What do we know about obesity and
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
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
Ed Mann, J. and Truswell, A.S., 2007. Essentials of Human
Nutrition, Oxford University Press, 3rd ed.
Obesity Australia 2016 Summit:
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.