What Is Intermittent Fasting? Methods, Results and Who It Suits

Intermittent fasting means eating only during a set window each day, such as 16:8, or eating very little on certain days of the week, such as 5:2. It works for weight loss mainly because it helps you eat less. In studies it performs about as well as normal calorie cutting, so use it if the schedule suits you.

How does intermittent fasting work?

When you go several hours without food, insulin drops and your body leans more on stored fat for energy. That is real, but it is not what drives long-term fat loss. The bigger effect is simple: a shorter eating window usually means fewer meals, fewer snacks and fewer calories.

Research backs this up. A review in the New England Journal of Medicine found fasting can improve blood sugar, blood pressure and other health markers (de Cabo and Mattson, 2019). But when trials compare fasting with regular dieting at similar calories, the weight loss is about the same (Trepanowski et al., 2017). One 12 week trial of 16:8 without calorie targets found almost no extra weight loss compared with three normal meals (Lowe et al., 2020).

So fasting is not a magic switch. It is a tool for controlling how much you eat.

What are the main intermittent fasting methods?

16:8

Fast for 16 hours, eat within 8. For example, eat from noon to 8 pm. This is my default for most people because it is simple and easy to keep, and it is my usual start for men on the Anti-Dad Bod directive. In resistance-trained men, eight weeks of 16:8 with lifting cut fat while keeping strength and muscle (Moro et al., 2016).

14:10

Fast for 14 hours, eat within 10. A gentler start. I use it with many women and with anyone who has a demanding schedule or trains early. Some women find longer fasts throw off their energy, sleep or cycle, so starting here is sensible. It is where most women on the Anti-Mom Bod directive start with me.

18:6

Fast for 18 hours, eat within 6. Tighter and harder to hit your protein in. I only use it with people who have done 16:8 comfortably for a few months.

One meal a day (OMAD)

All your food in one meal. It can work for people who prefer it, but it is very hard to eat enough protein and vegetables in one sitting, and it is easy to overeat junk. Not for beginners.

5:2

Eat normally five days a week and eat about 500 to 700 calories on two non-consecutive days. Good for people who want flexible weekends. Put the low days on lighter training days.

Alternate day fasting

Alternate very low calorie days with normal days. Effective but tough. In the trial above, more people dropped out of the alternate day group than the regular diet group (Trepanowski et al., 2017).

Extended fasts

Fasting for 24 hours or more. An occasional 24 hour fast is fine for many healthy adults. Anything past that needs medical supervision. I do not recommend extended fasting for fat loss.

Who should not do intermittent fasting?

Talk to your doctor first, or skip it, if any of these apply:

• You are pregnant or breastfeeding
• You have diabetes, especially on insulin or medications that lower blood sugar
• You have a history of disordered eating
• You are under 18
• You are underweight or struggling to gain weight

How do I start intermittent fasting?

1. Start with a 12 hour overnight fast for a week, like 8 pm to 8 am.
2. Move to 14:10 for two weeks.
3. Try 16:8 if you feel good.
4. Break your fast with a meal high in protein, like eggs, Greek yogurt or chicken with rice and vegetables.
5. Hit your protein target inside the window. See how to figure out your protein needs.
6. Drink water, black coffee or plain tea during the fast.

How do I train while intermittent fasting?

Most people lift best two to four hours into their eating window. Easy cardio fasted in the morning is fine if you feel good. If you train hard early in the morning, either shift your window earlier or use 14:10 so you can eat after the session.

What does a 16:8 day look like?

• 7 am: water and black coffee
• 12 pm: chicken, rice, vegetables and avocado
• 3:30 pm: Greek yogurt with berries and a scoop of protein
• 5 pm: train
• 7 pm: salmon, potatoes and a big salad
• 8 pm: window closes

For more on fat loss basics, read the formula for calories in, calories out and eating more can help you lose more weight. If you want a fasting plan matched to your body type, take the XPL quiz.