Provided is a cell-protecting agent that is safe even when taken for a long period of time, and exhibits an effect of preventing or ameliorating a decrease in mitochondrial function, and a cell-protecting effect. An agent for cell protection, comprising, as an active ingredient, a white white white extract, preferably a fish white hydrolyzate that has been reduced in molecular weight to contain a fraction having a molecular weight of 5000 or less. Such a cell-protecting agent has a mitochondrial function-improving action in normal liver model cells and fatty liver model cells, so that the agent can be used for the prevention of fatty liver, Prevention or amelioration (treatment) of a disease or condition (symptom) caused by a decrease in mitochondrial function, such as a decrease in oxidative phosphorylation associated with mitochondrial dysfunction due to aging, aging, or the like is expected. None

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