Intermittent Fasting For Dummies
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The alternate day intermittent fasting, also referred to as the 4:3 plan, has the most scientific data supporting its efficacy and safety of all the plans. Read on and see if perhaps the alternate day intermittent fasting plan is right for you.

The different versions of alternate day intermittent fasting plans

Strict alternate day intermittent fasting is one of the most extreme dietary interventions because you avoid all food for 36-hour periods. One day you eat, the next day you don’t, repeat. In other words, you fast on one day and then eat what you want the next day, then fast the next day, and so on. In other words, you eat four days during the week and fast three nonconsecutive days.

Alternate day intermittent fasting schedules aren’t all the same. The following list mentions some of the different ways that Alternate Day intermittent fasting plans can occur:

  • You switch back and forth between days when you eat more and days when you eat less.
  • You eat nothing or next to nothing on your fast days and as much as you want on your feast days.
  • You cut your usual food intake by a third to a half on your fasting days and allow yourself to eat more than your usual food intake on your feasting days. This is sometimes called calorie cycling.
  • You do a complete fast on Mondays, Wednesdays, and Fridays, so your intermittent fast is a three-day endeavor. This version is popular because you have the weekends to enjoy eating with friends and family.
Even though some alternate day fasting schedules only allow calorie-free drinks on fasting days, others allow small amounts of food (typically a maximum of 25 percent of your total daily calories) on fasting days.

The science of the alternate day intermittent fasting plan

As a scientist, the alternate day intermittent fasting plan is one of my favorites because I like to see the data. Low and behold, there is myriad sound scientific research regarding alternate day fasting and the associated miraculous health benefits.

For example, the journal Cell Metabolism published the results of a randomized clinical trial (the gold standard of scientific studies showing cause and effect) that examined the effects on the body of alternate day intermittent fasting. The largest study of its kind to look at the effects of strict alternate day intermittent fasting in healthy people showed a wide range of health benefits. The participants alternated 36 hours of zero-calorie intake with 12 hours of unlimited eating.

In this study, Austrian researchers enrolled 60 participants (subjects in both groups were all of normal weight and were healthy, aged 35 to 65 years old) into a four-week study and randomized the subjects into either an alternate day fasting group or a control group. The control group could eat as much as the group wanted. Here are the results detected in the intermittent fasting group:

  • The group had evidence of a continuous amount of ketones in the blood, even on nonfasting days. The ketone overflow has been shown to promote health in various ways.
  • The group had reduced levels of a blood marker linked to age-associated disease and inflammation called soluble intercellular adhesion molecule-1.
  • The group had lowered levels of a thyroid hormone called triiodothyronine without impaired thyroid gland function. Low levels of this hormone have been linked to longevity in humans.
  • The group had lowered levels of LDL cholesterol and triglycerides.
  • The group lost weight and body fat (a 9 percent loss of body fat, especially a reduction of harmful belly fat).
These intermittent fasters drank only water on their fasting days and continued to participate in their usual activity level. This figure depicts the intermittent fasting schedule used in this study (the circle-backslash symbol indicates complete water-only fasting).

Alternate Day intermittent fasting pattern Alternate Day intermittent fasting pattern used in this study

The subjects in this study were healthy, young and middle-aged, active adults. If you have any medical issues or conditions, you must get your physician’s consent before embarking on any intermittent fast.

Additional research on the alternate day intermittent fasting plan has shown a reduction in the following:
  • Asthma
  • Heart arrhythmias
  • Insulin resistance
  • Menopausal hot flashes
  • Seasonal allergies

Benefiting from the alternate day intermittent fasting plan

Another study examined the alternate day intermittent fasting plan and highlighted several benefits. Dr. Krista Varady, an associate professor of nutrition at the University of Illinois, refers to the alternate day intermittent fasting plan as the Every Other Day Diet; it's also referred to as the Up-Day, Down-Day plan. She has published a book and numerous well-constructed studies. This plan involves a fast day where individuals consume 25 percent of their calorie needs, alternated with a feed day where people eat as much as they want.

In a 12-week randomized clinical trial (article published in the Nutrition Journal), Varady recruited both normal weight and overweight subjects. After 12 weeks on the alternate day intermittent fast, the health benefits were compelling. The subjects:

  • Lost weight. Body weight was reduced by 6 percent (11 pounds) by the end of the trial.
  • Lowered body fat. Body fat decreased by 7.7 pounds with no change in muscle mass.
  • Felt full. Dietary satisfaction and feelings of fullness increased from baseline to post-treatment.
  • Showed positive changes in markers of heart disease risk. A significant reduction in triglyceride concentration (20 percent) was noted after 12 weeks. Plus, LDL particle size also increased post-treatment (LDL is bad cholesterol and bigger is healthier).
  • Experienced lower inflammation. Decreases in circulating c-reactive protein (CRP) concentrations were observed. CRP is a protein made by the liver that is a marker of inflammation in the body.
  • Had increased insulin sensitivity. An increase in adiponectin, the protein hormone that exhibits anti-diabetic, anti-inflammatory, and anti-atherogenic effects, and a hormone that functions as an insulin sensitizer.
Alternate Day intermittent fasting has had numerous additional scientific research findings as to its benefits. These include the following:
  • Increased weight and fat loss. A 2013 study published in the Nutrition Journal found that following this intermittent fast for 12 weeks caused a loss of nearly 8 pounds of body fat. If middle-aged spread is a problem, another recent study noted that people aged 50 to 59 years achieved greater weight loss with alternate day intermittent fasting compared to people of other age groups.
  • Improved heart health. Heart disease is the leading cause of death, globally. Alternate day intermittent fasting helps reduce the risk of heart disease in many ways that would be more fruitful when combined with a healthy Mediterranean diet, which is proven to promote heart health.
  • Improved insulin sensitivity and blood sugar level. High blood sugar levels occur when the body fails to produce enough insulin or can’t properly use available insulin (referred to as insulin resistance). Persistently high sugar levels can lead to diabetes. Studies have shown that alternate day intermittent fasting can help reduce fasting blood sugar levels by reducing the blood levels of insulin and increasing insulin sensitivity.
  • Promoted autophagy. Autophagy is the body's process of recycling unused, damaged, and potentially harmful cell components.
  • Promoted longevity (in animals). Restricting total calorie intake, which can be achieved from alternate day intermittent fasting, has been shown to significantly prolong the lifespan in animal studies.

Exercising during your alternate day intermittent fast

You can and should exercise during your alternate day intermittent fasting program. You may want to consider when and how to schedule in your different types of exercise bouts during your fasting calendar.

You may wonder why you’d want to add exercise to your alternate day intermittent fasting regimen. The answer is simple — so you can supercharge your weight loss! The journal Obesity published a study that showed participants doubled their weight loss with cardio. Sixty overweight subjects were divided into four groups:

  • Alternate Day fasting alone (diet)
  • Diet plus cardio exercise
  • No diet or exercise
  • Exercise alone
The participants who combined the alternate day intermittent fasting plan with cardio exercise burned at least twice as much fat as each individual approach. The researchers also showed that the combination produced superior changes in body composition (a significant loss of body fat and retention of muscle mass) and reduced indicators of heart disease risk compared to individual treatments.

Make sure to get consent from your personal physician before you engage in an exercise program, especially exercise combined with intermittent fasting.

Eyeing an alternate day intermittent fast — a sample 1-week calendar

You may have seen a few different examples of alternate day intermittent fasting floating around the internet. This figure shows you an example of incorporating this plan into your life.

Alternate Day intermittent fasting plan A sample 1-week alternate day intermittent fasting plan

Alternate day fasting is another difficult form of intermittent fasting not recommended for beginners. You can choose to make it easier by allowing yourself the 25 percent of your typical calories on your fasting days. You’ll still reap the massive health benefits regardless of which style you choose.

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