A disclaimer, because there have been questions. I’m not suggesting we eat only two or three foods! Not at all. Rather, this post imagines a three-food world to simplify the problem. Next, I plan to develop an algorithm that runs similar, but more complicated, calculations. Then, we can start to apply this logic to actual diets.
Calories per dollar is all good and well, but to eat well for the least money, there’s more to it.
A 16-ounce jar of natural peanut butter (ingredients: peanuts) at Wegmans is $2.99. That’s 936 calories per dollar. If your ideal caloric intake were 2,000 calories and you ate only peanut butter, your weekly grocery bill would average out to $14.98. For $781, you could feed yourself for a year.
Kale. It’s a different story. Assuming this bunch is about a pound, which lines up with the price and price per weight at my local Stop & Shop, you’ll buy 114 calories per dollar of kale. That weekly grocery bill is now $123.
Now, you can’t eat only kale and you can’t eat only peanut butter. No single food supplies the proper balance of nutrients. You might get the right amount of one thing, but you’d get too much and not enough of other things. To be healthy, a human must eat various foods.
For simplicity, we’ll pretend that you only need three things for a healthy diet: enough calories (let’s say 2,000), 75 grams of protein, and enough vitamin A (5,000 IU). Nothing else matters.
Kale and peanut butter both contain protein — in fact, nearly the same amount per calorie. A diet of only kale includes 120 grams of protein per 2,000 calories, and peanut butter, 90. So if you’re eating only kale and peanut butter, you’re going to consume between 90 and 120 grams of protein per 2,000 calories. That is fixed.
In this example, vitamin A is the critical variable. Kale contains a large amount of vitamin A, and peanut butter, none at all.
One serving of kale (1 1/2 cups, chopped) contains 310% of the recommended daily value of vitamin A. That’s a lot, but it’s OK to get “too much” vitamin A on one day. So let’s say you’ll eat that amount of kale. It will cost $0.44.
Because peanut butter is so much cheaper per calorie, the rest of your calories, 1,950 of them, should come from peanut butter.
At the end of the day, you’ll have spent $2.52, consumed 91 grams of protein (just a bit more than your goal), and 15,500 IU of vitamin A (310% of your goal).
What if you want to save the most money possible? Easy. Eat less kale, so that you’ll hit the daily intake of vitamin A on the dot. A half cup (chopped), to be precise. It costs $0.14. Eat just a bit more peanut butter, your protein remains basically the same, and your bill drops to $2.26.
You can see that in a world of kale and peanut butter, with only three important dietary elements (calories, protein, and vitamin A), this is how you might identify the optimal breakdown. If you are OK with spending a bit more money, you might eat more kale — a full serving, even. But maximizing your peanut butter intake is most cost-effective. You would eat the minimum amount of kale so as to consume enough vitamin A.
Now, let’s introduce a third food: canned tuna. Per calorie, tuna contains around four times as much protein as peanut butter and kale, so things could get interesting.
We’ll also introduce a fourth nutritional consideration: fat. For whatever reason, you’d like to limit your fat intake to 100 grams per day. Peanut butter is full of fat, and tuna costs more per calorie than peanut butter. At 117 calories per dollar, canned tuna is only slightly more expensive than kale per calorie.
Since canned tuna and kale both contain little to no fat, peanut butter is the main issue. Let’s aim to minimize cost. Recall that earlier, we designed a “diet” at $2.26 per day, where 1,984 of the 2,000 calories came from peanut butter. That included around 160 grams of fat.
Cut fat to 100 grams. Suddenly (and keeping your 16 calories of kale in mind), there’s a 734-calorie deficit. Enter tuna!
The bad news is that your cost will skyrocket. A day’s diet is now $7.72, $6.25 of which comes from canned tuna. On the other hand, this is starting to look somewhat more like a real diet. Your fat intake is 100 grams on the dot.
The other bad news is that your protein intake has risen above 200 grams, well above your goal of 75.
What you could do, then, is split the difference between your fat and protein goals — and save money. We’ll lower your protein intake and raise your fat intake, which amounts to more peanut butter and less tuna, calories held constant. Recall that peanut butter is much less expensive per calorie.
By relaxing your hard cap on fat and shifting the balance from tuna to peanut butter, you can reach a comfortable medium of 140 grams of fat and 135 grams of protein. Both exceed your goals, but neither has reached an extreme value. Calories remain at 2,000, kale is constant (maintaining your vitamin A levels), and cost has dropped to $4.00 on the nose.
The day’s food:
- 18 tablespoons of peanut butter
- Just under 1/2 cup of tuna (drained)
- 1/2 cup of kale (chopped)
2,000 calories, $4.00, 100% of your required vitamin A, and somewhat more protein and fat than you planned for. See where I’m going with this?
“Eat real food.” Michael Pollan’s simple, concise guidelines have real value. We are too busy and tired to dig into the data, memorize complicated guidelines, and spend time and money on resources to help us eat well.
But wait. It’s easy to let “eat real food” cost more. Often, it’s unavoidable. Not everyone is able to simply “eat real food” and absorb the cost.
That is why we must look at the details. As much as details confuse and overwhelm us and play into the hands of the diet industry, they are critical to reducing cost while eating a healthy diet, which is the path to food justice. The devil is in the details, and there is not a shortcut.
In a perfect world, healthy food would not cost more than unhealthy food. But since it does (according to the Harvard School of Public Health), it is even more important for consumers to understand how to navigate their food environments without spending as much money.
What to do, then? Is there an app for that?
We’re working on it.