It used to be your glands were blamed for obesity, as in,"Don't blame me, blame my pituitary." After several decades of searching for and failing to find an organ in the body that was causing the eater to consume too many doughnuts, the blame game switched to genes. I'd like a nickel for every weight-loss client who went through the genealogy of obese relatives concluding, "It runs in the family."
A recently reported analysis of studies on an obesity gene, FTO, has concluded that if obesity "runs in the family" then running will prevent the family from becoming obese. The study suggests if all your relatives on both sides of your family can't see their laps when they sit down, if you run or otherwise engage in physical activity, it is doubtful that you will be fat.
The study, published in an electronic journal PLoS Med, (1) examined the effect of physical activity on obesity among thousands of children and adults who inherited this gene. What they found is reassuring to any of us who may have looked with dismay upon the size of our relatives and wondered if we were genetically programmed to imitate them.
Apparently just having the gene is not sufficient to produce an obese body. The FTO gene does increase the risk of obesity by 23% but its effect, according to the report, may be limited to upping your body mass by 1 kg or a little over 2 pounds. This means that going on a cruise is more likely to add pounds than inheriting the gene. Also, the effects of the gene are greatly weakened among those who engage in regular physical activity. Of course, the corollary is that if you have the gene and don't exercise, you and your obese relatives may share the same dress or pants size.
Theses findings suggest that one reason for the global epidemic of obesity might be that those of us with the fat gene exercise less than our ancestors. If your great grandparents spent most of their waking hours engaged in physical work they were probably thin, regardless of whether they had the fat gene or not. Periodic food shortages may have been an additional factor. Few of us today spend as much time being physically active as our ancestors, so the fat gene has a better chance of exerting its effect on our size.
Should people be tested for this gene? The authors of the study, quite sensibly, equivocate. On the one hand, they say, knowing that you are predisposed to becoming fat might be the motivation you need to eat healthily and exercise, just as knowing that you have genetically- determined high cholesterol would lead to your avoidance of high cholesterol foods. On the other hand, they suggest that people may simply give up any attempt to reduce their weight. If obesity is written on their genome, why bother avoiding French fries and cheese steaks?
These findings on the genetic basis of obesity compel additional research. Are some people genetically programmed to eat too many calories, not because of some metabolic defect but because of genetically determined moods? This may seem more science fiction than science but it is worth thinking about.
Let's say that someone who simply can't lose weight or stop from gaining has a problem with emotional overeating. Whenever this individual becomes anxious, or feels under stress, she eats. Nothing genetic about this, or is there? For several years now, scientists have been finding variants in certain genes that might make someone susceptible to anxiety or depression (2--4). Could this inherited tendency toward anxiety be linked to obesity? It could if the anxiety provokes overeating.
People tend to choose carbohydrates (aka comfort foods) when they are upset. Although it may appear that the foods are eaten because of their taste, e.g. chocolate, potato chips, cookies their effect on mood far outlives their impact on the taste buds. When volunteers are given carbohydrates covertly; i.e. they don't know they are eating them, their moods improve (when they are covertly given protein, their moods stay the same.) Eating carbohydrates (with the exception of fructose) sets in motion a biochemical process that results in serotonin synthesis in the brain. This neurotransmitter brings about a sense of well-being and can change moods from anxious and worried to calm and focused. Of course the response is not universal; some people respond to eating carbohydrate by getting sleepy.
Might there might be genetic differences in how people respond to eating carbohydrates? . And if so, do those who use carbohydrates as an edible tranquilizer run the risk of gaining weight if the carbohydrates they choose to eat are also high in fat? One thing is certain: forbidding those who self-medicate with carbohydrates from doing so will sooner or later doom their diet. When the stress or anxiety becomes unbearable, they will search out those foods that make it less so.
When I, together with my co-author, wrote The Serotonin Power Diet, we included a chapter on how to deal with emotional overeating. Rather than forbidding it, we told our readers how to eat healthy, low fat, portion controlled carbohydrates to decrease their emotional distress. We reasoned that if the impulsive 'grab and eat' response to stress were replaced by a planned consumption of foods compatible with the diet, then at the very worst, the dieter might not lose any weight that day but would not be at risk for weight gain and abandoning the diet.
So do your genes condemn you to a lifetime battle with obesity? Just the contrary...If you have such genes (and at this point, even being tested for them is unlikely) they may motivate you to engage in regular physical activity, eat healthy carbohydrates, and refuse that second (or even first) piece of Thanksgiving pie, especially if it is offered by one of your obese relatives.
1) Kilpelainen TO, Qi L, Brage S, Sharp SJ Sonestedt E et al Physical Activity Attenuates the Influence of FTO Variants on Obesity Risk: A Meta-Analysis of 18,166 adults and l9,268 children. PLoS Med 8: e 1001116.doi: 10.1371/journal.pmed.1001116 2011
2) Ryan J, Scali, J Carriere I, Scarabin PY , Ritchie K, Ancelin ML Estrogen receptor gene variants are associated with anxiety disorders in older women Psychoneuroendocinology 36: 1582-1586 2011
4) Sen ,S Burmeister M , Ghosh D, Meta-Analysis of the association between a serotonin transporter promoter polymorphism (5HTTLPR) and anxiety-related personality traits American J of Medical Genetics 127: 85-89, 2004