A method of improving longevity and/or alleviating a symptom of aging or preventing age related diseases is provided. The method includes a step in which the subject's average and type of daily protein intake, IGF-I, and IGFBP1 levels, and risk factors for overall mortality, cancer and diabetes are determined. With respect to protein consumption, the relative amounts of protein calories from animal and plant sources are determined. A periodic normal calorie or low calorie but low protein fasting mimicking diet with frequencies of every 2 weeks to 2 months is provided to the subject if the subject's average daily protein intake level and type and/or IGF-I levels, and/or IGFBP1 levels is identified as being greater or lower than a predetermined cutoff intake/level and if the subject is younger than a predetermined age. The method is also shown to alleviate symptoms of chemotoxicity.
