Do We Blame Genetics?

Chapter summary

• Genes make a real difference to health. Contributions are found for cancer, cardiovascular disease, diabetes and behaviour.
• Obesity is a complex trait. Many genes are linked to it, including MC4R, MAF, NPC1 and FTO.
• Diet and lifestyle remain bigger contributors to weight and health than genes.

The FTO gene: two views

• The newspaper story: The Daily Mail reported a “hunger gene”. About 49% of people carry one risk version, and two copies mean a 70% higher chance of obesity. One copy means 30% higher.
• The supporting study: Professor Rachel Batterham tested 259 men. Those with two copies felt 20 to 25% hungrier for two hours after a meal. Their ghrelin (the hunger hormone) did not fall properly after eating. They ate up to 200 extra calories a day and weighed nearly 3kg (7 lb) more. Their brains also responded more to pictures of food.
• The large review: Peng and colleagues pooled studies of five FTO variants across ethnic groups, with 41,734 cases. They found a modest effect or none, depending on the group.
• The author’s reading: Both reports can be true. The headline overstates the finding. The pooled data shows a smaller effect. Unless you are an expert you will be confused, so read the journal and not only the newspaper.

Why genetics is hard to pin down

• More than 40 hormones and pathways are involved in hunger, linking gut, brain, vascular and lymphatic systems.
• Telomeres: These caps on chromosomes shorten with each cell division. Some researchers see this as a cause of ageing. Ornish and colleagues (2013) reported that lifestyle change was associated with longer telomeres, so lifestyle may slow the process.
• Epigenetics: Environment changes how genes express themselves. A “bad gene” is not a fixed fate.
• Genetic response may vary with age.

Two ways to use this

• Genes as excuse: Some people feel the finding frees them from responsibility. Hunger is partly biological, and dieting can feel doomed.
• Genes as information: The author sees it as a reason to plan. Knowing family history lets you choose prevention early.

Take-away points

• You cannot change your genes, but you can change diet and lifestyle.
• Check the original study before you accept a headline.
• Expect more knowledge soon. Today it is limited.

References

• Daily Mail. Are you a victim of the hunger gene? It’s why many diets fail and millions never feel full.
• Karra, E. et al. (2013) A link between FTO, ghrelin, and impaired brain food-cue responsivity. Journal of Clinical Investigation.
• Peng, S. et al. (2011) FTO gene polymorphisms and obesity risk: a meta-analysis. BMC Medicine 9:71.
• Ornish, D. et al. (2013) Effect of comprehensive lifestyle changes on telomerase activity and telomere length. Lancet Oncology.
• Bell, C.G., Walley, A.J. and Froguel, P. (2005) The genetics of human obesity. Nature Reviews Genetics 6:221-234.
• Meyre, D. et al. (2009) Genome-wide association study for early-onset and morbid adult obesity. Nature Genetics 41:157-159.