Intermittent fasting (IF) is an approach to eating, and not eating, which is gaining popularity among some health-minded individuals. Researchers are also interested in the effects of short periods of food deprivation on health. Studies that have been conducted in rodents have shown impressive results – decreased diabetes incidence, fasting glucose, fasting insulin, lower cholesterol, lower blood pressure, lower incidence of some cancers, and improved survival . The available research in humans is more limited, but some forms of IF are beginning to accumulate support in human trials.
Alternate day fasting (ADF) is the best studied form of intermittent fasting. ADF consists of alternating between unrestricted feeding days and fasting days. However, the fasting days typically include a single meal that is consumed midday. This meal contains about 25% of an individual’s normal calorie needs for a day.
Research in humans is beginning to reveal some fascinating results of following an ADF protocol. The majority of early studies were conducted in obese individuals, but now there are studies in overweight and normal weight subjects as well.
Here are some benefits that have been seen from alternate day fasting lasting from 22 days to 12 weeks:
In normal weight people:
- Decrease in body weight and fat mass [2,3]
- Decrease in triglycerides (fat circulating in the blood) 
- Decrease in some inflammatory markers 
In overweight people:
- Decrease in body weight and fat mass [2–5]
- Decrease in triglycerides 
- Decrease in some inflammatory markers 
In obese people:
- Decrease in body weight and fat mass [4–10]
- Decrease in total cholesterol and triglycerides [6–8]
- Increase in high density lipoprotein (HDL) cholesterol (“good” cholesterol) 
- Decrease in low density lipoprotein (LDL) cholesterol (“bad” cholesterol) [4,8]
- Decrease in blood pressure (both systolic blood pressure [5,7] and diastolic blood pressure )
As indicated above, ADF has been shown to be effective at modifying some risk factors associated with cardiovascular disease, as well as decreasing body weight and body fat.
One concern that many fitness-minded individuals have with fasting is that they will lose fat-free mass (i.e. – muscle mass). Three ADF studies that measured body composition have shown no change in fat-free mass [3,7,8], while three studies have shown decreases [2,9,10], and three did not measure or did not report fat-free mass changes [4–6]. However, the majority of the studies that showed a decrease in fat-free mass did not place the single meal on the fasting days. Studies that have placed the single meal on the fasting days have largely shown no change in lean body mass during ADF. This is good news for people interested in ADF because most people aren’t trying to lose weight by losing muscle mass. It is important to realize that the research subjects in these studies were not required to perform any type of exercise during these studies.
Very few studies have examined how ADF and different exercise programs interact. One study did examine the interaction between regular endurance exercise and an ADF meal pattern . The researchers found that the combination of regular aerobic exercise (three times per week for 25-40 minutes) and ADF produced better changes in body weight, body composition, and cardiovascular risk factors than either exercise or ADF alone.
For those of you interested in body composition improvement, you may be wondering just how much body weight and fat the subjects following ADF lost. Here are some sample numbers from several research studies:
- Normal weight and overweight subjects lost an average of 11.4 pounds of body weight, including 7.9 pounds of body fat in 12 weeks .
- Obese subjects lost 12 pounds of body weight and ~3% body fat in 8 weeks .
- Obese subjects participating in three sessions of aerobic exercise (25-40 min) on stationary bikes and elliptical machines lost 13 pounds of body weight, including 11 pounds of fat in 12 weeks .
Overall, ADF is one of the best-studied forms of intermittent fasting. While there are still plenty of research studies that need to be conducted, including combining exercise with ADF, the support for this dietary strategy is increasing. While it may not be ideal for everyone, it is one dietary strategy that can potentially decrease cardiovascular disease risk and improve body weight and body composition.
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