Obesity has more than tripled in Canada since 1981. In their new book “Food Intelligence,” Canadian co-authors Julia Belluz and Kevin Hall - an award-winning health and science journalist, and a prominent researcher on metabolism in the U.S. - argue that it’s not because of a collective loss of willpower. Instead, they say the foods we buy and eat have become more calorie-dense, delicious and addictive over the last 40 years.