The question
Imagine you walk every aisle of a grocery store with $10 and one goal: get the most calories you can. Not the healthiest food or the tastiest. Just the most energy for the money.
It's a harder question than it sounds. A big bag of chips feels like a lot of calories, but it also costs a lot. A cheap item can be mostly water. What you want is the item with the most calories packed into each dollar, and the only way to find it for sure is to check everything.
The data
The store is the Trader Joe's in Chicago's South Loop. It lists 2,566 items. The prices come from tjsprices-data, a public project that records the price of every Trader Joe's item at every store each day, using prices from Trader Joe's own website. The prices here are from a single day, so some will have changed since.
Calories came from two places. Most were matched by product name to Trader Joe's entries in Open Food Facts, an open database of nutrition labels. For plain staples with no good match, like flour, rice and oil, the calories per 100 grams come from the USDA's FoodData Central, the government's standard food nutrition tables.
Not every item could be matched to a calorie count. The ones that had both a price and calories came to 1,404 foods.
The math for one item
For each food you need one number: calories per dollar. You get it by dividing the calories in the whole package by its price. Then multiply by 10 to see how many calories $10 buys.
Take a jar of creamy salted peanut butter. The jar holds about 2,693 calories and costs $2.49.
2,693 ÷ $2.49 ≈ 1,082 calories per dollar
That's about 10,800 calories for $10. Multiplying by 10 treats your $10 as if it can buy part of a jar. You can't actually do that at the register, but it's the fair way to compare a $0.99 item with a $5.49 one.
The typical item
Line up all 1,404 foods from lowest to highest calories per dollar. The one in the middle, called the median, gets you about 173 calories per dollar. Half of the foods do worse than that and half do better. Ten dollars of that middle-of-the-pack food is about 1,700 calories.
The median is a better "typical" than the ordinary average here. A handful of foods score so high that they drag the average up to about 216, even though most items sit well below that.
And those high scorers are far above the rest.
The top five
These are ranked by kind of food. Otherwise salted and unsalted butter would take two spots, and four different 99-cent pastas would crowd out everything else.
- All-purpose flour: about 2,761 calories per dollar.
- 99-cent pasta: a $0.99 bag of fusilli holds about 1,701 calories, so about 1,700 calories per dollar. Macaroni is right behind it, and penne and spaghetti come in at about 1,636.
- Jasmine rice: about 4,967 calories for $3.99, or 1,245 calories per dollar. That's about 12,450 calories for $10.
- Butter: about 3,240 calories for $2.99, or 1,084 calories per dollar.
- Peanut butter: 1,082 calories per dollar, just 2 behind butter.
Gram for gram, butter and peanut butter hold far more calories than rice or flour, and they still lose. The plain starches are so cheap that they win on price.
The winner: a bag of flour
A 5-pound bag of Trader Joe's unbleached all-purpose flour costs $2.99. Five pounds is about 2,268 grams. The USDA lists all-purpose flour at 364 calories per 100 grams, so the bag holds about 8,255 calories.
8,255 ÷ $2.99 ≈ 2,761 calories per dollar
2,761 × 10 ≈ 27,600 calories for $10
That's 16 times the typical item in the store. It's even well ahead of the store's other all-purpose flour, an organic bag at $5.49 that comes to about 1,515 calories per dollar. Same food, nearly double the price per calorie.
If you only buy whole bags, $10 gets you three of them for $8.97. That's about 24,800 calories, still far ahead of anything else in the store.
What it means
Every food in the top five is an ingredient. You have to cook the rice and the pasta, bake the flour into something, or spread the butter and peanut butter on something else. The cheapest calories in the store are the ones nobody has done any work on yet.
It also shows how wide the range is. The best food in the store buys 16 times as many calories per dollar as the typical one. This was never a question about what you should eat. Raw flour is not a meal. But if the only thing you're counting is energy per dollar, a plain bag of flour beats everything else on the shelves.
Sources: prices from tjsprices-data (github.com/spencerrego/tjsprices-data) for Trader Joe's store 701, Chicago South Loop, on one day; calories from Open Food Facts (Trader Joe's products) and USDA FoodData Central (SR Legacy) for plain staples.