Intermittent fasting‘s positive impact on a person’s weight, blood sugar, and other important health markers has led to growing interest in it. Among the different types of fasts, alternate-day fasting is easier to stick to (and doesn’t require complete abstinence from calories).
This guide explores how alternate-day fasting works, the clinical trials associated with it, possible drawbacks, health benefits, and how to successfully perform this type of fast.
A Brief Overview
Alternate-day fasting (ADF) — sometimes referred to as the “every other day diet” by Dr. Krista Varady’s way of eating — is a fasting approach where you alternate days of fasting or energy restriction with non-fasting days.
Unlike other intermittent fasts or restricted diets, alternate-day fasting lets you consume 500 calories or just 25% of your average daily calorie intake. (1) 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 fasting diet is a matter of personal preference, alternate-day fasting regimens are 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
Research has shown that fasting every other day may be helpful for improving health, from heart health to weight management. Here are some of the effects of alternate-day fasting:
Improved Cardiovascular Health
Cardiovascular disease is a problem. Alternate-day fasting improves your lipid panel, a group of tests that screen for your risk of heart disease. ADF also decreases blood pressure.
This fasting diet has also been shown to create better changes in your plasma lipid profile when combined with physical activity than doing it alone. (2)
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, black coffee, and sugar-free gum, and were encouraged to stay properly hydrated with water. (3)
Related: Dry Fasting: How it Works, Benefits, Risks, and Safety
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 cholesterol particle size, which which is less atherogenic. (4)
Metabolic Flexibility
Metabolic flexibility is the ability to maintain energy homeostasis when transitioning between a fasted and fed state. (5) In other words, your metabolism can quickly adapt to whatever energy is available.One way to achieve metabolic flexibility – for sustained energy and better fat-burning – is alternate-day fasting. This is especially true when combining fasting with a keto diet. Eating low carb on “feed” days will allow you to maintain greater fat burning and deeper ketosis.
Improved Endothelial Function
For people 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 blood sugar levels and improved insulin sensitivity. (6)
ADF can also support individuals living with type 2 diabetes by improving endothelial function. (7) Endothelial dysfunction resulting from hyperglycemia makes a type 2 diabetic more vulnerable to cardiovascular disease. A 2013 study looking at individuals with obesity found that alternate day fasting led to improvements in brachial artery flow mediated dilation and adiponectin, signifying improvements in endothelial function. (8)
Weight Loss
Alternate-day fasting is great for weight maintenance. ADF promotes weight loss, just as traditional daily calorie restriction — where you reduce your calories by 15-40% daily. However, alternate-day fasting may be easier since you’ll only need to limit calories every other day.
According to 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 in a normal weight range. (9)
Where More Research Is Needed
According to a study by 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.” (10)
They noted that prolonged fasting reduces circulating blood glucose, decreasing 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 take a low-carb or keto-eating pattern during your feeding days to help your body enter a ketosis state when fasting.
Our free Keto Macro Calculator can help you determine the exact amount of carbs, fat, and protein you need to achieve your health goals on a ketogenic diet.
Alternate-Day Fasting Schedule and Meal Plan
There are no rules on when to have your 500 calories on a fasting day, so you can choose to eat them in one sitting or divide them into smaller meals.
There are also no rules on drink and food intake, but 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 (Feast 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 (Fast 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/low-calorie electrolytes, plain tea, or coffee.
- Day 3 (Feast day): Resume your usual calorie intake.
- Day 4 (Fast 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/low-calorie electrolytes, plain tea, or coffee.
- Day 5 (Feast day): Resume your usual calorie intake.
Potential Risks and Safety Considerations
Alternate-day fasting is safe for most people but has some side effects, though temporary.
As long as you nourish properly with whole foods during and outside your fasting windows, alternate-day fasting should not result in nutrient deficiencies. Fasting should never be starvation — not having calories and nutrients for prolonged periods to the point where your body wastes away.
Increased hunger and cravings on fasting days are common and are often true for first-time fasters. Studies have found that hunger occurs mainly during the first few days of a fast. (11) It becomes easier the more and the longer you fast.
Read More: The 5 Stages of Fasting (And The Benefits of Each One)
Other possible side effects – similar to 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 fasting efforts. 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.
You should not be deliberately fasting and restricting calories if you:
- Are pregnant and/or breastfeeding. Meeting your calorie needs is essential to support your health and your baby’s, and have a healthy supply of breast milk.
- Underweight and/or have a history of an eating disorder. Those struggling with gaining body weight need sufficient calories, while an eating disorder can trigger harmful eating disorders. Fasting can be dangerous for those with a low body mass index (BMI), so avoid fasting if you fall into this specific category of individuals.
Individuals who take medications to manage their blood sugar levels can do an alternate-day fast, but they need to speak with their doctor first.
Tips for Fasting
Eating every other day doesn’t have to be difficult. Here are some simple tips to follow that will increase your chances of success on this plan:
- Plan 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.
- Keep yourself preoccupied. During fasting periods, work or do 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 becoming fat-adapted or metabolically flexible. Once you reach this state, fasting becomes easier. Consider a ketogenic diet and try to exercise regularly (e.g. high-intensity interval training and endurance training), as this will help boost your insulin sensitivity.
- Focus on whole foods. If not keto, focus on minimizing your intake of sugar and highly processed foods. The goal is to prevent your blood sugar from rising too high and dipping too low. For 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.
- 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). (12)
The Takeaway
Though there are some minor side effects, alternate-day fasting is safe for most people. It can help promote weight loss, promote metabolic flexibility, and improve cardiovascular health.. Remember to get those 500 calories from healthy foods and make better food choices 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.
Read Next: OMAD (One Meal a Day): Benefits, Safety, and How to Do It Correctly
FAQs
How long should you do alternate-day fasting?
ADF proved to be safe for at least two months for individuals with obesity. (1)
Related: How Often Should You Fast?
Is ADF better than other fasting plans?
A systematic review has ranked ADF to be more effective than time-restricted eating and calorie energy-restriction diets. (13)
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 non-fasting days. Other factors that contribute to a weight loss stall include poor sleep, a sedentary lifestyle, and too much stress.