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One set of experiments shows that CR has no benefits in the housefly.[114] The authors hypothesize that the widely purported effects of CR may be because a diet containing more calories can increase bacterial proliferation, or because the type of high-calorie diets used in past experiments have a stickiness, general composition, or texture that reduces longevity. At one time, some researchers suggested that some of the effects of CR are artifacts because the laboratory model organisms are kept on non-physiological high-calorie diets. This would mean that calorie restriction simply means mimicking the energy supply of a natural environment.[115] However, many modern CR studies restrict the control animals by 10–20% below their ad libitum intake in order to avoid confounding by obesity. Additionally, "at least some laboratory mice under a caloric restriction regimen that maximizes longevity have been reported to cease estrous cycling. Because all existing wild mice populations must reproduce or become extinct, presumably they are eating relatively more than restricted laboratory mice during at least part of the year."[116] A study designed to evaluate the energy intake, expenditure, and balance of mice in the wild, ad libitum–fed laboratory mice, and calorie-restricted mice concluded that "CR experiments do in fact restrict energy consumption beyond that typically experienced by mice in nature. Therefore, the retarded aging observed with CR is not due to eliminating the detrimental effects of overeating."[117] |
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