Thursday May 29 2014
The FTO gene has long been associated with obesity
"Carriers of the FTO gene are more likely to succumb to impulsive hunger pangs and prefer high-calorie foods," the Mail Online reports.
A study of carriers of a variant of the FTO gene found reduced activity in areas of the brain associated with impulse control. This was associated with changes in weight, brain function, impulse eating and dietary intake as people got older.
All humans carry the FTO gene, a gene involved in appetite. There is a wide body of research that suggests that certain "high-risk" variants of FTO make people more vulnerable to becoming obese as they get older. It is still unclear why this is the case.
Brain scans suggest that carriers of a specific high-risk variant – rs1421085 – appeared to have decreased brain activity in areas of the brain associated with impulse control. The carriers may also have a "hardwired" preference to find eating high-fat food more enjoyable. Ongoing research did find that these carriers were more likely to become obese as they got older.
This study gives us more information about whether or not some people may have a genetic predisposition towards becoming overweight or obese, and why. It does not mean that this is inevitable, nor does it show that some people are genetically unable to resist impulse eating.
Whatever your genes, you can maintain a healthy weight. Why not try the NHS Choices 12-week diet and exercise plan?
Where did the story come from?
The study was carried out by researchers from the National Institute on Aging, Florida State University, and Johns Hopkins Medical Institutions in the US.
It was funded by the US National Institute on Aging and published in the peer-reviewed journal, Molecular Psychiatry.
The Mail Online's coverage was fatalistic in tone, implying that people with the "obesity gene" are unable to do much about their impulse eating or their weight.
But this study does not show that impulse eating is determined by our genes. It did not look at actual impulse eating, only self-reported "impulsivity" as a personality trait.
While brain scans were used to study areas of the brain associated with impulse control, at present this is a very inexact diagnostic tool. Brain scans certainly cannot prove that a person is genetically predisposed to impulse eating.
The true picture of obesity is far more complex. It is likely that there are many genes associated with obesity, some of them still unidentified. The study looked at only one particular variant in one of these genes.
There are also environmental factors to consider. The United States is notorious for being an obesogenic environment. This is an environment that makes inhabitants more prone to obesity because of a number of factors, such as the ready availability of cheap, energy-rich food and lack of opportunities to exercise.
What kind of research was this?
This was a cohort study of ageing which looked at what happened to people who carried a particular variation (rs1421085) in a gene known as the FTO gene as they aged.
This variation has been found to be associated with obesity in children and young people. Less research has been done on its effect in older people or on weight changes over time. The variant has also been found to be associated with mental health disorders and brain shrinkage in older people.
The researchers say that the biological basis of obesity-related behaviour is poorly understood. Overweight people are sometimes portrayed as being weak-willed and unable to control their eating.
However, the researchers argue that it is unclear whether a common biological mechanism underlies a predisposition to obesity, as well as impulse behaviour and a preference for calorie-dense foods.
They wanted to see if the FTO gene variant was associated with changes in body mass index (BMI), as well as changes in brain function and personality traits such as "impulsivity", as people grew older.
What did the research involve?
The researchers used a large long-running US study of ageing, which began in 1958. They identified which participants carried the FTO gene variant and which did not, and compared their BMIs, brain function and personality traits over time.
People carry two copies of any given gene, so participants were tested for whether they carried one or two copies of the FTO gene variant. They also underwent detailed examinations, including neuropsychological assessments and neurological, laboratory and radiological tests every two years.
The participants' height and weight was measured at each visit to determine changes in their BMI as they got older. They were also asked details about their physical activity.
A subset of participants also underwent regular brain scans, which began in 1994, to measure changes in blood flow to different parts of the brain and changes in brain function. The researchers were particularly interested in parts of the brain known to be involved in controlling impulses and response to taste.
Personality traits were also assessed as people aged using a validated 240-item questionnaire. For their current analysis, the researchers primarily focused on the personality traits of impulsivity, excitement-seeking, self-discipline and deliberation. These traits were assessed because they could potentially affect eating behaviour.
Dietary intake was assessed by seven-day dietary records reported by the participants and collected during four time periods – 1961-65, 1968-75, 1984-91 and 1993-2005. The participants were trained in the procedure for completing these records – such as how to assess portion size – by dietitians.
The final sample analysed in this study consisted of 697 participants who were cognitively normal (those with dementia or mild cognitive impairment were excluded). Their average age was 45 at the start of the study, and they had been followed up for between 11 and 35 years (average 23 years).
The analyses took into account factors (confounders) such as age, race, education and cardiovascular risk that might influence the results.
What were the basic results?
The researchers found that about 20% of the study's participants had two copies of the obesity-related FTO gene variant, and 48% carried one copy.
They found that over time, changes to BMI as people got older were significantly different between carriers and non-carriers of the gene variant.
Peak BMI (the highest BMI a person reached during the study) was highest in those with two copies of the variant, intermediate in those with one copy, and lowest in non-carriers. The difference appeared relatively small.
The researchers also found that carriers of the variant were more likely than non-carriers to have reduced activity in certain parts of the brain as they grew older. This included an area involved in impulse control.
They found that measures of impulsivity decreased over time in both carriers and non-carriers, while the trait of deliberation increased. However, the presence of the FTO gene variant was associated with less of a decline in excitement-seeking, with the largest effect found in those with two copies of the variant.
On dietary patterns, they found that all participants reported eating less fat and more carbohydrates over time. However, the presence of the obesity-related variant was associated with less of a decline in fat intake. It was also associated with less of an increase in carbohydrate intake.
Again, the effects were strongest in those with two copies of the variant, who showed some increase in fat intake at older ages.
How did the researchers interpret the results?
The researchers conclude that it is possible that the FTO gene may have an influence on brain function, personality and diet in older people.
They suggest that changes in brain function shown in the study may be associated with increasing impulsivity and greater preference for dietary fat among carriers.
This study has tried to further our understanding of how variations in the FTO gene associated with obesity result in people being overweight or obese. It found that a variation in the FTO gene was associated with BMI changes over time, as well as with changes in the brain and in impulsivity and diet as people age.
This genetic variant was already known to be associated with obesity, but this study is one of the few to look at changes over time. However, this study did not examine whether people were inclined to eat on impulse objectively, instead relying on participants reporting impulsivity as a personality trait themselves.
The researchers suggest that genetic variant-related changes in brain function may be linked to an increase in impulse eating, but at present this is just speculation.
The true picture of obesity is likely to be very complex. It is likely that there are many genes associated with obesity, some of them still unidentified, and that they work in different ways.
The study looked at only one particular variant in one of these genes. Carrying this single genetic variant is not a guarantee that a person will become overweight or obese, or that they cannot eat a healthy diet.
Research on the causes of obesity and on why some people may be predisposed to it is important. This study may be of interest to specialists, but as yet it does not really help anyone trying to keep to a healthy weight as they grow older.
There's no question that for many people this is a struggle, but a healthy diet and regular exercise is within everyone's reach. If you are having problems coping with cravings, there are low-calorie snacks that can help you feel full without derailing your diet.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.