The Method

The formula we are going to use over and over again in analyzing food involves only multiplication and division:
\[Cost\ Per\ Meal = {(Item\ Cost) * 667 \over {(Number\ of\ Servings) * (Calories\ Per\ Serving)}}\]
Let's walk through an example, finding the price of a gallon of skim milk. I have the following values at my local Costco.
\[Item\ Cost = $1.79\]
\[Number\ of\ Servings = 16\]
\[Calories\ Per\ Serving = 90\]
Using our formula above, this gives me a cost of \$0.83.
\[Cost\ Per\ Meal = {$1.79 * 667 \over {16 * 90}} = $0.83\]
What does this mean? Well, we looked at the jug of milk and found that it contained 1440 calories in total (the denominator of our formula). If we eat 2000 calories a day, a 'meal' consisting of one third of that total is 667 calories. Thus, our milk jug has a little over two 'meals' in it. If we get a full third of our days calories from that \$1.79 jug of milk, we will have spent \$0.83 on those calories. Imagine spending less than \$3 a day on food!

Now, I don't survive entirely off of milk, and I'm pretty sure you don't either. However, if I drink a more realistic amount of milk in a given day, such as one 8 oz serving, the 90 calories I get from that serving are actually pretty cost effective at a little over \$0.11. This is the actual price we eventually want to consider, but we will start by looking at the cost per meal to compare foods on a level playing field. Below, I've listed a few food items and the analysis described above for prices at my local Aldi or Costco.

\begin{array}{|c|c|} \hline Food\ Item&Cost&Quantity&\#\ Servings&Cal/Serving&Price\ per\ 'Meal' \\ \hline Skim\ Milk&\$1.79&1\ gal&16&90&\$0.83 \\ \hline Walnuts&\$9.99&3\ lbs&45&200&\$0.74 \\ \hline Strawberries&\$2.29&1\ lb&4.54&33&\$10.20 \\ \hline Onions&\$5.99&10\ lbs&45.4&40&\$2.20 \\ \hline Pears&\$6.99&6\ lbs&27.24&57&\$3.00 \\ \hline Flour&\$6.39&25\ lbs&378&110&\$0.10 \\ \hline Jasmine\ Rice&\$17.99&25\ lbs&227&180&\$0.29 \\ \hline Oats&\$7.99&2x80\ oz&113&150&\$0.31 \\ \hline \end{array}

Clearly, some foods are a lot cheaper by this metric than others! The cheapest foods here are mostly carbs, while vegetables and fruits are more expensive. Just eating rice and never touching vegetables will probably not go well, so we will rely on averaging our pricier but important foods with our cheaper sources of calories. If we can get a whole dish down to a price tag of \$1.50 or even \$1.00 per 'meal' without sacrificing the diversity of our food, then we have found a good recipe. Again, though, if we have a more expensive dish we want to eat on occasion, we just need to average it out against cheaper meals on other days. It all comes down to planning and balancing costs.