How do we know that genes influence how much weight we gain, surely people differ in how much food they eat and how much they exercise?

Some researchers have investigated this question using some very clever study designs. One example of this is Professor Bouchard Jr who studied 12 pairs of identical twins. All twins consumed over 1000kcal per day for 100 days, and were not allowed to do intense physical exercise. After 100 days some participants only gained 4kg, while others gained as much as 13kg. The weight gain was much more similar within twin pairs than between pairs, suggesting that weight gain is partly influenced by our genetic make-up.

What do you think?

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