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Post No.: 0794obesogenic


Fluffystealthkitten says:


At current estimates, the heritability of obesity is 40-70%. This suggests that genes do play a key role, and therefore some people are luckier than others if their genes are a better match for the environment they inhabit. Someone who has more ‘obesogenic’ (tending to cause obesity) genes is luckier in environments where food is scarce, and someone who has fewer such genes is luckier in environments where food is plentiful. The former is more likely to pack on excess fat (energy reserves) when food is everywhere. The latter is more likely to struggle in a pending famine survival situation if she/he finds it as difficult as herding cats to put on weight. These genes aren’t linked with unpreventable cancers, motor-neurone diseases or autoimmune diseases like lupus, for instance, which are considered disadvantages whatever the environment (and for these reasons medical research arguably would be better directed towards solving). So on the whole they’re not ‘good genes’ or ‘bad genes’ – just ones that suit different environments. It’s about an interaction between one’s genes and one’s environment.


Furthermore, obesity is hardly 100% heritable. There’s enough for the vast majority of people to be able to choose to eat more healthily and participate in enough physical activities in order to avoid obesity. There’s enough for most parents to be able to raise their children with healthy habits.


On paper, it’s still true that all we need to do is burn off as much as we consume to not put on weight. People aren’t going to break the laws of physics! This is the same for everybody – it’s not ‘one rule for some and another for others’. Some scientists claim that some people cannot become obese even if they wanted to – but everyone can avoid becoming overweight because no one is able to store energy from nothing i.e. if they don’t consume it.


‘Obesogenic genes’ may affect one’s hunger/satiety, the sense of reward from eating, taste preferences, body shape/fat storage and BMI. There are genes that influence putting on weight, and not putting on weight. But these don’t determine one’s weight but influence how much and what types of foods one might desire. Moreover, they only explain differences, on average, of a few kilograms from one person to the next – not a few stones!


So then perhaps the bigger culprits are people’s ‘obesogenic environments’? People can choose and shape their own immediate environments to suit their own personalities – but it’d help enormously if the wider environments where many people nowadays live were less obesogenic. Although we can underline the personal self-discipline to behave healthily, and perhaps there’s an element of this too (e.g. food labelling depends on consumers paying heed to them!) – the temptations presented by a high concentration of fast food outlets and home deliveries, places that encourage driving over walking or cycling, labour-saving appliances and sedentary leisure pursuits, the development of ever more calorie-dense foods and beverages, junk food advertising, and other physical, social, cultural, economic and government policy factors that promote obesity, collectively work to increase the likelihood that a population will overall experience an obesity crisis.


It must also be noted that one’s mental willpower to resist these temptations will also be partly genetically influenced. Some genes that affect obesity risk aren’t about things like how easily fat is stored but about things like one’s propensity towards addiction. Our personalities are partly down to our genetics. Having a ‘can do’, ‘give it a go’, ‘take control’ and ‘never give up’ attitude is partly down to our DNA. Thus outright personal blame, or praise, is difficult to justify when no one chooses, earns or therefore deserves (in a moral ‘merit’ sense) her/his own genetic makeup. No one chooses her/his own parents, or really upbringing either.


One’s upbringing is also an environmental influence, and this plays a large role in developing one’s habits regarding health. Human offspring have one of the longest incubation, then nurturing, periods of any animal before they fly the nest; indicating how important handing down knowledge and culture from generation-to-generation is. We know that the human brain is still undergoing major changes right through puberty and adolescence. This all indicates that human brains need to be raised for a very long time, and obviously preferably in healthy ways.


How a parent raises their own biological child will partly be influenced by that parent’s own genes, and how they were themselves raised, though(!) So it’s complicated. And once more, where really is strictly free choice in all this?


Well some regard choice as having the sense of being able to viably make a different choice. Save for extreme cases, like a relevant intellectual disability – there’s always a level of personal responsibility if one has any level of personal ability to make any kind of choice. It may not be your fault that you have a heightened genetic risk towards, say, heart disease – but it’ll be your responsibility if you didn’t live healthfully knowing you had such a risk.


Yet how viable an alternative choice is depends on environmental factors like the cost of healthy options like fruit and vegetables, and the accessibility of natural green outdoor public spaces. The surrounding place and time matters.


People’s genes bestowed upon them the brainpower to learn and adapt for whatever environment they happen to inhabit, so they’re never just the product of their unfettered genetic instincts. But people can learn healthy or unhealthy lessons. Tongans presently have a culture where they believe that being large represents masculinity and status. Victorian high-society culture exhibited penchants for certain foods that were considered high-status. Obese people tend to have obese family members or friends (although it’s difficult to say whether they influence each other environmentally and/or (in the case of family) genetically, and/or (in the case of friends) they simply gravitate towards each other). But a culture could promote healthy habits instead of those that prioritise impatience and consumption.


In a way, it’s inescapable that genes are directly or indirectly involved in every outcome related to life. Getting burnt is clearly an environmental event (spontaneous combustion is a dispelled myth), yet if one had genes that made one fireproof (maybe skin made out of silica?) then one would be fine in front of a flame.


But of course what we’re interested in here is comparing the relative outcomes between different individuals with different genes and environments and why some become obese while others don’t.


Some identified ‘obesogenic genes’ include the FTO gene and the MC4R gene. A risk mutation of the MC4R gene can make one slightly more prone to obesity. If you’ve got one or two copies of the FTO gene though, you can apparently reduce the sensitivity of it… by exercising! So it’s not fate, and the advice remains the same as it’s been for decades – do some exercise!


Also, some obese people don’t have these so-called ‘obesogenic genes’, and some people who have them don’t turn out obese. Plus the risk of obesity-related diseases is high when you’re obese, and low when you’re not, regardless of whether your genetic risk to obesity is high or low. Additionally, humans have plenty of genes that predispose them to physical activities – like those that gave them joints and muscles to move!


Monogenic diseases (which are caused by a variation in a single gene) do generally spell out a genetic fate (e.g. cystic fibrosis and some rare obesity cases). But polygenic diseases (which involve variations in multiple genes) are generally tempered or exacerbated by a large environmental component (e.g. diabetes and the vast majority of obesity cases).


Although it’s too easy to casually say (and Furrywisepuppy and I probably fall foul of this occasionally) – the most misleading word we can arguably hear in genetics is ‘for’, like a gene ‘for’ obesity. The situation for behaviours is far more complex than that, so a person with all of the apparent ‘obesogenic genes’ may not become obese at all. Relatively few traits or disorders are single-gene influenced or monogenic compared to multifactorial or polygenic. It’s rare in genetics for a trait to have a simple single-gene cause or be fated through genetic determinism.


People will often try to reduce a problem down to a single factor to point the claw at, but many problems are borne out of multiple contributory factors. The environment plays a massive role in influencing many phenotypes, thus it’s not just about one’s genotype. Read Post No.: 0589 about epigenetics too. Different mutations can also produce different effects on different individuals depending on what other genes they have, along with their environment. Many genes are multifunctional (pleiotropy) and interact in unexpected ways within the network of other genes, hence it’s difficult to determine the exact function(s) of many genes. Genetic evolution remains ongoing too, hence things don’t stand still even if we could (not just practically but for the humongous ethical hurdles), and wanted to, create ‘designer babies’. The environments of the future are also never 100% certain for us to know what’s ‘advantageous’ or ‘desirable’ for the future.


Diseases that are strongly or entirely caused by genes include muscular dystrophy, cystic fibrosis, Huntingdon’s disease, hereditary cancers and hereditary haemochromatoses. Most diseases are complex however and come about from an interaction between genetics and the environment, like toxic substances or microbes, and these include cancer, diabetes, hypertension, Crohn’s disease, Alzheimer’s disease, thromboses, pancreatitis and more. Some problems are almost entirely caused by the environment too, like intoxication, smoking-related illnesses, infectious diseases and accidents. This of course doesn’t mean that environmental factors will alone explain all diseases.


Well both epidemiologists and geneticists tend to agree that it requires both environmental stressors combined with the ‘right’ (or ‘wrong’) genes to increase the probability of developing certain diseases. So even if we cannot change our genes – we can feasibly change our home environments and lifestyles. And even if we cannot single-handedly choose our own cultures and wider environments – we can lobby our governments and vote with our wallets to help reshape them.


Multiple genes may subtly combine and complexly interact, in combination with the environment, in different ways, to different degrees, at different times during our lives. With obesity in particular – the key is the interaction with the environment. So we shouldn’t succumb to defeatism if we find out we have these ‘obesogenic genes’. Well for some, finding out they’ve been dealt a ‘bad hand’ will inform and encourage them to compensate by living more healthily.


There was research into whether obesity can be caused by ‘obesogenic viruses’, like the avian adenovirus SMAM-1 or human adenovirus AD-36, but – like with ‘obesogenic genes’ – there exist those who have the virus but aren’t obese and those who don’t yet are nonetheless obese, thus they’re not the complete story.


People’s gut microbiomes (the bacteria, fungi, viruses, parasites – basically other organisms that reside mainly in people’s lower intestines) are largely affected by their diets. Some microorganisms help break down lipids/fats faster. Environmental differences, which can affect food choices, can create different gut microbiomes in different individuals, thus make it easier for some to keep/lose weight than others.


But although it may be easier for some than others to maintain a healthy weight, it’s possible for virtually everyone to do so. Well if it’s down to one’s gut microbiome then changing one’s diet will work. So it’s not fate, and the advice remains the same as it’s been for decades – eat lots of different fruits and vegetables!


The situation of genetics, environment, parental responsibility and personal responsibility is complex. Notwithstanding, if we want the best, realistic chance of creating the biggest improvements to a nation’s health, we need to primarily look at changing the environmental factors, like reducing junk food advertising, reducing false advertising for supposed quick-fixes that’ll rescue us from our unhealthy lifestyles, restricting supermarket promotions on high-calorie snacks, nudging more physical activities via better town and building design, and so on.




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