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Is obesity all in the genes?

What do we know about obesity and genes?

 

There is a strong genetic influence as to where individuals store their fat and as to their body composition.  It is well known that some races have differing body composition; for example, those from some Asian populations, including the Indian subcontinent and China, have a greater fat mass which is more likely to be centrally distributed, while those from Polynesian descent have a greater lean body mass than Europeans.

 

Twin studies and adopted children studies show weight as adults is related to the weight of their biological parents rather than the weight of their adoptive parents indicating that genes are an important determinant of obesity. 

 

We also know that gender affects fat storage and body composition - men and post-menopausal women store fat centrally (think 'apple' shaped) and pre-menopausal women store fat on their hips and thighs (think 'pear' shaped).  Women also have more fat than men.  These elements are determined by hormones.

 

How else does the body affect our weight?

Our bodies like to hold onto excess weight and work hard to regain lost weight. Weight reduction brings about biological adaptations which cause the body to regain lost weight. 

There is lots of research into hormones that regulate appetite and hunger.  All are affected by weight loss.  Interestingly, the adaptive responses appear to be related to the amount of weight lost rather than how fast weight is lost.

Resting metabolic rate (RMR) has been shown to be lower than predicted after weight loss, whether weight loss is achieved rapidly or more moderately.

 

Genes versus environment or individual

The obesity epidemic is a relatively recent phenomenon so what are we doing that is different?  We have what is widely called an obesogenic environment with a wide range of food readily available which is extensively advertised, resulting in an increase in energy intake and our energy expenditure has decreased due to a reduction in physical activity for transport, sedentary social activities and increased appliance use for everyday living e.g. vacuuming instead of sweeping. 

 

Not everyone becomes obese in this environment so what else might be happening?

There is mounting evidence that obesity can be caused by epigenetic triggers that occur in the womb during pregnancy.  This means factors in our environment may switch on genes, for example, if a pregnant woman is poorly nourished there may be an adaptive response which results in the child's phenotype being oriented towards an environment which is nutritionally poor.  If the environment is unexpectedly nutritionally rich, it may result in obesity and resultant chronic disease consequences.

 

That doesn't mean you shouldn't try to lose weight

Research shows even with regained weight over the long term it is possible to keep off some lost weight.  Even a modest 5 to 10 per cent weight loss significantly reduces the likelihood and impact of several weight-related conditions including type 2 diabetes.

 

 

References:

Ed Mann, J. and Truswell, A.S., 2007. Essentials of Human Nutrition, Oxford University Press, 3rd ed.

 

Obesity Australia 2016 Summit: http://www.obesityaustralia.org/publications-and-documents

 

Colagiuri, S. Is Obesity a Disease? Economic Implications, Boden Institute and Charles Perkins Centre, University of Sydney

 

Studdert, L. Is obesity a disease? Implications for government policy, Department of Health

 

Griffiths, P. Obesity as Disease:  a perspective from evolutional biology and philosophy.

Sumithran, P., Proietto, P. Maintaining Weight Loss: an Ongoing Challenge. Current Obesity Reports, December 2016, Volume 5, Issue 4, pp 383-385

 

Proietto, J., You are fat, it is not your fault, Pathology, January 2014 Volume 46, Supplement 1, Pages S14-S15

 

Sumithran, P. et al. Editorial.  Obesity: recentinsights.  Molecular and Cellular Endocrinology.  418 (2015) 89.

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