Intermittent fasting: what you need to know

1. Suppression of Hunger-Reducing Hormones

There are a number of hormones at play in the body that regulate hunger, appetite, and satisfaction after a meal. In the long-term, you need your hunger hormones working if you want optimal body composition. 

A side effect of certain extended fasting protocols, is that your hunger hormones get out of balance, leading you to become unresponsive to cues that tell us you’re full and should stop eating. For example, if cells become insensitive to leptin or insulin, your brain won’t register satisfaction and hunger will remain elevated.

Most people who experience altered hunger hormones in response to fasting will find themselves battling an uncontrollable appetite. Then, once they do eat, satisfaction cues that should tell them to stop eating won’t register. This makes binging a common side effect. Once people understand that they need to alter their fasting protocol or go back to more regular eating patterns, their hunger hormones will take some time before they start working for them again.
How to avoid: Don’t fast for extended periods of time but rather opt for a more moderate approach in which you only eat for a 10 - 12 hour eating window where you will receive the benefits of fasting such as fat burning and insulin sensitivity, without the suppression of hunger hormones.

2. Excess stress and insomnia

When you go without food for a long period, you will activate the flight-or-flight sympathetic nervous system and increase cortisol secretion for your body to mobilise energy stores. For some people, e.g. those who are overweight, this could prove beneficial since it improves the body’s ability to burn fat for fuel. However, for those who suffer from high stress or who have an elevated cortisol curve, skipping meals and abnormal eating patterns may increase stress.

High cortisol triggers food intake, and leads to strong cravings for high-carb foods. The combination of fasting and cortisol can produce obsessive thoughts about food, which in turn raises anxiety, causing further release of cortisol. Preoccupation with food can turn into disordered eating pretty quickly. 

Finally, the combination of high cortisol and activation of the hypocretin neurons, which incite wakefulness, can trigger insomnia and trouble sleeping. 

How to avoid: Establish a healthy eating pattern with frequent meals eaten at the same time each day. This should allow you to avoid hunger and cravings and get your cortisol in check prior to starting a fasting protocol. 

3. Reproductive Hormone Imbalances

It’s been shown through animal experiments that females don’t respond well to fasting. Female rats that are deprived of food “masculinise.” This means they become infertile, hyper alert, and sleep much less. Research suggests that when their bodies detect a starvation state, they develop traits that will help them find food.

There isn’t enough sufficient data on humans’ reproductive hormones and the effects of fasting. 

Studies done within the Muslim community during the Ramadan fast show an increase in the amount of women experiencing differences in their menstrual cycle from fasting. The Muslim men who fasted showed significant alterations in testosterone release over Ramadan, suggesting changes of circadian function. This is logical based on how sensitive the human biorhythm is to the slightest changes in eating and sleeping behavior.

How to avoid: Athletes, leaner individuals, and those with more stressful lifestyles are the populations who are most at risk for sustained alterations to reproductive function from fasting. A time-restricted eating model is the best alternative that may not negatively affect androgen hormones, and it’s best to stick to an eating window of 10 - 12 hours. Obese individuals are less likely to experience problems and may even benefit from fasting because a reduction in body fat can significantly improve reproductive capacity.