5 Major Signs You Need a Break From Intermittent Fasting, According to a Dietitian

Intermittent fasting (IF) is the latest in a line-up of eating methods promising everything from weight loss to a long, healthy life. There’s some solid research backing the benefits of fasting, but it’s not for everyone.

Here, we explore what intermittent fasting involves and the red flags signaling you might need to reconsider if this eating method is for you.

What is intermittent fasting?

IF is a popular eating strategy that involves temporary periods of fasting (ranging from 16-24 hours), followed by designated eating windows (of no more than eight hours duration). The three most common regimes are:

1. Alternate day fasting (fasting every other day);

2. The 5:2 method - five days of normal eating and two days of low-calorie consumption; and

3. Daily time-restricted feeding - each day you eat only within a certain window, with16:8 being the most popular option. 

The idea behind IF is that the body starts to burn fat once its carbohydrates stores are depleted. This tends to occur 12-24 hours after fasting, hypothetically leading to weight loss and improved health.

While research is mixed (and observed mostly from animal studies), it can be perceived by some as a more flexible approach to weight loss when compared to a continuous energy restricted (CER) diet.

Other reported benefits of IF include, of course, weight loss, (of 8-13 per cent in human studies), reduced body fat and waist circumference, improved metabolism, lower blood sugar levels, reduced inflammation and an overall long-term reduced risk of disease and ill-health. Interestingly, however, it has been found to be no more effective than a CER diet, from a weight loss perspective.

It’s important to note that there are certain people in the community who should not attempt the IF diet, including underweight or highly active individuals, those living with irritable bowel syndrome (IBS) or diabetes, pregnant or breastfeeding women, and of course those who have a history of disordered eating. If this doesn’t include you and you would like to try the IF diet, it is important to keep in mind the potential negative side effects of IF, which could suggest this type of diet is not right for you.

How do you know when to stop intermittent fasting?

1. Nausea, dizziness, and headaches

IF can lead to low blood sugar levels, which can in fact cause a variety of symptoms including nausea, headache, and dizziness. If these start to become troublesome, then it may be worth re-assessing your weight-loss regime.

2. Lethargy, brain fog, and trouble concentrating

Low energy stores caused by fasting can be the cause of an overall feeling of lethargy, excessive tiredness, and a lack of vitality. This can lead to trouble concentrating, which may have an impact on your work quality and general day-to-day activity levels.

3. Depressed mood, anxiety, stress, and exhaustion

Fasting can also increase levels of cortisol in the body, which is the body’s stress hormone. It is not surprising that low energy stores caused by IF, can lead to feelings of anxiety and/or depression. It can also reduce the amount of REM sleep, leading to reduced sleep quality overall. Sleep is vital to maintain our energy and vitality, so this is another red flag.

4. Increased hunger and hanger

Whilst a play on words, feeling ‘hangry’ is a genuine emotion, which describes an overall feeling of irritability and moodiness, brought on by hunger and/or low blood sugar. Feeling ‘hangry’ may also trigger overeating, which defeats the purpose of IF. If fasting causes mood swings and starts to affect your family and work colleagues, then you may need to consider an alternative eating method. 

5. Disordered eating

Fasting can be a trigger for an otherwise healthy eater to adopt disordered eating habits, such as binge eating, thinking excessively about food intake, and obsessing over healthy eating (known as orthorexia). These negative side effects may heavily impact one’s overall mental health and wellbeing.  

Always seek the guidance of your doctor, dietitian or other qualified health professional prior to starting a new eating plan. 

Explore more content like this in our series, Ask a Dietitian

Health & Performance Collective is the brainchild of Sydney Dietitians Jessica Spendlove and Chloe McLeod. They use their 20 years of combined knowledge and skills as dietitians to work with motivated people to live and perform at their best.

Here's how the most popular diets (hello, vegan and intermittent fasting) can wreak havoc on your sleep.

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