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There are lots of good reasons to try

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and follow a healthier diet. You

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lose weight, you feel good, but the

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main reason? To live

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a longer, happier, more productive

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life. Welcome to

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the Nutrition Facts Podcast. I'm your

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host, Dr. Michael Greger. Today

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we feature some of the research

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on the influence of genetics on

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longevity, and we start with

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a study of thousands of twin pairs.

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It has long been said that the best

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hope for a long life is to

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choose your parents wisely. After

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all, doesn't longevity just run in the

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family? Centenarians are people who

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live to be at least 100, and

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their siblings are certainly more likely

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to become centenarians themselves, and

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the parents of centenarians have been found to

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be more likely to have lived to at least 90

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years old. On the

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other hand, the lifespans of spouses

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sometimes correlate as much, or even

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more than those of genetic relative. Your

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partner may have as much

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of an impact as your parent.

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After all, genes aren't the only things that

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get passed down. Perhaps grandma's healthy

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recipes, or even a lifelong love

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of running, runs in the family

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too. To tease

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out the role of genetics, researchers

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turn to twin studies, comparing differences

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between identical twins and

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fraternal twins. For

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example, imagine you're trying to determine

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the role of genetics in cancer, the

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role played by genes versus other factors

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that we may have control over. Since

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identical twins share 100% of

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their genes, whereas on average regular twins only

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share 50%, if

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genes play a large role, then you'd expect

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that identical twins would be more likely to

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share the same fate than fraternal twins, right?

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If there was no difference in the

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chances that both sets of twins got

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the same disease, then it would appear

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there's no genetic contribution. It

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turns out that the overwhelming contributor

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to the causation of cancer is not

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genetics, but rather what we're exposed

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to. Primary genetic factors may

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only account for 5 to 10%

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of all cancers. The BRCA

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genes, popularized by Angelina

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Jolie, for example, may

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account for as little as 2% of breast cancers.

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If one identical twin gets breast cancer, the likelihood

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the other will too is only 13%, despite

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having essentially identical DNA.

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Now, that's higher than shared rates

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among non-identical twin women, so there

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is a genetic component, but genes

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only appear to make a minor

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contribution to cancer risk. This

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is consistent with the rates of common cancers

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profoundly differing by as much as 200-fold around

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the world. What

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do twin studies have to say about

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the heritability of lifespan? Based

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on a study of the thousands of

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twin pairs, the heritability of longevity was

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26% for men and 23% for women. Subsequent

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twin studies have arrived at a

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similar estimate. Approximately 25% of our

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lifespan is determined by our

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genetic differences, which means how we

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live our lives may determine the

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bulk of our destiny. Estimates

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using other methods tend to fall in the 15 to

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30% range. For

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example, an analysis of millions of family

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trees from 86 million

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public profiles in an online genealogy

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database led to an estimate of 16%, though

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due to so-called assortive mating, meaning

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the fact that we tend to pair up with

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mates similar to ourselves rather than at random, that

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may actually be an overestimate. Chosen

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partners often have similar lifestyles, so some of

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that 16% estimate may have been influenced

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by families sharing similar diets and

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healthy habits and not exclusively their

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genes. Taking that into account, the

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actual heritability of lifespan may even

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be well...