What is intermittent fasting?

Intermittent fasting is a diet that consists of a fasting pattern that allows for alternating periods of fasting and eating. These patterns can be daily, such as alternate day fasting, or time restricted, such as eating during 6 hours of the day and fasting for the other 18 hour window.

It’s important to note that this is different from calorie restriction. Calorie restricted diets limit total daily calorie intake without regard to timing. When intermittent fasting, a person is still meeting their daily calorie requirements, just in a shorter window than usual.

Metabolic benefits of intermittent fasting

Some studies have found that intermittent fasting can improve insulin sensitivity and triglyceride levels as well as lead to weight loss. It also has the potential for decreasing risk of cardiovascular disease. This is not to say that every study on intermittent fasting has found these results. Some find little to no differences between intermittent fasting and calorie restriction, or intermittent fasting and regular eating patterns.  It’s also important to think about whether or not the timing of food itself creates benefits or whether the limited window for eating leads to inadvertent caloric restriction.  Often times, when someone limits the hours during which they eat, they end up eating less! This could make some data tricky to trust because we don’t know if it’s simple caloric restriction or timing of meals that makes a difference…

Effects of intermittent fasting on Circadian Rhythm 

Or do we?!….One reason we see benefits from intermittent fasting may be because it can align with the circadian rhythm based on when you choose to time your meals. The circadian rhythm controls sleep cycles, blood pressure, heart beat, body temperature and hormone secretion. When eating patterns are not lined up with your circadian rhythm, it can negatively impact your metabolism. Many folks who engage in intermittent fasting choose to skip breakfast, fast until noon or later, and condense their eating to the latter half of the day. When we think about natural circadian rhythms, the body wants to be awake and energized (aka fueled!) as our bodies wake up in the morning and need energy.  Our metabolisms actually prefer to get most of the energy intake we will have in a day during the first ⅔-¾ of the day.  That being said, more metabolic benefit can come from eating in accordance with circadian rhythm (that means, having a full and early breakfast, a complete lunch, and a regular dinner while ending food intake a bit earlier) rather than focusing on the time window limitations of intermittent fasting.  Rather than sticking to an 18 hour fast, try eating earlier for more benefit!

Interestingly, there is promising research on intermittent fasting and PCOS. One study found that meal timing could be a potential treatment option for women with PCOS. Intermittent fasting has been shown to decrease estrogen and androgen levels in females, which are the hormones that contribute to PCOS symptoms when imbalanced. Balancing these hormones through treatment such as intermittent fasting could help relieve symptoms. 

The Downsides

Short term side effects of intermittent fasting include dizziness, weakness, electrolyte imbalance and hypoglycemia (low blood sugar). It can also be harmful for people with hormone imbalances, pregnant or breastfeeding women, those with immunodeficiencies or anyone with a history of disordered eating or eating disorder.

There has not been a lot of research on the long term effects of intermittent fasting, therefore, there is not a lot of data on whether or not the benefits will last in the long term, or if there are any other benefits or downsides that occur when intermittent fasting is done for longer durations.

It is also important to note that most intermittent fasting research has been done on men (both in animal and human models). Since some of the benefits of intermittent fasting have been linked to the circadian rhythm, we have to look at how that applies to changes in hormones. Women and men have different levels of various hormones and different hormone cycles. For example, men have 24-hour hormonal cycles while women have monthly hormonal cycles. This difference is one of the reasons why intermittent fasting may affect men and women differently and why we can’t be so quick to expand all benefits from research to females. Unfortunately, research on intermittent fasting in females and its effects on the menstrual cycle is very limited, so it’s hard to draw any conclusions.

Another downside of intermittent fasting that is sometimes neglected in research is the feasibility of it. With work schedules, family life and social norms, it can be difficult to stick to a strict intermittent fasting schedule. It can be difficult to enjoy food with friends and family if your eating time is a narrow band during the day. Fasting for extended periods of time may also cause a decrease in energy, making it difficult to get through a busy day.

The Takeaway

Despite the extensive research that has been done on intermittent fasting, there are still gaps that need to be more thoroughly studied. This includes effects on females, long term effects, and effects on the endocrine system.

The potential benefits of intermittent fasting, such as improved insulin sensitivity and decreased risk of cardiovascular disease are promising. However, it is important to keep in mind whether this is something that could fit into your lifestyle as well as how it will affect your mental health. If limiting eating to certain times of day would be stressful or feel restrictive, it’s not going to be beneficial because the stress of the diet will outweigh any benefit. Intermittent fasting shows promise for use with certain diseases, but is not something that would be ideal for everyone.

Intermittent fasting can at times mean we are ignoring our hunger and fullness cues. At Michelle Pillepich Nutrition, we prefer to promote listening to your body and trusting it!  If you’re considering this or any diet, reach out to us! We would love to guide you in your nutrition concerns and help you feel your best with the fewest rules possible.  Check out my services page to learn more.