Alternate Day Fasting vs Intermittent Fasting

Understand alternate day fasting

If you are comparing alternate day fasting to other types of intermittent fasting, it helps to start with clear definitions. Alternate day fasting is one specific style of intermittent fasting. You are still practicing intermittent fasting, you are just following a different pattern from the more familiar 16:8 or 5:2 plans.

With alternate day fasting (often shortened to ADF), you repeat a simple rhythm:

• One “fast” day
• One “feast” or normal eating day
• Then repeat

In most research, alternate day fasting is actually “modified” alternate day fasting. On fasting days you typically eat about 500 calories and can have calorie free drinks. On non fasting days you eat to appetite without strict calorie limits (Healthline, Diet Doctor).

Intermittent fasting overall is a broader category. It includes:

• Time restricted eating, such as 16:8 or 14:10
• The 5:2 diet, 2 low calorie days per week, 5 regular days
• Alternate day fasting and modified alternate day fasting

All of these approaches change when you eat rather than focusing only on what you eat.

Compare alternate day fasting and other IF styles

How the patterns differ

Here is how alternate day fasting compares to two other common intermittent fasting styles:

All three are considered intermittent fasting. They mainly differ in how often you have a reduced calorie day and how strict your daily schedule feels.

Weight loss results in studies

A large meta analysis of 24 randomized controlled trials from 2011 to 2021 looked at different intermittent fasting regimens as well as traditional calorie restriction. In that review:

• Alternate day fasting and modified alternate day fasting ranked as the most effective intermittent fasting methods for weight loss
• However, when researchers compared all intermittent fasting styles to standard daily calorie restriction, the average difference in weight loss was very small, about 0.26 kg, and not statistically significant (Obesity, via PMC)

In other words, you can lose weight with alternate day fasting, other intermittent fasting patterns, or simple daily calorie reduction. Results are broadly similar. What matters most is finding an approach you can stick with.

Across studies that lasted from 2 to 52 weeks:

• Alternate day fasting produced about 0.77% to 12.97% weight loss
• The 5:2 diet produced about 1.70% to 7.97% weight loss
• Time restricted eating produced about 0.95% to 8.60% weight loss (Obesity, via PMC)

These ranges are wide because the studies differed in length, diet details, and participants. The main takeaway for you is that all of the approaches can lead to clinically meaningful weight loss when you follow them consistently.

Short term versus longer term

In shorter studies, usually under three months, adherence to intermittent fasting is generally high:

• Many studies report adherence above 70 percent
• For alternate day fasting and modified alternate day fasting, adherence ranged from 71.7 percent up to 98 percent (Obesity, via PMC)

When you look at longer term research, sticking with alternate day fasting becomes harder. Some studies that lasted more than three months had retention as low as 8 percent. Hunger, irritability, and dissatisfaction with the eating pattern were common reasons for quitting (Harvard Health Publishing).

If you are thinking about alternate day fasting, it is important to be honest about your own lifestyle. You might find that a daily time restricted eating window or a simple calorie limit feels easier to maintain month after month.

Look at health effects beyond weight

Weight is only one part of the story. You might also want to know whether alternate day fasting or other intermittent fasting styles help with blood sugar, cholesterol, and other health markers.

Cardiometabolic markers with ADF

A 2020 systematic review and meta analysis of seven randomized controlled trials including 269 adults found that alternate day fasting led to:

• Significant reductions in body weight, on average about 4.30 kg
• Lower body mass index, about 1.20 units lower
• Decreases in total cholesterol, LDL cholesterol, triglycerides, and both systolic and diastolic blood pressure (Frontiers in Nutrition)

These shifts suggest that alternate day fasting can improve cardiovascular risk factors in the short to medium term.

Several other reviews and summaries note that alternate day fasting may:

• Lower fasting insulin
• Improve some markers of insulin resistance, especially in people who are already insulin resistant
• Improve multiple cardiovascular health markers in people with overweight or obesity (Healthline, Diet Doctor)

Evidence is mixed on whether alternate day fasting is better than traditional daily calorie restriction for these health outcomes. So far, both approaches appear beneficial for people with extra weight when they lead to sustained weight loss.

Longer term insights from a one year study

A yearlong study of 100 adults with obesity compared alternate day fasting to daily calorie restriction and to a control group. By six months:

• Both the alternate day fasting group and the daily calorie restriction group lost about 5.5 percent of their body weight, around 12 pounds
• By 12 months, both groups regained roughly 1.8 percent of their weight, about 4 pounds
• Both groups showed improvements in blood pressure, blood sugar, insulin, and inflammatory markers compared with the control group (Harvard Health Publishing)

However, the alternate day fasting group in this study had some concerning findings:

• LDL cholesterol increased by about 11.5 mg/dL compared to the daily calorie restriction group at 12 months
• There was a higher dropout rate, with 12 participants quitting and almost half of those citing hunger and irritability on fasting days
• Over time, people in the alternate day fasting group started eating more on fasting days and less on feast days, so their overall intake ended up similar to those on daily calorie restriction (Harvard Health Publishing)

The study had several limitations, including small sample size and the exclusion of people with conditions like high blood pressure, high cholesterol, or diabetes. That means the findings might not fully apply if you have these conditions, but they still highlight that alternate day fasting is not necessarily superior to a straightforward daily calorie deficit.

Metabolism and body composition

One interesting potential advantage of alternate day fasting is its effect on resting metabolic rate. Some research suggests that alternate day fasting does not cause the usual drop in resting metabolic rate that often appears with continuous calorie restriction (Healthline).

This might help you avoid or delay a weight loss plateau. However, other work shows that alternate day fasting can reduce both fat mass and lean mass:

• In the 2020 meta analysis, alternate day fasting significantly reduced fat mass by about 4.96 kg
• It also reduced lean mass by about 1.38 kg (Frontiers in Nutrition)

If you are already at risk for muscle loss, for example if you are older, have a chronic illness, or are very inactive, you may want to be cautious, prioritize protein intake, and include resistance training if you consider alternate day fasting.

Consider sustainability and lifestyle fit

Hunger and day to day experience

On paper, alternate day fasting is simple. In real life, you still have to get through those reduced calorie days.

Common experiences on fasting days include:

• Noticeable hunger, especially in the first one to two weeks
• Lower energy and irritability for some people
• Possible difficulty concentrating or working if your job is physically demanding

In the Harvard one year trial, dissatisfaction with alternate day fasting was a key reason for dropping out, while no one in the daily calorie restriction group left due to diet dissatisfaction (Harvard Health Publishing).

Other intermittent fasting patterns often feel less extreme. Time restricted eating still lets you eat every day. The 5:2 plan limits you to two low calorie days per week instead of every other day.

If you want an intermittent fasting approach that is more compatible with family meals or social events, a daily eating window or a weekly pattern like 5:2 might feel more flexible than strict alternate day fasting.

Exercise and alternate day fasting

Some studies suggest that combining alternate day fasting with endurance exercise can increase weight loss significantly, in some cases:

• About twice as much weight loss compared with alternate day fasting alone
• Up to six times as much weight loss as endurance exercise alone (Healthline, Diet Doctor)

If you already exercise or want to start, that combination could be appealing. Still, you might prefer to schedule harder workouts on non fasting days so that you have more energy and can recover well.

Whatever fasting pattern you choose, pairing it with movement tends to improve results for weight, cardiovascular health, and overall wellbeing.

Who might want to be cautious

Intermittent fasting, including alternate day fasting, is not right for everyone. You should talk with a healthcare provider before trying it if you:

• Are pregnant or breastfeeding
• Have a history of disordered eating
• Take medications that must be taken with food or at specific times
• Have certain medical conditions, especially if they require stable blood sugar levels
• Are underweight or in a phase of life where growth is still happening, such as adolescence

Many intermittent fasting studies exclude people with uncontrolled high blood pressure, high cholesterol, or diabetes. That means you need personalized guidance if you have these conditions.

Decide which approach fits you

With all of this in mind, you might still be asking whether you should choose alternate day fasting or another form of intermittent fasting.

Here is a simple way to think about it.

When alternate day fasting may make sense

Alternate day fasting might be worth exploring if you:

• Prefer very clear rules, such as “today is a 500 calorie day”
• Like the idea of eating more freely on non fasting days
• Are comfortable planning life around alternating higher and lower calorie days
• Have discussed it with a healthcare provider and do not have conditions that make fasting unsafe

If you take this route, starting with modified alternate day fasting, about 500 calories on fasting days, can be more sustainable than trying to do complete no calorie fasts.

When a different intermittent fasting style might be better

You might be better off with time restricted eating, the 5:2 diet, or straightforward daily calorie reduction if you:

• Dislike feeling very hungry or irritable
• Have a schedule that make it hard to manage strict fast days
• Prefer small, consistent changes over large swings in intake
• Want something you can easily maintain during social events, travel, or holidays

A large meta analysis suggests that all of these options, including traditional calorie restriction, can be similarly effective for weight loss when you follow them (Obesity, via PMC). That gives you permission to focus on what you can live with long term.

Practical questions to ask yourself

Before you choose a specific plan, you can ask:

• Can I imagine eating this way most weeks for the next 6 to 12 months?
• How will this pattern fit with my work schedule and family routines?
• Do I have a plan for getting enough protein and nutrients, especially on low calorie days?
• Am I willing to adjust or stop if I notice negative effects, such as poor sleep, excessive fatigue, or obsessive thoughts about food?

Your honest answers can guide you toward an intermittent fasting approach that supports your health without taking over your life.

Key takeaways

• Alternate day fasting is one form of intermittent fasting, not a separate category. You alternate low calorie days, usually about 500 calories, with normal eating days.
• Research shows that alternate day fasting, time restricted eating, the 5:2 diet, and traditional daily calorie restriction can all lead to similar weight loss when you stick to them (Obesity, via PMC).
• Alternate day fasting can improve body weight, body fat, cholesterol, blood pressure, and some metabolic markers, but it can also reduce lean mass and may increase LDL cholesterol in some longer term settings (Frontiers in Nutrition, Harvard Health Publishing).
• Many people find alternate day fasting harder to maintain than simpler patterns, and dropout rates can be higher.
• The “best” fasting method for you is usually the one that fits your life, protects your health, and feels realistic for the long haul.

If you are curious about alternate day fasting, you can start by talking with your doctor, then testing a gentle version for a few weeks. Pay attention to how your body and your daily life respond, and remember that you can always adjust to a different intermittent fasting style that feels more sustainable for you.

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