The Dirty Dozen

I don’t follow trends in organic foods too much, but people who do likely heard the phrase “the dirty dozen” earlier this year.

The dirty dozen are twelve foods, mostly fruits, that are considered by scientists and nutritionists to be worth buying organic because their non-organic versions contain significantly more pesticides that people are likely to ingest. A few examples are peaches, pears, and bell peppers.

On the other hand, there is also a list of clean foods, ones that scientists and nutritionists don’t necessarily recommend shoppers buy from the organic section. Some of these include bananas, avocados, and mangoes.

By and large -- but not exclusively -- the difference between the two lists comes down to what type of outer layer the food has. We’re not likely to eat a the husk of the corn, which is on the clean list, or the shell of a scooped-out avocado, but we almost always consume the skin of pears, peaches, apples, and bell peppers (capsicums). Fruits with no outer skin, like strawberries, celery, and spinach are on the dirty list, whereas peas, which grow in a pod that is not typically consumed, and pineapple, with its pine cone-esque protective layer are on “doesn’t make a difference if you buy organic” list.

I searched for these lists online recently after attending a talk in San Francisco by Christopher Gardner, a nutritional scientist and associate professor of medicine at Stanford University, who was speaking at a lecture series known as Science Café.

One of the most alarming points Gardner made the night of his talk, which was held back in June in a San Francisco coffee shop in the Mission district, was about why and how researchers choose their research.

Researchers need to craft research studies that will get funded. Funding is most likely to go to studies that look at “acute deficiencies diseases,” Gardner said, meaning diseases that lend themselves well to being studied in isolation, and studies that look at isolated causes and effects of acute deficiencies diseases. Scientifically speaking, that type of pinpointed research is the most reliable. However, it completely eradicates a holistic approach to health and wellness. Gardner says the NHS is running out of money to give, and the more it runs low on grant money, the less likely it is to fund research that falls outside the “acute deficiency” criterion.

From a cultural perspective, Gardner said, we scientists should study eating patterns as a whole, not the effects of one nutrient. The diseases and problems most affecting our generation nutritionally are chronic, like heart diseases and adult onset diabetes, which often are the result of long-term and complex habits, not single factors in isolation as is the case for, say, anemia. “We are not going to find out nutritionally how to prevent chronic disease,” Gardner said.

Gardner talked about the dirty dozen list only briefly. He also mentioned that organics, as a market, has been doubling each year.

But even on this supposedly reliably list of foods consumers should buy in organic form, I found a discrepancy between two major sources (MSNBC and One includes raspberries while the other swaps it for lettuce. It seems to me that well-funded research is even less reliable than Gardner implied it was.

Two 'Dirty Dozen' Lists (must-buy organic foods because they are most contaminated)
1. apples
2. cherries
3. grapes, imported (Chili)
4. nectarines
5. peaches
6. pears
7. raspberries
8. strawberries
9. bell peppers
10. celery
11. potatoes
12. spinach

1. peaches
2. apples
3. sweet bell peppers
4. celery
5. nectarines
6. strawberries
7. cherries
8. pears
9. grapes (imported)
10. spinach
11. lettuce
12. potatoes

12 Least Contaminated Foods
1. onions
2. avocados
3. sweet corn (frozen)
4. pineapples
5. mangoes
6. asparagus
7. sweet peas (frozen)
8. kiwi fruits
9. bananas
10. cabbage
11. broccoli
12. papayas

Update: The "dirty dozen" list might have originated with a Consumer Reports article from 2006, which lists: apples, bell peppers, celery, cherries, imported grapes, nectarines, peaches, pears, potatoes, red raspberries, spinach, and strawberries.