity of macro and micro nutrients are necessary for neurotransmitter and hormone production
- Healthy fats are essential for mental health, and 60% of our brains is made of fats, so a deficit of healthy fats can have a negative impact on mental health Parletta, N., Milte, C. and Meyer, B. (2013). Nutritional modulation of cognitive function and mental health. [online] The Journal of Nutritional Biochemistry, 24 (5), pp. 725–743. Available at: https://www.ncbi.nlm.nih.gov/pubmed/23517914 [accessed 24 Aug. 2017].