The biology of obesity
A review in Proceedings of the Nutrition Society (2005), 65, 31-38 Trayburn P
Obesity is a preoccupation of modern nutrition. The founding fathers of our science would never have believed that the eradication of some major nutritional problems would lead to this particular epidemic.
The biology of obesity includes]
The fundamental mechanisms of energy balance and its regulation, genes, appetite, endocrine factors.
The biological basis for the development of obesity
Adipose tissue function
The biological description of the obese state ( particularly physiological adaptations)
The pathological consequences of obsess, i.e. associated disorders
The physiological basis of treatment strategies
It has always been axiomatic that obesity is fundamentally a problem of energy balance. That obesity can only develop when energy intake is in excess of energy expenditure, differences in input and output being buffered primarily by changes in fat stores.
There are two immutable “ Laws of Obesity”.
That for obesity to develop, intake must be in excess of expenditure
obese subjects have a higher energy expenditure and therefore a higher average energy intake than lean subjects. They have a larger relative mass to move about.
Appetite. It is understood that the central hypothalamus controls food intake. Several peripheral signals are recognised in the regulation of food intake eg ghreli, peptide YY and leptin. Leptin is secreted from the white adipose tissue.
The attractive work on thermogenesis of 20 to 30 years ago, has not stood the examination of time. That is the uncoupling of oxidative phosphorylation by brown adipose tissue mitochondria.
White Adipose tissue. The buffering of energy intake and expenditure is through triacylglycerol deposition in White Adipose Tissue. Obesity is due the laying down of white fat mass ( >85%). Adipose tissue is the source of endocrine signals e.g. leptin. There is a rich array of different glucose transporters more than 8 different types.
White Adipose Tissue is also an important endocrine system. Secreting adipokines.
Inflammation A number of inflammation related proteins e.g. nerve growth factor (NGF) are released by white adipocytes. It has been suggested that obesity and diabetes are associated with chronic low grade inflammation. This tissue related inflammation may play a role in the development of insulin resistance and associated pathologies.
Several thoughts come to mind in reading this very interesting review albeit somewhat tardily
There has always been the aphorism that within every fat person is a thin person struggling to get out. Maybe that within every thin person there is a fat person at risk of struggling in. Are we all at risk or only certain people.
If one goes round a super market , the fattest people are to be found in the crisp and confectionary isles tossing goodies into their trolleys. Cheap delicious high energy foods.. Greed has been carefully cultivated in our society either for readily eaten food or alcohol
The concept of low grade inflammation is fascinating. I was reared in Gastroenterology where the pre-occupation was duodenal ulcer disease. Everyone knew that this was a result of too much acid produced by the stomach. Everyone knew that this was due to stress. Reduce acid and stress and all would be ok. The chronic low grade inflammation in the stomach duodenum was ignored until the Helicobacter that causes gastric and duodenal inflammation was found. Eradication of the helicobacter led to a disappearance of duodenal ulceration. Maybe there is a message here for diabetes and obesity.
Appetite preferences are also important. The heavy consumption of sweets, crisps and alcohol is an exaggeration of appetite needs. Who are those who can so indulge themselves.?
That exercise is so important. The reduction of the involvement of schools in games and the reduced time given to energy expending games eg soccer, rugby and running cannot be good. Playing fields being lost for housing developments cannot be good for exercising children.
- Martin Eastwood