Intermittent fasting is a currently popular diet trend that does not restrict what or how much you eat, but rather when you eat. There are several versions of intermittent fasting:
- Alternate day fasting: no eating for 24 hours for anywhere from 1 to 4 non-consecutive days per week, most commonly 1-2 days of fasting per week, while eating normally on the other days.
- 5:2 diet
- Eating 500-600 calories per day on 2 non-consecutive days per week while eating normally on the other days.
- 16/8 Method
- Time restricted eating: limiting the window of eating from 4-10 hours per day and fasting the other 14-20 hours.
The most commonly used pattern is an 8-hour eating window with 16 hours of fasting.
Does it work?
Intermittent fasting has been shown to be about equally effective in weight loss when compared to a generally restrictive diet in the few studies that have been done.
Besides weight-loss, intermittent fasting has been shown to:
- Improve insulin sensitivity
- Improve glucose levels and/or insulin levels
- Improve blood pressure
- Improve lipid profile
- Reduce inflammatory markers and oxidative stress
But, are the cardiovascular and metabolic benefits just from losing weight?
One small study of 8 prediabetic men looked at intermittent fasting using a 6-hour window vs eating during a 12-hour window daily while keeping the calorie count high enough to maintain weight. Intermittent fasting was shown to improve insulin levels, insulin sensitivity, blood pressure, and reduce oxidative stress despite maintaining weight.
Does it matter when I eat if doing the time restricted eating method?
There is limited evidence, but some studies have suggested that an earlier fasting window is works better than a late fasting window. The thought is that the earlier window works better with our natural circadian rhythm.
So, can I just eat whatever I want during the non-fasting periods?
Technically, yes. However, for best results it is recommended to not stray too far outside of typical calorie recommendations which range from 1500-2500 calories per day depending on current weight, activity level, and weight loss goals. Also, it is always recommended to try to eat a well-balanced diet rich in whole, plant-based foods.
Can anyone try intermittent fasting?
If you are:
- Breast feeding
- Have any major medical conditions requiring medications
Please consult your doctor prior to starting any type of intermittent fasting diet.
Dr. Christine Townsend
Physical Medicine and Rehabilitation