Scientific studies are often speckled with words like 鈥渃an,鈥 鈥渃ould,鈥 鈥渕ay,鈥 鈥渁ppear,鈥 鈥渓inked鈥 or 鈥渃orrelated.鈥 This is bothersome. These terms are just too 鈥渋ffy鈥 to allow for any solid conclusions to be drawn. I wish sometimes scientists could cast doubt aside and say 鈥渨ill鈥 or 鈥渄oes.鈥
Let鈥檚 look at an example to illustrate what I mean. A study reported in the Journal of Alzheimer鈥檚 Disease found 鈥渢hat people who integrate mushrooms into their diets 鈥渁ppear鈥 to have a lower risk of mild cognitive impairment which often precedes Alzheimer鈥檚 disease.鈥 That conclusion was arrived at by researchers in Singapore upon analyzing food frequency questionnaires periodically filled out over six years by some six hundred seniors who also underwent various tests for cognitive abilities. Their summary stated that 鈥渆ating more than two portions of cooked mushrooms per week (a portion being defined as three quarters of a cup of cooked mushrooms) could lead to a fifty percent lower risk of mild cognitive impairment.鈥 They went on to say that 鈥渢his correlation is surprising and encouraging.鈥 Note the 鈥渃ould鈥 and 鈥渃orrelation,鈥 terms that emphasize the study is permeated with uncertainty.
Correlation cannot prove a causal relationship. People who eat more mushrooms likely eat more fruits and vegetables and may have different activity levels. Consider also that food frequency questionnaires are notoriously problematic because people have difficulty remembering exactly what they ate, are not reliable in judging amounts, and are also likely to emphasize foods they think they should have eaten instead of what they actually ate. Furthermore, different varieties of mushrooms have different chemical profiles, and whether the subjects were eating oyster, shiitake, golden, or button mushrooms isn鈥檛 clear. So, yes, 鈥淓ating mushrooms could slash risk of cognitive decline by 50%鈥 as one headline screamed. Or perhaps not.
Another recent paper in the European Journal of Cancer Prevention 鈥渇ound that eating mushrooms may reduce the risk of gastric cancer.鈥 In that review, researchers pooled a number of studies in which patients with gastric cancers had filled out food frequency questionnaires and then compared the data with that obtained from people without cancer. The relative risk of gastric cancer for the highest mushroom consumers versus the lowest was found to be 0.82. This means that high mushroom consumers have an 18% reduced risk of gastric cancer when compared to low mushroom consumers. That sounds significant, but there are some issues to consider.
First, 鈥渉igh mushroom consumption鈥 was determined by number of servings a week but what people consider to be a serving is variable. Furthermore, the studies differed in the number of servings that defined high consumption. Then about the 18% reduction. You have to ask 18% of what? In other words, what is the risk of developing gastric cancer in the first place? It turns out that the incidence is about 10 in a thousand over a lifetime for men, less for women. So, with an 18% reduction, this would mean, 8 in a thousand. One way to look at this is that if a thousand men ate a high mushroom diet, 2 would be saved from contracting stomach cancer. In other words, switching to a high mushroom diet gives you a 1 in 500 chance of avoiding stomach cancer. Again, it is unlikely that outside of their mushroom consumption, the low and high mushroom eaters have similar diets.
We are still not done. The kicker is that the mushroom benefit was seen only in Asian countries, not in Europe or America. Maybe Asians eat different varieties. Or more likely, eating mushrooms is just a marker for a different lifestyle. The bottom line here is that because mushroom eaters in some parts of the world have a lower rate of gastric cancer, we cannot conclude it is because of the mushrooms. It 鈥渕ay鈥 be. Or maybe not.
The 鈥渕ay鈥 can actually be strengthened by noting that mushrooms contain various compounds such as scabronine, ergothioneine or lentinan that in the laboratory can be shown to have nerve-growth, antioxidant, anti-inflammatory and even anti-cancer effects. But that also can be said for numerous compounds found in fruits, vegetables, grains and spices. Let鈥檚 also remember that the human body is not a giant petri dish. Many compounds show activity 鈥渋n vitro鈥 that is not replicated 鈥渋n vivo.鈥
All this being said, I think there is enough evidence to suggest that it is a good idea to incorporate mushrooms into the diet. They can serve as a tasty replacement for meat in some dishes. My favourite is mushroom goulash. Fry onions in a little extra virgin olive oil, add sliced mushrooms (I use button, Portobello and shiitake), a diced tomato, a chopped green pepper, garlic, pepper and a bit of salt. If you like zucchini, you can add that as well. Then the key ingredient, a heaping spoonful of Szegedi paprika! Talk about a spice that is rich in carotenoids and polyphenols! Cook with occasional stirring until the mushrooms are soft. Goes well with spaetzli or rice. I am willing to go out on a limb and say that this dish 鈥渄oes鈥 taste great and you 鈥渨ill鈥 enjoy it! It 鈥渕ay鈥 even benefit your health.
