It isn’t true, but the idea has been purported by many old-school physiologists who still refer to their 1960’s and 70’s text books.
Let me drag you and your professor into the 21st century with some more recent research. Excess carbohydrate intake can make you fat via three ways that tend to work together.
First, your body will store carbs as body fat when muscles and the liver are full of glycogen.
Second, high insulin levels caused by high carb intake activates your body’s cellular fat-storing machinery and shuts off the body’s ability to burn fat.
Third, and here’s a little bit of biochemistry for you to look up; excessive carb intake can directly increase fat storage via de novo lipogenesis, which is the conversion of carbohydrates to fats. The latter is not a preferred pathway, however, when more carbs are consumed than the body needs these three processes work together to store the excess energy as fat.
So make no mistake about it, excessive carb intake can make you fat.
