For all metrics except the price of food energy, the authors find that healthy foods cost less than less healthy foods (defined for this study as foods that are high in saturated fat, added sugar, and/or sodium, or that contribute little to meeting dietary recommendations).The argument turns largely on three different methods of measuring the cost of food:
- price per unit of weight ($ / 100g of edible weight)
- price per serving ($ per cup or ounce equivalent)
- price per unit of food energy (cents per Calorie)
You might think this is a delightfully arcane and nerdy point of contention. Yet, the new study has major news coverage today, including a surprisingly complete explanation of this whole units issue. The Wall Street Journal quotes one of the report's authors, my colleague Andi Carlson:
Often, less-healthy food options are made up of empty calories, prompting people to eat even more, said Andrea Carlson, lead researcher of the report.
"Take a chocolate glazed donut which is 240 calories," she said. "You can easily eat one, if not two or three without any trouble at all. However, a banana, which has a lot of nutrients in it and will make you feel quite full, has only 105 calories. You will feel fuller if you eat the banana versus the donut."I can think of reasons to like each measurement method in certain circumstances. Beverages provide an example of a comparison where it seems the per-serving approach is sensible. If we compare the cost of milk to sugary soda, a per-Calorie comparison makes soda look cheaper when it really just has more Calories. The per-serving comparison better captures the choice consumers really face.
On the other hand, if you think of the cost of a day's food supply, consumers' bodies generally regulate total food energy intake. For such comparisons, perhaps price per unit of food energy does make some sense.
For those who want more detail, here is a summary graphic from the USDA report. It is a bit complex. Generally, the high-carbohydrate category is fairly inexpensive, which corroborates the conventional wisdom. But, the fruit and vegetable categories are less expensive than meat by the preferred second and third measurement methods, which is USDA's main point.