You can tell by the title that it’s Friday again, that time of the week when I yabber about odd stuff that I learned from trawling the web.

NPR correspondent David Kestenbaum noticed something weird recently when he bought two packs of M&M’s, one regular and one peanut butter: the peanut butter M&M’s weighed slightly less than the regular version. Both packs were similarly sized, and both cost the same amount of money.


Kestenbaum did what any other person with a Ph.D in physics would do: he took the question to two experts:┬áSanat Kumar, chair of Columbia University’ chemical engineering department, and Bill Edwards, a former Rowntree executive who has had a lot of experience investigating rival products (which would include M&M’s). And like proper scientists, they posited possible theories and went on to test them.


Theory 1: Peanut butter M&M’s are more expensive to manufacture, so there are less in each pack.

Edwards pointed out that peanut butter actually costs less to make compared to chocolate, so if cost is the deciding factor, there should be comparatively more peanut butter M&M’s.

Result: False.


Theory 2: All M&M packs are filled with a fixed number of M&M’s. Peanut butter M&M’s weigh less than regular M&M’s, so the corresponding packs would be lighter.

Using Kumar’s precision equipment, peanut butter M&M’s were found to be larger and much heavier compared to regular M&M’s. Also, different packs of peanut butter M&M’s were found to contain different numbers of M&M’s

Result: False.


Even though both theories proved to be false, the fact that peanut butter M&M’s were larger provided a clue. Kestenbaum managed to get the following statement from Mars, the manufacturer of M&M’s.

Mars Chocolate North America is committed to health and nutrition, which includes efforts to manage portions and calories, so all of our products are 250 calories or less per portion. This means that weights may vary from pack to pack, and are always clearly labeled on the product package.

That provided the key to cracking the peanut butter M&M code: because of its larger size, adding a single peanut butter M&M to a pack would push its total calorie count over 250 calories. Kestenbaum and Kumar did some calculations and confirmed it.

So now we know. Don’t down too many peanut butter M&M’s this weekend. And stay curious.

Some related reads (if you’re into the whole calorie counting thing)