Source: National Institutes of Health (NIH)
Intermittent fasting is still very much in the research phase—but there are some promising findings. However, there’s also plenty of evidence that it can cause negative side effects, and you shouldn’t hop onboard without consulting a doctor first.
It is no surprise that hunger is one of the most common side effects related to intermittent fasting. When you reduce your calorie intake or go long periods without taking in calories, you may experience increased hunger.
Digestive issues like constipation, diarrhoea, nausea, and bloating, are symptoms you might experience if you do intermittent fasting. The reduction in food intake that comes along with some intermittent fasting regimens may negatively affect your digestion.
Studies show that some people practicing various methods of intermittent fasting experience fatigue and low energy levels. Plus, intermittent fasting may lead to sleep disturbances in some people, which can cause tiredness during the day.
Low blood sugar, or hypoglycaemia, can occur during periods of calorie restriction or over periods of fasting. This can lead to irritability, anxiety, and poor concentration.
Headaches are a common side effect of intermittent fasting. They typically occur during the first few days of a fasting protocol. Researchers have suggested that low blood sugar and caffeine withdrawal may contribute to headaches during intermittent fasting.
Women who lose a dramatic amount of weight or are consistently not getting enough calories every day might find their menstrual cycles slow down or even stop completely, as noted in a 2021 study published in Experimental Gerontology.