Actually zands, while the majority of tubers tend to mainly be starches some tubers do have decent amounts of protein in them. But compared to legumes, nuts, etc... they do quite poorly. Rice probably beats most or all the tubers in terms of protein percentage, but many of the other grains / pseudo grains are poor on protein (of course amaranth and quiona do quite well)
If one was reduced to a one food vegetable diet tubers wouldn't be such a bad choice because carbohydrates are actually the ideal fuel for humans. That being said, one food vegetable diets are NOT a good idea. I'm not certain but in terms of minerals and vitamins I think tubers are often better than grains.
Amaranth quiona buckwheat are spinach cousins are not real grains grasses. Please give me the best protein count you can find on a tuber.
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Feb 17, 2012 – Not quite grains, buckwheat, amaranth and quinoa are the seeds of broad-leafed plants. Grains, in case you're wondering, are the seeds of ...
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If you actually read what I wrote I said "grains / pseudo grains" pseudo grains are crops that aren't true grains but are eaten as such (amaranth, quiona, corn).
I'm not claiming tubers are a powerhouse of protein, just that a few of them (again not most as I said) might beat some of the grains. Grains like wheat have been drastically reduced in protein during the time they've been cultivated (if you went back to the original wheat(s) in the middle east and europe you'd find they'd have a much higher protein content. If you are doing a one source vegetable diet things like corn are horrible because they have unbalanced amino acids, so if you eat them alone it is like their protein content is a lot less than it actually is (and corn isn't that great to begin with).
As mentioned in my original post (go back and read it) the average tuber checks in poor in terms of protein but some of the basic grains we have now aren't that great either (better than the average tuber but nothing to shout about). Some tubers will beat some grains (I can look it up if you really want).
Also as mentioned tubers can have decent vitamins minerals. Like potatoes having good vitamin C for instance. Vitamins and minerals are a lot more essential than protein (the need for which is often overstated in the US).
If you can only eat one plant, tubers aren't so bad (but still you will have nutrient deficiency disease as a result).