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General Nutrition and Diet Facts

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Overweight and obesity

 

Why is there an epidemic of increasing obesity?

Although the external influences and internal processes are both very complex the ultimate causes of obesity are under exercising and/or over-eating: energy intake > energy expenditure. But the development of obesity, via overweight is usually so slow and insidious that people hardly notice it is happening.
The body’s homeostatic energy regulation is better able to defend against insufficient food than against a little more food, a little less energy expenditure.

Energy balance

1 kg body weight gained has energy of approx 7000 kcal
10 kg weight gain over 5 years = 70 0000/ 5*365 = 38 kcal/day
This is a daily error of energy balance of + 1.5%
OR 10 minutes’ walk
OR one square (1/8) of a 2oz milk chocolate bar
OR half a digestive biscuit

Possible reasons for over-eating these days:
  • more varied foods; supermarkets
  • advertising and promotion of foods
  • more eating outside the home (pubs, ethnic restaurants, fast food chains, etc)
  • more fatty food; more snack foods
  • over-eating because of anxiety (for example, work stress) or depression (for example, unemployment)
  • grazing and irregular meal times
  • fewer people now smoke (smoking suppresses appetite)
Possible reasons for under-exercising these days:
  • more labour-saving machinery at work and at home (fork-lift trucks, power tools, washing machines, even automatic doors and lifts)
  • television (couch potatoes)
  • personal computers (“mouse potatoes”) and email
  • more cars; less walking and cycling
  • less open space for recreation
  • fear of violence in the streets
  • central heating might also reduce energy expenditure
Complications of obesity

Most of the medical complications of obesity are well known. Risks of cardiovascular complications and diabetes are greater in people with abdominal obesity. This can be assessed clinically by measuring waist circumference. In men the normal measurement is up to 94 cm and metabolic complications are substantially increased at above 102 cm. The corresponding waist circumferences in women are: healthy less than 80 cm, increased risk 80-88 cm, substantially increased risk 88 cm. Considerable weight gain in a short time carries greater risks than reaching the same weight slowly.

Causes

Obesity secondary to hypothalamic conditions that increase appetite is rare, and to endocrine disorders uncommon. Obesity may follow

(a) enforced inactivity such as bed rest, arthritis, stroke, change to a less active job, sports injury, or
(b) over-eating associated with psychological disturbances, for example, depression or anxiety, or some drugs that increase the appetite. Pregnancy and stopping smoking contribute to overweight.

The genetic influence on obesity was clearly shown in a study. A strong relation existed between the weight class of the adoptees (thin, acceptable, overweight, or obese) and the body mass index of their biological, but not their adoptive, parents. In twins body mass index is more strongly correlated between monozygotic than dizygotic twins, even when they are reared apart.
Wide searches are going on to see if mutations of candidate genes for peptides and receptors involved in energy regulation are associated with obesity. Mutations of MC4R the melanocortin receptor, of beta1, beta2 and beta3 adrenoreceptors, of the leptin receptor and of leptin have been found associated with obesity. In the great majority of obese people the weight gain is polygenic.

In most people obesity is primary. There is no obvious predisposing condition. If the patient says (s)he eats little:

(1) the weight gain may have been in the past
(2) some people undoubtedly need less food than others apparently comparable; they are efficient metabolisers with a low basal metabolic rate (but normal thyroid) and may feel the cold sooner than others,
(3) repeated periods on low calorie diets, weight cycling, may lead to further adaptive lowering of the basal metabolic rate.
In surveys, obese people have often reported that they do not eat more than thin people. But it is showed that the energy expenditure of a group of obese people was higher than their self-recorded food energy intakes. In other words, obese people tend to under-report their food intake.


 


 
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