Credible nutrition journals present the following that may explain why tired and weak may result from vegan exclusion of fish/meat factor:
1) ammoglycom carbohydrate in fish breaks up phytic acid complexes in rice, resulting in 50 percent more iron absorption.
2) fish provides more protein, and the amino acid pattern of the protein may compliment the amino acid pattern of the rice, possibly compensating for a limited supply of certain amino acids in rice.
3) fish prevents loss of muscle carnitine transport capacity, which may reduce muscle ability to utilize energy, or reduce the amount of energy available, in other words, the rate of energy delivery may be reduced. Inclusion of fish restores the transport capacity.
4) without fish, meat, insects, certain fermented products, or a B12 supplement; a serious condition of B12 deficiency develops.
One or more of the above may be why adding one 5 ounce can of chunk style pink salmon to a large dinner of rice and vegetables, makes a big difference.