In my opinion, most people would benefit from having a window in their day with no food. How long that window is and what time of day this window should occur varies depending on your health status.
But first - Why is a window without food helpful?
1) It allows the gut to rest and this activates something called the Migratory Motor Complex which is a fancy way of saying "getting the gut moving" - think of it as the street sweeper that moves our gut along and cleans it out - very important and often impaired in conditions like SIBO (small intestinal bacterial overgrowth).
2) It allows your blood sugar and insulin to return to a normal level - this is beneficial for our metabolic health and can help some people lose weight - particularly if you have insulin resistance, pre-diabetes, leptin resistance (insulin is a fat storage hormone - a constantly high insulin level signals your body to store fat).
However, here are some caveats to consider:
- Studies have shown if you consume most of your food earlier on in the day, your blood sugar response is more stable throughout the day vs if you consumed food later in the day. For this reason, I always eat breakfast, and if I was to skip a meal - it'll usually be dinner. There has also been suggestions that skipping breakfast may be associated with a higher risk of gallstones in women. Everyone is different, and this may not apply to you - but this is what the data currently shows.
- Anyone with hormone imbalance, particularly thyroid or HPA axis dysfunction (some people like to call it 'adrenal fatigue'), or already has irregular periods (unless overweight), needs to be extra careful with fasting. Essentially, fasting puts stress on the body. It is signaling to the body that food is scarce and to start conserving energy. Depending on your health status, the body may then temporarily turn down thyroid function - so it is possible prolonged fasting can alter thyroid and adrenal function, as well as sex hormones (a recent study showed it lowered DHEA in postmenopausal women - so if you have hormone issues, definitely check with your doctor first as fasting may impact sex hormones) - this is where individuality is so important. Fasting may help some women, but it may not be good for others.
- if you are wanting to conceive, are underweight, are pregnant, breast-feeding, or have an eating disorder - fasting is not a good idea.
What do I do?
I love Circadian Rhythm Fasting with a 12-hour fasting window. I do this most nights, and over the holidays, if I've overindulged and feel sluggish, I may extend this to 14-15 hours for a day.
This is when you eat within a 10-12-hour window, and fast for 12-14 hours, but time it with your body clock - i.e. you eat during daylight hours and stop eating when the sun goes down.
In a small human study conducted by the Salk Institute, participants ate in a 10-hour eating window, with a 14-hour break. After completion, all participants reported better sleep and decreased blood sugar levels, blood pressure, cholesterol, and less body fat.
An example might be breakfast at around 7AM, lunch around 1PM, and dinner around 5PM. And then there's no food (water and herbal tea without sweetener are ok) - until your breakfast the next day.
This is a lot easier to do for most people, and also leaves plenty of time for your body to digest your food before you sleep, thus improving the quality of your deep sleep - something that plays a key role in satiety and hunger signaling too.
It has been suggested that our microbiome has a body clock too - i.e. some friendly bugs are active during the day and some at night; they have different functions. Although a lot more research is needed, we know that our gut microbiome is involved with digestion and calorie extraction. This may be one reason why intermittent fasting can aid with weight management and gut health, and why it is better to consume most of your food earlier on during the day when you are more insulin sensitive.
So… in summary - I think we can all benefit from giving our bodies a break from eating.
If you are feeling the holiday excesses, taking a 12-13 hour food-free break can be beneficial (make sure you stay hydrated).
Now if you want to dive deeper into the science of fasting - read more below!