In a nutshell, intermittent fasting is just that: fasting intermittently.
It’s limiting calorie intake during certain hours/day or days/week. It’s more of an eating pattern than a diet. It limits when to eat, and not so much what to eat. And that’s part of it’s appeal to people who don’t want to count calories or use their food log to track everything.
Some would say that it’s a more natural way to eat because humans evolved without refrigerators, drive-throughs, or 24-hour convenience stores. We now have access to food (including junk food) all day long, so eating several meals per day plus snacks may be less natural than fasting from time to time.
There are lots of variations on this theme. They include:
- 16/8 which is 16 hours of fasting, and eating only within the other 8 hours (often 1:00 pm. – 9:00 p.m.);
- 5:2 days of fasting, where you eat regularly for five days of the week, then take in just 500-600 calories/day for the other two (non-consecutive)
Is intermittent fasting effective for weight loss?
Intermittent fasting can help to lose weight because it can help you to eat fewer calories, and burn more calories too.
Lots of people say they have success with it. But what do the studies say?
According to one review study, intermittent fasting helped people to lose 3-8% of their weight over 3-24 weeks. In this study, people also lost 4-7% of their waist circumference (i.e., belly fat).
Another study of 100 people with obesity showed that after a year, the people who fasted on alternate days lost more weight than people who didn’t change their eating pattern. But, (and here’s where it’s interesting) they didn’t lose any more weight than those on a calorie restricted diet. Out of the people who were to follow the intermittent fasting protocol, 38% of them dropped out.
Sticking with a diet is one of the keys to weight loss success. So, if you can’t stay with a weight-loss diet, you’re less likely to lose the weight and keep it off.
Before you consider intermittent fasting
Intermittent fasting is not for everyone. People who are underweight, or have eating disorders shouldn’t fast. Neither should women who are pregnant, trying to get pregnant, or are breastfeeding.
If you are recovering from burnout or HPA Axis dysregulation (AKA adrenal fatigue) or low functioning thyroid, intermittent fasting may not be the optimal for your health goals for now.
Certain medical conditions can be worsened with longer periods of fasting. Also, people taking certain medications can be prone to side effects with intermittent fasting as well.
One of the reasons people drop out of the intermittent fasting eating pattern is that it’s hard to stick with the fasting part. They eat more than the allowed (low-level of) calories when they’re supposed to be fasting. And when they finish fasting, they may overindulge due to the reaction of the appetite hormones and hunger drive while fasting. None of these will help with weight loss.
Also, the hours and days of fasting can be very difficult. So having strong social support will be key to those intermittent periods of fasting. Sticking to a (healthy, nutrient-dense) weight loss diet is the key to success, and intermittent fasting can be difficult for many people to stick with.