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Causes of Obesity

The general consensus among health care professionals is that obesity is caused by the intake of more calories (by eating and drinking) than are burnt up by the body (by everyday living).

The reasons for the imbalance between calorie intake and consumption vary individually, but factors which may contribute to this imbalance include:

All of these factors can have some influence on our weight.

Slower metabolism than lean peers is not one of the causes of obesity. Studies have shown that obese individuals typically have a higher metabolism than lean people due to the fact that it takes more energy to maintain a greater body mass.

The ‘big two’ as they are referred to, ie poor diet and lack of ‘exercise’ are clearly important to the growing weight problem of Western societies1, but some scientists contend that they cannot solely be responsible for the alarming rise in obesity2,3.

(1) poor diet

Bigger portions of readily available, calorie dense and rich tasting food is believed to be one of the underlying factors fuelling the obesity epidemic.

Research by thefast food Food and Agriculture Organization has shown that global food production was equivalent to 2600cal per person per day in 20024. That is estimated to increase to around 3000 cal per person per day by the year 2030. The major contributors to this increase are refined sugars and vegetable oil.

The situation in the US is more alarming still. The average calories available per person per day in the US had risen to 3754 by 20035.

Research into calorie consumption over time however is mixed.

National Food Survey data from the 1940 - 1994 showed that the consumption of calories in the UK has declined by about 20% since the 1970’s6.

The picture is different in the US. Dietary intake in the US has increased. Research showed that the average calorie consumption per person rose by around 200cal per day from 1977 to 19967.

How can both be correct?

Simple ... we are all burning far fewer calories than we used to in the past.

(2) lack of ‘exercise’

Sitting disease as one expert calls it8, in both our work and home environments is thought to be the other major factor contributing to obesity.sedentary work environment

Evidence from the insurance industry showed that even by 1992, only 20% of men and 10% of women in the UK were involved in an active occupation9.

For many of us, leisure time pursuits now involve television viewing and other inactive pastimes. The average US teenager spends 30h per week watching television10. This activity is not only sedentary, but it is often associated with eating fast food, calorie dense snacks rather than fruit and vegetables11, whilst under the influence of a barrage of food commercials12.

(3) car culture – increased urbanization, commuting, driving the kids to school

As we partition land up for specific uses - be it for housing, shopping centres, industrial zones or public parks, we increase the demands for better transportation to reach those areas. This complex pattern of low density land use, now called ‘urban sprawl’, has led to the creation of extensive road networks to allow suburban residents to travel between these specific regions. In many areas there are no walkways to get from A to B on foot13.

car_cultureThe increasing reliance on the roads has meant that residents now make simple journeys (taking the kids to school, or even buying milk or the daily newspaper) by car.

In the US from 1969 to 2001, the population grew by 41 percent. However, the increases in numbers of households (72%), workers (91%) and drivers (85%) were all far larger indicating a need for more space and therefore more sprawl. The most obvious increase, however, came in the number of cars, up 181% from 196914.urban_sprawl

In one report using data from the 2000 US Census, researchers discovered that there is an association between this urban sprawl and the risk of being overweight or obese as an adult in the US. They discovered that for every 1-point rise in an urban sprawl index (0-100 scale), the risk for being overweight increased by 0.2% and the risk for being obese increased by 0.5%15.

(4) not enough or poor quality sleep

Reduced levels of sleep has become the norm in modern society. To go along with this, sleep related disorders have also increased. There is evidence to suggest that sleep loss, either disease-related or behavioural and poor quality sleep, may contribute to the development of obesity16.poor_sleeping_habits

In 1999 it was discovered that animals unable to make hypocretin-1, an appetite stimulating hormone, suffered from narcolepsy17 – the condition of falling into a deep sleep spontaneously, which suggested that there is a link between the regulation of hunger and after meal satisfaction and the regulation of our sleep cycle18.

Our natural body clock interacts with this appetite hormone system to determine our metabolic state in relation to the light/dark cycle. Mice with mutated genes, lacking a natural body clock, have a weaker daytime feeding rhythm and tend to overeat and become obese19.

Studies have shown a link between obesity levels and hours of sleep per night in both adults and children20,21.

Evidence is increasing that disruption of our natural body clock and sleep deprivation can cause significant changes to our body composition and thus lead ultimately to obesity.

(5) alcohol consumption

The effects of alcohol on body weight are still hotly debated and investigated by scientists22.

alcoholDespite the fact that alcohol is energy dense, providing 7 calories per gram (compared to protein and carbs at 4 cal/gram and fat at 9 cal/gram), mixed effects on body weight have been observed on consumption of alcohol.

This is believed to be due to alcohol having multiple effects upon fat metabolism and essentially all lipids in the blood are affected by alcohol. These effects are dependent on both the regularity and the levels of consumption and the function of the liver.

Due to the fact that alcohol suppresses fat burning in the body, moderate alcohol consumption should probably be regarded as a risk factor for obesity, especially in consumption with a high fat diet where the risk of consuming a calorie imbalance is greater.

(6) stress

 Chronic exposure to environmental life stress may play a role in weight gain. Stress appears to alter overall food intake –resulting in a greater preference for nutrient and energy dense foods – namely those high in sugar and fat.stress

In one study23, women with ‘stress related obesity’ put on more weight and much faster than a group of unstressed women. This appeared to be related to the levels of cortisol in their urine (cortisol is used as a measure of stress, its the hormone designed to maintain our blood pressure under a stressful ‘fight or flight’ situation so the more prolonged the stress – the more cortisol we produce)24.

In another study of over 800 participants, the researchers found that those people in the groups with the highest stress and more prone to emotional eating as a consequence, were over 13 times more likely to be overweight or obese than the participants with the lowest stress levels25.

(7) decreased variability in the temperature of our surroundings (air con, heating, indoor lifestyles).

indoor_lifestylesThe temperature of our surroundings may play some part in our increasing weight problem. When we are cold we shiver – when we are hot we sweat ... both of those bodily processes burn calories in our attempts to maintain a stable body temperature.

When we are thermally comfortable ie. not too hot or too cold, we do not require energy consumption to maintain our body temperature, as our clothing and environmental heating or air con serve that function for us. This is what scientists call our thermoneutral zone (TNZ) and evidence suggests that we spend more time in this state than we used to in the past.

British household temperatures have risen by 5°C (9°F) over the past three decades from 1970. U.S. indoor thermal standards for winter comfort have risen from 18°C (64°F) in 1923 to 24.6°C (76°F) in 198626,27.air conditioning

In the US, the proportion of households with no air conditioning dropped from 44% in 1978 to 28% in 1997. Taking a look at the extreme case, by 1997, 93% of households in the southern US (where some of the highest obesity rates in the world are found) had some form of air conditioning, compared with 74% in 197828.

Even in the UK, the amount of energy consumed by air conditioning has risen dramatically as more shop, offices and cars are fitted with air con to improve comfort levels29.

(8) endocrine [hormonal] disruptors

These are industrially produced substances that are found in the environment and food chain, which have an impact on our metabolism due to their hormone-like activity.

chemical_plantRecent evidence suggests that these endocrine-disrupting chemicals might cause changes in normal hormonal regulation and alter other processes involved in our natural weight balance, which may then lead to weight gain by increasing the size of our body fat mass. It is suspected that these synthetic chemicals make an unhelpful, but telling contribution to our growing weight epidemic. Yet of the approximately 70,000 documented synthetic chemicals, few have been examined to determine their effects on our endocrine system30.

(9) medication

The explosive growth in the use of medication for the management of a range of health conditions over the last thirty years is suspected to play a role in the cause of obesity31.

Antipsychotics, both traditional and the newer types are associated with weight gain. Both olanzapine and clozapine result in mean weight gains of over 4 kg at 10 weeks32.pills

Many antidiabetics, including insulin, thiazolidinediones and sulfonylureas also promote body fat production, especially the newer thiazolidinediones, which promote fat cell proliferation33.

Other types of drug thought to be involved in weight gains are antihistamines, with the more potent types inducing greater weight gain, beta-blockers, HIV anti-retrovirals and some evidence points to oral contraceptives and selective serotonin reuptake inhibitors producing weight gains34.

(10) hormonal imbalances (eg polycystic ovarian syndrome, Cushing syndrome, hypothyroidism)

(11) genetics and rare genetic disorders (eg Prader-Willi syndrome) – although simply having obese relatives does not guarantee that you will be obese

(12) decreased rates of smoking and other stimulant withdrawal

(13) metabolic disorders, which could be caused by yo-yo dieting

(14) eating disorders (such as binge eating, bulimia, night eating syndrome)

(15) emotional issues (depression, hopelessness, anger, fear, boredom)later_childbirth

(16) pregnancy (on average a woman’s weight settles at about 4-6 lb heavier after the birth of each child)

(17) pregnancy at a later age

(18) positive natural selection of people with a higher BMI

(19) assortative mating - people tend to form relationships with each other (birds of a feather) depending upon body type.

(20) age (we tend to lose muscle and gain fat as we age. Our metabolism also slows. Both of these lower our calorie requirements)

Bottom Line

There are many causes of obesity. Although the 'big two' are generally regarded as the sole contributors to obesity in the general press, many researchers are studying other lifestyle factors as causes of obesity, which may open up alternative strategies for improved weight loss and improved health. Some of these 'additional' causes of obesity may offer opportunities for weight loss for those slimmers aware of the potential within these causes.

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