Intermittent Fasting: Types, Benefits and Who Should Avoid It

1The Main Types of Fasting

Time Restricted Feeding (TRF)

A shortened window of time in which a person consumes calories from food and drink. Also called “prolonged nightly fasting”, it usually extends your typical overnight fast — for example, only eating between 8am and 4pm. Typically a stretch of 12–16 hours without eating meets the criteria.

Alternate Day Fasting (ADF)

Also called fasting intervals — a cycle of fasting one day and eating the next. On fasting days people typically restrict to no more than 600 calories; some consume only water and electrolytes. It can also mean fasting every third day, or on a more personalised schedule.

Modified Fasting

Restricting calories by 20–30%, or reducing to around 600 calories per day, for a specified number of days each week. Also called intermittent energy restriction.

Fasting Mimicking Diet (FMD)

A ketogenic-style plan typically followed for five days once a month. This very low-calorie, low-carbohydrate structured plan has been shown in a limited number of studies to improve body composition and lower blood pressure after three consecutive monthly cycles.

2What Fasting May Improve

May improve:

• Blood pressure
• Antioxidant activity
• Blood sugar metabolism
• Brain function

May decrease:

• Cholesterol
• Free radicals
• Inflammation
• Triglycerides

3Who Benefits From Fasting?

Work with your healthcare practitioner to determine whether fasting is appropriate for you, and which type. Shorter-duration human and animal studies suggest fasting may benefit insulin resistance, blood sugar, blood pressure, inflammation, short-term weight loss and brain health. Longer-term research on sustained weight loss and other outcomes is still needed.

4Who Should Not Fast, or Fast With Caution

Fasting is not recommended for everyone. Some people with diabetes, metabolic syndrome or recurring hypoglycaemia may be “metabolically inflexible”. These individuals should work with an experienced practitioner first to improve metabolic flexibility, so they may be able to fast eventually if appropriate. Some studies suggest Time Restricted Feeding is easier to maintain long-term than Alternate Day Fasting.

5Fasting Safely

• Drink plenty of filtered water on fasting days. Your practitioner may also recommend electrolytes or other supplements personalised to you.
• High-intensity exercise is not recommended while fasting — walking, yoga or other light activity is preferable.
• Be aware of your movement, as you may feel dizzy or lightheaded, especially when first starting.
• Prioritise whole, unprocessed, nutrient-dense foods, especially while limiting your intake.
• Stop fasting if you feel unwell, and contact your Functional Medicine provider.

6A Sample 600-Calorie Day

• Breakfast: One egg scrambled with ½ cup spinach sautéed in a small amount of chicken broth, topped with ¼ of a whole avocado, a pinch of sea salt and pepper.
• Lunch: About 2 ounces of cooked turkey or chicken over 2 cups of mixed baby greens, the juice of ½ a lemon and 1 tsp olive oil drizzled over, with sea salt and cracked pepper.
• Dinner: About 3 ounces of poached or broiled salmon and ½ cup steamed broccoli, drizzled with ½ tsp olive oil, juice of ½ a lemon or lime, a pinch of sea salt and fresh herbs of choice.

Common Questions About Fasting