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Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 11:39 AM BST
on bmj.com
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First: 7/4/2011 Last: 19/6/2013 |
The latest BMJ Head to Head looks at what are the fundamental causes behind the rising rates of obesity: is it environmental or is it genetic? http://www.bmj.com/content/345/bmj.e5843 http://www.bmj.com/content/345/bmj.e5844 John Wilding, professor of medicine, and arguing that environmental factors are the cause says that whilst “regulation of body weight and fat content is under powerful biological control...40-70% of body fatness is inherited.2” It may seem counterintuitive to suggest that the main causes lie in our environment. However, known single gene defects, such as leptin deficiency, are rare causes of obesity,3 and the only common gene polymorphism with well characterised effects on body weight, FTO, has a relatively small effect size (about 3 kg greater weight for those who are homozygous for the variant associated with obesity, and about 1.5 kg for heterozygotes).4 For someone to become obese, overall energy balance (the difference between energy consumed in the form of food and that expended in normal biological processes and physical activity) must be positive over time. Of course, this is more likely to occur in those genetically predisposed to gaining weight, especially if the environment is more conducive to increased consumption and decreased activity. The increase in the prevalence of obesity has mainly occurred over the past 30 years and has been seen in most parts of the world. Such rapid change cannot be due to genetic (or even epigenetic) changes. In contrast, the evidence that the environment has changed is overwhelming. The environmental changes are complex and include substantial shifts in the production and availability of food, occurring simultaneously with alterations in the physical environment that encourage sedentary behaviour.” Timothy M Frayling, professor of human genetics, arguing on the genetics side, writes “changes in the environment (decreased need for physical activity and greater availability of cheap food) mean we are all at increased risk of obesity compared with our parents and grandparents. So why do many people remain slim, while others gain weight? Genetic variation influences our appetites, metabolism, and tolerance of physical activity. This creates a strong genetic component to variation in body mass index in today’s environment. An analogy can be made with smoking—if everyone inhaled the same amount of cigarette smoke every day, the strongest risk factor for lung cancer would be genetic susceptibility to the adverse effects of cigarette smoke (G Davey Smith, personal communication).” In a recent systematic review of five adoption studies with several hundred parent-biological child and parent-adoptee comparisons, children’s body mass index was consistently more strongly correlated with that of their biological parents than of their adoptive parents.2 Genetic factors influence substantially where you are on the body mass index scale in a given population at a given time. Evidence is accumulating that these genetic factors may operate largely through appetite control. If true, plans based on changing our environment, such as banning the sale of supersized sugary drinks,12 will make genetic factors less important and be more successful than plans to increase awareness through education.”
What do you think? Are you genetically predisposed to be overweight or sedentary/environmental factors which make people overweight? Or could it be that some of us have genes that make us overweight (either through biology or behaviour) and the environment just accelerates this process? And as Prof Frayling says, is education about diet and weight just a waste of time? |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 1:08 PM BST
on bmj.com
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Posts: 3007
First: 10/3/2009 Last: 19/6/2013 |
I think dietitians and erroneous dietary philosophy have caused a huge change in the way we eat compared with that of the 1950's when I was a child. Banning sugary drinks is just one more nanny state solution. Why not ban breathing out CO2 as it is contributing to global warming? People in general tends towards energy conservation as they have all read the Laws of Thermodynamics. We are automating almost every activity. I can now get my computer to type with just my voice. Soon this will extend to all walks of life; fridge, doors, computer, etc and we will have household robots rather than illegal immigrants. How many people will wait several minutes for a lift/elevator to go down one floor. I see it all day at the hospital. I rarely use a lift. A for going up two floors, they just stand like dummies waiting to go up twenty feet which on stairs takes less than 20 seconds. I am now seeing patients weighing over 200kg. Indeed, obesity and fatty liver are the most common things I see all day. We are doomed. It is impossible in my opinion to change human nature. We are on the slipway heading off to Diabetic Land and the Isle of Doom. The cave man in us has found the remote, opens a beer and lies back peering at the box over his corpulent abdomen while eating French fries and a Big Mac cheering his football team while too unfit to even walk up stairs let alone play football. How many adults do you know regularly play sport? Stand at the checkout for five minutes and observe what gets checked out. Sitting for even a hour increases cardiovascular morbidities. Thin Homer who knew the Plains of Troas is now fat Homer and within the Trojan Horse are sheaves of domesticated wheat and domesticated fruit trees. We are hooked on carbs without the exercise to burn them. . Had we stuck with a sacrificed lamb on the spit, yoghurt and tabouli; simple Mediterranean food we might have had a chance. It is too late. We are doomed. |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 4:00 PM BST
on bmj.com
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Posts: 3059
First: 27/3/2012 Last: 13/6/2013 |
Very interesting post. Both, environmental as well as genetic factors are implicated for 'obesity' but more important factor to be blamed is the genetic predisposition. |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 4:14 PM BST
on bmj.com
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Posts: 330
First: 12/11/2010 Last: 8/6/2013 |
The laws of thermodynamics can be stated as: 1) You can't win. 2) You can break even only on a very cold day. 3) It never gets that cold. |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 7:04 PM BST
on bmj.com
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Posts: 499
First: 12/7/2010 Last: 11/6/2013 |
The arguments put forth by Prof. John Wilding are quite convincing for me. Surely there may be some genetic component - every bodily function/activity has some genetic basis but that doesn't rule out the major role of the environment. |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 7:27 PM BST
on bmj.com
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Posts: 1336
First: 13/4/2010 Last: 16/6/2013 |
I think it's clear to anyone with half a brain that it is almost certainly a combination of the two. Odysseus my good friend - it's easy to use pejoratives such as "nanny state" when it comes to slagging off recommendations about reducing our intake of sugar and refined carbs (especially in our kids) - the sugar-related industries do it all the time and behave exactly as the cigarette manufacturers did in the 60s and 70s until it was clear they were defending the indefensible. A good read of the evidence in both English language and non-English texts suggest a clear link between our obesity epidemic and a marked increase in our consumption of sugar and refined carbohydrates. Much of this research was done in Germany in the 1920s and 30 and published in German. Conveniently the rise of the Nazis and WW2 allowed German language research to be suppressed in favour of English language research, largely out of the USA, at a time when US and UK sugar giants and manufacturers of sugar-saturated fizzy drinks and breakfast cereals applied massive lobbying pressure to down play any links between sugar/refined carbs and poor health - behaving, as I said, exactly like the cigarette manufacturers. Sad but true. |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 9:35 PM BST
on bmj.com
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Posts: 3007
First: 10/3/2009 Last: 19/6/2013 |
In Response to Re: Are environmental or genetic factors to blame for obesity?: The laws of thermodynamics can be stated as: 1) You can't win. 2) You can break even only on a very cold day. 3) It never gets that cold. Or for sanitation engineers: 1) There is shit 2) It gets deeper 3) A convenient hole to hide it in is not available. The same applies to humans. If you consume energy and do not burn it, you store it and get fat [which can be difficult to hide - so the 3rd law applies to us as well]. It has been clearly demonstrated that the average energy consumption per person has DECREASED over the last 50 years. That ought to mean that overall we lose weight; but the average energy Expenditure has decreased by even more than the intake; so naturally, this excess is converted to fat. We have an inherent tendency to store food ready for the next famine, but at the moment the supermarlets open nearly full time, so there is no restriction on food availability - so we get fat. This may of course change. All that is needed is a couple of massive volcanic eruptions to cut food production for a few years [i.e. a slightly bigger event than Mount Tambora in 1816 which caused the year without a summer], and it could get very interesting... Posted by TimReynolds Here, here. A man after my own heart. We are steam engines heading down the dead-end precipice of entropy. |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 12/9/2012 10:00 PM BST
on bmj.com
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Posts: 3007
First: 10/3/2009 Last: 19/6/2013 |
In Response to Re: Are environmental or genetic factors to blame for obesity?: I think it's clear to anyone with half a brain that it is almost certainly a combination of the two. Odysseus my good friend - it's easy to use peioratives such as "nanny state" when it comes to slagging off recommendations about reducing our intake of sugar and refined carbs (especially in our kids) - the sugar-related industries do it all the time and behave exactly as the cigarette manufacturers did in the 60s and 70s until it was clear they were defending the indefensible. A good read of the evidence in both English language and non-English texts suggest a clear link between our obesity epidemic and a marked increase in our consumption of sugar and refined carbohydrates. Much of this research was done in Germany in the 1920s and 30 and published in German. Conveniently the rise of the Nazis and WW2 allowed German language research to be suppressed in favour of English language research, largely out of the USA, at a time when US and UK sugar giants and manufacturers of sugar-saturated fizzy drinks and breakfast cereals applied massive lobbying pressure to down play any links between sugar/refined carbs and poor health - behaving, as I said, exactly like the cigarette manufacturers. Sad but true. Posted by skyesteve My Dear Stephanos, King of Skye, as one who lives in one of the most nanny of nanny states, I must take exception to your taking exception about slagging off (slag is spit in Ozalian) at nanny states. The role of government is to intrude into every aspect of the citizen's life. For example, last week I had to get a permit for my new artificial prostate machine in the bedroom and now they are trying to ban stairs as a man fell down one last week and died. The Battle of the Tryphidiae; What is really happening with obesity is about our war with plants and they are now winning this silent battle. About five thousand or more years ago, their peace was disturbed by Bronze Age man with the new axes, sickles and scythes. Now trees and plants are intelligent and have feelings. They peacefully take CO2 out of the air by day and effortlessly make energy from this and photons and water and store it as CHO whereas we have to go to work each day. We can't even store our excess solar generation in Oz. I think in the UK there is no sun so you are OK. We cut down trees by millions and enslaved plants into silent obedient rows in fields by the millions of acres and then cut them down each year ungratefully from the Fertile Crescent to the paddy fields of Cambodia and the gloomy fields of Britain. Secretly they despise us. They are winning this insidious war on humans as they are now making us slow, fat, arthritic and diabetic until our whole species will eventually become manure for plants again. It will be a crumbling, weed and tree-infested New York after Mad Max 2. All the CO2 we are now making from plants eg coal, oil and farting is now being recycled by plants and deposited not as coal but as fat on our hips, omenta (note Latin neuter pleural) and coronary arteries. The human species is doomed. Plants will win and they are talking amongst themselves about this everyday. We think plants are dumb like fish but we are the dummies. Sequoias are the largest living things on Earth. The Great Barrier Reef is arguably the largest marine bio- structure. We are mere cockroaches and when we go they will be bigger too as they once were in days before us. May the Nanny Force be with you. Odysseus |
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Re: Are environmental or genetic factors to blame for obesity?
posted at 13/9/2012 8:51 AM BST
on bmj.com
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Posts: 1336
First: 13/4/2010 Last: 16/6/2013 |
The human species is doomed. Plants will win and they are talking amongst themselves about this everyday. I always thought it was going to be cockroaches and scorpions... 
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Re: Are environmental or genetic factors to blame for obesity?
posted at 13/9/2012 11:32 AM BST
on bmj.com
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Posts: 3007
First: 10/3/2009 Last: 19/6/2013 |
In Response to Re: Are environmental or genetic factors to blame for obesity?: The human species is doomed. Plants will win and they are talking amongst themselves about this everyday. I always thought it was going to be cockroaches and scorpions... Posted by skyesteve They will live in the plants and trees. |
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