What has more of an influence on obesity ,nature or nurture?

There is little doubt that there are many reasons for a person becoming obese, and many studies have pointed to both genetic (nature) and environmental (nuture) factors as contributing. 
Twin studies are often used to identify the effect of genetics on the development of obesity, and generally this research suggests that genetic factors have a substantial effect on variations in body weight, particularly in children and adolescents.   
The fact that obesity is rapidly increasing in Western countries, however, suggests that environment also plays a significant role in the likelihood of becoming obese.  LIkely causes include an increase in the consumption of ‘empty calories’ and reduced energy expenditure through physical activity.   There is an increasing availability of energy dense, high kilojoule foods and drinks and it takes little energy expenditure to access them – no long hikes through the bush to find sustenance, just get in the car and pop around to the shops!   Changes to family structure, with an increase in both parents working or single parent working families appears to have increased the reliance on takeaway foods and processed, pre-prepared meals. There are increasing numbers of children who have no idea how fruit and vegetables grow, or where milk comes from (apart from the supermarket fridge) . A reduction in physical activity may be partly attributed to the wide spread availability of technology such as computers, mobile phones and televisions.
So which has more impact - nature or nurturet? Like most things, there is no simple answer to this and I believe that it is very likely that  it varies from person to person.   We cannot group all obese people together , but instead need to consider the wide range of factors that have contributed to an individual’s weight gain, including physical and psychological influences and use this knowledge to help them make positive changes to their lifestyle to achieve a healthier weight range.

Who knows? There is a genetic component with all of us that does impact the way our body shapes are and then how we operate in our environment is really how that gets exposed or gets exacerbated. The bottom line is that you can't control your genes. You can control what you put in your mouth.

Even if you come from a bigger-boned group of people, moderating the types of things that may encourage you to grow into that shape is what I really get people to focus on.

Clear evidence from research reflected on at the Australian Lifestyle Medicine conference last weekend in Sydney showed that there was clear evidence adopted children who had obese biological parents were still bigger even when brought up by adopted parents who were of healthy weight. Studies are now showing that stress in young children and cognitive function at years old can be linked to children who become obese now. New research is also investigating the link between higher environmental toxicity in the gut micro flora in obese individuals when compared to healthy weight individuals.

We must however also look at the fact that perhaps these unhealthy guts are also due to more heavily processed foods and higher packaged foods which are usually also very high in kilojoules so the verdict is still out.
Without a doubt though there is now evidence that suggests people who are obese form child age will always struggle with obesity due to the fact that there leptin and grehlin hormones are regulated to feel a need for more food.
ALso remember that 30% of obese individuals are still metabolically healthy. So, it is the 70% of obese people that should be wondering what changes they can make.
Also: we have an innate response built into us from many hundreds of years ago that tells us to store energy. Perhaps evolution had been able to change some of us so that energy is burned easier but for others they may still be trying to store for the days we can’t find food to eat or are cold and have to stay in the cave!
There is also evidence that if you are obese from child hood through to adult hood you will probably have developed more fat cells than a person who is not obese as a child. This could mean that when you attempt to lose weight as an adult you will be able to decrease your fat cell size but not the amount you developed. Another reason to focus on body composition in terms of muscle to fat ratios and hydration as well as pathology over weight on the scales.

It is a really interesting question, and I would say they are both influential. There is more and more information coming out about the impact of genetics. Our genes can evolve from generation to generation, depending on what we consume. Basically we may have a predetermined set point with our ways but we can change that depending on what our environment is. Obviously, being in an environment that is conducive to overeating and a very relaxed, lazy lifestyle is not going to be of benefit. They are both very influential.

It is clear that both can have an impact, and each individual’s influences are different.

There are various lifestyle factors that should be addressed in obesity including food (and drink) quality (as well as quantity), exercise (but more importantly limiting non sedentary activity), sleep, medications and stress.

There are also genes that impact hormones and metabolism, which may be switched on/off with certain lifestyle factors mentioned above.

In a study that included more than 5,000 identical and non-identical twin pairs, researchers found heredity to be a much bigger predictor of childhood obesity than lifestyle. They concluded that three-quarters of a child's risk for becoming overweight is due to genetic influences, while just under a quarter of risk can be attributed to environment. Researcher Susan Carnell, PhD, says the fact that genes play such an important role in a child's weight was somewhat surprising.
 
The obesity rate among children in the U.S. has more than doubled for preschoolers and teenagers over the past three decades and more than tripled for children between the ages of 6 and 11.Similar increases have been seen across the globe, including in the U.K., where the twin study was conducted. Carnell and colleagues studied twins in an effort to quantify the impact of genetic and environmental influences.
 
“Twin studies provide a unique method for disentangling nature and nurture by taking advantage of the fact that (identical) twins share all of their genes, whereas (fraternal) twins on average share half of their segregating genes,” they wrote.
 
A total of 5,092 identical and non-identical twin pairs who were enrolled in the larger ongoing trial took part in the study; the participants were born between 1994 and 1996. Researchers measured each child's body mass index  (BMI) and waist circumference and then compared the findings between the identical and non-identical twins. Using a standardized genetic modeling analysis, the researchers concluded that the differences in the children's BMI and waist circumferences were 77% attributable to genes.
One must not conclude that bad Genes make obesity inevitable!
The findings do not mean that becoming overweight or obese is inevitable for children who are genetically susceptible, but it does mean that these children may need some extra support. It may be that genes influence behaviour through appetite or by making it harder for some people to resist food. So while one child might be perfectly OK living in a home filled with  chips and cakes, another might find it very challenging. Diet, lifestyle, and other environmental influences play a major role in obesity, especially for genetically predisposed children. This type of genetic predisposition could not be expressed if there wasn't so much food around. We would all be skinny. It is our environment that is allowing our genetic susceptibility to express itself. It would benefit everyone if we did more as a society to encourage activity and healthy, but it would be especially beneficial for children who are highly susceptible to their environment.

Adding to what Arlene wrote (which I agree with 100%) there is a link to the study (very technical) that she described here:
http://ajcn.nutrition.org/content/87/2/398.long