A type of fasting that has been well-researched is intermittent fasting (IF). IF is actually a pattern of fasting and eating that alternates between periods of fasting (usually meaning consumption of water only) and non-fasting.
Alternate day fasting (ADF) is a form of IF that is a 48-hour routine typically composed of a 24-hour fast followed by a 24-hour non-fasting period. Like other types of fasting, ADF has come under criticism. Research using rats has suggested that extended periods of ADF may be detrimental to the heart. According to one study, chronic ADF in rats resulted in the development of diastolic dysfunction with diminished cardiac reserve.
The researchers concluded that “The deleterious effect of ADF in rats suggests that additional studies of ADF effects on cardiovascular functions in humans are warranted.” It should be noted, however, that other research suggested that short-term ADF had positive effect on the heart.
As with other types of fasting, the design of the fast may be the key factor in study outcomes. For example, research has suggested that intermittent fasting is most beneficial and safest when there are at least five days of refeeding with reasonable caloric intake between the periods of time in which the individual is fasting.
Research into IF began around the 1940s using rats. A 1945 study found that the life span of rats was significantly increased by using IF. Tests in which one group of rats were allowed the same food every day and other groups received IF showed an increased life span of approximately 20% in males and 15% in females in the IF group as compared to the control group. The pre-experimental condition of the individual rats was also found to be an important factor determining the life spans.
In human studies using IF as an intervention, similar beneficial results were found. In one study, ADF produced significant improvements in several markers, such as LDL cholesterol at the eight week mark. In another study, male patients receiving IF had reduced triglycerides and the females had increased HDL cholesterol.
IF has been used successfully as a complementary treatment for chemotherapy. In one study, the researchers found that IF produced a type of protection from the toxicity of chemotherapy treatments, allowing higher doses to be used, thereby resulting in a more effective treatment.