I found several simple (four to seven total foods) diets that, with carefully specified amounts of each food, appear, at face value, to provide full, proper nutrition. Here are a few, with amounts given per day.
fish/olive/etc
450 g cooked tilapia
450 g ripe olives (yes, that's a lot)
200 g romaine lettuce
200 g cooked lentils
400 g whole-wheat bread (roughly 13 slices)
100 g sweet yellow pepper (half a pepper to one pepper)
tuna/kale/etc
300 g canned solid-white tuna
150 g walnuts
400 g kale (yes, that's a lot)
700 g boiled pinto beans
chicken/kale/etc
200 g chicken drumstick (roughly two drumsticks)
100 g mozzarella cheese
300 g flaxseed
300 g kale
salmon/broccoli/etc
400 g cooked salmon
30 g cheddar cheese (small amount)
200 g almonds (yes, that's a lot)
300 g broccoli
100 g carrots
600 g boiled pinto beans
Each of these is probably deficient in some small (but crucial) ways. Check for yourself before committing to one.
Under stricter circumstances that demand calculated laziness, I might actually follow one of these diets. In practice, I ignore the details and eat with more variety. My diet — as I strive, at least — is based on a food-group heuristic averaged from these specifics of "nerdtrition" (nerd nutrition):
300 g to 400 g of animal products (ideally fish, second-best dairy)
150 g to 500 g of fatty plants (nuts, avocados, olives, etc)
400 g to 700 g of starchy plants (whole-wheat bread, beans, and potatoes being some better ones)
200 g to 400 g of nutritionally-complex vegetables (kale, broccoli, spinach, etc)
0 g to 200 g of fruit (sweet peppers being one of the better ones)
All else, I see as superfluous, including, especially, processed foods.
Methods
Compile a list of nutrients to keep track of.
macronutrients
water
saturated fat
unsaturated fat
total carbohydrates
sugars
fibre
protein
cholesterol
minerals — here, only those with common deficiency diseases
Comparative-advantage, eyeball, and gradient-descend your way to a few-item diet.
Look for nutrients best provided by few specific foods, e.g. vitamin D in fish, or vitamin A in carrots.
Start a list of a couple foods providing some of those distinctive nutrients.
Add other foods dense in specific nutrients, and adjust amounts (with the help of a spreadsheet), to address deficiencies and excesses.
Caveats
The whole process to come up with these diets — and the claim that any one of them suffices — relied on several assumptions, each of which could be wrong:
every nutrient with any real risk of deficiency is accounted for in the list used
minima and maxima used of nutrients are accurate
nutrition data is correct about which foods contain how much of which nutrients
versions of foods you get in real life have roughly the same composition as versions measured by the source of nutrition data
you can properly and reliably absorb nutrients from all relevant foods
you will follow the diet precisely, to within the tolerance for which it suffices
adding up macro- and micronutrients actually suffices as the logical basis of a healthy diet
In particular, assumption 1 is wrong in the case of iodine. All diets given here expect iodine supplements, which you'd usually get in practice as iodised salt. Some of the diets (except the ones using salmon) also expect vitamin D supplements.
These caveats may make nutrition seem worryingly fragile. Most people eat healthily-enough with much less worry by accepting a wider variety than seven foods. Nerdtrition was an exercise in minimalism, which taught me a bunch about nutrition in the process.
I found several simple (four to seven total foods) diets that, with carefully specified amounts of each food, appear, at face value, to provide full, proper nutrition. Here are a few, with amounts given per day.
Each of these is probably deficient in some small (but crucial) ways. Check for yourself before committing to one.
Under stricter circumstances that demand calculated laziness, I might actually follow one of these diets. In practice, I ignore the details and eat with more variety. My diet — as I strive, at least — is based on a food-group heuristic averaged from these specifics of "nerdtrition" (nerd nutrition):
All else, I see as superfluous, including, especially, processed foods.
Methods
Caveats
The whole process to come up with these diets — and the claim that any one of them suffices — relied on several assumptions, each of which could be wrong:
In particular, assumption 1 is wrong in the case of iodine. All diets given here expect iodine supplements, which you'd usually get in practice as iodised salt. Some of the diets (except the ones using salmon) also expect vitamin D supplements.
These caveats may make nutrition seem worryingly fragile. Most people eat healthily-enough with much less worry by accepting a wider variety than seven foods. Nerdtrition was an exercise in minimalism, which taught me a bunch about nutrition in the process.