Hunger
Hunger is likely the most common side effect of fasting.
The key is to recognize that most hunger is benign and can be ignored.
Many find that hunger comes and goes in waves; simply ignoring it will help it disappear.
Others find distractions helpful. Going for a walk, engaging in conversation, or engaging your brain in a challenge ( e.g. a work project, a puzzle, or a game) are all activities that can help. Others find that sparkling water, hot water with lemon, or water with salt can also reduce hunger feelings.
The most important thing is to anticipate that you might feel hungry and realize this is okay. Plan ahead how you will respond to this sometimes nagging feeling, so you aren’t caught off guard.
Weakness
Some people find they become a bit weak while fasting. It may require decreasing the intensity and/or duration of exercise, but time-restricted eating should not prevent you from exercising at all.
Those with physically demanding jobs, however, may find this to be an issue. Staying well-hydrated and supplementing with salt are two potential ways to prevent feelings of weakness.
While mild weakness is normal, you should not feel extreme weakness or difficulty walking or standing. If that is the case, you should break your fast and contact your healthcare professional.
Headache and dizziness
As with weakness, mild headaches or dizziness are relatively common and may be prevented with hydration and salt intake.
However, severe, debilitating headaches or severe dizziness are not typical and indicate it is time to break the fast.
Confusion
Some may feel less mentally sharp while fasting, but this practice should not lead to outright confusion. If that is the case, break the fast and consult your healthcare professional. Conversely, many people feel mentally sharper as they go deeper into ketosis with fasting. It may be worth experimenting to see how you respond.
Constipation
It makes sense that if you are eating less, you will naturally have fewer bowel movements. Going to the bathroom less frequently is a normal consequence of fasting, and does not mean you are constipated.
If you do not feel bloated or uncomfortable and you don’t have to strain to have a bowel movement, then you likely are not constipated. However, if you experience these symptoms, you may want to increase your hydration or try magnesium supplements.
Heartburn
For some, fasting can relieve heartburn symptoms. For others, it can worsen symptoms. Again, experimenting with fasting will help you determine how you respond.
Elevated blood sugar
While fasting may benefit overall blood sugar control, some find their morning blood sugar rises.
This is called the “dawn phenomenon.” It occurs when the liver releases glucose into the bloodstream in response to receiving signals that the body may need more energy after a long rest.
Those who follow a low-carb diet and experience elevated blood sugar with fasting usually find their highest levels are upon waking (almost always less than 120mg/dl), and the rest of the day, they have normal, flat blood sugar levels.
As we discuss in our guide on the dawn effect, these mildly elevated fasting blood sugar levels may not be of clinical concern, especially if they are only present while fasting. However, if someone’s fasting blood sugar increases regularly above 130, they may want to consult their physician.
Low blood sugar
Low blood sugar in the absence of glucose-lowering medications is rare.
If someone feels sweaty, extremely weak, nauseous, or overly lightheaded, it is possible – but not likely – they are suffering from hypoglycemia. In this situation, it’s helpful to check a blood sugar reading— if it can be done safely. Otherwise, you should break your fast right away and consult your healthcare provider.
Refeeding syndrome
This is an extremely rare but very serious condition that can occur after prolonged fasting in those who are underweight or malnourished.
These people can experience potentially fatal shifts in fluids and electrolytes during refeeding.
Most practitioners of intermittent fasting will never have to worry about this, and it is one reason why fasting is contraindicated for underweight or malnourished individuals.
Leave a Reply