There seems to be a growing interest in intermittent fasting due to its positive impact on a person’s weight, blood sugar, and other important health markers. Among the different types of fasts, one that’s easier to stick to (and doesn’t require complete abstinence from calories) is alternate-day fasting.
This detailed guide explores how it works, studies, possible drawbacks, and how to do alternate-day fasting.
What is Alternate-Day Fasting?
Alternate-day fasting or ADF for short — and sometimes referred to as the “every other day diet” by those who follow Dr. Krista Varady’s way of eating — is a fasting approach where you alternate fasting days with feeding days. For example, eating normally on Monday, fasting on Tuesday, and then eating again on Wednesday.
However, unlike the 16:8 and 24-hour intermittent fasts, alternate-day fasting is more of a modified version of fasting that lets you consume 500 calories or just 25% of your average daily calorie intake (*). Instead of doing a full fast with no food and liquid calories, you simply eat fewer calories, which still allows you to reap many benefits of strict fasting.
While the best way to fast is a matter of personal preference, alternate-day fasting is a good option for those who find it extremely difficult to forgo food. The same holds true for those who are taking supplements with food (e.g., fat-soluble vitamins) and want to fast.
Potential Health Benefits of Alternate-Day Fasting
Research has shown that fasting every other day may be helpful for improving health. Here are some of the results to expect from this fasting strategy:
1. Weight loss
A strict fasting schedule increases weight loss by depleting your glycogen stores, stimulating ketosis, and using your own body fat for energy.
Depending on how full your glycogen stores are, alternate-day fasting may or may not lead to ketosis; however, it does promote weight loss by way of calorie restriction.
It works like traditional calorie restriction where you reduce your calories by 15-40% daily — although alternate-day fasting may be easier since you’ll only need to limit calories every other day.
According to long-term human trials lasting 2-3 months, ADF is effective at reducing body weight by about 3-7%. Furthermore, it can substantially reduce the risk factors of diseases, whether a person is overweight or healthy (*).
2. Metabolic flexibility in combination with the keto diet
Metabolic flexibility is defined as a person’s ability to easily switch from a fed state to a fasted state to maintain energy homeostasis (*).
In other words, your metabolism can quickly adapt to whatever energy is available. You can fast today and eat more tomorrow without your energy levels fluctuating.
There are many ways to achieve metabolic flexibility for sustained energy and better fat-burning, one of which is alternate-day fasting.
This is especially true when you combine fasting with a keto diet. It means that outside your fasting window, you eat lower carbohydrate meals and fill up on healthy fats and protein.
3. Better lipid profile
Fasting every other day can be good for your heart health. It improves your lipid panel, which is a group of tests that screen for your risk of cardiovascular disease.
Alternate-day fasting has also been shown to create better changes in your plasma lipid profile when combined with physical activity than doing it alone (*).
In one 12-week randomized controlled trial, subjects consumed 25% of their energy needs for 24 hours and then ate as much as they desired the next day. They were allowed to consume calorie-free drinks like unsweetened tea and black coffee as well as sugar-free gum. They were also encouraged to stay properly hydrated with water (*).
The results found that the ADF group had lower triglyceride levels at week 12 compared to the control group. Lowering triglycerides is vital for reducing your likelihood of a heart attack and stroke (*).
Additionally, the fasting group had increased LDL particle size, which does not contribute to the atherosclerotic process (* , *).
4. Improved endothelial function in Type 2 Diabetes
For people who are diagnosed with type 2 diabetes — a condition where your body doesn’t use insulin properly — fasting can be an effective tool. Alternate-day fasting results in reduced fasting blood sugar levels and improved insulin sensitivity (*).
Additionally, ADF improves endothelial function, which is compromised due to hyperglycemia (*). Endothelial dysfunction makes a type 2 diabetic vulnerable to atherosclerosis or plaque buildup within the arteries (*).
A 2022 research article on mice with type 2 diabetes found that alternate-day fasting “rescues” endothelial dysfunction through enhanced adiponectin, which has anti-inflammatory and protective properties (*).
5. Potential for cancer treatment and prevention
Besides weight loss, calorie restriction (which is done in alternate-day fasting) has anti-cancer effects.
According to an article in Nature, “short periods of very low caloric intake, including either periods of short-term fasting (2–4 days) or dietary manipulation of specific macronutrients, can be effective at delaying primary tumor growth.” (*)
Furthermore, it noted that prolonged fasting reduces circulating blood glucose, which decreases tumor growth (*). This makes sense because both normal cells and cancer cells depend on glucose for energy.
In contrast, cancer cells cannot use ketones as fuel — but normal cells can. On that note, it would be a good idea to go low-carb or keto during your feeding days to help your body enter a ketosis state when fasting.
Alternate-Day Fasting Schedule and Meal Plan
There are no definitive rules on when to consume your 500 calories on a fasting day. You can choose whether to eat them in one sitting (for example, lunch or dinner) or divide them into smaller meals.
Although there are also no rules on the type of foods and drinks to consume, we recommend focusing on those that support healthy blood sugar levels. Low-carb and low-GI (glycemic index) options are great. Here is a complete list of intermittent fasting foods.
Below is a sample alternate-day fasting schedule you can follow:
- Day 1 (feeding day): Eat normally. To avoid blood sugar swings the next day, eat a variety of meats and non-starchy vegetables and fruits, such as spinach, cauliflower avocados, and berries. Eat to satiety.
- Day 2 (fasting day): Consume up to 500 calories only. A sample 500-calorie meal would look like a 4-ounce steak + 2 boiled eggs + 1 cup of broccoli. Drink water, zero-calorie electrolytes, plain tea, or coffee.
- Day 3 (feeding day): Resume your usual calorie intake.
- Day 4 (fasting day): Consume up to 500 calories only. Here’s another example of a 500-calorie meal: 4 ounces of chicken wings + 1 cup of beef bone broth + 1 cup of brussels sprouts + 2 ounces of cheddar cheese. Drink water, zero-calorie electrolytes, plain tea, or coffee.
- Day 5 (feeding day): Resume your usual calorie intake.
Potential Risks of Alternate-Day Fasting
Like other types of intermittent fasting, ADF has some side effects, though they’re temporary.
Increased hunger and cravings on fasting days are common. This is often true for people who practice fasting for the first time. A 2019 observational study found that hunger occurred mainly during the first few days of a fast (*). The more and the longer you fast, the easier it becomes.
If you’re ready to do a full fast (no calorie intake at all), you can try the 16:8 fast.
Other possible side effects, which are similar to the keto flu, include low energy, fatigue, headache, and irritability. Reduce these symptoms by taking a calorie-free electrolyte powder (mixed with plain water). If you exercise, make sure to lower its intensity and get plenty of rest.
Binge eating or overeating may also happen, which can ruin your effort. From a health standpoint, binge eating after you complete a fast will cause your blood sugar levels to rise immediately — all the more so if you break the fast with processed carbohydrates.
Tips for Alternate-Day Fasting
Eating every other day doesn’t have to be difficult. Below are simple rules to follow that will increase your chances of success on this plan.
- Plan your meals ahead of time. Know exactly what to eat once you break your fast. Stick with low-carbohydrate and low-glycemic meals like eggs, salmon, beef, and leafy greens.
- On a fasting day, keep yourself preoccupied with other things, such as work or a hobby, so you don’t think about food all the time.
- Stay hydrated. Drink lots of water and electrolytes. Black coffee also helps by making you alert and curbing hunger until your next meal.
- Work on getting fat-adapted or metabolically flexible. Fasting becomes easier once you reach a fat-adapted state. Consider a ketogenic diet. Exercise regularly (e.g., high-intensity interval training and endurance training) as it will boost your insulin sensitivity.
- If you don’t do keto, at least focus on whole foods. Minimize your intake of sugar and highly processed foods. The goal is to prevent your blood sugar from rising too high and dipping too low.
- Get 7-9 hours of sleep each night. There’s evidence showing that sleep deprivation decreases leptin (which prevents hunger) and increases ghrelin (which stimulates appetite) (*).
Is Alternate-Day Fasting Safe?
As for the safety of fasting every other day, the answer is yes — not only is it safe for most people but it also has important health benefits.
Some people tend to confuse fasting for starving, which isn’t the case. Fasting is intentionally refraining from food — and in the case of ADF, eating some food within a set number of calories — while starvation is not having calories and nutrients for prolonged periods to such a point where your body wastes away.
Alternate-day fasting should not result in nutrient deficiencies as long as you nourish properly with whole foods during and outside your fasting windows.
Who Should Not Alternate-Day Fast?
Certain individuals should not be deliberately fasting and restricting their calories, such as pregnant women and breastfeeding mothers. Meeting their calorie needs is essential to support their health and their baby’s, and have a healthy supply of breast milk.
People who are underweight and have a history of an eating disorder should not fast as well. Those struggling with weight gain need sufficient calories, while an eating disorder can trigger harmful eating disorders.
Individuals who are taking medications to manage their blood sugar levels can do an alternate-day fast, but they need to speak with their doctor first.
Frequently Asked Questions
Below are commonly asked questions about alternate-day fasting.
How much weight can you lose on alternate-day fasting?
You can lose 3-7% of your body weight within 3 months or 12 weeks on ADF. However, it’s important to keep in mind that other factors also affect your weight loss progress. One is your eating habits when you’re not fasting.
How long should you do alternate-day fasting?
On alternate-day fasting, you limit yourself to under 500 calories for a full 24 hours. After 24 hours, you may resume your normal calorie intake.
Can I eat anything during alternate-day fasting?
Yes, you’re allowed to eat whatever you like on your non-fasting days. But, if you want optimal results, it’s best to follow a healthy diet in general. Low-carb foods with lots of healthy fats and protein help keep your blood glucose within a normal range.
Is ADF better than OMAD?
Not necessarily. Both can be equally good for you. Whether you choose ADF or one meal a day (OMAD) will depend on what you can tolerate. The only obvious difference between how these fasts are done is that ADF allows only 500 calories while OMAD lets you eat as many calories as needed in just one meal or within 1 hour.
Why am I not losing weight doing alternate-day fasting?
A common reason is that you consume too many high-carb, high-sugar, and highly processed foods during your feeding window. Other factors that contribute to a weight loss stall include poor sleep, a sedentary lifestyle, and too much stress.
The Bottom Line
Alternate-day fasting or ADF has been shown to promote weight loss and improve your lipid profile, among other benefits. Besides feeling tired and hungrier, and possibly keto flu symptoms, this type of fast is safe for most people.
It’s also less restrictive than traditional calorie restriction where you reduce your average calories each day. Remember to get those 500 calories from healthy foods. Make better food choices as well even when you’re not fasting!
Before doing an alternate-day fast, speak with your healthcare provider if you’re taking glucose-lowering medications like insulin.