Alternate-day fasting is a version of intermittent fasting, which is currently one of the world’s most popular weight loss trends.
Recently, a group of scientists examined the effects of 8-week alternate-day fasting on appetite ratings, appetite hormones and body weight.
Here is a detailed summary of their results.
Alternate-day fasting (ADF) is a weight loss technique that has recently become popular (1).
One popular version of ADF restricts calories by 75% every second day, while allowing unrestricted eating in between.
Human trials have shown that this method may lead to 4–8% weight loss in just 2–3 months. Here is a summary of study results from over the years:
- 2005: 16 non-obese men and women fasted every other day for 22 days and lost 2.5% of their initial body weight (2).
- 2007: 9 overweight asthma patients consumed 20% of their calorie needs every second day for 8 weeks and lost 8% of their initial body weight (3).
- 2009: 16 obese people consumed 25% of their calorie needs every second day for 8 weeks and lost 12.4 lbs (5.6 kg) (4).
- 2013: 32 obese people fasted every other day for 8 weeks and lost 4.8% of their body weight on a high-fat diet (45% fat), but 4.2% on a low-fat diet (25% fat) (5).
- 2013: 32 obese people fasted every other day for 12 weeks and lost 6.6 lbs (3 kg). When fasting and doing endurance exercise, they lost 13.2 lbs (6 kg) (6).
- 2013: 15 overweight or obese women fasted every other day for 6 weeks and lost 7% of their initial body weight (7).
Additionally, giving in to hunger and cravings is the main reason why people fail to adhere to a diet (8).
This seems to be less common during ADF, though the reason is not clear (9).
This trial examined how ADF affects appetite ratings, appetite hormones and weight.
This trial examined the effects of 8-week ADF on subjective ratings of appetite, appetite hormones and body weight.
It should be noted that results from this study have been published before (10).
A total of 59 middle-aged, obese adults completed the trial, or 80% of those who initially started. 84% of the participants were women.
The study was divided into 3 periods:
- Control period 1: For 2 weeks, the participants followed their habitual diets. Initial measurements took place during this period.
- Alternate-day fasting: For 8 weeks, the participants fasted every second day.
- Control period 2: Immediately after the ADF, participants followed their habitual diet for 2–3 days before final appetite measurements were taken.
Bottom Line: This trial examined how ADF affects appetite and body weight. The study included 59 people, and was divided into three periods.
For 8 weeks, the participants fasted every second day, with 75% calorie restriction. Conversely, on “feed days” they were allowed to eat whatever they wanted.
To improve compliance, all participants were provided with the food they were allowed to eat on fast days.
This food contained 60% of calories from carbs, 24% from fat and 16% from protein. Participants were allowed to consume unlimited amounts of calorie-free drinks.
Every week, the researchers measured body weight. Fat mass, lean mass and intra-abdominal fat were also measured using DXA.
Bottom Line: The participants consumed 25% of their calorie needs every other day for 8 weeks.
Subjective ratings of appetite were assessed after a 12-hour fast, before and after a standardized meal.
The standardized meal consisted of a liquid meal, providing 440 calories. It was designed to have a similar macronutrient profile as a typical breakfast, or 60% of calories from carbs, 24% from fat and 16% from protein.
Fasting blood samples were taken before the meal. Blood was also drawn immediately after the meal, and at 30, 90 and 120 minutes afterwards.
The blood was analyzed for total ghrelin, peptide YY (PYY) and several other hormones. Immediately before each of the blood draws, the participants rated their appetite using a visual analog scale (VAS).
Bottom Line: Appetite hormones and subjective ratings of appetite were assessed before and after the 8 weeks of ADF.
Finding 1: Body Weight Decreased
During eight weeks of ADF, the participants lost 8.6 lbs (3.9 kg).
This weight loss was largely due to loss of fat — 4.9 lbs (2.2 kg) — but also lean mass (water and muscle) — 3.1 lbs (1.4 kg).
The chart below shows the changes in fat mass and lean mass.
Bottom Line: Fasting every other day for 8 weeks led to 8.6 lbs (3.9 kg) weight loss.
Finding 2: Fullness After Meals Increased
Subjective ratings of fullness after the test meal were significantly higher after 8 weeks of ADF, as shown below.
Similar to fullness, PYY levels after meals increased after 8 weeks of ADF. The reason why ADF increased PYY levels and fullness is unclear.
Bottom Line: Post-meal fullness was greater after 8 weeks of ADF, compared to before.
Finding 3: Ratings of Hunger Remained Unchanged
Eight weeks of ADF did not change hunger ratings.
Taken together, these findings indicate that intermittent calorie restriction is easier to stick to than continuous dieting or fasting.
However, levels of the hunger hormone ghrelin were significantly higher after the test meal at the end of the trial, compared to its levels before the trial.
The reason for these findings is unknown.
Bottom Line: Despite the loss of weight, subjective ratings of hunger didn’t change. This indicates that ADF is easier to adhere to than dieting.
This study had a few limitations.
First, meals were not standardized the day before the appetite measurements took place. Even though the tests were preceded by a 12-hour fast, the previous evening’s meal might have affected the findings.
Second, one of the authors, Krista Varady, wrote the book The Every Other Day Diet, creating a conflict of interest. None of the other authors reported competing interests.
Summary and Real-Life Application
ADF is an effective weight loss strategy, causing significant weight loss after 8 weeks. Yet despite the weight loss, hunger ratings after a standardized meal remained unchanged.
Additionally, when the ADF was over and the participants went back on their regular diets, subjective ratings of fullness were significantly higher after the standardized meal, compared to a similar meal before the fast.
These findings suggest that ADF is relatively easy to stick to. However, further studies need to examine its long-term effects.