Fasting - Friend or Foe?
Fasting is booming. Google Trends shows us that interest in fasting has jumped exponentially since 2004, and there is no shortage of books, podcasts and articles available on the topic. Of course, the act of fasting is not new. It's been intentionally practiced for thousands of years.The idea of eating during certain hours makes a lot of sense, given that humans have evolved to be in sync with the day/night cycle (i.e. circadian biology). From an evolutionary perspective, fasting is embedded within our physiology, triggering several essential cellular functions. But of course, there are many ways to fast with no shortage of variations!
What are the most popular types of fasting?
“Intermittent fasting” is when fasting periods are longer than the normal overnight fast of 8-12 hours.“
Time-restricted eating” refers to when eating is limited to a certain number of hours a day and is usually referred as 16:8 (a 16 hour fast, with an 8-hour eating window), or 14:10 for example."
Alternate day intermittent fasting" focuses on fasting periods on alternating days throughout the week. This approach was made popular several years ago with Michael Mosley’s book, “The 5:2 diet”. This is when 2 days/week, less than 500 calories/day is consumed, with no restrictions on the other 5 days of the week.
Some of the benefits which can (but don't always) accompany fasting include:
Weight loss, improved lipid profile, increased lean muscle mass, a reduction in chronic inflammation, a reduction in oxidative stress, improved glucose tolerance and insulin sensitivity, improvements in metabolic repair and increased healing capacity.
Since oxidative stress shortens telomeres, reducing this type of stress will help preserve them, which is linked to longevity and why intermittent fasting is sometimes called the "anti-aging diet".
With more information coming to light about intermittent fasting however, we're learning more about who WILL benefit most… more importantly, who WON'T.
When intermittent fasting may be helpful:
For weight loss or metabolic disorders such as insulin resistance, chronic inflammation, and high cholesterol. Note however that the benefits seem to be more pronounced for men and much of the research has been done on men with metabolic dysfunction.
On days when activity and expenditure is low (i.e. on rest days or light intensity days)
When intermittent fasting may not be appropriate:
Around moderate-high intensity exercise/ endurance training
In people who have Gilbert’s syndrome (fasting is a potent contributor to elevated bilirubin in these patients)
When pregnant or breastfeeding
When there is a history of disordered eating, or a diagnosed eating disorder
For young children
Anyone with pre-existing liver or kidney disease
Anyone with severe anaemia/ malnutrition
If someone is highly stressed, has a busy workload or is highly anxious (i.e. high cortisol states)
Those with a tendency for gout
I’ve also had clients who are parents (with children still at home) raise very valid concerns about the potential for negative psychological consequences if their children perceive their parents are ‘skipping meals’, without fully grasping the concept of intermittent fasting.
Any type of dietary approach (fasting included) you adopt obviously needs to fit with your family's needs, values and culture.
Why is there controversy around fasting for women?
Dr Stacy Sims, an expert in female physiology, exercise and nutrition, stresses that men respond very differently to fasting states when compared to women. In men, periods of fasting can up-regulate the parasympathetic nervous system response (the ‘rest and digest’ arm of the nervous system), but in women, it can up-regulate the sympathetic nervous system, which can increase physiological states of stress. This can lead to an increase in visceral fat levels, heightened anxiety through an elevation in stress hormones and reproductive hormone abnormalities. Not ideal!
This doesn't necessarily mean that fasting can be detrimental to ALL women, but factors such as menstrual status (i.e. pre or post menopause), activity levels and stress levels need to be taken into account.
Sims argues that from a health perspective only, exercise results in the same range benefits as intermittent fasting, because it promotes autophagy, changes telomere length, improves blood sugar regulation and reduces visceral fat levels. She makes a great point.
As always, weigh up the risks vs benefits!
Before taking a deep dive into the world of fasting, please consider the above situations where it may NOT be so beneficial. If you do want to give intermittent fasting a go, and none of the above considerations are applicable to you, here are some tips:
1. Start slowly by slightly extending the natural nightly fasts.
2. Always ‘break the fast’ with the SLOW consumption of high quality, nutrient dense foods (i.e. you won't necessary experience the benefits if you break the fast with a coffee and a muffin eaten on the go!).
3. Do what works best for you. I’ve had some clients how have achieve amazing outcomes doing the 5:2 diet for many months, while others have felt their health deteriorate as a result.
4. Unless you're a shift worker, always aim to eat during daylight hours and minimise night-time eating. Your ‘fasting’ window will always be more beneficial to your health if it’s done at night, not the opposite.
