For humans, what's the difference between an edible leaf like lettuce, and a non-edible (in the sense of null nutritional value) leaf like grass?
closed as too broad by John, theforestecologist♦ Jun 11 at 19:36
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For grasses leaves tend to be inedible due do with the high quantity of silica deposited in the leaves to form structures known as phytoliths Wikipedia.
While this has been shown to inhibit digestion by insects (Hunt et. al., 2008, Massey et.al., 2006), I'm not aware of any studies on how this affects digestibility for humans. There are however anecdotes about people starving to death with grass stains around their mouths during the Irish Potato famine.
Nutrient content of lettuce and grass can be similar.
According to USDA.gov, 100 g of green leaf lettuce contains:
- Protein = 1,4 g
- Digestible carbohydrates = 1.5 g
- Calcium = 36 mg
- Potassium = 194 mg
- Magnesium = 13 mg
- Fiber (cellulose or similar) = 1.3 g
According to Feedipedia (see Nutritional Tables), 100 g of Bahia grass contains:
- Protein = 3.5 g
- Digestible carbohydrates = 0.6 mg
- Calcium = 160 mg
- Potassium = 400 mg
- Magnesium = 27 mg
- Fiber (cellulose) = 7.8 g
The "leaves" (shoots) of most grasses are considered inedible, because they:
- are unpalatable
- are hard to chew because of high cellulose content
- can probably make you sick; at least it can make dogs vomit (PNAS)
- contain silica that can wear your teeth; some types of grass are also toxic (eattheweeds.com)
Would it make sense to eat grass in a survival situation? No, because 100 g of grass contains only about 20 Kilocalories, mainly from protein and a little bit from cellulose fermentation by intestinal flora in the colon (gut.bmj.com). It's also quite possible you would vomit or get diarrhea after eating grass.